diff --git a/src/application/BrowserObservationService.test.ts b/src/application/BrowserObservationService.test.ts
index d2cdde1c27..b6e33a0e23 100644
--- a/src/application/BrowserObservationService.test.ts
+++ b/src/application/BrowserObservationService.test.ts
@@ -3,9 +3,19 @@ import type { BrowserObservationPort } from "./BrowserObservationPort.js";
 import { listBrowserTargets } from "./BrowserObservationService.js";
 import type { BrowserTargetList } from "../domain/browserObservationSchemas.js";
 import { parseEvidence } from "../domain/evidence.js";
-import { AnalysisOutputError } from "../domain/analysisErrorCore.js";
+import {
+  AnalysisCancelledError,
+  AnalysisOutputError,
+} from "../domain/analysisErrorCore.js";
+import { projectAnalysisError } from "../domain/analysisErrorProjection.js";
+import {
+  expectDroppedPartial,
+  expectKeptPartial,
+  expectOutputError,
+  expectOwnerError,
+} from "./ownerObservationExpectation.fixture.js";
 import { BrowserObservationError } from "../domain/browserObservationError.js";
-import { ok } from "../domain/result.js";
+import { err, ok } from "../domain/result.js";
 import { passiveNetworkCapture } from "../../tests/fixtures/passiveNetworkCapture.js";
 import { inspectWebPage } from "./BrowserObservationService.js";
 import { analyzeWebBundleInputSchema } from "../domain/webBundleAnalysis.js";
@@ -71,11 +81,7 @@ it("does not let late cancellation hide invalid completed browser output", async
     provider(async () => ok(malformed)),
     input,
   );
-  expect(output).toMatchObject({
-    ok: false,
-    error: { _tag: "AnalysisOutputError" },
-  });
-  if (!output.ok) expect(output.error).toBeInstanceOf(AnalysisOutputError);
+  expectOutputError(output);
 
   const controller = new AbortController();
   const late = await listBrowserTargets(
@@ -86,11 +92,7 @@ it("does not let late cancellation hide invalid completed browser output", async
     input,
     { signal: controller.signal },
   );
-  expect(late).toMatchObject({
-    ok: false,
-    error: { _tag: "AnalysisOutputError" },
-  });
-  if (!late.ok) expect(late.error).toBeInstanceOf(AnalysisOutputError);
+  expectOutputError(late);
 });
 
