fix(browser): keep cancellation for scenario captures cancelled during startup

capture_browser_scenario turned a cancellation into unreadable_output
whenever the retained capture failed the completed-report schema. A capture
cancelled while the initial navigation was pending retains no steps and no
completeness, which the partial-observation type deliberately allows, so the
caller lost both the typed cancellation and the retained observation. Only a
capture that reports completeness now claims to be a completed report; other
cancelled captures keep their cancellation and raw partial observation.

Fixes #5364

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/application/BrowserScenarioCaptureService.test.ts

@@ -1,6 +1,9 @@
 import { expect, it } from "vitest";
 
-import { AnalysisCancelledError } from "../domain/analysisErrorCore.js";
+import {
+  AnalysisCancelledError,
+  AnalysisOutputError,
+} from "../domain/analysisErrorCore.js";
 import { BrowserObservationError } from "../domain/browserObservationError.js";
 import { parseEvidence } from "../domain/evidence.js";
 import { browserScenarioInputSchema } from "../domain/browserScenario.js";
@@ -77,6 +80,45 @@ it("converts a raw scenario capture retained after cleanup failure", async () =>
   }
 });
 
+it("keeps cancellation and the incomplete capture retained before navigation finished", async () => {
+  const { completeness: _completeness, ...complete } = capture;
+  // The startup failure path retains no steps and no completeness.
+  const incomplete = { ...complete, steps: [] };
+  const failure = new AnalysisCancelledError("capture_browser_scenario", {
+    partialObservation: {
+      kind: "browser-scenario-observation",
+      capture: incomplete,
+    },
+  });
+  const provider: BrowserScenarioCapturePort = {
+    identity: () => ({ id: "fixture", name: "fixture", version: "1" }),
+    captureScenario: async () => err(failure),
+  };
+  const result = await captureBrowserScenario(provider, scenario);
+  if (result.ok) throw new Error("Expected cancellation");
+  expect(result.error).toBe(failure);
+  expect(result.error.partialObservation).toEqual({
+    kind: "browser-scenario-observation",
+    capture: incomplete,
+  });
+});
+
+it("rejects a cancelled capture that claims completeness but is malformed", async () => {
+  const failure = new AnalysisCancelledError("capture_browser_scenario", {
+    partialObservation: {
+      kind: "browser-scenario-observation",
+      capture: { ...capture, steps: [] },
+    },
+  });
+  const provider: BrowserScenarioCapturePort = {
+    identity: () => ({ id: "fixture", name: "fixture", version: "1" }),
+    captureScenario: async () => err(failure),
+  };
+  const result = await captureBrowserScenario(provider, scenario);
+  if (result.ok) throw new Error("Expected failure");
+  expect(result.error).toBeInstanceOf(AnalysisOutputError);
+});
+
 it.each([
   null,
   { request: "opaque cancellation" },

src/application/BrowserScenarioCaptureService.ts

@@ -53,7 +53,13 @@ export const captureBrowserScenario = async (
           provider.identity(),
         );
       } else if (!report.success) {
-        if (captured.error instanceof AnalysisCancelledError)
+        // Only a capture that reports completeness claims to be a completed
+        // report; one cancelled earlier, e.g. during initial navigation, is a
+        // legitimately incomplete observation and keeps its cancellation.
+        if (
+          captured.error instanceof AnalysisCancelledError &&
+          "completeness" in partial.capture
+        )
           return err(
             new AnalysisOutputError(
               OPERATION,