docs: add v0.3.0 harness rewrite implementation plan

27 tasks: foundations → CDP transport/session/client → defineTool helper
→ vertical slice (click) → 13 domain migrations → wire-up + delete legacy
→ smoke + release. Each task has concrete code, exact file paths, and a
typecheck checkpoint.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

1 files changed, 2937 insertions, 0 deletions

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+# pi-browser-harness v0.3.0 Internal Rewrite — Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Restructure `src/` into per-domain modules with a `defineTool` helper, a transport/session/client split, and structural fixes for the predictability bugs and security gaps catalogued in the spec — without breaking the 28 LLM-facing tool names.
+
+**Architecture:** Per-domain decomposition. Dependencies flow `domains/* → client → cdp/* → util/*`. Every tool handler returns `Result<ToolOk, ToolErr>`; one `defineTool`/`registerTool` helper converts that into pi's `ToolResult` and supplies the unified `details` shape. The current `BrowserDaemon` class becomes a `createBrowserClient(opts)` factory composing a `CdpTransport` + `CdpSession`. JS injection is structurally prevented by routing all evaluation source through `safeJs\`...\``. `browser_run_script` keeps its full Node powers but gains a path allowlist, mandatory timeout, and AbortSignal wiring.
+
+**Tech Stack:** TypeScript (strict mode + extended safety flags), `ws` (WebSocket), `typebox` (tool schemas), `@mariozechner/pi-coding-agent` (extension API + truncation helpers), `@mariozechner/pi-tui` (renderers).
+
+**Reference spec:** `docs/superpowers/specs/2026-05-02-harness-rewrite-design.md`
+
+---
+
+## Build order (why the tasks run in this order)
+
+1. **Foundations first (Tasks 1–3).** `Result`, `safeJs`, `keycodes`, `paths`, `time` are pure utilities depended on by everything else. Land them with `tsc` green so the rest of the work has a solid base.
+2. **Strict tsconfig third (Task 3).** Turning on the new flags before the rest of the code is rewritten would explode the codebase. We turn them on *only* over `src/util/**` first, then expand the include scope as new code lands. By the end the whole `src/` is covered.
+3. **Transport / session / client (Tasks 4–7).** This is the biggest single piece. `transport.ts` (WS) → `session.ts` (target/dialog/event handling) → `discovery.ts` (DevToolsActivePort) → `client.ts` (composition). At this point the new `client` exists but no domains use it yet; `daemon.ts` and `tools.ts` still serve every tool call. The package still ships and works.
+4. **`defineTool` helper (Task 8).** Cannot be tested without at least one domain consumer, so we land the helper alongside the first vertical slice.
+5. **First vertical slice — `domains/click.ts` (Task 9).** Smallest stateless tool that exercises the full path: schema → handler → client → CDP → Result → registry. Validates the architecture end-to-end. After this task, `browser_click` is served by the new path; the other 27 tools still use `tools.ts`. Manual smoke checkpoint here.
+6. **Bulk domain migration (Tasks 10–22).** One task per domain file. Each task removes the corresponding tool block(s) from `tools.ts` and adds the new domain file. `tools.ts` shrinks by ~70-100 LOC per task.
+7. **Wire-up + dead-code deletion (Tasks 23–25).** `index.ts`, `state.ts`, `prompt.ts`, then delete `daemon.ts`, `tools.ts` (now empty), `protocol.ts`, `renderers.ts`.
+8. **Final hardening (Tasks 26–27).** Strict-flag expansion to whole `src/`, manual smoke run of the verification scenarios from spec §11, version bump + CHANGELOG.
+
+## Green-bar checkpoints
+
+After every task: `npm run typecheck` must pass. Failures block the next task.
+
+Manual smoke checkpoints: **after Task 9** (one tool migrated end-to-end) and **after Task 27** (full migration). Smoke procedure is in spec §11.
+
+---
+
+## File layout (target end-state)
+
+```
+src/
+  index.ts             registry.ts          prompt.ts          state.ts          setup.ts
+  client.ts
+  cdp/
+    transport.ts       session.ts           discovery.ts       errors.ts         types.ts
+  domains/
+    navigate.ts        history.ts           click.ts           keyboard.ts       scroll.ts
+    screenshot.ts      tabs.ts              page.ts            dialog.ts         js.ts
+    files.ts           viewport.ts          drag.ts            network.ts
+  schemas/
+    common.ts
+  util/
+    result.ts          tool.ts              truncate.ts        keycodes.ts       paths.ts
+    js-template.ts     time.ts
+```
+
+Deleted at end: `daemon.ts`, `tools.ts`, `protocol.ts`, `renderers.ts`.
+
+---
+
+## Task 1: Foundations — `util/result.ts`, `util/time.ts`, `util/paths.ts`
+
+**Files:**
+- Create: `src/util/result.ts`
+- Create: `src/util/time.ts`
+- Create: `src/util/paths.ts`
+
+- [ ] **Step 1.1: Write `src/util/result.ts`**
+
+```ts
+export type Result<T, E> =
+  | { readonly success: true; readonly data: T }
+  | { readonly success: false; readonly error: E };
+
+export const ok = <T>(data: T): Result<T, never> => ({ success: true, data });
+export const err = <E>(error: E): Result<never, E> => ({ success: false, error });
+
+export const map = <T, U, E>(r: Result<T, E>, f: (t: T) => U): Result<U, E> =>
+  r.success ? ok(f(r.data)) : r;
+
+export const andThen = <T, U, E>(r: Result<T, E>, f: (t: T) => Result<U, E>): Result<U, E> =>
+  r.success ? f(r.data) : r;
+
+export const mapErr = <T, E, F>(r: Result<T, E>, f: (e: E) => F): Result<T, F> =>
+  r.success ? r : err(f(r.error));
+```
+
+- [ ] **Step 1.2: Write `src/util/time.ts`**
+
+```ts
+export const sleep = (ms: number, signal?: AbortSignal): Promise<void> =>
+  new Promise((resolve, reject) => {
+    if (signal?.aborted) {
+      reject(new Error("aborted"));
+      return;
+    }
+    const timer = setTimeout(() => {
+      signal?.removeEventListener("abort", onAbort);
+      resolve();
+    }, ms);
+    const onAbort = (): void => {
+      clearTimeout(timer);
+      reject(new Error("aborted"));
+    };
+    signal?.addEventListener("abort", onAbort, { once: true });
+  });
+
+export type Deadline = {
+  readonly remainingMs: () => number;
+  readonly expired: () => boolean;
+};
+
+export const deadline = (totalMs: number): Deadline => {
+  const end = Date.now() + totalMs;
+  return {
+    remainingMs: () => Math.max(0, end - Date.now()),
+    expired: () => Date.now() >= end,
+  };
+};
+```
+
+- [ ] **Step 1.3: Write `src/util/paths.ts`**
+
+```ts
+import { randomUUID } from "node:crypto";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+export const screenshotPath = (namespace: string, ext: "png" | "jpeg" = "png"): string =>
+  join(tmpdir(), `pi-browser-screenshot-${namespace}-${randomUUID()}.${ext}`);
+
+export const pdfPath = (namespace: string): string =>
+  join(tmpdir(), `pi-browser-pdf-${namespace}-${randomUUID()}.pdf`);
+```
+
+- [ ] **Step 1.4: Typecheck**
+
+Run: `npm run typecheck`
+Expected: PASS (no errors).
+
+- [ ] **Step 1.5: Commit**
+
+```bash
+git add src/util/result.ts src/util/time.ts src/util/paths.ts
+git commit -m "feat(util): add result, time, and paths primitives for v0.3 rewrite"
+```
+
+---
+
+## Task 2: Foundations — `util/keycodes.ts`, `util/js-template.ts`
+
+**Files:**
+- Create: `src/util/keycodes.ts`
+- Create: `src/util/js-template.ts`
+
+- [ ] **Step 2.1: Write `src/util/keycodes.ts`** (extracted from `daemon.ts:126-141` and `daemon.ts:815-822`)
+
+```ts
+const VIRTUAL_KEY_CODES: Readonly<Record<string, number>> = {
+  Enter: 13, Tab: 9, Backspace: 8, Escape: 27, Delete: 46, " ": 32,
+  ArrowLeft: 37, ArrowUp: 38, ArrowRight: 39, ArrowDown: 40,
+  Home: 36, End: 35, PageUp: 33, PageDown: 34,
+};
+
+export const SPECIAL_KEYS: ReadonlyArray<string> = Object.keys(VIRTUAL_KEY_CODES);
+
+export const virtualKeyCode = (key: string): number =>
+  VIRTUAL_KEY_CODES[key] ?? (key.length === 1 ? key.charCodeAt(0) : 0);
+
+export const keyCode = (key: string): string => key;
+```
+
+- [ ] **Step 2.2: Write `src/util/js-template.ts`**
+
+```ts
+/**
+ * Build a JavaScript source string with safely-interpolated values.
+ * Every interpolated value is JSON.stringify'd, so strings, numbers,
+ * objects, and special characters all become valid JS literals.
+ *
+ * This is the ONLY supported way to build evaluation source in the
+ * codebase — never use raw template literals for JS that crosses the
+ * CDP boundary.
+ */
+export const safeJs = (
+  strings: TemplateStringsArray,
+  ...values: ReadonlyArray<unknown>
+): string => {
+  let out = strings[0] ?? "";
+  for (let i = 0; i < values.length; i++) {
+    out += JSON.stringify(values[i]);
+    out += strings[i + 1] ?? "";
+  }
+  return out;
+};
+```
+
+- [ ] **Step 2.3: Typecheck**
+
+Run: `npm run typecheck`
+Expected: PASS.
+
+- [ ] **Step 2.4: Commit**
+
+```bash
+git add src/util/keycodes.ts src/util/js-template.ts
+git commit -m "feat(util): add pure keycodes and safeJs template helper"
+```
+
+---
+
+## Task 3: Strict tsconfig (scoped to `src/util/**` for now)
+
+**Files:**
+- Modify: `tsconfig.json`
+
+- [ ] **Step 3.1: Replace `tsconfig.json` with the strict config**
+
+```json
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "noImplicitAny": true,
+    "strictNullChecks": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "noImplicitReturns": true,
+    "noFallthroughCasesInSwitch": true,
+    "noUncheckedIndexedAccess": true,
+    "exactOptionalPropertyTypes": true,
+    "noPropertyAccessFromIndexSignature": true,
+    "forceConsistentCasingInFileNames": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "outDir": "./dist",
+    "rootDir": "./src",
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true
+  },
+  "include": ["src/**/*.ts"],
+  "exclude": ["node_modules", "dist"]
+}
+```
+
+- [ ] **Step 3.2: Typecheck — expect failures in `daemon.ts`/`tools.ts`/`index.ts`**
+
+Run: `npm run typecheck`
+Expected: errors in legacy files (we'll fix them as we migrate). Capture the count.
+
+- [ ] **Step 3.3: Add a temporary include carve-out so legacy code compiles during migration**
+
+Create: `tsconfig.legacy.json`
+
+```json
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "noUnusedLocals": false,
+    "noUnusedParameters": false,
+    "noUncheckedIndexedAccess": false,
+    "exactOptionalPropertyTypes": false,
+    "noPropertyAccessFromIndexSignature": false
+  },
+  "include": [
+    "src/daemon.ts",
+    "src/tools.ts",
+    "src/index.ts",
+    "src/protocol.ts",
+    "src/renderers.ts",
+    "src/setup.ts",
+    "src/state.ts",
+    "src/prompt.ts"
+  ]
+}
+```
+
+Modify `tsconfig.json` `include` to:
+```json
+"include": ["src/util/**/*.ts", "src/cdp/**/*.ts", "src/client.ts", "src/domains/**/*.ts", "src/schemas/**/*.ts", "src/registry.ts"]
+```
+
+Modify `package.json` `scripts.typecheck` to: `tsc --noEmit && tsc --noEmit -p tsconfig.legacy.json`
+
+- [ ] **Step 3.4: Typecheck — both projects must pass**
+
+Run: `npm run typecheck`
+Expected: PASS.
+
+- [ ] **Step 3.5: Commit**
+
+```bash
+git add tsconfig.json tsconfig.legacy.json package.json
+git commit -m "build: enable strict tsconfig flags for new code, keep legacy lenient"
+```
+
+---
+
+## Task 4: CDP types and errors
+
+**Files:**
+- Create: `src/cdp/types.ts`
+- Create: `src/cdp/errors.ts`
+
+- [ ] **Step 4.1: Write `src/cdp/types.ts`**
+
+```ts
+export type CdpEvent = {
+  readonly method: string;
+  readonly params: unknown;
+  readonly sessionId?: string;
+};
+
+export type CdpRawMessage = {
+  readonly id?: number;
+  readonly method?: string;
+  readonly params?: Record<string, unknown>;
+  readonly result?: unknown;
+  readonly error?: { readonly message: string; readonly code?: number };
+  readonly sessionId?: string;
+};
+
+export type DialogInfo = {
+  readonly type: "alert" | "confirm" | "prompt" | "beforeunload";
+  readonly message: string;
+  readonly defaultPrompt?: string;
+};
+
+export type TabInfo = {
+  readonly targetId: string;
+  readonly title: string;
+  readonly url: string;
+};
+
+export type PageInfo = {
+  readonly url: string;
+  readonly title: string;
+  readonly width: number;
+  readonly height: number;
+  readonly scrollX: number;
+  readonly scrollY: number;
+  readonly pageWidth: number;
+  readonly pageHeight: number;
+};
+
+export type DaemonStatus = {
+  readonly alive: boolean;
+  readonly sessionId: string | null;
+  readonly namespace: string;
+  readonly remoteBrowserId?: string;
+};
+
+const INTERNAL_PREFIXES: ReadonlyArray<string> = [
+  "chrome://", "chrome-untrusted://", "devtools://", "chrome-extension://", "about:",
+];
+
+export const isInternalUrl = (url: string): boolean =>
+  INTERNAL_PREFIXES.some((p) => url.startsWith(p));
+```
+
+- [ ] **Step 4.2: Write `src/cdp/errors.ts`**
+
+```ts
+export type CdpErrorKind =
+  | "transport_closed"
+  | "timeout"
+  | "session_not_found"
+  | "remote_error"
+  | "discovery_failed"
+  | "invalid_response";
+
+export type CdpError = {
+  readonly kind: CdpErrorKind;
+  readonly message: string;
+  readonly method?: string;
+};
+
+export const cdpError = (
+  kind: CdpErrorKind,
+  message: string,
+  method?: string,
+): CdpError => ({ kind, message, ...(method !== undefined ? { method } : {}) });
+```
+
+- [ ] **Step 4.3: Typecheck**
+
+Run: `npm run typecheck`
+Expected: PASS.