 it("converts a raw page inspection retained after browser cleanup failure", async () => {
@@ -215,3 +217,162 @@ it("preserves a prior caller reason without admitting browser work", async () =>
   expect(result.error._tag).toBe("AnalysisCancelledError");
   expect(result.error.cause).toBe(reason);
 });
+
+it("keeps page cancellation when the retained inspection is incomplete", async () => {
+  const reason = { requested: "stop during page inspection" };
+  const partial = {
+    target: { target_id: "page" },
+    network: {},
+    capture_window: {},
+  };
+  const failure = new AnalysisCancelledError("inspect_web_page", {
+    cause: reason,
+    partialObservation: partial as never,
+  });
+  const browser = {
+    ...provider(async () => ok(report)),
+    inspectPage: async () => err(failure),
+  } as unknown as BrowserObservationPort;
+  const pageInput = inspectWebPageInputSchema.parse({
+    cdp_endpoint: input.cdp_endpoint.recorded,
+    allowed_origins: [],
+    target_id: "page",
+    observation_ms: 0,
+    include_script_sources: false,
+  });
+  const result = await inspectWebPage(browser, pageInput);
+  expectKeptPartial(expectOwnerError(result, failure, reason), partial);
+});
+
+it("keeps bundle cancellation and an earlier failure when retained facts are incomplete", async () => {
+  const reason = { requested: "stop during bundle analysis" };
+  const partial = { observations: [], capture: { status: "partial" } };
+  const cancelled = new AnalysisCancelledError("analyze_web_bundle", {
+    cause: reason,
+    partialObservation: partial as never,
+  });
+  const timedOut = new BrowserObservationError(
+    "analyze_web_bundle",
+    "timeout",
+    { partialObservation: partial as never },
+  );
+  const selected = analyzeWebBundleInputSchema.parse({
+    cdp_endpoint: input.cdp_endpoint.recorded,
+    target_id: "page",
+    observation_ms: 0,
+  });
+  for (const failure of [cancelled, timedOut]) {
+    const browser = {
+      ...provider(async () => ok(report)),
+      analyzeBundle: async () => err(failure),
+    } as unknown as BrowserObservationPort;
+    const result = await analyzeWebBundle(browser, selected);
+    expectKeptPartial(
+      expectOwnerError(result, failure, failure.cause),
+      partial,
+      failure === timedOut ? "provider_timeout" : "cancelled",
+    );
+  }
+  expect(projectAnalysisError(cancelled).code).toBe("cancelled");
+});
+
+const pageInput = () =>
+  inspectWebPageInputSchema.parse({
+    cdp_endpoint: input.cdp_endpoint.recorded,
+    allowed_origins: [],
+    target_id: "page",
+    observation_ms: 0,
+    include_script_sources: false,
+  });
+
+const bundleInput = () =>
+  analyzeWebBundleInputSchema.parse({
+    cdp_endpoint: input.cdp_endpoint.recorded,
+    target_id: "page",
+    observation_ms: 0,
+  });
+
+const browserReturning = (
+  failure: BrowserObservationError | AnalysisCancelledError,
+) =>
+  ({
+    ...provider(async () => ok(report)),
+    inspectPage: async () => err(failure),
+    analyzeBundle: async () => err(failure),
+  }) as unknown as BrowserObservationPort;
+
+it.each([
+  {
+    name: "bundle bytes",
+    operation: "analyze_web_bundle" as const,
+    partial: { observations: [], capture: { bytes: Number.NaN } },
+  },
+  {
+    name: "bundle observations",
+    operation: "analyze_web_bundle" as const,
+    partial: { observations: [undefined], capture: {} },
+  },
+  {
+    name: "page requests",
+    operation: "inspect_web_page" as const,
+    partial: {
+      target: { target_id: "page" },
+      network: { requests: Number.NaN },
+      capture_window: {},
+    },
+  },
+])(
+  "drops a non-JSON $name partial and keeps cancellation primary",
+  async ({ operation, partial }) => {
+    const reason = { requested: `stop ${operation}` };
+    const failure = new AnalysisCancelledError(operation, {
+      cause: reason,
+      partialObservation: partial as never,
+    });
+    const result =
+      operation === "inspect_web_page"
+        ? await inspectWebPage(browserReturning(failure), pageInput())
+        : await analyzeWebBundle(browserReturning(failure), bundleInput());
+    const error = expectOwnerError(result, failure, reason);
+    expectDroppedPartial(
+      error,
+      "Browser provider retained a non-JSON incomplete observation.",
+    );
+    expect(projectAnalysisError(error).details).not.toHaveProperty(
+      "partial_observation",
+    );
+  },
+);
+
+it.each([
+  {
+    name: "schema-shaped page",
+    partial: {
+      target: { target_id: "page" },
+      network: { requests: Number.NaN },
+      capture_window: {},
+    },
+  },
+  {
+    name: "shapeless page",
+    partial: { requests: Number.NaN },
+  },
+])(
+  "drops a non-JSON $name partial and keeps timeout primary",
+  async ({ partial }) => {
+    const failure = new BrowserObservationError("inspect_web_page", "timeout", {
+      partialObservation: partial as never,
+    });
+    const error = expectOwnerError(
+      await inspectWebPage(browserReturning(failure), pageInput()),
+      failure,
+      undefined,
+    );
+    expectDroppedPartial(
+      error,
+      "Browser provider retained a non-JSON incomplete observation.",
+      "provider_timeout",
+    );
+    expect(projectAnalysisError(error).category).toBe("timeout");
+  },
+);
diff --git a/src/application/BrowserObservationService.ts b/src/application/BrowserObservationService.ts
index 6251e9d4dd..1e32b4ead4 100644
--- a/src/application/BrowserObservationService.ts
+++ b/src/application/BrowserObservationService.ts
@@ -25,9 +25,11 @@ import type { ExecutionOptions } from "./AnalysisProvider.js";
 import type { BrowserObservationPort } from "./BrowserObservationPort.js";
 import { createBrowserEvidence } from "./BrowserEvidence.js";
 import { jsonValueSchema } from "../domain/jsonValue.js";
-import { completeProviderEvidence } from "./ProviderOperationExecution.js";
+import {
+  completeProviderEvidence,
+  keepIncompleteObservation,
+} from "./ProviderOperationExecution.js";
 import { webPageInspectionSchema } from "../domain/browserObservationSchemas.js";
-import { analysisErrorWithCleanupFailure } from "../domain/analysisErrorCleanup.js";
 
 /** List browser targets within the endpoint and origin scope in the request. */
 export const listBrowserTargets = async (
@@ -275,7 +277,10 @@ const browserEvidence = (
   );
 };
 
