fix(browser): honor cancellation during CDP cleanup

Complete owned teardown before deciding whether a successful observation can be published. Classify an exactly propagated source-map abort reason as cancellation while preserving unrelated failures.

Validation: all four cleanup/cancellation boundary tests pass, retaining detach, socket and target-liveness assertions. Based on #2893.

src/browser/CdpBrowserProvider.ts

@@ -167,6 +167,11 @@ export class CdpBrowserProvider implements BrowserObservationPort {
         ),
       );
     } catch (cause: unknown) {
+      // fetchWebSourceMaps rethrows the exact abort reason. Preserve cancellation
+      // even when a caller supplied an AnalysisError as that reason.
+      if (options.signal?.aborted === true && cause === options.signal.reason) {
+        return err(new AnalysisCancelledError("analyze_web_bundle", { cause }));
+      }
       return err(providerError(cause, "analyze_web_bundle", options.signal));
     }
   }
@@ -305,6 +310,7 @@ const withTargetSession = async <
     options.signal,
   );
   let targetSession: CdpTargetSession | undefined;
+  let output: Output;
   try {
     const target = authorizeTarget(endpoint.discovery, input);
     const scopedInput = scopeToTargetOrigin(input, target);
@@ -322,7 +328,7 @@ const withTargetSession = async <
             operation,
             options.signal,
           );
-    return await work({
+    output = await work({
       connection: targetSession.connection,
       sessionId: targetSession.sessionId,
       discovery: endpoint.discovery,
@@ -341,6 +347,14 @@ const withTargetSession = async <
     // An unadopted browser socket is closed here; closing is idempotent.
     await endpoint.connection?.close();
   }
+
+  // Cancellation during teardown must not publish the completed observation.
+  // Errors from work or cleanup still propagate through the try/finally above.
+  if (options.signal?.aborted === true)
+    throw new AnalysisCancelledError(operation, {
+      cause: options.signal.reason,
+    });
+  return output;
 };
 
 const selectTargets = (

tests/boundary/browser/cdpCleanupCancellation.test.ts

@@ -73,7 +73,13 @@ it("releases cleanup when cancellation arrives after capture completes", async (
   });
   controller.abort();
   const result = await pending;
-  expect(result.ok).toBe(true);
+  expect(result).toMatchObject({
+    ok: false,
+    error: {
+      _tag: "AnalysisCancelledError",
+      operation: "observe_web_session",
+    },
+  });
   expect(browser.commands.map(({ method }) => method)).toContain(
     "Target.detachFromTarget",
   );