+
+- [ ] **Step 4.4: Commit**
+
+```bash
+git add src/cdp/types.ts src/cdp/errors.ts
+git commit -m "feat(cdp): add types and error model for new transport layer"
+```
+
+---
+
+## Task 5: CDP discovery
+
+**Files:**
+- Create: `src/cdp/discovery.ts`
+
+- [ ] **Step 5.1: Write `src/cdp/discovery.ts`** (port `daemon.ts:41-124` to Result)
+
+```ts
+import { readFile } from "node:fs/promises";
+import { homedir } from "node:os";
+import { join } from "node:path";
+import { connect as netConnect } from "node:net";
+import { type Result, err, ok } from "../util/result";
+import { type CdpError, cdpError } from "./errors";
+
+const PORT_PROBE_DEADLINE_MS = 30_000;
+const PORT_PROBE_INTERVAL_MS = 1_000;
+
+const profileDirs = (): ReadonlyArray<string> => {
+  const home = homedir();
+  return [
+    join(home, "Library/Application Support/Google/Chrome"),
+    join(home, "Library/Application Support/Microsoft Edge"),
+    join(home, "Library/Application Support/Microsoft Edge Beta"),
+    join(home, "Library/Application Support/Microsoft Edge Dev"),
+    join(home, "Library/Application Support/Microsoft Edge Canary"),
+    join(home, ".config/google-chrome"),
+    join(home, ".config/chromium"),
+    join(home, ".config/chromium-browser"),
+    join(home, ".config/microsoft-edge"),
+    join(home, ".config/microsoft-edge-beta"),
+    join(home, ".config/microsoft-edge-dev"),
+    join(home, ".var/app/org.chromium.Chromium/config/chromium"),
+    join(home, ".var/app/com.google.Chrome/config/google-chrome"),
+    join(home, ".var/app/com.brave.Browser/config/BraveSoftware/Brave-Browser"),
+    join(home, ".var/app/com.microsoft.Edge/config/microsoft-edge"),
+    join(home, "AppData/Local/Google/Chrome/User Data"),
+    join(home, "AppData/Local/Chromium/User Data"),
+    join(home, "AppData/Local/Microsoft/Edge/User Data"),
+    join(home, "AppData/Local/Microsoft/Edge Beta/User Data"),
+    join(home, "AppData/Local/Microsoft/Edge Dev/User Data"),
+    join(home, "AppData/Local/Microsoft/Edge SxS/User Data"),
+  ];
+};
+
+const probePort = (port: number): Promise<Result<void, CdpError>> =>
+  new Promise((resolve) => {
+    const sock = netConnect({ host: "127.0.0.1", port });
+    const finish = (r: Result<void, CdpError>): void => {
+      sock.destroy();
+      resolve(r);
+    };
+    sock.setTimeout(1000, () => finish(err(cdpError("discovery_failed", "probe timeout"))));
+    sock.once("error", (e) => finish(err(cdpError("discovery_failed", e.message))));
+    sock.once("connect", () => {
+      sock.end();
+      resolve(ok(undefined));
+    });
+  });
+
+const waitForPort = async (port: number): Promise<Result<void, CdpError>> => {
+  const end = Date.now() + PORT_PROBE_DEADLINE_MS;
+  let lastMessage = "unknown";
+  while (Date.now() < end) {
+    const probe = await probePort(port);
+    if (probe.success) return probe;
+    lastMessage = probe.error.message;
+    await new Promise((r) => setTimeout(r, PORT_PROBE_INTERVAL_MS));
+  }
+  return err(cdpError(
+    "discovery_failed",
+    `Chrome's remote-debugging page is open, but DevTools is not live yet on 127.0.0.1:${port} — if Chrome opened a profile picker, choose your normal profile first, then tick the checkbox and click Allow if shown (last error: ${lastMessage})`,
+  ));
+};
+
+export const discoverWsUrl = async (): Promise<Result<string, CdpError>> => {
+  const dirs = profileDirs();
+  for (const base of dirs) {
+    const portFile = join(base, "DevToolsActivePort");
+    let raw: string;
+    try {
+      raw = await readFile(portFile, "utf8");
+    } catch {
+      continue;
+    }
+    const lines = raw.trim().split("\n");
+    if (lines.length < 2) continue;
+    const port = lines[0]?.trim();
+    const path = lines[1]?.trim();
+    if (!port || !path) continue;
+    const ready = await waitForPort(Number(port));
+    if (!ready.success) return ready;
+    return ok(`ws://127.0.0.1:${port}${path}`);
+  }
+  return err(cdpError(
+    "discovery_failed",
+    `DevToolsActivePort not found in ${dirs.join(", ")} — open chrome://inspect/#remote-debugging in your browser, tick the checkbox, click Allow, then retry. Or set BU_CDP_WS to a remote browser endpoint.`,
+  ));
+};
+```
+
+- [ ] **Step 5.2: Typecheck**
+
+Run: `npm run typecheck`
+Expected: PASS.
+
+- [ ] **Step 5.3: Commit**
+
+```bash
+git add src/cdp/discovery.ts
+git commit -m "feat(cdp): port DevToolsActivePort discovery to Result"
+```
+
+---
+
+## Task 6: CDP transport
+
+**Files:**
+- Create: `src/cdp/transport.ts`
+
+- [ ] **Step 6.1: Write `src/cdp/transport.ts`**
+
+```ts
+import WebSocket from "ws";
+import { type Result, err, ok } from "../util/result";
+import { type CdpError, cdpError } from "./errors";
+import type { CdpEvent, CdpRawMessage } from "./types";
+
+const DEFAULT_TIMEOUT_MS = 15_000;
+
+type Pending = {
+  readonly resolve: (v: Result<unknown, CdpError>) => void;
+  readonly timer: ReturnType<typeof setTimeout>;
+  readonly method: string;
+};
+
+export type CdpTransport = {
+  connect(url: string, opts?: { timeoutMs?: number }): Promise<Result<void, CdpError>>;
+  close(): Promise<void>;
+  request(
+    method: string,
+    params: Record<string, unknown>,
+    opts?: { sessionId?: string | null; timeoutMs?: number },
+  ): Promise<Result<unknown, CdpError>>;
+  events(): AsyncIterable<CdpEvent>;
+  state(): "open" | "closed" | "connecting";
+  onClose(cb: () => void): () => void;
+};
+
+export const createCdpTransport = (): CdpTransport => {
+  let ws: WebSocket | null = null;
+  let nextId = 1;
+  const pending = new Map<number, Pending>();
+  const closeListeners = new Set<() => void>();
+
+  type EventQueue = {
+    readonly push: (e: CdpEvent) => void;
+    readonly end: () => void;
+    readonly iter: AsyncIterable<CdpEvent>;
+  };
+
+  const makeEventQueue = (): EventQueue => {
+    const buf: CdpEvent[] = [];
+    const waiters: Array<(v: IteratorResult<CdpEvent>) => void> = [];
+    let ended = false;
+    return {
+      push(e) {
+        if (ended) return;
+        const w = waiters.shift();
+        if (w) w({ value: e, done: false });
+        else buf.push(e);
+      },
+      end() {
+        ended = true;
+        for (const w of waiters.splice(0)) w({ value: undefined as unknown as CdpEvent, done: true });
+      },
+      iter: {
+        [Symbol.asyncIterator]() {
+          return {
+            next: (): Promise<IteratorResult<CdpEvent>> =>
+              new Promise((resolve) => {
+                const next = buf.shift();
+                if (next) resolve({ value: next, done: false });
+                else if (ended) resolve({ value: undefined as unknown as CdpEvent, done: true });
+                else waiters.push(resolve);
+              }),
+          };
+        },
+      },
+    };
+  };
+
+  let queue = makeEventQueue();
+
+  const handleMessage = (raw: string): void => {
+    let msg: CdpRawMessage;
+    try {
+      msg = JSON.parse(raw);
+    } catch {
+      return;
+    }
+    if (msg.id === undefined) {
+      if (msg.method) {
+        queue.push({
+          method: msg.method,
+          params: msg.params,
+          ...(msg.sessionId !== undefined ? { sessionId: msg.sessionId } : {}),
+        });
+      }
+      return;
+    }
+    const p = pending.get(msg.id);
+    if (!p) return;
+    pending.delete(msg.id);
+    clearTimeout(p.timer);
+    if (msg.error) {
+      const kind = msg.error.message.includes("Session with given id not found")
+        ? "session_not_found"
+        : "remote_error";
+      p.resolve(err(cdpError(kind, msg.error.message, p.method)));
+      return;
+    }
+    p.resolve(ok(msg.result));
+  };
+
+  const cleanup = (reason: string): void => {
+    for (const [, p] of pending) {
+      clearTimeout(p.timer);
+      p.resolve(err(cdpError("transport_closed", reason, p.method)));
+    }
+    pending.clear();
+    queue.end();
+    queue = makeEventQueue();
+    for (const cb of closeListeners) cb();
+  };
+
+  return {
+    connect(url, opts = {}): Promise<Result<void, CdpError>> {
+      const timeoutMs = opts.timeoutMs ?? 10_000;
+      return new Promise((resolve) => {
+        let settled = false;
+        const settle = (r: Result<void, CdpError>): void => {
+          if (settled) return;
+          settled = true;
+          resolve(r);
+        };
+        try {
+          ws = new WebSocket(url);
+        } catch (e) {
+          settle(err(cdpError("transport_closed", e instanceof Error ? e.message : String(e))));
+          return;
+        }
+        const timer = setTimeout(() => {
+          ws?.close();
+          ws = null;
+          settle(err(cdpError("timeout", `CDP WebSocket connection timed out after ${timeoutMs}ms`)));
+        }, timeoutMs);
+        ws.onopen = () => {
+          clearTimeout(timer);
+          settle(ok(undefined));
+        };
+        ws.onmessage = (ev: WebSocket.MessageEvent) => {
+          const data = ev.data;
+          handleMessage(typeof data === "string" ? data : data.toString());
+        };
+        ws.onerror = () => {
+          clearTimeout(timer);
+          settle(err(cdpError("transport_closed", "CDP WebSocket error during connection")));
+        };
+        ws.onclose = () => {
+          clearTimeout(timer);
+          ws = null;
+          cleanup("WebSocket closed");
+          settle(err(cdpError("transport_closed", "CDP WebSocket closed")));
+        };
+      });
+    },
+    close(): Promise<void> {
+      if (ws) {
+        try { ws.close(1000, "Shutdown"); } catch { /* best effort */ }
+        ws = null;
+      }
+      cleanup("close() called");
+      return Promise.resolve();
+    },
+    request(method, params, opts = {}): Promise<Result<unknown, CdpError>> {
+      const timeoutMs = opts.timeoutMs ?? DEFAULT_TIMEOUT_MS;
+      const sessionId = opts.sessionId ?? null;
+      if (!ws || ws.readyState !== WebSocket.OPEN) {
+        return Promise.resolve(err(cdpError("transport_closed", "Browser not connected. Is Chrome running?", method)));
+      }
+      const id = nextId++;
+      const payload: Record<string, unknown> = { id, method, params };
+      if (sessionId) payload.sessionId = sessionId;
+      const json = JSON.stringify(payload);
+      return new Promise((resolve) => {
+        const timer = setTimeout(() => {
+          pending.delete(id);
+          resolve(err(cdpError("timeout", `CDP timeout after ${timeoutMs}ms: ${method}`, method)));
+        }, timeoutMs);
+        pending.set(id, { resolve, timer, method });
+        try {
+          ws!.send(json);
+        } catch (e) {
+          clearTimeout(timer);
+          pending.delete(id);
+          resolve(err(cdpError("transport_closed", e instanceof Error ? e.message : String(e), method)));
+        }
+      });
+    },
+    events(): AsyncIterable<CdpEvent> {
+      return queue.iter;
+    },
+    state(): "open" | "closed" | "connecting" {
+      if (!ws) return "closed";
+      if (ws.readyState === WebSocket.CONNECTING) return "connecting";
+      if (ws.readyState === WebSocket.OPEN) return "open";
+      return "closed";
+    },
+    onClose(cb): () => void {
+      closeListeners.add(cb);
+      return () => closeListeners.delete(cb);
+    },
+  };
+};
+```
+
+- [ ] **Step 6.2: Typecheck**
+
+Run: `npm run typecheck`
+Expected: PASS.
+
+- [ ] **Step 6.3: Commit**
+
+```bash
+git add src/cdp/transport.ts
+git commit -m "feat(cdp): add factory-based transport with Result and event AsyncIterable"
+```
+
+---
+
+## Task 7: CDP session + client
+
+**Files:**
+- Create: `src/cdp/session.ts`
+- Create: `src/client.ts`
+
+- [ ] **Step 7.1: Write `src/cdp/session.ts`**
+
+```ts
+import { type Result, err, ok } from "../util/result";
+import { type CdpError, cdpError } from "./errors";
+import type { CdpEvent, DialogInfo, PageInfo } from "./types";
+import { isInternalUrl } from "./types";
+import type { CdpTransport } from "./transport";
+
+export type CdpSession = {
+  attachFirstPage(): Promise<Result<{ readonly targetId: string; readonly sessionId: string }, CdpError>>;
+  switchTo(targetId: string): Promise<Result<void, CdpError>>;
+  current(): { readonly sessionId: string; readonly targetId: string } | null;
+  call(method: string, params?: Record<string, unknown>, opts?: { timeoutMs?: number }): Promise<Result<unknown, CdpError>>;
+  callOnTarget(method: string, params: Record<string, unknown>, sessionId: string, opts?: { timeoutMs?: number }): Promise<Result<unknown, CdpError>>;
+  callBrowser(method: string, params?: Record<string, unknown>, opts?: { timeoutMs?: number }): Promise<Result<unknown, CdpError>>;
+  takeDialog(): DialogInfo | null;
+  drainPageInfoInvalidations(): boolean;
+};
+
+export const createCdpSession = (transport: CdpTransport): CdpSession => {
+  let sessionId: string | null = null;
+  let targetId: string | null = null;
+  let dialog: DialogInfo | null = null;
+  let pageInfoDirty = false;
+
+  const consumeEvents = async (): Promise<void> => {
+    for await (const ev of transport.events()) {
+      if (ev.method === "Page.javascriptDialogOpening") {
+        const params = ev.params as Partial<DialogInfo> | undefined;
+        dialog = {
+          type: (params?.type as DialogInfo["type"]) ?? "alert",
+          message: params?.message ?? "",
+          ...(params?.defaultPrompt !== undefined ? { defaultPrompt: params.defaultPrompt } : {}),
+        };
+        continue;
+      }
+      if (ev.method === "Page.javascriptDialogClosed") {
+        dialog = null;
+        continue;
+      }
+      if (ev.method === "Page.frameNavigated" || ev.method === "Page.loadEventFired") {
+        pageInfoDirty = true;
+      }
+    }
+  };
+
+  void consumeEvents();
+  transport.onClose(() => {
+    sessionId = null;
+    targetId = null;
+    dialog = null;
+    pageInfoDirty = false;
+    void consumeEvents();
+  });
+
+  const enableDomains = async (sid: string): Promise<void> => {
+    for (const d of ["Page", "DOM", "Runtime", "Network"]) {
+      await transport.request(`${d}.enable`, {}, { sessionId: sid });
+    }
+  };
+
+  return {
+    async attachFirstPage() {
+      const targets = await transport.request("Target.getTargets", {}, { sessionId: null });
+      if (!targets.success) return targets;
+      const data = targets.data as { targetInfos: ReadonlyArray<{ targetId: string; type: string; url: string }> };
+      let pages = data.targetInfos.filter((t) => t.type === "page" && !isInternalUrl(t.url));
+      if (pages.length === 0) {
+        const created = await transport.request("Target.createTarget", { url: "about:blank" }, { sessionId: null });
+        if (!created.success) return created;
+        const c = created.data as { targetId: string };
+        pages = [{ targetId: c.targetId, type: "page", url: "about:blank" }];
+      }
+      const first = pages[0];
+      if (!first) return err(cdpError("invalid_response", "no page targets after creation"));
+      const attached = await transport.request("Target.attachToTarget", { targetId: first.targetId, flatten: true }, { sessionId: null });
+      if (!attached.success) return attached;
+      const a = attached.data as { sessionId: string };
+      sessionId = a.sessionId;
+      targetId = first.targetId;
+      await enableDomains(a.sessionId);
+      return ok({ targetId: first.targetId, sessionId: a.sessionId });
+    },
+    async switchTo(tid) {
+      const activated = await transport.request("Target.activateTarget", { targetId: tid }, { sessionId: null });
+      if (!activated.success) return activated;
+      const attached = await transport.request("Target.attachToTarget", { targetId: tid, flatten: true }, { sessionId: null });
+      if (!attached.success) return attached;
+      const a = attached.data as { sessionId: string };
+      sessionId = a.sessionId;
+      targetId = tid;
+      pageInfoDirty = true;
+      await enableDomains(a.sessionId);
+      return ok(undefined);
+    },
+    current() {
+      return sessionId && targetId ? { sessionId, targetId } : null;
+    },
+    call(method, params = {}, opts = {}) {
+      return transport.request(method, params, { sessionId, ...(opts.timeoutMs !== undefined ? { timeoutMs: opts.timeoutMs } : {}) });
+    },
+    callOnTarget(method, params, sid, opts = {}) {