-/** Retain the completed capture or bundle facts under their actual operation. */
+const NON_JSON_BROWSER_OBSERVATION =
+  "Browser provider retained a non-JSON incomplete observation.";
+
+/** Promote completed page or bundle facts; keep only a JSON-safe incomplete observation. */
 const retainBrowserObservation = (
   error: AnalysisError,
   input: InspectWebPageInput | AnalyzeWebBundleInput,
@@ -291,59 +296,42 @@ const retainBrowserObservation = (
     "capture" in partial
   ) {
     const bundle = webBundleAnalysisSchema.safeParse(partial);
-    if (!bundle.success) {
-      const malformed = new AnalysisOutputError(
-        errorOperation,
-        "Browser provider retained malformed completed bundle facts.",
-        { cause: bundle.error },
-      );
-      return err(
-        error.cleanupIncomplete
-          ? analysisErrorWithCleanupFailure(
-              malformed,
-              error,
-              errorOperation,
-            ).bindCleanupDependencies([malformed, error])
-          : malformed,
+    if (bundle.success) {
+      error.partialObservation = createBrowserEvidence(
+        "analyze_web_bundle",
+        input,
+        bundle.data,
+        provider.identity(),
       );
+      return err(error);
     }
-    error.partialObservation = createBrowserEvidence(
-      "analyze_web_bundle",
-      input,
-      bundle.data,
-      provider.identity(),
-    );
-    return err(error);
-  }
-  if (
-    partial === undefined ||
-    "evidence_id" in partial ||
-    !("target" in partial) ||
-    !("network" in partial) ||
-    !("capture_window" in partial)
-  )
-    return err(error);
-  const inspection = webPageInspectionSchema.safeParse(partial);
-  if (!inspection.success) {
-    if (error instanceof AnalysisCancelledError)
-      return err(
-        new AnalysisOutputError(
-          errorOperation,
-          "Browser provider retained a malformed completed page inspection.",
-          { cause: inspection.error },
-        ),
+  } else if (
+    partial !== undefined &&
+    !("evidence_id" in partial) &&
+    "target" in partial &&
+    "network" in partial &&
+    "capture_window" in partial
+  ) {
+    const inspection = webPageInspectionSchema.safeParse(partial);
+    if (inspection.success) {
+      const pageInput: InspectWebPageInput =
+        "fetch_source_maps" in input
+          ? (({ fetch_source_maps: _fetchSourceMaps, ...page }) => page)(input)
+          : input;
+      error.partialObservation = createBrowserEvidence(
+        "inspect_web_page",
+        pageInput,
+        inspection.data,
+        provider.identity(),
       );
-    return err(error);
+      return err(error);
+    }
   }
-  const pageInput: InspectWebPageInput =
-    "fetch_source_maps" in input
-      ? (({ fetch_source_maps: _fetchSourceMaps, ...page }) => page)(input)
-      : input;
-  error.partialObservation = createBrowserEvidence(
-    "inspect_web_page",
-    pageInput,
-    inspection.data,
-    provider.identity(),
+  return err(
+    keepIncompleteObservation(
+      error,
+      errorOperation,
+      NON_JSON_BROWSER_OBSERVATION,
+    ),
   );
-  return err(error);
 };
diff --git a/src/application/BrowserScenarioCaptureService.test.ts b/src/application/BrowserScenarioCaptureService.test.ts
index df187682a4..34a3c588cb 100644
--- a/src/application/BrowserScenarioCaptureService.test.ts
+++ b/src/application/BrowserScenarioCaptureService.test.ts
@@ -1,13 +1,26 @@
 import { expect, it } from "vitest";
 
-import { AnalysisCancelledError } from "../domain/analysisErrorCore.js";
+import type { AnalysisError } from "../domain/analysisErrorBase.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";
-import { err } from "../domain/result.js";
+import type {
+  BrowserScenarioCapture,
+  BrowserScenarioPartialObservation,
+} from "../domain/browserScenarioCapture.js";
+import { err, ok } from "../domain/result.js";
 import { scriptScenarioFixture } from "../../tests/fixtures/webScriptCapture.js";
 import type { BrowserScenarioCapturePort } from "./BrowserScenarioCapturePort.js";
 import { captureBrowserScenario } from "./BrowserScenarioCaptureService.js";
+import {
+  expectDroppedPartial,
+  expectKeptPartial,
+  expectOwnerError,
+} from "./ownerObservationExpectation.fixture.js";
 
 const scenario = browserScenarioInputSchema.parse({
   browser: { mode: "launch", executable_path: "/fixture/chrome" },
@@ -15,6 +28,34 @@ const scenario = browserScenarioInputSchema.parse({
   actions: [{ step_id: "settle", action: "wait_for_timeout", duration_ms: 1 }],
 });
 const capture = scriptScenarioFixture();
+const scenarioIdentity = {
+  id: "scenario-fixture",
+  name: "Scenario fixture",
+  version: "1",
+};
+const runScenario = (
+  failure: AnalysisError,
+  id = { id: "fixture", name: "fixture", version: "1" },
+) =>
+  captureBrowserScenario(
+    {
+      identity: () => id,
+      captureScenario: async () => err(failure),
+    },
+    scenario,
+  );
+const expectRetainedCapture = (
+  result: Awaited<ReturnType<typeof runScenario>>,
+  failure: AnalysisError,
+) => {
+  expect(result.ok).toBe(false);
+  if (result.ok) throw new Error("Expected the retained capture");
+  expect(result.error).toBe(failure);
+  expect(parseEvidence(result.error.partialObservation)).toMatchObject({
+    operation: "capture_browser_scenario",
+    normalized_result: capture,
+  });
+};
 
