fix: kill leaked Chrome processes on profile seed failure

When a profile is pinned and ProcessSingleton fails to delegate, the
spawned Chrome process starts a full second browser instance. The
sentinel never appeared, but the spawned process was never killed
(detached + unref'd + reference discarded), accumulating zombie
browsers that consume RAM.

Three changes:
- Store child process ref and expose kill() on ProfileWindowHandle.
  Call kill() when the sentinel doesn't appear within the timeout.
- Only clear profileContextId when the browser UUID changes (Chrome
  mints a fresh UUID on every launch), avoiding unnecessary re-spawns.
- Don't clear profileContextId in setProfilePin when the pin hasn't
  changed, preventing gratuitous re-spawns on session_start.

5 files changed, 32 insertions, 10 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 772d9bb..5e09777 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,14 @@
 
 All notable changes to pi-browser-harness will be documented in this file.
 
+## 0.10.1 — 2026-07-26
+
+### Fixed
+
+- **Chrome process leak on profile seed failure.** When a profile is pinned and `seedProfileWindow` spawns Chrome via `openProfileWindow`, the spawned child is kept as `detached: true` + `unref()`. If Chromium's ProcessSingleton fails to delegate (user-data-dir mismatch, multiple browsers, Chrome busy/crashed), the spawned process starts a full second browser instance. The sentinel never appears, the seed times out, but the spawned Chrome process was never killed — accumulating zombie browser instances that consume RAM. The fix stores the child process reference, exposes a `kill()` on the returned handle, and calls it on seed timeout.
+- **Unnecessary Chrome re-spawns on every `start()`.** `profileContextId` was unconditionally cleared on every `start()`, forcing a new profile-window launch via ProcessSingleton even when Chrome hadn't restarted and the context was still valid. Now the context is cleared only when the browser UUID in the WebSocket URL changes — which Chrome re-mints on every launch.
+- **`setProfilePin` no longer clears context when the pin hasn't changed.** Loading the same pin from disk on `session_start` was clearing `profileContextId`, forcing yet another Chrome spawn on the next `start()`.
+
 ## 0.10.0 — 2026-07-25
 
 ### Added
diff --git a/package.json b/package.json
index 6e7cd50..8fcf9e1 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "pi-browser-harness",
-  "version": "0.10.0",
+  "version": "0.10.1",
   "description": "Browser control extension for pi — navigate, click, type, screenshot, and extract data from real Chrome via CDP",
   "keywords": [
     "pi-package",
diff --git a/src/client.ts b/src/client.ts
index 1049212..4d8c3a8 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -170,11 +170,12 @@ export const createBrowserClient = (opts: BrowserClientOptions): BrowserClient =
     }
     const connected = await transport.connect(wsUrl, { timeoutMs: 10_000 });
     if (!connected.success) return connected;
-    if (!remote) {
-      remote = { cdpUrl: wsUrl, browserId: wsUrl.split("/").pop() ?? "unknown" };
+
+    const newBrowserId: string = wsUrl.split("/").pop() ?? "unknown";
+    if (!remote || remote.browserId !== newBrowserId) {
+      profileContextId = undefined;
     }
-    // A fresh browser run invalidates any context id resolved earlier.
-    profileContextId = undefined;
+    remote = { cdpUrl: wsUrl, browserId: newBrowserId };
     const seeded = await seedIfPinned();
     if (!seeded.success) {
       await transport.close();
@@ -397,9 +398,13 @@ export const createBrowserClient = (opts: BrowserClientOptions): BrowserClient =
     userDataDir: () => userDataDir,
     profilePin: () => profilePin,
     setProfilePin: (pin) => {
+      const changed = pin === null
+        ? profilePin !== null
+        : profilePin === null || profilePin.userDataDir !== pin.userDataDir || profilePin.profileDir !== pin.profileDir;
       profilePin = pin;
-      // The old profile's context no longer describes where tabs should go.
-      profileContextId = undefined;
+      if (changed) {
+        profileContextId = undefined;
+      }
     },
     profileContextId: () => profileContextId,
     setProfileContextId: (contextId) => {
diff --git a/src/profile/bind.ts b/src/profile/bind.ts
index aeb59d3..10b38a3 100644
--- a/src/profile/bind.ts
+++ b/src/profile/bind.ts
@@ -93,7 +93,7 @@ export const seedProfileWindow = async (
     return err(cdpError("discovery_failed", `${launched.error} — ${manualFallbackHint(pin)}`));
   }
 
-  const { sentinelUrl, cleanup } = launched.data;
+  const { sentinelUrl, cleanup, kill } = launched.data;
   const deadline = Date.now() + SEED_DEADLINE_MS;
   let seed: PageTarget | undefined;
   while (Date.now() < deadline && !seed) {
@@ -102,6 +102,7 @@ export const seedProfileWindow = async (
   }
 
   if (!seed) {
+    kill();
     await cleanup();
     return err(cdpError(
       "timeout",
diff --git a/src/profile/launch.ts b/src/profile/launch.ts
index 4f8f65a..fd93d3d 100644
--- a/src/profile/launch.ts
+++ b/src/profile/launch.ts
@@ -15,7 +15,7 @@
  * identification correct when the user opens tabs at the same moment.
  */
 
-import { spawn } from "node:child_process";
+import { spawn, type ChildProcess } from "node:child_process";
 import { randomUUID } from "node:crypto";
 import { rm, writeFile } from "node:fs/promises";
 import { tmpdir } from "node:os";
@@ -42,6 +42,7 @@ export type ProfileWindowHandle = {
   readonly sentinelUrl: string;
   /** Remove the sentinel file. Safe to call more than once. */
   readonly cleanup: () => Promise<void>;
+  readonly kill: () => void;
 };
 
 const SENTINEL_HTML = (token: string): string =>
@@ -68,10 +69,11 @@ export const openProfileWindow = async (
   if (req.explicitUserDataDir) args.push(`--user-data-dir=${req.explicitUserDataDir}`);
   args.push(`--profile-directory=${req.profileDir}`, "--new-window", sentinelUrl);
 
+  let child: ChildProcess | null = null;
   try {
     // No shell: arguments are passed as an array, so profile names and paths
     // containing spaces survive intact on every platform.
-    const child = spawn(req.exePath, args, { detached: true, stdio: "ignore" });
+    child = spawn(req.exePath, args, { detached: true, stdio: "ignore" });
     child.unref();
     // The launcher process exits as soon as the running browser takes over the
     // command line; an error here means the binary itself could not be started.
@@ -86,5 +88,11 @@ export const openProfileWindow = async (
     cleanup: async () => {
       await rm(file, { force: true }).catch(() => {});
     },
+    kill: () => {
+      if (child) {
+        try { child.kill("SIGTERM"); } catch {}
+        child = null;
+      }
+    },
   });
 };