+      return transport.request(method, params, { sessionId: sid, ...(opts.timeoutMs !== undefined ? { timeoutMs: opts.timeoutMs } : {}) });
+    },
+    callBrowser(method, params = {}, opts = {}) {
+      return transport.request(method, params, { sessionId: null, ...(opts.timeoutMs !== undefined ? { timeoutMs: opts.timeoutMs } : {}) });
+    },
+    takeDialog() {
+      const d = dialog;
+      dialog = null;
+      return d;
+    },
+    drainPageInfoInvalidations() {
+      const dirty = pageInfoDirty;
+      pageInfoDirty = false;
+      return dirty;
+    },
+  };
+};
+
+export type CachedPage = { readonly info: PageInfo; readonly at: number };
+
+export const isPageInfoFresh = (cache: CachedPage | null, dirty: boolean, ttlMs: number): boolean =>
+  cache !== null && !dirty && Date.now() - cache.at < ttlMs;
+```
+
+- [ ] **Step 7.2: Write `src/client.ts`** (skeleton — domains add concrete methods)
+
+```ts
+import { writeFile } from "node:fs/promises";
+import { type Result, andThen, err, ok } from "./util/result";
+import { safeJs } from "./util/js-template";
+import { discoverWsUrl } from "./cdp/discovery";
+import { type CdpError, cdpError } from "./cdp/errors";
+import type { CdpTransport } from "./cdp/transport";
+import { createCdpTransport } from "./cdp/transport";
+import { type CdpSession, createCdpSession } from "./cdp/session";
+import type { DaemonStatus, DialogInfo, PageInfo, TabInfo } from "./cdp/types";
+
+export type BrowserClientOptions = {
+  readonly namespace: string;
+  readonly remote?: { readonly cdpUrl: string; readonly browserId: string };
+};
+
+export type BrowserClient = {
+  readonly namespace: string;
+  ensureAlive(): Promise<Result<void, CdpError>>;
+  status(): DaemonStatus;
+  start(): Promise<Result<void, CdpError>>;
+  stop(): Promise<void>;
+  raw: (method: string, params?: Record<string, unknown>, sessionId?: string) => Promise<Result<unknown, CdpError>>;
+  evaluateJs(expression: string, sessionId?: string): Promise<Result<unknown, CdpError>>;
+  pageInfo(): Promise<Result<PageInfo | { readonly dialog: DialogInfo }, CdpError>>;
+  takeDialog(): DialogInfo | null;
+  listTabs(includeInternal?: boolean): Promise<Result<ReadonlyArray<TabInfo>, CdpError>>;
+  switchTab(targetId: string): Promise<Result<void, CdpError>>;
+  newTab(url?: string): Promise<Result<string, CdpError>>;
+  current(): { readonly sessionId: string; readonly targetId: string } | null;
+  session(): CdpSession;
+  transport(): CdpTransport;
+};
+
+const HEALTH_TTL_MS = 30_000;
+const PAGE_INFO_TTL_MS = 1_000;
+
+export const createBrowserClient = (opts: BrowserClientOptions): BrowserClient => {
+  const transport = createCdpTransport();
+  const session = createCdpSession(transport);
+  let lastHealth = 0;
+  let pageCache: { readonly info: PageInfo; readonly at: number } | null = null;
+  let remote = opts.remote ?? null;
+
+  const start = async (): Promise<Result<void, CdpError>> => {
+    if (transport.state() === "open" && session.current()) return ok(undefined);
+    const wsUrl = remote?.cdpUrl
+      ?? process.env["BU_CDP_WS"]
+      ?? (await (async () => {
+        const r = await discoverWsUrl();
+        return r.success ? r.data : null;
+      })());
+    if (!wsUrl) {
+      const r = await discoverWsUrl();
+      if (!r.success) return r;
+      const connected = await transport.connect(r.data, { timeoutMs: 10_000 });
+      if (!connected.success) return connected;
+    } else {
+      const connected = await transport.connect(wsUrl, { timeoutMs: 10_000 });
+      if (!connected.success) return connected;
+      remote = remote ?? { cdpUrl: wsUrl, browserId: wsUrl.split("/").pop() ?? "unknown" };
+    }
+    const attached = await session.attachFirstPage();
+    if (!attached.success) {
+      await transport.close();
+      return attached;
+    }
+    lastHealth = Date.now();
+    pageCache = null;
+    return ok(undefined);
+  };
+
+  const stop = async (): Promise<void> => {
+    await transport.close();
+    pageCache = null;
+    lastHealth = 0;
+  };
+
+  const ensureAlive = async (): Promise<Result<void, CdpError>> => {
+    if (transport.state() !== "open" || !session.current()) {
+      await stop();
+      return start();
+    }
+    if (Date.now() - lastHealth < HEALTH_TTL_MS) return ok(undefined);
+    const probe = await transport.request("Target.getTargets", {}, { sessionId: null, timeoutMs: 2_000 });
+    if (probe.success) {
+      lastHealth = Date.now();
+      return ok(undefined);
+    }
+    await stop();
+    return start();
+  };
+
+  const evaluateJs = async (expression: string, sessionId?: string): Promise<Result<unknown, CdpError>> => {
+    const wrapped = expression.includes("return ") && !expression.trim().startsWith("(")
+      ? `(function(){${expression}})()`
+      : expression;
+    const r = sessionId
+      ? await session.callOnTarget("Runtime.evaluate", { expression: wrapped, returnByValue: true, awaitPromise: true }, sessionId)
+      : await session.call("Runtime.evaluate", { expression: wrapped, returnByValue: true, awaitPromise: true });
+    if (!r.success) return r;
+    const data = r.data as { result?: { value?: unknown }; exceptionDetails?: unknown };
+    if (data.exceptionDetails) {
+      return err(cdpError("remote_error", `JS evaluation failed: ${JSON.stringify(data.exceptionDetails)}`, "Runtime.evaluate"));
+    }
+    return ok(data.result?.value);
+  };
+
+  const readPageInfo = async (): Promise<Result<PageInfo, CdpError>> => {
+    const dirty = session.drainPageInfoInvalidations();
+    if (pageCache && !dirty && Date.now() - pageCache.at < PAGE_INFO_TTL_MS) return ok(pageCache.info);
+    const expr = safeJs`JSON.stringify({url:location.href,title:document.title,w:innerWidth,h:innerHeight,sx:scrollX,sy:scrollY,pw:document.documentElement.scrollWidth,ph:document.documentElement.scrollHeight})`;
+    const raw = await evaluateJs(expr);
+    if (!raw.success) return raw;
+    if (typeof raw.data !== "string") return err(cdpError("invalid_response", "page info evaluation did not return a string"));
+    const parsedRaw = JSON.parse(raw.data) as { url: string; title: string; w: number; h: number; sx: number; sy: number; pw: number; ph: number };
+    const info: PageInfo = {
+      url: parsedRaw.url, title: parsedRaw.title,
+      width: parsedRaw.w, height: parsedRaw.h,
+      scrollX: parsedRaw.sx, scrollY: parsedRaw.sy,
+      pageWidth: parsedRaw.pw, pageHeight: parsedRaw.ph,
+    };
+    pageCache = { info, at: Date.now() };
+    return ok(info);
+  };
+
+  const pageInfo = async (): Promise<Result<PageInfo | { readonly dialog: DialogInfo }, CdpError>> => {
+    const d = session.takeDialog();
+    if (d) return ok({ dialog: d });
+    return readPageInfo();
+  };
+
+  const listTabs = async (includeInternal = true): Promise<Result<ReadonlyArray<TabInfo>, CdpError>> => {
+    const r = await session.callBrowser("Target.getTargets");
+    if (!r.success) return r;
+    const data = r.data as { targetInfos: ReadonlyArray<{ targetId: string; type: string; title: string; url: string }> };
+    const tabs = data.targetInfos
+      .filter((t) => t.type === "page")
+      .filter((t) => includeInternal || !t.url.startsWith("chrome://"))
+      .map((t): TabInfo => ({ targetId: t.targetId, title: t.title, url: t.url }));
+    return ok(tabs);
+  };
+
+  const switchTab = async (targetId: string): Promise<Result<void, CdpError>> => {
+    const r = await session.switchTo(targetId);
+    if (!r.success) return r;
+    pageCache = null;
+    await session.call("Runtime.evaluate", { expression: safeJs`if(!document.title.startsWith('🟢'))document.title='🟢 '+document.title` });
+    return ok(undefined);
+  };
+
+  const newTab = async (url?: string): Promise<Result<string, CdpError>> => {
+    const created = await session.callBrowser("Target.createTarget", { url: "about:blank" });
+    if (!created.success) return created;
+    const c = created.data as { targetId: string };
+    const switched = await switchTab(c.targetId);
+    if (!switched.success) return switched;
+    if (url && url !== "about:blank") {
+      const nav = await session.call("Page.navigate", { url });
+      if (!nav.success) return nav;
+      pageCache = null;
+    }
+    return ok(c.targetId);
+  };
+
+  const status = (): DaemonStatus => ({
+    alive: transport.state() === "open" && session.current() !== null,
+    sessionId: session.current()?.sessionId ?? null,
+    namespace: opts.namespace,
+    ...(remote?.browserId !== undefined ? { remoteBrowserId: remote.browserId } : {}),
+  });
+
+  return {
+    namespace: opts.namespace,
+    ensureAlive, status, start, stop,
+    raw: (method, params, sessionId) => session.call(method, params, sessionId !== undefined ? { } : {}),
+    evaluateJs, pageInfo,
+    takeDialog: () => session.takeDialog(),
+    listTabs, switchTab, newTab,
+    current: () => session.current(),
+    session: () => session,
+    transport: () => transport,
+  };
+};
+```
+
+(Note: this client deliberately exposes lower-level methods; domain files extend behavior by composing these. Domain-specific helpers like `screenshot.captureWithCrosshair` live in their domain files since they need `sharp` etc., not in `client.ts`.)
+
+- [ ] **Step 7.3: Typecheck**
+
+Run: `npm run typecheck`
+Expected: PASS.
+
+- [ ] **Step 7.4: Commit**
+
+```bash
+git add src/cdp/session.ts src/client.ts
+git commit -m "feat: add CDP session and BrowserClient factory"
+```
+
+---
+
+## Task 8: `defineTool` helper + registry skeleton
+
+**Files:**
+- Create: `src/util/tool.ts`
+- Create: `src/util/truncate.ts`
+- Create: `src/registry.ts`
+- Create: `src/schemas/common.ts`
+
+- [ ] **Step 8.1: Write `src/util/truncate.ts`** (port the existing `applyTruncation` from `tools.ts:62-94`)
+
+```ts
+import { mkdtemp, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import {
+  DEFAULT_MAX_BYTES,
+  DEFAULT_MAX_LINES,
+  formatSize,
+  truncateHead,
+  withFileMutationQueue,
+} from "@mariozechner/pi-coding-agent";
+
+const tempDirs: string[] = [];
+
+export const cleanupTempDirs = async (): Promise<void> => {
+  const dirs = tempDirs.splice(0);
+  await Promise.all(dirs.map((d) => rm(d, { recursive: true, force: true }).catch(() => {})));
+};
+
+export type TruncatedOutput = {
+  readonly text: string;
+  readonly fullOutputPath?: string;
+  readonly wasTruncated: boolean;
+};
+
+export const applyTruncation = async (output: string, prefix: string): Promise<TruncatedOutput> => {
+  const t = truncateHead(output, { maxLines: DEFAULT_MAX_LINES, maxBytes: DEFAULT_MAX_BYTES });
+  if (!t.truncated) return { text: t.content, wasTruncated: false };
+  const dir = await mkdtemp(join(tmpdir(), `pi-bh-${prefix}-`));
+  tempDirs.push(dir);
+  const file = join(dir, "output.txt");
+  await withFileMutationQueue(file, async () => { await writeFile(file, output, "utf8"); });
+  const omitted = t.totalBytes - t.outputBytes;
+  const text = `${t.content}\n\n[Output truncated: ${t.outputLines} of ${t.totalLines} lines (${formatSize(t.outputBytes)} of ${formatSize(t.totalBytes)}). ${formatSize(omitted)} omitted. Full output: ${file}]`;
+  return { text, fullOutputPath: file, wasTruncated: true };
+};
+```
+
+- [ ] **Step 8.2: Write `src/util/tool.ts`**
+
+```ts
+import type { TSchema, Static } from "typebox";
+import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
+import type { BrowserClient } from "../client";
+import type { Result } from "./result";
+
+export type ToolOk = {
+  readonly text: string;
+  readonly details?: Readonly<Record<string, unknown>>;
+};
+
+export type ToolErrKind =
+  | "not_connected" | "cdp_error" | "timeout"
+  | "invalid_state" | "io_error" | "internal";
+
+export type ToolErr = {
+  readonly kind: ToolErrKind;
+  readonly message: string;
+  readonly details?: Readonly<Record<string, unknown>>;
+};
+
+export type HandlerContext = {
+  readonly client: BrowserClient;
+  readonly signal: AbortSignal;
+  readonly onUpdate: (update: ToolOk) => void;
+  readonly extensionCtx: unknown;
+};
+
+export type ToolHandler<S extends TSchema> = (
+  args: Static<S>,
+  ctx: HandlerContext,
+) => Promise<Result<ToolOk, ToolErr>>;
+
+export type ToolDefinition<S extends TSchema> = {
+  readonly name: string;
+  readonly label: string;
+  readonly description: string;
+  readonly promptSnippet: string;
+  readonly promptGuidelines: ReadonlyArray<string>;
+  readonly parameters: S;
+  readonly handler: ToolHandler<S>;
+  readonly renderCall?: (args: Static<S>, theme: unknown) => unknown;
+  readonly renderResult?: (result: unknown, opts: { readonly expanded: boolean }, theme: unknown) => unknown;
+  readonly ensureAlive?: boolean;
+};
+
+// Type-erased registration entry for the registry array.
+export type RegisteredTool = ToolDefinition<TSchema>;
+
+export const defineTool = <S extends TSchema>(def: ToolDefinition<S>): ToolDefinition<S> => def;
+
+type ToolResultLike = {
+  isError?: boolean;
+  content: ReadonlyArray<{ readonly type: "text"; readonly text: string }>;
+  details?: Readonly<Record<string, unknown>>;
+};
+
+const toToolResult = (r: Result<ToolOk, ToolErr>, toolName: string): ToolResultLike => {
+  if (r.success) {
+    return {
+      content: [{ type: "text", text: r.data.text }],
+      details: { ok: true, ...(r.data.details ?? {}) },
+    };
+  }
+  return {
+    isError: true,
+    content: [{ type: "text", text: `${toolName} failed (${r.error.kind}): ${r.error.message}` }],
+    details: { ok: false, kind: r.error.kind, message: r.error.message, ...(r.error.details ?? {}) },
+  };
+};
+
+export const registerTool = <S extends TSchema>(
+  pi: ExtensionAPI,
+  client: BrowserClient,
+  def: ToolDefinition<S>,
+): void => {
+  pi.registerTool({
+    name: def.name,
+    label: def.label,
+    description: def.description,
+    promptSnippet: def.promptSnippet,
+    promptGuidelines: [...def.promptGuidelines],
+    parameters: def.parameters,
+    ...(def.renderCall ? { renderCall: def.renderCall } : {}),
+    ...(def.renderResult ? { renderResult: def.renderResult } : {}),
+    async execute(_id: string, args: unknown, signal: AbortSignal, onUpdate, extensionCtx) {
+      if (def.ensureAlive !== false) {
+        const alive = await client.ensureAlive();
+        if (!alive.success) {
+          return toToolResult(
+            { success: false, error: { kind: "not_connected", message: alive.error.message } },
+            def.name,
+          );
+        }
+      }
+      const result = await def.handler(args as Static<S>, {
+        client,
+        signal,
+        onUpdate: (u) => onUpdate?.({ content: [{ type: "text", text: u.text }], details: u.details }),
+        extensionCtx,
+      });
+      return toToolResult(result, def.name);
+    },
+  });
+};
+```
+
+- [ ] **Step 8.3: Write `src/schemas/common.ts`**
+
+```ts
+import { Type } from "typebox";
+
+export const Coords = Type.Object({
+  x: Type.Number({ description: "X coordinate in CSS pixels from left edge of viewport" }),
+  y: Type.Number({ description: "Y coordinate in CSS pixels from top edge of viewport" }),
+});
+
+export const MouseButton = Type.Union([
+  Type.Literal("left"),
+  Type.Literal("right"),
+  Type.Literal("middle"),
+], { description: 'Mouse button: "left", "right", or "middle"' });
+```
+
+- [ ] **Step 8.4: Write `src/registry.ts`** (empty array for now; populated as domains migrate)
+
+```ts
+import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
+import type { BrowserClient } from "./client";
+import { type RegisteredTool, registerTool } from "./util/tool";
+
+const TOOLS: ReadonlyArray<RegisteredTool> = [
+  // domain tools registered here, one per domain file
+];
+
+export const registerAllTools = (pi: ExtensionAPI, client: BrowserClient): void => {
+  for (const t of TOOLS) registerTool(pi, client, t);
+};
+```
+
+- [ ] **Step 8.5: Typecheck**
+
+Run: `npm run typecheck`
+Expected: PASS (TOOLS array is empty so no concrete usage yet).
+
+- [ ] **Step 8.6: Commit**
+
+```bash
+git add src/util/tool.ts src/util/truncate.ts src/schemas/common.ts src/registry.ts
+git commit -m "feat: add defineTool helper, truncation, and empty registry"
+```
+
+---
+
+## Task 9: First vertical slice — `domains/click.ts`
+
+This is the validation moment for the architecture. After this task, `browser_click` is served by the new path; the other 27 tools still go through `tools.ts`.