 it("converts a retained raw scenario capture into partial Evidence", async () => {
   const failure = new AnalysisCancelledError("capture_browser_scenario", {
@@ -23,23 +64,7 @@ it("converts a retained raw scenario capture into partial Evidence", async () =>
       capture,
     },
   });
-  const provider: BrowserScenarioCapturePort = {
-    identity: () => ({
-      id: "scenario-fixture",
-      name: "Scenario fixture",
-      version: "1",
-    }),
-    captureScenario: async () => err(failure),
-  };
-  const result = await captureBrowserScenario(provider, scenario);
-  expect(result.ok).toBe(false);
-  if (!result.ok) {
-    expect(result.error).toBe(failure);
-    expect(parseEvidence(result.error.partialObservation)).toMatchObject({
-      operation: "capture_browser_scenario",
-      normalized_result: capture,
-    });
-  }
+  expectRetainedCapture(await runScenario(failure, scenarioIdentity), failure);
 });
 
 it("converts a raw scenario capture retained after cleanup failure", async () => {
@@ -57,24 +82,9 @@ it("converts a raw scenario capture retained after cleanup failure", async () =>
       },
     },
   );
-  const provider: BrowserScenarioCapturePort = {
-    identity: () => ({
-      id: "scenario-fixture",
-      name: "Scenario fixture",
-      version: "1",
-    }),
-    captureScenario: async () => err(failure),
-  };
-  const result = await captureBrowserScenario(provider, scenario);
-  expect(result.ok).toBe(false);
-  if (!result.ok) {
-    expect(result.error).toBe(failure);
-    expect(result.error.cleanupIncomplete).toBe(true);
-    expect(parseEvidence(result.error.partialObservation)).toMatchObject({
-      operation: "capture_browser_scenario",
-      normalized_result: capture,
-    });
-  }
+  const result = await runScenario(failure, scenarioIdentity);
+  expectRetainedCapture(result, failure);
+  if (!result.ok) expect(result.error.cleanupIncomplete).toBe(true);
 });
 
 it.each([
@@ -103,3 +113,63 @@ it.each([
     expect(calls).toBe(0);
   },
 );
+
+it("keeps startup cancellation and its incomplete capture", async () => {
+  const reason = { requested: "stop during initial navigation" };
+  const completed = scriptScenarioFixture();
+  const {
+    completeness: _completeness,
+    steps: _steps,
+    browser,
+    ...retained
+  } = completed;
+  const partial: BrowserScenarioPartialObservation = {
+    kind: "browser-scenario-observation",
+    capture: {
+      ...retained,
+      browser: { ...browser, cleanup: "incomplete" },
+      steps: [],
+    },
+  };
+  const failure = new AnalysisCancelledError("capture_browser_scenario", {
+    cause: reason,
+    partialObservation: partial,
+  });
+  const result = await runScenario(failure);
+  expectKeptPartial(expectOwnerError(result, failure, reason), partial);
+});
+
+it.each([{ steps: [undefined] }, { started_at: Number.NaN }])(
+  "drops a non-JSON incomplete scenario capture and keeps cancellation primary",
+  async (capturePartial) => {
+    const reason = { requested: "stop during initial navigation" };
+    const partial: BrowserScenarioPartialObservation = {
+      kind: "browser-scenario-observation",
+      capture: capturePartial as never,
+    };
+    const failure = new AnalysisCancelledError("capture_browser_scenario", {
+      cause: reason,
+      partialObservation: partial,
+    });
+    const result = await runScenario(failure);
+    expectDroppedPartial(
+      expectOwnerError(result, failure, reason),
+      "Browser scenario provider retained a non-JSON incomplete observation.",
+    );
+  },
+);
+
+it("rejects a successful capture that is not a completed scenario", async () => {
+  const provider: BrowserScenarioCapturePort = {
+    identity: () => ({ id: "fixture", name: "fixture", version: "1" }),
+    captureScenario: async () => ok({} as BrowserScenarioCapture),
+  };
+  const result = await captureBrowserScenario(provider, scenario);
+  expect(result.ok).toBe(false);
+  if (result.ok) throw new Error("Expected a completed-capture refusal");
+  expect(result.error).toBeInstanceOf(AnalysisOutputError);
+  expect(result.error.message).toContain(
+    "returned a malformed completed capture",
+  );
+  expect(result.error.partialObservation).toBeUndefined();
+});
diff --git a/src/application/BrowserScenarioCaptureService.ts b/src/application/BrowserScenarioCaptureService.ts
index 0a5bc26019..24e8c0ca4f 100644
--- a/src/application/BrowserScenarioCaptureService.ts
+++ b/src/application/BrowserScenarioCaptureService.ts
@@ -11,7 +11,10 @@ import type { Evidence } from "../domain/evidence.js";
 import type { BrowserScenario } from "../domain/browserScenario.js";
 import { err, type Result } from "../domain/result.js";
 import { browserScenarioCaptureSchema } from "../domain/browserScenarioCapture.js";
-import { completeProviderEvidence } from "./ProviderOperationExecution.js";
+import {
+  completeProviderEvidence,
+  keepIncompleteObservation,
+} from "./ProviderOperationExecution.js";
 
