refactor: one door from a tool to the browser

Four routes coexisted: cdpCall, a raw client.session().call, a session
held in a local and called directly, and client.evaluateJs — and five
files mixed two or three of them. The CdpError-to-ToolErr mapping was
hand-copied at nine sites, plus a private copy in isolated-tab.ts.

domains/cdp-call.ts now owns all of it: cdpErrToToolErr, cdpCall,
cdpCallOnTarget, cdpCallBrowser, evalJs. Every other file under
src/domains goes through them, which also removes a pile of
`if (!r.success) return err({ kind: "cdp_error", ... })` boilerplate in
favour of returning the failed Result as-is.

Two scanner rules keep it that way, scoped to src/domains/ so the layer
that legitimately owns the session — cdp/ and client.ts — is unaffected.
Scoping is new to the rule model; without it the rules fired on the
transport itself.

One deliberate behaviour change: a CDP timeout now surfaces as
kind "timeout" rather than "cdp_error". isolated-tab.ts already did this
and the other 13 sites flattened it; the shared mapper uses the honest
label rather than preserving the mislabel.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

2 files changed, 20 insertions, 2 deletions

diff --git a/scripts/boundary-allowlist.ts b/scripts/boundary-allowlist.ts
index bb34139..512aa40 100644
--- a/scripts/boundary-allowlist.ts
+++ b/scripts/boundary-allowlist.ts
@@ -42,6 +42,19 @@ export const ALLOWLIST: ReadonlyArray<Exemption> = [
       "renderCall is stored under a per-tool Static<S> but invoked through the erased TSchema form; the generic-correlation limit makes this unavoidable and the value is the tool's own handler, created with the same S",
   },
   {
+    path: "src/domains/cdp-call.ts",
+    rule: "raw-cdp-call",
+    count: 3,
+    reason:
+      "the one door from a tool to CDP: cdpCall, cdpCallOnTarget and cdpCallBrowser each reach the session once and map CdpError to ToolErr, so no other file under src/domains needs to",
+  },
+  {
+    path: "src/domains/cdp-call.ts",
+    rule: "raw-evaluate",
+    count: 1,
+    reason: "evalJs is the single wrapper over client.evaluateJs, for the same reason",
+  },
+  {
     path: "src/domains/js.ts",
     rule: "trailing-cast",
     count: 1,
diff --git a/scripts/check-boundaries.ts b/scripts/check-boundaries.ts
index c438b83..7dd97e2 100644
--- a/scripts/check-boundaries.ts
+++ b/scripts/check-boundaries.ts
@@ -11,7 +11,8 @@ export type Violation = {
   readonly text: string;
 };
 
-const RULES: ReadonlyArray<{ readonly rule: string; readonly re: RegExp }> = [
+// `scope` restricts a rule to one layer: the tool layer must go through domains/cdp-call.ts, while cdp/ and client.ts are the layer that owns the session.
+const RULES: ReadonlyArray<{ readonly rule: string; readonly re: RegExp; readonly scope?: RegExp }> = [
   { rule: "as-any", re: /\bas\s+any\b/ },
   { rule: "ts-ignore", re: /@ts-(ignore|expect-error|nocheck)/ },
   { rule: "non-null-assertion", re: /[A-Za-z_$)\]]!\s*(?:[.[(;,)\]}]|$)/ },
@@ -20,6 +21,8 @@ const RULES: ReadonlyArray<{ readonly rule: string; readonly re: RegExp }> = [
   { rule: "named-cast", re: /\bas\s+(?:new\s+)?[A-Z][A-Za-z0-9_]*/ },
   { rule: "function-cast", re: /\bas\s+\(/ },
   { rule: "trailing-cast", re: /\bas\s*$/ },
+  { rule: "raw-cdp-call", re: /(?:session\(\)|\bsession)\.call(?:OnTarget|Browser)?\(/, scope: /^src\/domains\// },
+  { rule: "raw-evaluate", re: /\.evaluateJs\(/, scope: /^src\/domains\// },
 ];
 
 export type SourceFile = { readonly path: string; readonly text: string };
@@ -37,8 +40,10 @@ const budgets = (exemptions: ReadonlyArray<Exemption>): Map<string, number> => {
 const rawHits = (files: ReadonlyArray<SourceFile>): ReadonlyArray<Violation> => {
   const out: Violation[] = [];
   for (const file of files) {
+    const path = normalise(file.path);
     for (const [i, line] of file.text.split("\n").entries()) {
-      for (const { rule, re } of RULES) {
+      for (const { rule, re, scope } of RULES) {
+        if (scope && !scope.test(path)) continue;
         if (re.test(line)) out.push({ path: file.path, line: i + 1, rule, text: line.trim() });
       }
     }