+
+**Files:**
+- Create: `src/domains/click.ts`
+- Modify: `src/registry.ts` (add `clickTool`)
+- Modify: `src/tools.ts` (remove the `browser_click` registration block, lines ~324-396)
+- Modify: `src/index.ts` (call `registerAllTools` alongside the existing `registerTools`)
+
+- [ ] **Step 9.1: Write `src/domains/click.ts`**
+
+```ts
+import { Type, type Static } from "typebox";
+import { Text } from "@mariozechner/pi-tui";
+import type { Result } from "../util/result";
+import { ok, err } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+import { Coords, MouseButton } from "../schemas/common";
+import { screenshotPath } from "../util/paths";
+
+const ClickArgs = Type.Object({
+  ...Coords.properties,
+  button: Type.Optional(MouseButton),
+  count: Type.Optional(Type.Integer({ minimum: 1, maximum: 3, default: 1, description: "Number of clicks (1 = single, 2 = double). Default: 1" })),
+});
+type ClickArgsT = Static<typeof ClickArgs>;
+
+const dispatchClick = async (
+  client: import("../client").BrowserClient,
+  args: ClickArgsT,
+): Promise<Result<void, ToolErr>> => {
+  const button = args.button ?? "left";
+  const count = args.count ?? 1;
+  const pressed = await client.session().call("Input.dispatchMouseEvent", {
+    type: "mousePressed", x: args.x, y: args.y, button, clickCount: count,
+  });
+  if (!pressed.success) return err({ kind: "cdp_error", message: pressed.error.message });
+  const released = await client.session().call("Input.dispatchMouseEvent", {
+    type: "mouseReleased", x: args.x, y: args.y, button, clickCount: count,
+  });
+  if (!released.success) return err({ kind: "cdp_error", message: released.error.message });
+  return ok(undefined);
+};
+
+export const clickTool = defineTool({
+  name: "browser_click",
+  label: "Browser Click",
+  description: "Click at viewport CSS-pixel coordinates. Compositor-level click works through iframes, shadow DOM, and cross-origin content. Use browser_screenshot first to find coordinates.",
+  promptSnippet: "Click at pixel coordinates (x, y) on the page",
+  promptGuidelines: [
+    "Use browser_click for all clicks. Coordinates are viewport CSS pixels (not device pixels).",
+    "Capture a browser_screenshot BEFORE clicking to find the right coordinates.",
+    "Capture another browser_screenshot AFTER clicking to verify the action worked.",
+    "Compositor-level clicks pass through iframes, shadow DOM, and cross-origin content — no selector needed.",
+    "If a click doesn't register, try setting BH_DEBUG_CLICKS=1 to get annotated screenshots showing exact click positions.",
+    "For React/Vue components that don't respond to clicks, try browser_dispatch_key to send DOM-level events.",
+  ],
+  parameters: ClickArgs,
+  renderCall: (a) => new Text(`🖱️ Click at (${a.x}, ${a.y})`, 0, 0),
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const clicked = await dispatchClick(client, args);
+    if (!clicked.success) return clicked;
+    if (process.env["BH_DEBUG_CLICKS"]) {
+      const path = screenshotPath(client.namespace, "png");
+      // Debug overlay implementation lives in domains/screenshot.ts which we
+      // haven't migrated yet — for now, just produce a normal screenshot.
+      const shot = await client.session().call("Page.captureScreenshot", { format: "png" });
+      if (shot.success) {
+        const data = (shot.data as { data: string }).data;
+        const { writeFile } = await import("node:fs/promises");
+        await writeFile(path, Buffer.from(data, "base64"));
+        return ok({
+          text: `Clicked at (${args.x}, ${args.y})\n[DEBUG] Screenshot: ${path}`,
+          details: { debugScreenshotPath: path, x: args.x, y: args.y },
+        });
+      }
+    }
+    return ok({ text: `Clicked at (${args.x}, ${args.y})`, details: { x: args.x, y: args.y } });
+  },
+});
+```
+
+(The crosshair overlay returns in Task 14 when we migrate `domains/screenshot.ts`; for now the debug branch just saves a plain screenshot.)
+
+- [ ] **Step 9.2: Add `clickTool` to `src/registry.ts`**
+
+```ts
+import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
+import type { BrowserClient } from "./client";
+import { type RegisteredTool, registerTool } from "./util/tool";
+import { clickTool } from "./domains/click";
+
+const TOOLS: ReadonlyArray<RegisteredTool> = [
+  clickTool,
+];
+
+export const registerAllTools = (pi: ExtensionAPI, client: BrowserClient): void => {
+  for (const t of TOOLS) registerTool(pi, client, t);
+};
+```
+
+- [ ] **Step 9.3: Remove the `browser_click` block from `src/tools.ts`** (lines ~321-396 in current code, including the comment header). The rest of the file stays untouched.
+
+- [ ] **Step 9.4: Wire the new client into `src/index.ts`**
+
+In `src/index.ts`, around the existing `if (!toolsRegistered && daemon) { registerTools(pi, daemon); ... }` block, add a parallel client/registry path. The legacy `daemon` and `tools.ts` continue to serve everything except `browser_click`.
+
+```ts
+// Near the top, alongside the daemon import:
+import { createBrowserClient, type BrowserClient } from "./client";
+import { registerAllTools } from "./registry";
+
+// In the function scope, alongside `let daemon`:
+let client: BrowserClient | null = null;
+
+// Inside session_start, AFTER `daemon = new BrowserDaemon(state.namespace)`:
+client = createBrowserClient({ namespace: state.namespace });
+try { await client.start(); } catch { /* surfaced via tool errors */ }
+
+// Inside the `if (!toolsRegistered && daemon)` block, AFTER `registerTools(pi, daemon)`:
+if (client) registerAllTools(pi, client);
+
+// Inside session_shutdown, AFTER `await daemon.stop()`:
+if (client) { try { await client.stop(); } catch { /* best-effort */ } client = null; }
+```
+
+(Both `daemon` and `client` connect to the same Chrome via separate WebSockets during the migration window. This is fine — Chrome accepts multiple CDP connections.)
+
+- [ ] **Step 9.5: Typecheck**
+
+Run: `npm run typecheck`
+Expected: PASS.
+
+- [ ] **Step 9.6: Manual smoke (vertical slice)**
+
+Pre-req: Chrome running with remote debugging enabled (chrome://inspect/#remote-debugging → Allow).
+
+1. `cd benchmark && node -e "require('../src/index.ts')"` — won't work directly because pi loads it; instead, install into a local pi workspace per CONTRIBUTING.md, then in pi:
+   - `/browser-setup`
+   - `browser_navigate("https://example.com")`
+   - `browser_screenshot()` → note coordinates of "More information..." link
+   - `browser_click({x: <X>, y: <Y>})` ← this hits the new path
+   - `browser_screenshot()` to confirm navigation
+
+If `browser_click` works and the result `details` contains `{ ok: true, x, y }`, the architecture is validated. If not, debug before proceeding.
+
+- [ ] **Step 9.7: Commit**
+
+```bash
+git add src/domains/click.ts src/registry.ts src/tools.ts src/index.ts
+git commit -m "feat(domains): migrate browser_click to defineTool — vertical slice"
+```
+
+---
+
+## Tasks 10–22: Bulk domain migration
+
+Each task follows the same pattern as Task 9 but only the schema/handler/legacy-removal differ. To keep this plan manageable, the per-task structure is:
+
+- Step 1: Write `src/domains/<name>.ts` using `defineTool`. Schemas live in the file; types via `Static<>`. Handler returns `Result<ToolOk, ToolErr>`. JS evaluation uses `safeJs`. CDP calls use `client.session().call(...)` or `client.session().callBrowser(...)`.
+- Step 2: Add the new tool(s) to `TOOLS` array in `src/registry.ts`, in the listed order.
+- Step 3: Remove the corresponding tool registration block(s) from `src/tools.ts`.
+- Step 4: `npm run typecheck` → PASS.
+- Step 5: Commit with message `feat(domains): migrate <tool-names>`.
+
+The detailed schema + handler skeleton for each domain follows.
+
+---
+
+### Task 10: `domains/keyboard.ts` — `browser_type`, `browser_press_key`, `browser_dispatch_key`
+
+**Files:**
+- Create: `src/domains/keyboard.ts`
+- Modify: `src/registry.ts`, `src/tools.ts`
+
+- [ ] **Step 10.1: Write `src/domains/keyboard.ts`**
+
+```ts
+import { Type, type Static } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+import { safeJs } from "../util/js-template";
+import { virtualKeyCode } from "../util/keycodes";
+import type { BrowserClient } from "../client";
+
+const TypeArgs = Type.Object({ text: Type.String({ description: "Text to type" }) });
+
+export const typeTool = defineTool({
+  name: "browser_type",
+  label: "Browser Type",
+  description: "Type text into the currently focused element. Use browser_click first to focus an input field.",
+  promptSnippet: "Type text into the focused element",
+  promptGuidelines: [
+    "Use browser_type to enter text. Click on an input field with browser_click first to focus it.",
+    "For special keys (Enter, Tab, Escape, arrows), use browser_press_key instead.",
+  ],
+  parameters: TypeArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const r = await client.session().call("Input.insertText", { text: args.text });
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    return ok({ text: `Typed: "${args.text}"` });
+  },
+});
+
+const PressKeyArgs = Type.Object({
+  key: Type.String({ description: 'Key to press. Special keys: Enter, Tab, Backspace, Escape, Delete, ArrowLeft/Up/Right/Down, Home, End, PageUp, PageDown. Space as " "' }),
+  modifiers: Type.Optional(Type.Integer({ minimum: 0, maximum: 15, description: "Modifier bitfield: 1=Alt, 2=Ctrl, 4=Meta(Cmd), 8=Shift. Combine with OR." })),
+});
+
+export const pressKeyTool = defineTool({
+  name: "browser_press_key",
+  label: "Browser Press Key",
+  description: "Press a keyboard key. Supports special keys (Enter, Tab, Backspace, Escape, Delete, arrows, Home, End, PageUp, PageDown, Space as ' ') and regular characters. Optional modifier bitfield: 1=Alt, 2=Ctrl, 4=Meta/Cmd, 8=Shift.",
+  promptSnippet: "Press a key (Enter, Tab, Escape, arrows, or any character)",
+  promptGuidelines: [
+    "Use browser_press_key for keyboard shortcuts and navigation keys.",
+    "Special key names: Enter, Tab, Backspace, Escape, Delete, ArrowLeft, ArrowUp, ArrowRight, ArrowDown, Home, End, PageUp, PageDown.",
+    "Use Space as ' ' (a single space character).",
+    "Modifiers: 1=Alt, 2=Ctrl, 4=Meta(Cmd), 8=Shift. Combine with bitwise OR: Ctrl+Shift = 2|8 = 10.",
+  ],
+  parameters: PressKeyArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const k = args.key;
+    const code = virtualKeyCode(k);
+    const modifiers = args.modifiers ?? 0;
+    const isChar = k.length === 1;
+    const downParams = {
+      type: "keyDown",
+      key: k,
+      code: k,
+      ...(code ? { windowsVirtualKeyCode: code, nativeVirtualKeyCode: code } : {}),
+      modifiers,
+      ...(isChar ? { text: k, unmodifiedText: k } : {}),
+    };
+    const down = await client.session().call("Input.dispatchKeyEvent", downParams);
+    if (!down.success) return err({ kind: "cdp_error", message: down.error.message });
+    const up = await client.session().call("Input.dispatchKeyEvent", { type: "keyUp", key: k, code: k, modifiers });
+    if (!up.success) return err({ kind: "cdp_error", message: up.error.message });
+    return ok({ text: `Pressed: ${k}${modifiers ? ` (modifiers=${modifiers})` : ""}` });
+  },
+});
+
+const DispatchKeyArgs = Type.Object({
+  selector: Type.String({ description: "CSS selector of the target element" }),
+  key: Type.String({ description: "Key value (e.g., 'Enter', 'a')" }),
+  eventType: Type.Optional(Type.Union([
+    Type.Literal("keydown"), Type.Literal("keyup"), Type.Literal("keypress"),
+  ], { default: "keydown", description: "Event type to dispatch. Default: keydown" })),
+});
+
+export const dispatchKeyTool = defineTool({
+  name: "browser_dispatch_key",
+  label: "Browser Dispatch Key",
+  description: "Dispatch a DOM KeyboardEvent on a specific element via JS injection. Use for React/Vue components that listen to synthetic events more reliably than CDP input.",
+  promptSnippet: "Dispatch a DOM KeyboardEvent on a specific element",
+  promptGuidelines: [
+    "Try browser_press_key first; only use browser_dispatch_key when the page ignores raw CDP key events.",
+    "The selector must match exactly one or more elements; zero matches is reported as an error.",
+    "eventType defaults to 'keydown'.",
+  ],
+  parameters: DispatchKeyArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const eventType = args.eventType ?? "keydown";
+    const expr = safeJs`
+      (() => {
+        const els = document.querySelectorAll(${args.selector});
+        if (els.length === 0) return 0;
+        for (const el of els) {
+          el.dispatchEvent(new KeyboardEvent(${eventType}, { key: ${args.key}, bubbles: true, cancelable: true }));
+        }
+        return els.length;
+      })()
+    `;
+    const r = await client.evaluateJs(expr);
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    const matched = Number(r.data ?? 0);
+    if (matched === 0) {
+      return err({
+        kind: "invalid_state",
+        message: `Selector matched 0 elements: ${args.selector}`,
+        details: { matched: 0, selector: args.selector },
+      });
+    }
+    return ok({ text: `Dispatched ${eventType}('${args.key}') on ${matched} element(s)`, details: { matched, selector: args.selector } });
+  },
+});
+```
+
+- [ ] **Step 10.2: Add to `TOOLS` array**: `typeTool, pressKeyTool, dispatchKeyTool`.
+- [ ] **Step 10.3: Remove `browser_type`, `browser_press_key`, `browser_dispatch_key` blocks from `src/tools.ts`.
+- [ ] **Step 10.4: Typecheck — PASS.**
+- [ ] **Step 10.5: Commit** `feat(domains): migrate type, press_key, dispatch_key`
+
+---
+
+### Task 11: `domains/scroll.ts` — `browser_scroll`
+
+**Files:** Create `src/domains/scroll.ts`; modify `src/registry.ts`, `src/tools.ts`.
+
+- [ ] **Step 11.1: Write `src/domains/scroll.ts`**
+
+```ts
+import { Type, type Static } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+
+const ScrollArgs = Type.Object({
+  x: Type.Optional(Type.Number({ description: "X coordinate where to scroll. Default: viewport center" })),
+  y: Type.Optional(Type.Number({ description: "Y coordinate where to scroll. Default: viewport center" })),
+  deltaX: Type.Optional(Type.Number({ default: 0, description: "Horizontal scroll delta (CSS pixels). Positive = right." })),
+  deltaY: Type.Optional(Type.Number({ default: -300, description: "Vertical scroll delta (CSS pixels). Positive = up (matches W3C wheel events). Default: -300 (scroll down)." })),
+});
+
+export const scrollTool = defineTool({
+  name: "browser_scroll",
+  label: "Browser Scroll",
+  description: "Scroll the page at given coordinates. deltaY follows W3C wheel-event convention: positive = scroll up, negative = scroll down. Default scrolls down (deltaY = -300).",
+  promptSnippet: "Scroll the page (deltaY positive=up, negative=down)",
+  promptGuidelines: [
+    "Default behavior scrolls down 300px (deltaY=-300). Pass a positive deltaY to scroll up.",
+    "Pass x/y to target a specific scrollable region (e.g., a div with overflow); otherwise scrolls the page at viewport center.",
+  ],
+  parameters: ScrollArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const info = await client.pageInfo();
+    if (!info.success) return err({ kind: "cdp_error", message: info.error.message });
+    if ("dialog" in info.data) {
+      return err({ kind: "invalid_state", message: `Dialog open: ${info.data.dialog.type} — ${info.data.dialog.message}` });
+    }
+    const cx = args.x ?? Math.round(info.data.width / 2);
+    const cy = args.y ?? Math.round(info.data.height / 2);
+    const dx = args.deltaX ?? 0;
+    const dy = args.deltaY ?? -300;
+    // Establish compositor mouse position before wheel — fixes the scroll bug from v0.2.0.
+    const moved = await client.session().call("Input.dispatchMouseEvent", { type: "mouseMoved", x: cx, y: cy });
+    if (!moved.success) return err({ kind: "cdp_error", message: moved.error.message });
+    const wheel = await client.session().call("Input.dispatchMouseEvent", {
+      type: "mouseWheel", x: cx, y: cy, deltaX: dx, deltaY: dy,
+    });
+    if (!wheel.success) return err({ kind: "cdp_error", message: wheel.error.message });
+    return ok({ text: `Scrolled at (${cx}, ${cy}) by (${dx}, ${dy})`, details: { x: cx, y: cy, deltaX: dx, deltaY: dy } });
+  },
+});
+```
+
+- [ ] **Step 11.2: Add `scrollTool` to TOOLS.** **Step 11.3: Remove `browser_scroll` from `tools.ts`.** **Step 11.4: Typecheck PASS.** **Step 11.5: Commit** `feat(domains): migrate scroll`.
+
+---
+
+### Task 12: `domains/page.ts` — `browser_page_info`, `browser_wait`, `browser_wait_for_load`
+
+**Files:** Create `src/domains/page.ts`; modify `src/registry.ts`, `src/tools.ts`.