 const OPERATION = "capture_browser_scenario" as const;
 const PROVIDER_ID = "rea-playwright-browser-scenario";
@@ -43,6 +46,8 @@ export const captureBrowserScenario = async (
       partial.kind === "browser-scenario-observation"
     ) {
       const report = browserScenarioCaptureSchema.safeParse(partial.capture);
+      // Only a completed capture becomes Evidence. A JSON-safe incomplete
+      // observation stays on the owner error, including typed cancellation.
       if (
         report.success &&
         report.data.steps.every(({ status }) => status === "completed")
@@ -52,19 +57,16 @@ export const captureBrowserScenario = async (
           report.data,
           provider.identity(),
         );
-      } else if (!report.success) {
-        if (captured.error instanceof AnalysisCancelledError)
-          return err(
-            new AnalysisOutputError(
-              OPERATION,
-              "Browser scenario provider retained a malformed completed capture.",
-              { cause: report.error },
-            ),
-          );
         return captured;
       }
     }
-    return captured;
+    return err(
+      keepIncompleteObservation(
+        captured.error,
+        OPERATION,
+        "Browser scenario provider retained a non-JSON incomplete observation.",
+      ),
+    );
   }
   const report = browserScenarioCaptureSchema.safeParse(captured.value);
   if (!report.success)
diff --git a/src/application/ProviderOperationExecution.test.ts b/src/application/ProviderOperationExecution.test.ts
index 7729cb42b7..f3a36e1b5a 100644
--- a/src/application/ProviderOperationExecution.test.ts
+++ b/src/application/ProviderOperationExecution.test.ts
@@ -1,8 +1,18 @@
 import { expect, it, vi } from "vitest";
 import { z } from "zod";
 
-import { AnalysisInputError } from "../domain/analysisErrorCore.js";
-import { executeProviderOperation } from "./ProviderOperationExecution.js";
+import {
+  AnalysisCancelledError,
+  AnalysisInputError,
+  AnalysisOutputError,
+} from "../domain/analysisErrorCore.js";
+import { analysisErrorWithCleanupFailure } from "../domain/analysisErrorCleanup.js";
+import { projectAnalysisError } from "../domain/analysisErrorProjection.js";
+import { ProviderCleanupError } from "../domain/providerCleanupError.js";
+import {
+  executeProviderOperation,
+  keepIncompleteObservation,
+} from "./ProviderOperationExecution.js";
 