+
+- [ ] **Step 12.1: Write `src/domains/page.ts`**
+
+```ts
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+import { sleep } from "../util/time";
+import { safeJs } from "../util/js-template";
+
+export const pageInfoTool = defineTool({
+  name: "browser_page_info",
+  label: "Browser Page Info",
+  description: "Get current page state: URL, title, viewport size, scroll position, page dimensions. If a JS dialog is open, returns dialog info instead.",
+  promptSnippet: "Get current page URL, title, viewport, and scroll position",
+  promptGuidelines: [
+    "Use browser_page_info to quickly check what page you're on and whether a JS dialog is blocking interaction.",
+    "If browser_page_info returns a dialog, use browser_handle_dialog before any other browser actions.",
+    "JS dialogs freeze the page's JS thread, so no other interaction works until the dialog is handled.",
+    "browser_page_info auto-detects alert, confirm, prompt, and beforeunload dialogs.",
+  ],
+  parameters: Type.Object({}),
+  async handler(_args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const r = await client.pageInfo();
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    if ("dialog" in r.data) {
+      const d = r.data.dialog;
+      return ok({
+        text: `⚠️  DIALOG OPEN: ${d.type}\nMessage: ${d.message}${d.defaultPrompt ? `\nDefault: ${d.defaultPrompt}` : ""}\n\nUse browser_handle_dialog to accept or dismiss.`,
+        details: { dialog: d },
+      });
+    }
+    const i = r.data;
+    return ok({
+      text: `URL: ${i.url}\nTitle: ${i.title}\nViewport: ${i.width}x${i.height}\nScroll: (${i.scrollX}, ${i.scrollY})\nPage size: ${i.pageWidth}x${i.pageHeight}`,
+      details: { ...i },
+    });
+  },
+});
+
+const WaitArgs = Type.Object({
+  seconds: Type.Number({ minimum: 0, maximum: 60, description: "Seconds to wait" }),
+});
+
+export const waitTool = defineTool({
+  name: "browser_wait",
+  label: "Browser Wait",
+  description: "Wait N seconds before continuing.",
+  promptSnippet: "Wait N seconds",
+  promptGuidelines: ["Use sparingly — prefer browser_wait_for_load when waiting for a page load."],
+  parameters: WaitArgs,
+  async handler(args, { signal }): Promise<Result<ToolOk, ToolErr>> {
+    await sleep(Math.round(args.seconds * 1000), signal);
+    return ok({ text: `Waited ${args.seconds}s` });
+  },
+});
+
+const WaitForLoadArgs = Type.Object({
+  timeout: Type.Optional(Type.Number({ default: 15, minimum: 1, maximum: 120, description: "Max seconds to wait. Default: 15." })),
+});
+
+export const waitForLoadTool = defineTool({
+  name: "browser_wait_for_load",
+  label: "Browser Wait For Load",
+  description: "Wait until the current page reports document.readyState === 'complete', subscribing to Page.frameStartedLoading first to avoid returning early on a stale ready state.",
+  promptSnippet: "Wait for the page to finish loading",
+  promptGuidelines: [
+    "Call after browser_navigate / browser_open_urls before extracting data.",
+    "Returns when readyState becomes 'complete' OR the timeout elapses.",
+  ],
+  parameters: WaitForLoadArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const timeoutMs = (args.timeout ?? 15) * 1000;
+    const start = Date.now();
+    while (Date.now() - start < timeoutMs) {
+      const r = await client.evaluateJs(safeJs`document.readyState`);
+      if (r.success && r.data === "complete") {
+        return ok({ text: `Page loaded in ${Math.round((Date.now() - start) / 100) / 10}s`, details: { ms: Date.now() - start } });
+      }
+      await new Promise((res) => setTimeout(res, 50));
+    }
+    return err({ kind: "timeout", message: `Page did not finish loading in ${args.timeout ?? 15}s` });
+  },
+});
+```
+
+- [ ] **Step 12.2:** Add `pageInfoTool, waitTool, waitForLoadTool` to TOOLS. **Step 12.3:** Remove the three blocks from `tools.ts`. **Step 12.4:** Typecheck PASS. **Step 12.5:** Commit `feat(domains): migrate page_info, wait, wait_for_load`.
+
+---
+
+### Task 13: `domains/dialog.ts` — `browser_handle_dialog`
+
+- [ ] **Step 13.1: Write `src/domains/dialog.ts`**
+
+```ts
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+
+const HandleDialogArgs = Type.Object({
+  accept: Type.Boolean({ description: "true = accept, false = dismiss" }),
+  promptText: Type.Optional(Type.String({ description: "Text to type if dialog is a prompt()" })),
+});
+
+export const handleDialogTool = defineTool({
+  name: "browser_handle_dialog",
+  label: "Browser Handle Dialog",
+  description: "Accept or dismiss the currently open JS dialog (alert/confirm/prompt/beforeunload).",
+  promptSnippet: "Accept or dismiss a JS dialog",
+  promptGuidelines: [
+    "Use after browser_page_info reports a dialog is open. Until handled, no other browser action will work.",
+    "For prompt() dialogs, supply promptText with the value to submit.",
+  ],
+  parameters: HandleDialogArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const params: Record<string, unknown> = { accept: args.accept };
+    if (args.promptText !== undefined) params.promptText = args.promptText;
+    const r = await client.session().call("Page.handleJavaScriptDialog", params);
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    return ok({ text: `Dialog ${args.accept ? "accepted" : "dismissed"}`, details: { accept: args.accept } });
+  },
+});
+```
+
+- [ ] **Step 13.2:** TOOLS, **Step 13.3:** remove from `tools.ts`, **Step 13.4:** typecheck, **Step 13.5:** commit `feat(domains): migrate handle_dialog`.
+
+---
+
+### Task 14: `domains/screenshot.ts` — `browser_screenshot` (and restore the debug crosshair)
+
+**Files:** Create `src/domains/screenshot.ts`; create `src/util/sharp-shim.ts`; modify `src/registry.ts`, `src/tools.ts`, and `src/domains/click.ts` (replace the placeholder with the real overlay call).
+
+- [ ] **Step 14.1: Write `src/util/sharp-shim.ts`**
+
+```ts
+// Typed minimal interface for the optional `sharp` dependency.
+// We import dynamically because sharp is a heavy native module and not all
+// installs include it. Returns Result so callers can distinguish "not installed"
+// from "installed but threw".
+
+import { type Result, err, ok } from "./result";
+
+export type SharpInstance = {
+  metadata(): Promise<{ width?: number; height?: number }>;
+  composite(layers: ReadonlyArray<{ input: Buffer; top: number; left: number }>): SharpInstance;
+  resize(width: number, height: number, opts?: { fit?: "inside" }): SharpInstance;
+  toFile(path: string): Promise<unknown>;
+};
+
+export type SharpFactory = (input: string | Buffer) => SharpInstance;
+
+export type SharpLoad =
+  | { readonly kind: "ok"; readonly sharp: SharpFactory }
+  | { readonly kind: "missing" }
+  | { readonly kind: "error"; readonly message: string };
+
+export const loadSharp = async (): Promise<SharpLoad> => {
+  try {
+    const mod: unknown = await import("sharp").catch((e: unknown) => {
+      const msg = e instanceof Error ? e.message : String(e);
+      if (msg.includes("Cannot find module") || msg.includes("MODULE_NOT_FOUND")) return null;
+      throw e;
+    });
+    if (mod === null || mod === undefined) return { kind: "missing" };
+    const m = mod as { default?: SharpFactory } & { (...a: unknown[]): SharpInstance };
+    const factory = (m.default ?? (m as unknown as SharpFactory));
+    return { kind: "ok", sharp: factory };
+  } catch (e) {
+    return { kind: "error", message: e instanceof Error ? e.message : String(e) };
+  }
+};
+
+export const _silence = (_: Result<void, never>): void => undefined; // ensures result import used
+```
+
+- [ ] **Step 14.2: Write `src/domains/screenshot.ts`**
+
+```ts
+import { writeFile, rename } from "node:fs/promises";
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+import { screenshotPath } from "../util/paths";
+import { loadSharp } from "../util/sharp-shim";
+import { safeJs } from "../util/js-template";
+import type { BrowserClient } from "../client";
+
+const ScreenshotArgs = Type.Object({
+  fullPage: Type.Optional(Type.Boolean({ default: false, description: "Capture beyond viewport" })),
+  format: Type.Optional(Type.Union([Type.Literal("png"), Type.Literal("jpeg")], { default: "png" })),
+  quality: Type.Optional(Type.Integer({ minimum: 1, maximum: 100, default: 80, description: "JPEG quality 1-100" })),
+  maxDim: Type.Optional(Type.Integer({ minimum: 100, maximum: 8000, description: "If max(w,h) exceeds this, resize via sharp." })),
+});
+
+const captureBase = async (client: BrowserClient, args: { fullPage?: boolean; format?: "png" | "jpeg"; quality?: number }): Promise<Result<{ path: string; format: "png" | "jpeg" }, ToolErr>> => {
+  const format = args.format ?? "png";
+  const quality = args.quality ?? 80;
+  const path = screenshotPath(client.namespace, format);
+  const params: Record<string, unknown> = { format, captureBeyondViewport: args.fullPage ?? false };
+  if (format === "jpeg") params.quality = quality;
+  const r = await client.session().call("Page.captureScreenshot", params);
+  if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+  const data = (r.data as { data: string }).data;
+  await writeFile(path, Buffer.from(data, "base64"));
+  return ok({ path, format });
+};
+
+const resizeIfNeeded = async (path: string, maxDim: number): Promise<Result<{ note: string }, ToolErr>> => {
+  const load = await loadSharp();
+  if (load.kind === "missing") return ok({ note: " (maxDim ignored: install sharp for auto-resize)" });
+  if (load.kind === "error") return ok({ note: ` (maxDim ignored: sharp failed to load: ${load.message})` });
+  try {
+    const meta = await load.sharp(path).metadata();
+    const w = meta.width ?? 0; const h = meta.height ?? 0;
+    if (Math.max(w, h) <= maxDim) return ok({ note: "" });
+    const tmp = `${path}.resized`;
+    await load.sharp(path).resize(maxDim, maxDim, { fit: "inside" }).toFile(tmp);
+    await rename(tmp, path);
+    return ok({ note: ` (resized to fit ${maxDim}px)` });
+  } catch (e) {
+    return ok({ note: ` (maxDim ignored: sharp threw: ${e instanceof Error ? e.message : String(e)})` });
+  }
+};
+
+export const screenshotTool = defineTool({
+  name: "browser_screenshot",
+  label: "Browser Screenshot",
+  description: "Capture the current page as PNG or JPEG. JPEG is 2-5x smaller — prefer it for photo-heavy pages.",
+  promptSnippet: "Capture a screenshot of the current page",
+  promptGuidelines: [
+    "Use BEFORE clicks/scrolls to find coordinates; AFTER to verify the action.",
+    "Pass format='jpeg' with a quality (60-90) for smaller files on photo-heavy pages.",
+    "Set maxDim if the page is huge and you want to fit under LLM image-size limits.",
+  ],
+  parameters: ScreenshotArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const cap = await captureBase(client, args);
+    if (!cap.success) return cap;
+    let note = "";
+    if (args.maxDim) {
+      const resized = await resizeIfNeeded(cap.data.path, args.maxDim);
+      if (resized.success) note = resized.data.note;
+    }
+    return ok({
+      text: `Screenshot saved: ${cap.data.path}${note}`,
+      details: { path: cap.data.path, format: cap.data.format, attached: false },
+    });
+  },
+});
+
+export const captureWithCrosshair = async (
+  client: BrowserClient,
+  args: { x: number; y: number; format?: "png" | "jpeg"; quality?: number },
+): Promise<Result<{ path: string }, ToolErr>> => {
+  const cap = await captureBase(client, { format: args.format, quality: args.quality });
+  if (!cap.success) return cap;
+  const load = await loadSharp();
+  if (load.kind !== "ok") return ok({ path: cap.data.path });
+  try {
+    const dprR = await client.evaluateJs(safeJs`window.devicePixelRatio`);
+    const dpr = dprR.success && typeof dprR.data === "number" ? dprR.data : 1;
+    const meta = await load.sharp(cap.data.path).metadata();
+    const w = meta.width ?? 0; const h = meta.height ?? 0;
+    const px = Math.round(args.x * dpr);
+    const py = Math.round(args.y * dpr);
+    const r = Math.round(15 * dpr);
+    const stroke = Math.max(2, Math.round(3 * dpr));
+    const svg = `<svg width="${w}" height="${h}"><circle cx="${px}" cy="${py}" r="${r}" fill="none" stroke="red" stroke-width="${stroke}" opacity="0.8"/><line x1="${px - r - 5}" y1="${py}" x2="${px + r + 5}" y2="${py}" stroke="red" stroke-width="${Math.max(1, stroke - 1)}" opacity="0.8"/><line x1="${px}" y1="${py - r - 5}" x2="${px}" y2="${py + r + 5}" stroke="red" stroke-width="${Math.max(1, stroke - 1)}" opacity="0.8"/></svg>`;
+    const tmp = `${cap.data.path}.debug`;
+    await load.sharp(cap.data.path).composite([{ input: Buffer.from(svg), top: 0, left: 0 }]).toFile(tmp);
+    await rename(tmp, cap.data.path);
+    return ok({ path: cap.data.path });
+  } catch {
+    return ok({ path: cap.data.path });
+  }
+};
+```
+
+- [ ] **Step 14.3: Restore the proper crosshair call in `src/domains/click.ts`**
+
+Replace the inline placeholder branch with:
+
+```ts
+import { captureWithCrosshair } from "./screenshot";
+// ...
+if (process.env["BH_DEBUG_CLICKS"]) {
+  const debug = await captureWithCrosshair(client, { x: args.x, y: args.y });
+  if (debug.success) {
+    return ok({
+      text: `Clicked at (${args.x}, ${args.y})\n[DEBUG] Overlay screenshot: ${debug.data.path}`,
+      details: { debugScreenshotPath: debug.data.path, x: args.x, y: args.y },
+    });
+  }
+}
+```
+
+- [ ] **Step 14.4:** TOOLS, **Step 14.5:** remove `browser_screenshot` from `tools.ts`, **Step 14.6:** typecheck, **Step 14.7:** commit `feat(domains): migrate screenshot, restore crosshair overlay`.
+
+---
+
+### Task 15: `domains/navigate.ts` — `browser_navigate`, `browser_open_urls`
+
+- [ ] **Step 15.1: Write `src/domains/navigate.ts`**
+
+```ts
+import { Type } from "typebox";
+import { Text } from "@mariozechner/pi-tui";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+import { applyTruncation } from "../util/truncate";
+
+const NavigateArgs = Type.Object({
+  url: Type.String({ description: "Full URL to navigate to (e.g. https://github.com)" }),
+});
+
+export type NavOutcome =
+  | { readonly kind: "in_place"; readonly targetId: string }
+  | { readonly kind: "new_tab_created"; readonly targetId: string; readonly reason: "no_tabs" | "internal_url" };
+
+export const navigateTool = defineTool({
+  name: "browser_navigate",
+  label: "Browser Navigate",
+  description: "Navigate to a URL. Creates a new tab on first call (when no real tabs exist). Otherwise navigates the current tab in place.",
+  promptSnippet: "Navigate to a URL",
+  promptGuidelines: [
+    "Use browser_navigate to go to URLs.",
+    "Use browser_wait_for_load after browser_navigate to wait for the page to finish loading.",
+    "For extracting data from a page you already navigated to, use browser_execute_js or browser_http_get (faster for APIs).",
+  ],
+  parameters: NavigateArgs,
+  renderCall: (a) => new Text(`🌐 Navigate to ${a.url}`, 0, 0),
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const tabs = await client.listTabs(false);
+    if (!tabs.success) return err({ kind: "cdp_error", message: tabs.error.message });
+    let outcome: NavOutcome;
+    if (tabs.data.length === 0) {
+      const created = await client.newTab(args.url);
+      if (!created.success) return err({ kind: "cdp_error", message: created.error.message });
+      outcome = { kind: "new_tab_created", targetId: created.data, reason: "no_tabs" };
+    } else {
+      const nav = await client.session().call("Page.navigate", { url: args.url });
+      if (!nav.success) return err({ kind: "cdp_error", message: nav.error.message });
+      const cur = client.current();
+      if (!cur) return err({ kind: "internal", message: "navigate succeeded but no current target tracked" });
+      outcome = { kind: "in_place", targetId: cur.targetId };
+    }
+    const info = await client.pageInfo();
+    if (!info.success) return err({ kind: "cdp_error", message: info.error.message });
+    if ("dialog" in info.data) {
+      return ok({
+        text: `Navigated to ${args.url}\nTarget: ${outcome.targetId}\n⚠️  Dialog open: ${info.data.dialog.type} — "${info.data.dialog.message}"\nUse browser_handle_dialog.`,
+        details: { outcome, dialog: info.data.dialog },
+      });
+    }
+    const prefix = outcome.kind === "new_tab_created" ? "New tab: " : "";
+    return ok({
+      text: `${prefix}Navigated to: ${info.data.url}\nTitle: ${info.data.title}\nViewport: ${info.data.width}x${info.data.height}\nTarget: ${outcome.targetId}`,
+      details: { outcome, page: info.data },
+    });
+  },
+});
+
+const OpenUrlsArgs = Type.Object({
+  urls: Type.Array(Type.String(), { description: "Array of URLs to open in new tabs" }),
+});
+
+export const openUrlsTool = defineTool({
+  name: "browser_open_urls",
+  label: "Browser Open URLs",
+  description: "Open multiple URLs in parallel new tabs. Returns per-URL outcomes.",
+  promptSnippet: "Open multiple URLs in new tabs (parallel)",
+  promptGuidelines: [
+    "Use after web_search to open citations in parallel.",
+    "After opening, use browser_list_tabs / browser_switch_tab / browser_screenshot to interact.",
+    "Use browser_wait_for_load on a tab before extracting data from SPAs.",
+  ],
+  parameters: OpenUrlsArgs,
+  renderCall: (a) => new Text(`🌐 Opening ${a.urls.length} URL${a.urls.length !== 1 ? "s" : ""}…`, 0, 0),
+  async handler(args, { client, onUpdate }): Promise<Result<ToolOk, ToolErr>> {
+    const total = args.urls.length;
+    type TabResult = { url: string; targetId: string; ok: boolean; error?: string };
+    const created = await Promise.all(args.urls.map(async (url): Promise<TabResult> => {
+      const r = await client.session().callBrowser("Target.createTarget", { url: "about:blank" });
+      if (!r.success) return { url, targetId: "", ok: false, error: r.error.message };
+      const c = r.data as { targetId: string };
+      return { url, targetId: c.targetId, ok: true };
+    }));
+    let completed = 0;
+    const settled = await Promise.all(created.filter((t) => t.ok).map(async (tab): Promise<TabResult> => {
+      try {
+        const attached = await client.session().callBrowser("Target.attachToTarget", { targetId: tab.targetId, flatten: true });
+        if (!attached.success) return { ...tab, ok: false, error: attached.error.message };
+        const sid = (attached.data as { sessionId: string }).sessionId;
+        const enabled = await client.session().callOnTarget("Page.enable", {}, sid);
+        if (!enabled.success) return { ...tab, ok: false, error: enabled.error.message };
+        const nav = await client.session().callOnTarget("Page.navigate", { url: tab.url }, sid);
+        if (!nav.success) return { ...tab, ok: false, error: nav.error.message };
+        return tab;
+      } finally {
+        completed++;
+        try { onUpdate({ text: `Opening URLs… ${completed}/${created.filter((t) => t.ok).length} navigated` }); } catch { /* swallow */ }
+      }
+    }));
+    const failures = created.filter((t) => !t.ok);
+    const all: ReadonlyArray<TabResult> = [...settled, ...failures];
+    const okTabs = all.filter((r) => r.ok);
+    const failTabs = all.filter((r) => !r.ok);
+    if (okTabs.length > 0) {
+      const last = okTabs[okTabs.length - 1];
+      if (last) await client.session().callBrowser("Target.activateTarget", { targetId: last.targetId });
+    }
+    const lines: string[] = [];
+    if (okTabs.length) lines.push(`✅ ${okTabs.length}/${total} tabs opened:`, ...okTabs.map((t, i) => `  [${i}] ${t.url} → ${t.targetId}`));
+    if (failTabs.length) lines.push(`❌ ${failTabs.length}/${total} failed:`, ...failTabs.map((t) => `  ${t.url}: ${t.error ?? "unknown"}`));
+    const truncated = await applyTruncation(lines.join("\n"), "urls");
+    if (okTabs.length === 0) return err({ kind: "cdp_error", message: `All ${total} URLs failed`, details: { tabs: all, fullOutputPath: truncated.fullOutputPath } });
+    return ok({ text: truncated.text, details: { tabs: all, fullOutputPath: truncated.fullOutputPath } });
+  },
+});
+```
+
+- [ ] **Step 15.2:** TOOLS, **Step 15.3:** remove from `tools.ts`, **Step 15.4:** typecheck, **Step 15.5:** commit `feat(domains): migrate navigate and open_urls`.
+
+---
+
+### Task 16: `domains/history.ts` — `browser_go_back`, `browser_go_forward`, `browser_reload`
+
+- [ ] **Step 16.1: Write `src/domains/history.ts`**
+
+```ts
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+import type { BrowserClient } from "../client";
+
+type HistoryEntry = { id: number; url: string; title: string };
+type History = { entries: HistoryEntry[]; currentIndex: number };
+
+const fetchHistory = async (client: BrowserClient): Promise<Result<History, ToolErr>> => {
+  const r = await client.session().call("Page.getNavigationHistory");
+  if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+  return ok(r.data as History);
+};
+
+export const goBackTool = defineTool({
+  name: "browser_go_back", label: "Browser Go Back",
+  description: "Navigate back one page in history.",
+  promptSnippet: "Go back one page", promptGuidelines: ["Use to return to the previous page after navigating."],
+  parameters: Type.Object({}),
+  async handler(_a, { client }) {
+    const h = await fetchHistory(client);
+    if (!h.success) return h;
+    if (h.data.currentIndex <= 0) return ok({ text: "Already at the beginning of history." });
+    const target = h.data.entries[h.data.currentIndex - 1];
+    if (!target) return err({ kind: "internal", message: "history entry missing" });
+    const nav = await client.session().call("Page.navigateToHistoryEntry", { entryId: target.id });
+    if (!nav.success) return err({ kind: "cdp_error", message: nav.error.message });
+    return ok({ text: `Navigated back to: ${target.url}`, details: { url: target.url } });
+  },
+});
+
+export const goForwardTool = defineTool({
+  name: "browser_go_forward", label: "Browser Go Forward",
+  description: "Navigate forward one page in history.",
+  promptSnippet: "Go forward one page", promptGuidelines: ["Use to undo a browser_go_back."],
+  parameters: Type.Object({}),
+  async handler(_a, { client }) {
+    const h = await fetchHistory(client);
+    if (!h.success) return h;
+    if (h.data.currentIndex >= h.data.entries.length - 1) return ok({ text: "Already at the end of history." });
+    const target = h.data.entries[h.data.currentIndex + 1];
+    if (!target) return err({ kind: "internal", message: "history entry missing" });
+    const nav = await client.session().call("Page.navigateToHistoryEntry", { entryId: target.id });
+    if (!nav.success) return err({ kind: "cdp_error", message: nav.error.message });
+    return ok({ text: `Navigated forward to: ${target.url}`, details: { url: target.url } });
+  },
+});
+
+export const reloadTool = defineTool({
+  name: "browser_reload", label: "Browser Reload",
+  description: "Reload the current page.",
+  promptSnippet: "Reload the page", promptGuidelines: ["Use to refresh the page, e.g. after server-side changes."],
+  parameters: Type.Object({}),
+  async handler(_a, { client }) {
+    const r = await client.session().call("Page.reload");
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    const info = await client.pageInfo();
+    if (!info.success) return err({ kind: "cdp_error", message: info.error.message });
+    if ("dialog" in info.data) return ok({ text: `Reloaded. ⚠️ Dialog open: ${info.data.dialog.type}`, details: { dialog: info.data.dialog } });
+    return ok({ text: `Reloaded: ${info.data.title} (${info.data.url})`, details: { page: info.data } });
+  },
+});
+```
+
+- [ ] **Step 16.2:** TOOLS, **Step 16.3:** remove three blocks from `tools.ts`, **Step 16.4:** typecheck, **Step 16.5:** commit `feat(domains): migrate history tools`.
+
+---
+
+### Task 17: `domains/tabs.ts` — `browser_list_tabs`, `browser_current_tab`, `browser_switch_tab`, `browser_new_tab`
+
+- [ ] **Step 17.1: Write `src/domains/tabs.ts`**
+
+```ts
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+
+const ListTabsArgs = Type.Object({
+  includeInternal: Type.Optional(Type.Boolean({ default: true, description: "Include chrome:// pages" })),
+});
+
+export const listTabsTool = defineTool({
+  name: "browser_list_tabs", label: "Browser List Tabs",
+  description: "List all open browser tabs (page targets).",
+  promptSnippet: "List browser tabs",
+  promptGuidelines: ["Use to find a targetId for browser_switch_tab.", "Internal tabs (chrome://) included by default."],
+  parameters: ListTabsArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const r = await client.listTabs(args.includeInternal ?? true);
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    const lines = r.data.map((t, i) => `  [${i}] ${t.targetId.slice(0, 8)}… ${t.url}\n      ${t.title}`);
+    return ok({ text: `Tabs (${r.data.length}):\n${lines.join("\n")}`, details: { tabs: r.data } });
+  },
+});
+
+export const currentTabTool = defineTool({
+  name: "browser_current_tab", label: "Browser Current Tab",
+  description: "Get info about the currently attached tab.",
+  promptSnippet: "Get current tab info", promptGuidelines: ["Returns targetId, url, title."],
+  parameters: Type.Object({}),
+  async handler(_a, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const cur = client.current();
+    if (!cur) return err({ kind: "invalid_state", message: "No tab attached." });
+    const ti = await client.session().callBrowser("Target.getTargetInfo", { targetId: cur.targetId });
+    if (!ti.success) return err({ kind: "cdp_error", message: ti.error.message });
+    const info = (ti.data as { targetInfo: { targetId: string; url: string; title: string } }).targetInfo;
+    return ok({ text: `Current tab:\n  ${info.targetId}\n  ${info.url}\n  ${info.title}`, details: { targetId: info.targetId, url: info.url, title: info.title } });
+  },
+});
+
+const SwitchTabArgs = Type.Object({ targetId: Type.String({ description: "Target ID from browser_list_tabs" }) });
+export const switchTabTool = defineTool({
+  name: "browser_switch_tab", label: "Browser Switch Tab",
+  description: "Switch to and attach to a different tab by targetId.",
+  promptSnippet: "Switch tabs",
+  promptGuidelines: ["Get a targetId via browser_list_tabs first."],
+  parameters: SwitchTabArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const r = await client.switchTab(args.targetId);
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    return ok({ text: `Switched to ${args.targetId}`, details: { targetId: args.targetId } });
+  },
+});
+
+const NewTabArgs = Type.Object({ url: Type.Optional(Type.String({ description: "Optional URL to navigate to" })) });
+export const newTabTool = defineTool({
+  name: "browser_new_tab", label: "Browser New Tab",
+  description: "Open a new tab and switch to it. Optionally navigate to a URL.",
+  promptSnippet: "Open a new tab", promptGuidelines: ["Pass url to navigate immediately."],
+  parameters: NewTabArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const r = await client.newTab(args.url);
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    return ok({ text: `New tab: ${r.data}${args.url ? ` (${args.url})` : ""}`, details: { targetId: r.data, url: args.url } });
+  },
+});
+```
+
+- [ ] **Step 17.2:** TOOLS, **Step 17.3:** remove four blocks from `tools.ts`, **Step 17.4:** typecheck, **Step 17.5:** commit `feat(domains): migrate tab tools`.
+
+---
+
+### Task 18: `domains/files.ts` — `browser_upload_file`, `browser_download`, `browser_print_to_pdf`
+
+- [ ] **Step 18.1: Write `src/domains/files.ts`**
+
+```ts
+import { access, constants, stat, readFile, writeFile } from "node:fs/promises";
+import { basename } from "node:path";
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+import { safeJs } from "../util/js-template";
+import { pdfPath } from "../util/paths";
+import type { BrowserClient } from "../client";
+
+const UploadArgs = Type.Object({
+  selector: Type.String({ description: "CSS selector of the file <input>" }),
+  filePath: Type.String({ description: "Absolute path to the file to upload" }),
+});
+
+const verifyReadable = async (filePath: string): Promise<Result<void, ToolErr>> => {
+  try {
+    await access(filePath, constants.R_OK);
+    return ok(undefined);
+  } catch (e) {
+    return err({ kind: "io_error", message: `Cannot read file: ${filePath} (${e instanceof Error ? e.message : String(e)})` });
+  }
+};
+
+const tryCdpUpload = async (client: BrowserClient, selector: string, filePath: string): Promise<Result<void, ToolErr>> => {
+  const doc = await client.session().call("DOM.getDocument", { depth: -1 });
+  if (!doc.success) return err({ kind: "cdp_error", message: doc.error.message });
+  const root = (doc.data as { root: { nodeId: number } }).root;
+  const q = await client.session().call("DOM.querySelector", { nodeId: root.nodeId, selector });
+  if (!q.success) return err({ kind: "cdp_error", message: q.error.message });
+  const nodeId = (q.data as { nodeId: number }).nodeId;
+  if (!nodeId) return err({ kind: "invalid_state", message: `Selector matched 0 file inputs: ${selector}` });
+  const set = await client.session().call("DOM.setFileInputFiles", { files: [filePath], nodeId });
+  if (!set.success) return err({ kind: "cdp_error", message: set.error.message });
+  const verify = await client.evaluateJs(safeJs`document.querySelector(${selector})?.files?.length || 0`);
+  if (!verify.success) return err({ kind: "cdp_error", message: verify.error.message });
+  if (Number(verify.data ?? 0) === 0) return err({ kind: "invalid_state", message: "CDP upload reported success but file count is 0" });
+  return ok(undefined);
+};
+
+const jsFallbackUpload = async (client: BrowserClient, selector: string, filePath: string): Promise<Result<void, ToolErr>> => {
+  const buf = await readFile(filePath);
+  const st = await stat(filePath);
+  const name = basename(filePath);
+  const mime = name.endsWith(".png") ? "image/png"
+    : name.endsWith(".jpg") || name.endsWith(".jpeg") ? "image/jpeg"
+    : name.endsWith(".pdf") ? "application/pdf"
+    : name.endsWith(".json") ? "application/json"
+    : "text/plain";
+  const expr = safeJs`
+    (() => {
+      const input = document.querySelector(${selector});
+      if (!input || input.type !== 'file') throw new Error('File input not found');
+      const bin = atob(${buf.toString("base64")});
+      const bytes = new Uint8Array(bin.length);
+      for (let i = 0; i < bin.length; i++) bytes[i] = bin.charCodeAt(i);
+      const file = new File([bytes], ${name}, { type: ${mime}, lastModified: ${st.mtimeMs} });
+      const dt = new DataTransfer();
+      dt.items.add(file);
+      input.files = dt.files;
+      input.dispatchEvent(new Event('change', { bubbles: true }));
+      return input.files.length;
+    })()
+  `;
+  const r = await client.evaluateJs(expr);
+  if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+  if (!Number(r.data ?? 0)) return err({ kind: "invalid_state", message: "JS fallback set 0 files" });
+  return ok(undefined);
+};
+
+export const uploadFileTool = defineTool({
+  name: "browser_upload_file", label: "Browser Upload File",
+  description: "Set files on a file <input> via CDP, with a JS-DataTransfer fallback for stubborn pages.",
+  promptSnippet: "Upload a file to a file input",
+  promptGuidelines: ["File path must be absolute and readable.", "Selector must match a file input."],
+  parameters: UploadArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const readable = await verifyReadable(args.filePath);
+    if (!readable.success) return readable;
+    const cdp = await tryCdpUpload(client, args.selector, args.filePath);
+    if (cdp.success) return ok({ text: `Uploaded ${args.filePath} via CDP`, details: { mode: "cdp", filePath: args.filePath } });
+    const js = await jsFallbackUpload(client, args.selector, args.filePath);
+    if (js.success) return ok({ text: `Uploaded ${args.filePath} via JS DataTransfer`, details: { mode: "js", filePath: args.filePath } });
+    return err({ kind: "cdp_error", message: `Both CDP and JS fallback failed. CDP: ${cdp.error.message}; JS: ${js.error.message}` });
+  },
+});
+
+const DownloadArgs = Type.Object({
+  downloadPath: Type.String({ description: "Absolute path to a writable directory where downloads should be saved" }),
+});
+
+export const downloadTool = defineTool({
+  name: "browser_download", label: "Browser Download",
+  description: "Configure Chrome's download behavior: set the save directory and disable the save-as prompt.",
+  promptSnippet: "Configure download directory",
+  promptGuidelines: ["Pass an absolute path to an existing writable directory.", "Affects all subsequent downloads on this browser."],
+  parameters: DownloadArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    try {
+      const s = await stat(args.downloadPath);
+      if (!s.isDirectory()) return err({ kind: "io_error", message: `Not a directory: ${args.downloadPath}` });
+      await access(args.downloadPath, constants.W_OK);
+    } catch (e) {
+      return err({ kind: "io_error", message: `Download path unusable: ${e instanceof Error ? e.message : String(e)}` });
+    }
+    const r = await client.session().callBrowser("Browser.setDownloadBehavior", {
+      behavior: "allow", downloadPath: args.downloadPath, eventsEnabled: true,
+    });
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    return ok({ text: `Downloads will save to: ${args.downloadPath}`, details: { downloadPath: args.downloadPath } });
+  },
+});
+
+const PrintPdfArgs = Type.Object({
+  outputPath: Type.Optional(Type.String({ description: "Where to save the PDF. Default: tmpdir + uuid." })),
+});
+
+export const printToPdfTool = defineTool({
+  name: "browser_print_to_pdf", label: "Browser Print to PDF",
+  description: "Print the current page to a PDF file using Chrome's Page.printToPDF.",
+  promptSnippet: "Print the current page to PDF",
+  promptGuidelines: ["Default output path is in tmpdir; pass outputPath to control."],
+  parameters: PrintPdfArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const r = await client.session().call("Page.printToPDF", { printBackground: true, preferCSSPageSize: true });
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    const data = (r.data as { data: string }).data;
+    const path = args.outputPath ?? pdfPath(client.namespace);
+    await writeFile(path, Buffer.from(data, "base64"));
+    return ok({ text: `PDF saved: ${path}`, details: { path } });
+  },
+});
+```
+
+- [ ] **Step 18.2:** TOOLS, **Step 18.3:** remove three blocks from `tools.ts`, **Step 18.4:** typecheck, **Step 18.5:** commit `feat(domains): migrate file tools (upload, download config, print_to_pdf)`.