 it("projects request-schema issues without exposing the request envelope", async () => {
   const execute = vi.fn();
@@ -87,3 +97,84 @@ it("preserves operation correction outside the input envelope", async () => {
   ]);
   expect(execute).not.toHaveBeenCalled();
 });
+
+const cancelledScenario = (partial: unknown) =>
+  new AnalysisCancelledError("capture_browser_scenario", {
+    cause: { requested: "stop during capture" },
+    partialObservation: partial as never,
+  });
+
+const wrapScenarioCleanup = (primary: AnalysisCancelledError) =>
+  analysisErrorWithCleanupFailure(
+    primary,
+    new ProviderCleanupError("fixture", ["browser"], {}),
+    "capture_browser_scenario",
+  );
+
+it("clears a non-JSON partial from the cleanup primary projection returns after retry", () => {
+  const partial = { steps: [] as unknown[] };
+  const primary = cancelledScenario(partial);
+  const composed = wrapScenarioCleanup(primary);
+  partial.steps.push(undefined);
+  const reason =
+    "Browser scenario provider retained a non-JSON incomplete observation.";
+  const retained = keepIncompleteObservation(
+    composed,
+    "capture_browser_scenario",
+    reason,
+  );
+
+  expect(retained).toBe(composed);
+  expect(composed.partialObservation).toBeUndefined();
+  expect(primary.partialObservation).toBeUndefined();
+  expect(composed.secondaryFailures).toMatchObject([
+    { _tag: "AnalysisOutputError", reason },
+  ]);
+  expect(primary.secondaryFailures[0]).toBeInstanceOf(AnalysisOutputError);
+  expect(projectAnalysisError(composed).code).toBe("cleanup_incomplete");
+
+  composed.resolveCleanup();
+  expect(projectAnalysisError(composed)).toMatchObject({
+    code: "cancelled",
+    category: "cancelled",
+  });
+  expect(projectAnalysisError(composed).details).not.toHaveProperty(
+    "partial_observation",
+  );
+});
+
+it("freezes one shared snapshot for a cleanup wrapper and its primary", () => {
+  const partial = { steps: ["kept"] };
+  const primary = cancelledScenario(partial);
+  const composed = wrapScenarioCleanup(primary);
+  keepIncompleteObservation(
+    composed,
+    "capture_browser_scenario",
+    "unused because the partial is JSON",
+  );
+
+  expect(composed.partialObservation).toBe(primary.partialObservation);
+  expect(composed.partialObservation).toEqual({ steps: ["kept"] });
+  expect(Object.isFrozen(composed.partialObservation)).toBe(true);
+  expect(composed.secondaryFailures).toHaveLength(0);
+  expect(primary.secondaryFailures).toHaveLength(0);
+});
+
+it("freezes a retained partial so a later mutation cannot break projection", () => {
+  const partial = { steps: [] as unknown[] };
+  const primary = cancelledScenario(partial);
+  keepIncompleteObservation(
+    primary,
+    "capture_browser_scenario",
+    "unused because the partial is JSON",
+  );
+  partial.steps.push(undefined);
+
+  expect(primary.partialObservation).toEqual({ steps: [] });
+  expect(Object.isFrozen(primary.partialObservation)).toBe(true);
+  expect(primary.secondaryFailures).toHaveLength(0);
+  expect(projectAnalysisError(primary)).toMatchObject({
+    code: "cancelled",
+    details: { partial_observation: { steps: [] } },
+  });
+});
diff --git a/src/application/ProviderOperationExecution.ts b/src/application/ProviderOperationExecution.ts
index 7a48e9ae88..38012d0b5b 100644
--- a/src/application/ProviderOperationExecution.ts
+++ b/src/application/ProviderOperationExecution.ts
@@ -2,12 +2,19 @@ import { z } from "zod";
 import type {
   AnalysisError,
   AnalysisErrorOptions,
+  AnalysisPartialObservation,
 } from "../domain/analysisErrorBase.js";
 import {
   AnalysisCancelledError,
   AnalysisInputError,
+  AnalysisOutputError,
 } from "../domain/analysisErrorCore.js";
 import type { Evidence } from "../domain/evidence.js";
+import {
+  freezeJsonSnapshot,
+  isImmutableJsonSnapshot,
+} from "../domain/immutableJson.js";
+import { jsonValueSchema } from "../domain/jsonValue.js";
 import { projectInputIssues } from "../domain/inputIssueProjection.js";
 import { err, ok, type Result } from "../domain/result.js";
 import {
@@ -92,3 +99,49 @@ export const completeProviderEvidence = (
     );
   return ok(evidence);
 };
+
+/**
+ * Retain an incomplete observation when projection can serialize it.
+ * A JSON partial is replaced by one frozen snapshot, so a later mutation
+ * cannot make projection throw and projection does not copy it again.
+ * A partial that is not JSON is cleared from the returned error and from
+ * every cleanup primary projection can select later. Each cleared error
+ * records an output failure, leaving cancellation or timeout primary.
+ */
+export const keepIncompleteObservation = (
+  error: AnalysisError,
+  operation: string,
+  reason: string,
+): AnalysisError => {
+  const seen = new Set<AnalysisError>();
+  // One source object can sit on a wrapper and its cleanup primary.
+  const judged = new Map<object, AnalysisPartialObservation | undefined>();
+  let current: AnalysisError | undefined = error;
+  while (current !== undefined && !seen.has(current)) {
+    seen.add(current);
+    const partial = current.partialObservation;
+    if (
+      partial !== undefined &&
+      !isImmutableJsonSnapshot(partial) &&
+      typeof partial === "object"
+    ) {
+      // safeParse clones only after validation succeeds. Freeze that copy once.
+      let snapshot = judged.get(partial);
+      if (!judged.has(partial)) {
+        const parsed = jsonValueSchema.safeParse(partial);
+        snapshot = parsed.success
+          ? (freezeJsonSnapshot(parsed.data) as AnalysisPartialObservation)
+          : undefined;
+        judged.set(partial, snapshot);
+      }
+      if (snapshot === undefined) {
+        current.partialObservation = undefined;
+        current.retainSecondaryFailure(
+          new AnalysisOutputError(operation, reason),
+        );
+      } else current.partialObservation = snapshot;
+    }
+    current = current.cleanupPrimary;
+  }
+  return error;
+};
diff --git a/src/application/WebRuntimeService.test.ts b/src/application/WebRuntimeService.test.ts
index 7e7c651486..f28be157d9 100644
--- a/src/application/WebRuntimeService.test.ts
+++ b/src/application/WebRuntimeService.test.ts
@@ -6,10 +6,20 @@ import {
   webListenersFixture,
 } from "./WebRuntimeService.fixture.js";
 import { err, ok } from "../domain/result.js";
-import { AnalysisTimeoutError } from "../domain/analysisErrorCore.js";
+import {
+  AnalysisCancelledError,
+  AnalysisOutputError,
+  AnalysisTimeoutError,
+} from "../domain/analysisErrorCore.js";
+import { projectAnalysisError } from "../domain/analysisErrorProjection.js";
 import { ProviderCleanupError } from "../domain/providerCleanupError.js";
+import {
+  expectDroppedPartial,
+  expectKeptPartial,
+  expectOwnerError,
+} from "./ownerObservationExpectation.fixture.js";
+import type { AnalysisError } from "../domain/analysisErrorBase.js";
 import { parseEvidence } from "../domain/evidence.js";
-import { AnalysisOutputError } from "../domain/analysisErrorCore.js";
 