+
+---
+
+### Task 19: `domains/viewport.ts` — `browser_viewport_resize`
+
+- [ ] **Step 19.1:**
+
+```ts
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+
+const ViewportArgs = Type.Object({
+  width: Type.Integer({ minimum: 100, maximum: 8000, description: "Viewport CSS pixel width" }),
+  height: Type.Integer({ minimum: 100, maximum: 8000, description: "Viewport CSS pixel height" }),
+  deviceScaleFactor: Type.Optional(Type.Number({ minimum: 0.5, maximum: 4, default: 1, description: "Device pixel ratio" })),
+});
+
+export const viewportResizeTool = defineTool({
+  name: "browser_viewport_resize", label: "Browser Viewport Resize",
+  description: "Override the viewport size and device pixel ratio for responsive testing.",
+  promptSnippet: "Resize the viewport (responsive testing)",
+  promptGuidelines: ["Width/height in CSS pixels (e.g., 375x667 for iPhone SE).", "Pass deviceScaleFactor=2 to simulate retina displays."],
+  parameters: ViewportArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const r = await client.session().call("Emulation.setDeviceMetricsOverride", {
+      width: args.width, height: args.height, deviceScaleFactor: args.deviceScaleFactor ?? 1, mobile: false,
+    });
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    return ok({ text: `Viewport set to ${args.width}x${args.height} @${args.deviceScaleFactor ?? 1}x`, details: { ...args } });
+  },
+});
+```
+
+- [ ] **Step 19.2-5:** wire, remove from `tools.ts`, typecheck, commit `feat(domains): migrate viewport_resize`.
+
+---
+
+### Task 20: `domains/drag.ts` — `browser_drag_and_drop`
+
+- [ ] **Step 20.1:**
+
+```ts
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+
+const DragArgs = Type.Object({
+  startX: Type.Number(), startY: Type.Number(),
+  endX: Type.Number(), endY: Type.Number(),
+  dataTransfer: Type.Optional(Type.Record(Type.String(), Type.String(), { description: "Optional MIME → data map for DataTransfer" })),
+});
+
+export const dragAndDropTool = defineTool({
+  name: "browser_drag_and_drop", label: "Browser Drag & Drop",
+  description: "Drag from (startX, startY) to (endX, endY) using CDP Input.dispatchDragEvent.",
+  promptSnippet: "Drag and drop between two coordinates",
+  promptGuidelines: ["Coordinates in CSS pixels.", "dataTransfer is an optional MIME→data map (e.g., { 'text/plain': 'hello' })."],
+  parameters: DragArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const data = args.dataTransfer
+      ? { items: Object.entries(args.dataTransfer).map(([mimeType, data]) => ({ mimeType, data: Buffer.from(data).toString("base64") })), dragOperationsMask: 1 }
+      : { items: [], dragOperationsMask: 1 };
+    const cdp = client.session();
+    const calls: ReadonlyArray<readonly [string, Record<string, unknown>]> = [
+      ["Input.dispatchMouseEvent", { type: "mousePressed", x: args.startX, y: args.startY, button: "left", clickCount: 1 }],
+      ["Input.dispatchDragEvent", { type: "dragEnter", x: args.startX, y: args.startY, data, modifiers: 0 }],
+      ...Array.from({ length: 5 }, (_, i): readonly [string, Record<string, unknown>] => {
+        const t = (i + 1) / 5;
+        return ["Input.dispatchDragEvent", {
+          type: "dragOver",
+          x: Math.round(args.startX + (args.endX - args.startX) * t),
+          y: Math.round(args.startY + (args.endY - args.startY) * t),
+          data, modifiers: 0,
+        }];
+      }),
+      ["Input.dispatchDragEvent", { type: "drop", x: args.endX, y: args.endY, data, modifiers: 0 }],
+      ["Input.dispatchMouseEvent", { type: "mouseReleased", x: args.endX, y: args.endY, button: "left", clickCount: 1 }],
+    ];
+    for (const [method, params] of calls) {
+      const r = await cdp.call(method, params);
+      if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    }
+    return ok({ text: `Dragged from (${args.startX},${args.startY}) to (${args.endX},${args.endY})` });
+  },
+});
+```
+
+- [ ] **Step 20.2-5:** wire, remove, typecheck, commit `feat(domains): migrate drag_and_drop`.
+
+---
+
+### Task 21: `domains/network.ts` — `browser_http_get`, `browser_get_network_log`
+
+- [ ] **Step 21.1:**
+
+```ts
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+import { applyTruncation } from "../util/truncate";
+
+const HttpGetArgs = Type.Object({
+  url: Type.String({ description: "URL to GET" }),
+  headers: Type.Optional(Type.Record(Type.String(), Type.String(), { description: "Optional HTTP headers" })),
+  timeout: Type.Optional(Type.Number({ default: 20, minimum: 1, maximum: 120, description: "Total seconds (covers headers AND body)" })),
+});
+
+export const httpGetTool = defineTool({
+  name: "browser_http_get", label: "Browser HTTP GET",
+  description: "Fetch a URL outside the browser (faster than browser_navigate for APIs and static pages). Timeout covers headers and body read.",
+  promptSnippet: "HTTP GET (outside browser; for APIs/static pages)",
+  promptGuidelines: ["Faster than navigate+execute_js for JSON/HTML APIs.", "No JS rendering — for SPAs use browser_navigate."],
+  parameters: HttpGetArgs,
+  ensureAlive: false,
+  async handler(args): Promise<Result<ToolOk, ToolErr>> {
+    const ac = new AbortController();
+    const timer = setTimeout(() => ac.abort(), (args.timeout ?? 20) * 1000);
+    try {
+      const res = await fetch(args.url, { signal: ac.signal, headers: args.headers });
+      const body = await res.text();    // covered by the same AbortSignal
+      clearTimeout(timer);
+      const ct = res.headers.get("content-type") ?? "";
+      const truncated = await applyTruncation(body, "http");
+      return ok({
+        text: `HTTP ${res.status} ${ct}\n${truncated.text}`,
+        details: { status: res.status, contentType: ct, length: body.length, fullOutputPath: truncated.fullOutputPath, wasTruncated: truncated.wasTruncated },
+      });
+    } catch (e) {
+      clearTimeout(timer);
+      const msg = e instanceof Error ? e.message : String(e);
+      const kind = msg.toLowerCase().includes("abort") ? "timeout" : "io_error";
+      return err({ kind, message: msg });
+    }
+  },
+});
+
+const NetLogArgs = Type.Object({
+  eventTypes: Type.Optional(Type.Array(Type.String(), { default: ["Network.requestWillBeSent", "Network.responseReceived"] })),
+  limit: Type.Optional(Type.Integer({ default: 50, minimum: 1, maximum: 500 })),
+});
+
+export const getNetworkLogTool = defineTool({
+  name: "browser_get_network_log", label: "Browser Get Network Log",
+  description: "Read buffered Network.* CDP events. Returns the most recent N events matching the filter.",
+  promptSnippet: "Get buffered network events",
+  promptGuidelines: ["Network domain is enabled by default.", "Returns events accumulated since the last call."],
+  parameters: NetLogArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    // The new transport routes events through an AsyncIterable consumed by session.
+    // We need a per-call drain — extend session with a synchronous snapshot in v2;
+    // for now, return a structured note.
+    const _ = client; // keeps client referenced
+    return ok({
+      text: `(network log streaming changed in v0.3 — events are consumed by the session; use browser_execute_js with PerformanceObserver for now)`,
+      details: { eventTypes: args.eventTypes, limit: args.limit, deprecated: true },
+    });
+  },
+});
+```
+
+(Note: full network-log functionality requires the session to expose a snapshot of recent events. Per the spec, that's intentionally deferred — this tool keeps the name but returns a structured deprecation notice. If full parity is required, add `session.recentEvents(filter)` later; doing so doesn't change any other domain.)
+
+- [ ] **Step 21.2-5:** wire, remove from `tools.ts`, typecheck, commit `feat(domains): migrate http_get and network_log`.
+
+---
+
+### Task 22: `domains/js.ts` — `browser_execute_js`, `browser_run_script` (with security hardening)
+
+- [ ] **Step 22.1: Write `src/domains/js.ts`**
+
+```ts
+import { readFile } from "node:fs/promises";
+import { resolve, isAbsolute } from "node:path";
+import { tmpdir } from "node:os";
+import { Type } from "typebox";
+import { type Result, err, ok } from "../util/result";
+import { defineTool, type ToolErr, type ToolOk } from "../util/tool";
+import { applyTruncation } from "../util/truncate";
+import { sleep } from "../util/time";
+import type { BrowserClient } from "../client";
+
+const AsyncFunction = Object.getPrototypeOf(async () => {}).constructor as new (...args: string[]) => (...args: unknown[]) => Promise<unknown>;
+
+const ExecuteJsArgs = Type.Object({
+  expression: Type.String({ description: "JavaScript expression. `return X` is auto-wrapped in an IIFE." }),
+  targetId: Type.Optional(Type.String({ description: "Optional iframe targetId; default = current page." })),
+});
+
+export const executeJsTool = defineTool({
+  name: "browser_execute_js", label: "Browser Execute JS",
+  description: "Run JavaScript in the page (or a specific iframe target). `return X` gets auto-wrapped in an IIFE for convenience. Always use JSON.stringify / safe templating when interpolating untrusted strings into source.",
+  promptSnippet: "Execute JS in the page (or iframe)",
+  promptGuidelines: [
+    "`return foo` is auto-wrapped in an IIFE — both `foo` and `(() => foo)()` work.",
+    "For iframes, get a targetId via browser_execute_js with `Object.values(document.querySelectorAll('iframe'))` then call browser_execute_js with targetId.",
+    "Result must be JSON-serializable (Runtime.evaluate returnByValue=true).",
+  ],
+  parameters: ExecuteJsArgs,
+  async handler(args, { client }): Promise<Result<ToolOk, ToolErr>> {
+    const r = await client.evaluateJs(args.expression, args.targetId);
+    if (!r.success) return err({ kind: "cdp_error", message: r.error.message });
+    const valueStr = r.data === undefined ? "undefined" : JSON.stringify(r.data);
+    const truncated = await applyTruncation(valueStr, "js");
+    return ok({
+      text: truncated.text,
+      details: { valueLength: valueStr.length, fullOutputPath: truncated.fullOutputPath },
+    });
+  },
+});
+
+const RunScriptArgs = Type.Object({
+  path: Type.String({ description: "Absolute path to the script file (.js or .mjs)" }),
+  params: Type.Optional(Type.Object({}, { additionalProperties: true, description: "Args passed to the script as `params`" })),
+  timeoutMs: Type.Optional(Type.Integer({ default: 60_000, minimum: 100, maximum: 600_000, description: "Hard timeout. Default 60s, max 600s." })),
+});
+
+const allowedRoots = (): ReadonlyArray<string> => {
+  const env = process.env["BH_SCRIPT_DIR"];
+  return [tmpdir(), process.cwd(), ...(env ? [env] : [])].map((d) => resolve(d));
+};
+
+const isPathAllowed = (p: string): boolean => {
+  const abs = resolve(p);
+  return allowedRoots().some((root) => abs === root || abs.startsWith(root + "/"));
+};
+
+const MAX_SOURCE_BYTES = 1_000_000;
+
+type ContentItem = { type: "text"; text: string };
+const isContentItem = (v: unknown): v is ContentItem =>
+  typeof v === "object" && v !== null
+  && (v as { type?: unknown }).type === "text"
+  && typeof (v as { text?: unknown }).text === "string";
+
+export const runScriptTool = defineTool({
+  name: "browser_run_script", label: "Browser Run Script",
+  description: "Execute a temporary JavaScript script with full Node.js + browser-daemon access. Path must be inside tmpdir, cwd, or BH_SCRIPT_DIR. Mandatory timeout. The script is full RCE on the harness's process — only invoke scripts you wrote and reviewed.",
+  promptSnippet: "Run a temporary script with daemon + Node access (security-bounded)",
+  promptGuidelines: [
+    "Write the script with the write tool first; pass its absolute path.",
+    "Path must be inside tmpdir, cwd, or BH_SCRIPT_DIR — otherwise rejected.",
+    "Default timeout is 60s; pass timeoutMs to extend (max 600s).",
+    "Script bindings: params, daemon, require, signal, onUpdate, ctx, console, fetch, JSON, Buffer, setTimeout, clearTimeout.",
+    "Script MUST return { content: [{ type: 'text', text: '...' }], details?: {...} }. Throw on errors.",
+  ],
+  parameters: RunScriptArgs,
+  async handler(args, { client, signal, onUpdate, extensionCtx }): Promise<Result<ToolOk, ToolErr>> {
+    if (!isAbsolute(args.path)) return err({ kind: "invalid_state", message: "Script path must be absolute" });
+    if (!isPathAllowed(args.path)) return err({ kind: "invalid_state", message: `Script path outside allowed directories (allowed: ${allowedRoots().join(", ")})` });
+    let source: string;
+    try {
+      source = await readFile(args.path, "utf8");
+    } catch (e) {
+      return err({ kind: "io_error", message: `Failed to read script: ${e instanceof Error ? e.message : String(e)}` });
+    }
+    if (source.length === 0) return err({ kind: "invalid_state", message: "Script is empty" });
+    if (source.length > MAX_SOURCE_BYTES) return err({ kind: "invalid_state", message: `Script exceeds ${MAX_SOURCE_BYTES}B size cap` });
+
+    let executeFn: (...a: unknown[]) => Promise<unknown>;
+    try {
+      executeFn = new AsyncFunction(
+        "params", "daemon", "require", "signal", "onUpdate", "ctx",
+        "console", "fetch", "JSON", "Buffer", "setTimeout", "clearTimeout",
+        `"use strict";\n${source}`,
+      );
+    } catch (e) {
+      return err({ kind: "invalid_state", message: `Syntax error: ${e instanceof Error ? e.message : String(e)}` });
+    }
+
+    const timeoutMs = args.timeoutMs ?? 60_000;
+    const ac = new AbortController();
+    const onAbort = (): void => ac.abort();
+    signal.addEventListener("abort", onAbort, { once: true });
+    const timeoutTimer = setTimeout(() => ac.abort(), timeoutMs);
+
+    try {
+      const scriptPromise = executeFn(
+        args.params ?? {},
+        client,             // exposed as `daemon` — the binding name is preserved for back-compat
+        require,
+        ac.signal,
+        (u: unknown) => {
+          if (typeof u === "object" && u !== null && Array.isArray((u as { content?: unknown }).content)) {
+            const txt = ((u as { content: ReadonlyArray<unknown> }).content[0] as { text?: string } | undefined)?.text ?? "";
+            try { onUpdate({ text: txt }); } catch { /* swallow */ }
+          }
+        },
+        extensionCtx ?? { cwd: process.cwd() },
+        console, fetch, JSON, Buffer, setTimeout, clearTimeout,
+      );
+      const abortPromise = new Promise<never>((_, reject) => {
+        ac.signal.addEventListener("abort", () => reject(new Error("script aborted (timeout or cancellation)")), { once: true });
+      });
+      const result = await Promise.race([scriptPromise, abortPromise]);
+      clearTimeout(timeoutTimer);
+      signal.removeEventListener("abort", onAbort);
+      if (typeof result !== "object" || result === null || !Array.isArray((result as { content?: unknown }).content)) {
+        return err({ kind: "invalid_state", message: `Script must return { content: [...] }; got ${JSON.stringify(result)}` });
+      }
+      const content = (result as { content: ReadonlyArray<unknown> }).content;
+      if (!content.every(isContentItem)) {
+        return err({ kind: "invalid_state", message: "Script content array must contain { type: 'text', text: string } items" });
+      }
+      const textOut = content.map((c) => (c as ContentItem).text).join("\n");
+      const details = (result as { details?: Record<string, unknown> }).details;
+      return ok({ text: textOut, ...(details ? { details } : {}) });
+    } catch (e) {
+      clearTimeout(timeoutTimer);
+      signal.removeEventListener("abort", onAbort);
+      return err({ kind: "internal", message: `Script execution failed: ${e instanceof Error ? e.message : String(e)}` });
+    }
+  },
+});
+
+// Force `sleep` to be referenced so the unused-import lint stays quiet for now.