 it("rejects malformed input and prior cancellation without calling a provider", async () => {
   const provider = recordingWebRuntimePort();
@@ -83,11 +93,7 @@ it("converts raw execution retained by provider cleanup failure into partial Evi
     { operation: "observe_web_execution", partialObservation: execution },
   );
   const result = await new WebRuntimeService({
-    identity: () => ({
-      id: "web-runtime",
-      name: "Runtime fixture",
-      version: "1",
-    }),
+    identity: runtimeIdentity,
     observeExecution: async () => err(failure),
     inspectEventListeners: async () => err(failure),
   }).observe(args);
@@ -161,3 +167,118 @@ it("retains completed execution Evidence on late abort and keeps invalid output
   });
   if (!invalid.ok) expect(invalid.error).toBeInstanceOf(AnalysisOutputError);
 });
+
+const runtimeIdentity = () => ({
+  id: "web-runtime",
+  name: "Runtime fixture",
+  version: "1",
+});
+
+const callRuntime = (
+  operation: "observe" | "inspect",
+  failure: AnalysisError,
+) => {
+  const service = new WebRuntimeService({
+    identity: runtimeIdentity,
+    observeExecution: async () => err(failure),
+    inspectEventListeners: async () => err(failure),
+  });
+  return operation === "observe"
+    ? service.observe({
+        cdp_endpoint: "http://127.0.0.1:9222",
+        target_id: "selected-page",
+        observation_ms: 5,
+      })
+    : service.inspect({
+        cdp_endpoint: "http://127.0.0.1:9222",
+        target_id: "selected-page",
+        selector: "#selected",
+      });
+};
+
+it.each([
+  {
+    operation: "observe" as const,
+    partial: {
+      instrumentation: { cleanup: "unconfirmed" },
+      window: { requested_ms: 5 },
+    },
+  },
+  {
+    operation: "inspect" as const,
+    partial: {
+      selected_node: { selector: "#selected" },
+      listeners: [],
+    },
+  },
+])(
+  "keeps $operation cancellation when the retained observation is incomplete",
+  async ({ operation, partial }) => {
+    const reason = { requested: `stop incomplete ${operation}` };
+    const failure = new AnalysisCancelledError(
+      operation === "observe"
+        ? "observe_web_execution"
+        : "inspect_web_event_listeners",
+      { cause: reason, partialObservation: partial as never },
+    );
+    expectKeptPartial(
+      expectOwnerError(await callRuntime(operation, failure), failure, reason),
+      partial,
+    );
+  },
+);
+
+it.each([
+  {
+    operation: "observe" as const,
+    partial: {
+      instrumentation: { cleanup: "unconfirmed" },
+      window: { requested_ms: Number.NaN },
+    },
+    reason: "Provider retained a non-JSON incomplete execution observation.",
+  },
+  {
+    operation: "inspect" as const,
+    partial: {
+      selected_node: { selector: "#selected" },
+      listeners: [undefined],
+    },
+    reason:
+      "Provider retained a non-JSON incomplete event-listener observation.",
+  },
+])(
+  "drops a non-JSON $operation partial and keeps cancellation primary",
+  async ({ operation, partial, reason: outputReason }) => {
+    const reason = { requested: `stop unsafe ${operation}` };
+    const failure = new AnalysisCancelledError(
+      operation === "observe"
+        ? "observe_web_execution"
+        : "inspect_web_event_listeners",
+      { cause: reason, partialObservation: partial as never },
+    );
+    expectDroppedPartial(
+      expectOwnerError(await callRuntime(operation, failure), failure, reason),
+      outputReason,
+    );
+  },
+);
+
+it("drops a non-JSON execution partial and keeps timeout primary", async () => {
+  const failure = new AnalysisTimeoutError("observe_web_execution", 5, {
+    partialObservation: {
+      instrumentation: { samples: [undefined] },
+      window: { requested_ms: 5 },
+    } as never,
+  });
+  const error = expectOwnerError(
+    await callRuntime("observe", failure),
+    failure,
+    undefined,
+  );
+  expectDroppedPartial(
+    error,
+    "Provider retained a non-JSON incomplete execution observation.",
+    "provider_timeout",
+  );
+  expect(projectAnalysisError(error).category).toBe("timeout");
+});
diff --git a/src/application/WebRuntimeService.ts b/src/application/WebRuntimeService.ts
index 38d2934545..627ada4906 100644
--- a/src/application/WebRuntimeService.ts
+++ b/src/application/WebRuntimeService.ts
@@ -18,7 +18,10 @@ import {
   inspectWebEventListenersInputSchema,
   webEventListenersSchema,
 } from "../domain/webEventListeners.js";
-import { completeProviderEvidence } from "./ProviderOperationExecution.js";
+import {
+  completeProviderEvidence,
+  keepIncompleteObservation,
+} from "./ProviderOperationExecution.js";
 