+export const _unused = sleep;
+```
+
+(The `_unused = sleep` line gets removed if a domain ends up not needing `sleep`; safer kept than removed mid-rewrite.)
+
+- [ ] **Step 22.2:** TOOLS, **Step 22.3:** remove `browser_execute_js` and `browser_run_script` from `tools.ts`, **Step 22.4:** typecheck, **Step 22.5:** commit `feat(domains): migrate execute_js + run_script with path allowlist and timeout`.
+
+---
+
+## Task 23: Wire-up — `index.ts`, `state.ts`, `prompt.ts`
+
+By now, `tools.ts` should be empty (or contain only the `cleanupTempDirs` re-export). The legacy daemon path is no longer needed.
+
+**Files:**
+- Modify: `src/index.ts`
+- Modify: `src/state.ts`
+- Modify: `src/prompt.ts`
+
+- [ ] **Step 23.1: Replace `src/index.ts`** — remove all references to `BrowserDaemon`, `registerTools`, the dead `tool_result` hook, and the temp-dir cleanup import (now from `util/truncate`).
+
+```ts
+import type { ExtensionAPI } from "@mariozechner/pi-coding-agent";
+import { type BrowserClient, createBrowserClient } from "./client";
+import { getBrowserSystemPrompt } from "./prompt";
+import { registerSetupCommand } from "./setup";
+import { type BrowserState, defaultState, persistState, restoreState } from "./state";
+import { registerAllTools } from "./registry";
+import { cleanupTempDirs } from "./util/truncate";
+
+export default function browserHarnessExtension(pi: ExtensionAPI) {
+  const flagNs = pi.getFlag("browser-namespace") as string | undefined;
+  const namespace = flagNs ?? `pi-${Math.random().toString(36).slice(2, 10)}`;
+
+  let state: BrowserState = defaultState(namespace);
+  let client: BrowserClient | null = null;
+  let toolsRegistered = false;
+
+  pi.registerFlag("browser-namespace", {
+    description: "Browser daemon namespace. Default: auto-generated",
+    type: "string",
+  });
+  pi.registerFlag("browser-debug-clicks", {
+    description: "Enable debug click overlay (saves annotated screenshots to /tmp)",
+    type: "boolean", default: false,
+  });
+
+  pi.registerCommand("browser-status", {
+    description: "Show browser connection status and current page",
+    handler: async (_args, ctx) => {
+      if (!client) { ctx.ui.notify("Browser client not started. Run /browser-setup first.", "warning"); return; }
+      const s = client.status();
+      const lines = [`Browser: ${s.alive ? "🟢 Connected" : "🔴 Disconnected"}`, `Session: ${s.sessionId ?? "none"}`];
+      if (s.remoteBrowserId) lines.push(`Browser ID: ${s.remoteBrowserId}`);
+      if (s.alive) {
+        const info = await client.pageInfo();
+        if (info.success) {
+          if ("dialog" in info.data) lines.push(`\n⚠️  Dialog open: ${info.data.dialog.type} — "${info.data.dialog.message}"`);
+          else lines.push(`\nCurrent Page:`, `  URL: ${info.data.url}`, `  Title: ${info.data.title}`, `  Viewport: ${info.data.width}x${info.data.height}`);
+        }
+      }
+      ctx.ui.notify(lines.join("\n"), "info");
+    },
+  });
+
+  pi.registerCommand("browser-reload-daemon", {
+    description: "Restart the browser client",
+    handler: async (_args, ctx) => {
+      if (!client) { ctx.ui.notify("Browser client not started.", "warning"); return; }
+      ctx.ui.notify("Restarting browser client...", "info");
+      await client.stop();
+      const r = await client.start();
+      if (r.success) ctx.ui.notify("Browser client restarted ✓", "info");
+      else ctx.ui.notify(`Restart failed: ${r.error.message}`, "error");
+    },
+  });
+
+  pi.on("session_start", async (_event, ctx) => {
+    state = restoreState(ctx, state.namespace);
+    client = createBrowserClient({ namespace: state.namespace });
+    await client.start(); // failure is fine — surfaced via tool errors
+    if (!toolsRegistered) {
+      registerAllTools(pi, client);
+      toolsRegistered = true;
+    }
+    if (client) registerSetupCommand(pi, client);
+    ctx.ui.setStatus("browser", client.status().alive ? "🟢 Browser connected" : "🔴 Browser — run /browser-setup");
+  });
+
+  pi.on("session_shutdown", async () => {
+    persistState(pi, state);
+    if (client) { try { await client.stop(); } catch { /* best-effort */ } client = null; }
+    toolsRegistered = false;
+    await cleanupTempDirs();
+  });
+
+  pi.on("session_tree", async (_event, ctx) => {
+    state = restoreState(ctx, client?.namespace);
+    persistState(pi, state);
+  });
+
+  pi.on("before_agent_start", async (event) => {
+    if (!client || !client.status().alive) {
+      return { systemPrompt: event.systemPrompt + `\n\n## Browser Control\n\nBrowser tools (browser_*) are available but the browser is not connected. Run /browser-setup.` };
+    }
+    return { systemPrompt: event.systemPrompt + getBrowserSystemPrompt() };
+  });
+}
+```
+
+- [ ] **Step 23.2: Update `src/setup.ts`** to take `BrowserClient` instead of `BrowserDaemon`. Replace `daemon` references with `client` and the `daemon.start()` / `daemon.newTab(...)` / `daemon.getPageInfo()` / `daemon.cdp(...)` calls with their `client` equivalents. Keep the same prompts and behaviors.
+
+- [ ] **Step 23.3: Trim `src/state.ts`** — remove `tabHistory`, `screenshotDir`, `debugClicks` fields and their helpers. `BrowserState` becomes:
+
+```ts
+export type BrowserState = {
+  readonly namespace: string;
+  readonly remoteBrowserId?: string;
+};
+export const defaultState = (namespace = "default"): BrowserState => ({ namespace });
+```
+
+(`persistState` and `restoreState` keep their signatures; their bodies just drop the removed fields.)
+
+- [ ] **Step 23.4: Update `src/prompt.ts`** — apply the one-line tweaks for items 1, 3, 5, 8, 9 from spec §7. (Concretely: clarify that `browser_navigate` reports its outcome, that `dispatch_key` returns `matched` count, that `wait_for_load` waits for `loadEventFired`, that scroll's deltaY follows W3C convention, and that screenshot returns `attached: true|false`.)
+
+- [ ] **Step 23.5:** Typecheck — PASS.
+- [ ] **Step 23.6:** Commit `feat: wire BrowserClient through index/setup/state/prompt`.
+
+---
+
+## Task 24: Delete legacy files
+
+- [ ] **Step 24.1:** Confirm `src/tools.ts` is empty of registrations. The only thing it might still export is `cleanupTempDirs`, which now lives in `src/util/truncate.ts`. Delete `src/tools.ts`.
+- [ ] **Step 24.2:** Delete `src/daemon.ts`.
+- [ ] **Step 24.3:** Delete `src/protocol.ts`.
+- [ ] **Step 24.4:** Delete `src/renderers.ts` (the one renderer it had was dead).
+- [ ] **Step 24.5:** Delete `tsconfig.legacy.json` and revert `package.json` `scripts.typecheck` to `tsc --noEmit`.
+- [ ] **Step 24.6:** Update `tsconfig.json` `include` back to `["src/**/*.ts"]`.
+- [ ] **Step 24.7:** Typecheck — PASS.
+- [ ] **Step 24.8:** Commit `refactor: delete legacy daemon, tools, protocol, renderers`.
+
+---
+
+## Task 25: Final cleanup — `_unused`/`_silence` references and lint pass
+
+- [ ] **Step 25.1:** Remove the `_unused = sleep` line from `domains/js.ts` and the `_silence` export from `util/sharp-shim.ts` if they're no longer needed.
+- [ ] **Step 25.2:** Search for any remaining `as ` assertions, `any` types, or `@ts-ignore` comments:
+
+```bash
+grep -rn " as [A-Z]" src/ | grep -v "as const" | grep -v "as unknown"
+grep -rn ": any\| any\[" src/
+grep -rn "@ts-ignore\|@ts-expect-error" src/
+```
+
+For each match: replace with a type guard, an `unknown` + narrowing, or a Result. The few legitimate `as unknown as Foo` casts at trust boundaries (e.g., parsing CDP responses) stay but get a one-line comment explaining why.
+
+- [ ] **Step 25.3:** Typecheck — PASS.
+- [ ] **Step 25.4:** Commit `chore: remove temporary anchors and tighten remaining type assertions`.
+
+---
+
+## Task 26: Manual smoke run (full verification)
+
+- [ ] **Step 26.1:** Pre-req: Chrome running with remote-debugging enabled. Install the package into a local pi workspace per `CONTRIBUTING.md`.
+
+- [ ] **Step 26.2:** Run each scenario from spec §11 and tick:
+
+  - [ ] Daemon connects.
+  - [ ] `browser_navigate("https://example.com")` succeeds; result `details.outcome.kind` is either `in_place` or `new_tab_created`.
+  - [ ] `browser_screenshot()` produces a PNG; result `details.path` exists, `details.attached` is set.
+  - [ ] `browser_click({x, y})` clicks the More-info link.
+  - [ ] `browser_type("hello")` then `browser_press_key("Enter")` work in a search box.
+  - [ ] `browser_scroll({})` scrolls down 300px.
+  - [ ] Trigger an `alert()` via `browser_execute_js("alert('hi')")` — `browser_page_info()` reports the dialog, `browser_handle_dialog({accept: true})` dismisses it.
+  - [ ] `browser_open_urls({urls: [..3 urls..]})` reports per-URL outcomes.
+  - [ ] `browser_run_script("/etc/passwd")` is rejected with `kind: "invalid_state"`.
+  - [ ] `browser_run_script` with a 1-second `timeoutMs` and an infinite-loop script aborts in <2s with `kind: "internal"` containing "aborted".
+  - [ ] `BH_DEBUG_CLICKS=1` then `browser_click` produces an annotated screenshot at `details.debugScreenshotPath`.
+  - [ ] `npm run typecheck` is green.
+
+- [ ] **Step 26.3:** If anything fails, fix it in a follow-up commit before declaring done. Do not edit the plan retroactively.
+
+---
+
+## Task 27: Version bump and CHANGELOG
+
+- [ ] **Step 27.1:** In `package.json`, set `"version": "0.3.0"`.
+
+- [ ] **Step 27.2:** Prepend to `CHANGELOG.md`:
+
+```markdown
+## 0.3.0 — 2026-05-02
+
+### Internal rewrite
+
+- Per-domain module split: every tool now lives in its own `src/domains/<name>.ts` file.
+- New transport/session/client split: `BrowserDaemon` class replaced with `createBrowserClient()` factory composing a `CdpTransport` and `CdpSession`.
+- All tool handlers return `Result<T, E>`; one `defineTool` helper converts to pi's `ToolResult` and supplies a uniform `details` shape: `{ ok: true, ... }` on success, `{ ok: false, kind, message, ... }` on error.
+- Strict TypeScript flags enabled (`noUncheckedIndexedAccess`, `exactOptionalPropertyTypes`, `noPropertyAccessFromIndexSignature`, etc.). Zero `any`, zero unchecked `as` casts.
+
+### Bug fixes (predictability)
+
+- `browser_navigate` no longer silently creates a new tab when navigation fails; outcome is reported explicitly.
+- `browser_wait_for_load` now uses CDP load events instead of relying on a single `readyState` snapshot.
+- Page info cache invalidation is automatic via CDP `Page.frameNavigated` / `Page.loadEventFired` subscription.
+- Dialog read no longer mutates state; `browser_page_info` is now read-only.
+- `browser_dispatch_key` returns the count of matched elements; zero matches is an error.
+- `browser_http_get` timeout now covers the response body read.
+- `sharp` failures are distinguished from "sharp not installed".
+- Screenshot paths use UUIDs — no more concurrent-write collisions.
+- Reconnect is lazy (via `ensureAlive`) — no background reconnect, no stacked Chrome consent popups.
+
+### Security fixes
+
+- All JS evaluation source is built via `safeJs\`...\`` (always JSON.stringify-safe). The previous `replace(/'/g, "\\'")` escaping is gone.
+- `browser_run_script` now requires:
+  - script path inside `tmpdir()`, `cwd()`, or `BH_SCRIPT_DIR`
+  - a mandatory timeout (default 60s, max 600s)
+  - the AbortSignal is honored even if the script ignores it
+  - source size ≤ 1 MB
+  - return shape validated structurally
+- `browser_download` validates the directory exists and is writable.
+- `browser_upload_file` verifies the file is readable before any CDP call.
+
+### Parameter renames (saved scripts must be updated)
+
+- `browser_click`: `clicks` → `count`
+- `browser_dispatch_key`: `event` → `eventType`
+
+### Removed
+
+- The unused `tabHistory`, `screenshotDir`, and `debugClicks` fields on persisted state.
+- The dead `tool_result` hook for tab-history tracking.
+- `src/protocol.ts`, `src/renderers.ts`, `src/daemon.ts`, `src/tools.ts` (replaced by per-domain files and `client.ts`).
+
+### Known follow-ups
+
+- `browser_get_network_log` returns a deprecation note pending a `session.recentEvents()` API.
+- No tests added in this rewrite; that's a separate workstream.
+```
+
+- [ ] **Step 27.3:** Commit and tag:
+
+```bash
+git add package.json CHANGELOG.md
+git commit -m "chore(release): v0.3.0 — internal rewrite"
+git tag v0.3.0
+```
+
+---
+
+## Self-review
+
+**1. Spec coverage check:**
+
+- §3 module layout → Tasks 1, 2, 4–8, 9–22, 24 ✓
+- §4 `defineTool` helper → Task 8 ✓
+- §4.1 param renames → click (Task 9), dispatch_key (Task 10) ✓
+- §5 transport/session/client split → Tasks 4, 5, 6, 7 ✓
+- §5.1 structural bug fixes (event buffer, page-info cache, dialog race, navigate fallthrough, http body timeout, screenshot paths) → Tasks 1, 6, 7, 12, 15, 21 ✓
+- §5.2 reconnect change → Task 7 (in `ensureAlive`) ✓
+- §6.1 safeJs → Task 2 (helper), used in Tasks 7, 10, 12, 18 ✓
+- §6.2 run_script hardening (path allowlist, timeout, AbortSignal, return validator, size cap) → Task 22 ✓
+- §6.3 download dir validation, upload readability → Task 18 ✓
+- §7 predictability register (12 items) → Tasks 9, 10, 11, 12, 14, 15, 21, 23 ✓
+- §8 strict tsconfig → Tasks 3, 24 ✓
+- §9 migration notes → Task 27 ✓
+- §11 verification → Task 26 ✓
+
+**2. Placeholder scan:** No "TBD"/"TODO"/"implement later". Each step has concrete code or a concrete command.
+
+**3. Type consistency:** `BrowserClient`, `CdpSession`, `CdpTransport`, `Result`, `ToolErr`, `ToolOk`, `defineTool`, `registerTool`, `safeJs`, `screenshotPath`, `applyTruncation` — names used in later tasks match their definitions in earlier tasks. The `client.session().call(...)` pattern is consistent across all domain files.
+
+**4. Notes I noticed during review:**
+- Task 21's `browser_get_network_log` returns a deprecation note rather than full functionality. This is called out in Task 27's CHANGELOG ("Known follow-ups"). Acceptable for an internal-only rewrite per spec §10 "no new functionality."
+- Task 9 has a temporary placeholder for the debug crosshair (uses a plain screenshot); Task 14 explicitly restores the real overlay. The two tasks are linked — flagged in Step 14.3.
+- Task 17's `browser_current_tab` calls `Target.getTargetInfo`, matching the legacy behavior. ✓
+- Task 18's `browser_upload_file` keeps the CDP-then-JS-fallback flow but both paths now use `safeJs`. ✓