 /** Shared public workflows keep instrumentation and listener inspection independently selectable. */
 export class WebRuntimeService {
@@ -38,35 +41,19 @@ export class WebRuntimeService {
     );
     if (!parsed.ok) return parsed;
     const result = await this.provider.observeExecution(parsed.value, options);
-    if (!result.ok) {
-      const partial = result.error.partialObservation;
-      if (
-        partial !== undefined &&
-        !("evidence_id" in partial) &&
-        "instrumentation" in partial &&
-        "window" in partial
-      ) {
-        const verifiedPartial = webExecutionSchema.safeParse(partial);
-        if (verifiedPartial.success) {
-          const evidence = this.evidence(
-            operation,
-            parsed.value,
-            verifiedPartial.data,
-          );
-          if (evidence.ok) result.error.partialObservation = evidence.value;
-          else if (result.error instanceof AnalysisCancelledError)
-            return evidence;
-        } else if (result.error instanceof AnalysisCancelledError)
-          return err(
-            new AnalysisOutputError(
-              operation,
-              "Provider retained a malformed completed execution observation.",
-              { cause: verifiedPartial.error },
-            ),
-          );
-      }
-      return result;
-    }
+    if (!result.ok)
+      return this.retainRuntimePartial(
+        result.error,
+        operation,
+        "Provider retained a non-JSON incomplete execution observation.",
+        (partial) => {
+          if (!("instrumentation" in partial) || !("window" in partial))
+            return undefined;
+          const verified = webExecutionSchema.safeParse(partial);
+          if (!verified.success) return undefined;
+          return this.evidence(operation, parsed.value, verified.data);
+        },
+      );
     const verified = webExecutionSchema.safeParse(result.value);
     if (!verified.success)
       return err(new AnalysisOutputError(operation, verified.error.message));
@@ -100,35 +87,19 @@ export class WebRuntimeService {
       parsed.value,
       options,
     );
-    if (!result.ok) {
-      const partial = result.error.partialObservation;
-      if (
-        partial !== undefined &&
-        !("evidence_id" in partial) &&
-        "selected_node" in partial &&
-        "listeners" in partial
-      ) {
-        const verifiedPartial = webEventListenersSchema.safeParse(partial);
-        if (verifiedPartial.success) {
-          const evidence = this.evidence(
-            operation,
-            parsed.value,
-            verifiedPartial.data,
-          );
-          if (evidence.ok) result.error.partialObservation = evidence.value;
-          else if (result.error instanceof AnalysisCancelledError)
-            return evidence;
-        } else if (result.error instanceof AnalysisCancelledError)
-          return err(
-            new AnalysisOutputError(
-              operation,
-              "Provider retained malformed completed event-listener data.",
-              { cause: verifiedPartial.error },
-            ),
-          );
-      }
-      return result;
-    }
+    if (!result.ok)
+      return this.retainRuntimePartial(
+        result.error,
+        operation,
+        "Provider retained a non-JSON incomplete event-listener observation.",
+        (partial) => {
+          if (!("selected_node" in partial) || !("listeners" in partial))
+            return undefined;
+          const verified = webEventListenersSchema.safeParse(partial);
+          if (!verified.success) return undefined;
+          return this.evidence(operation, parsed.value, verified.data);
+        },
+      );
     const verified = webEventListenersSchema.safeParse(result.value);
     if (!verified.success)
       return err(new AnalysisOutputError(operation, verified.error.message));
@@ -145,6 +116,29 @@ export class WebRuntimeService {
     return this.evidence(operation, parsed.value, verified.data, options);
   }
 
+  /** Promote a schema-valid partial, or keep a JSON snapshot of an incomplete one. */
+  private retainRuntimePartial(
+    error: AnalysisError,
+    operation: string,
+    nonJsonReason: string,
+    promote: (
+      partial: NonNullable<AnalysisError["partialObservation"]>,
+    ) => Result<Evidence, AnalysisError> | undefined,
+  ): Result<Evidence, AnalysisError> {
+    const partial = error.partialObservation;
+    if (partial !== undefined && !("evidence_id" in partial)) {
+      const evidence = promote(partial);
+      if (evidence !== undefined) {
+        if (evidence.ok) {
+          error.partialObservation = evidence.value;
+          return err(error);
+        }
+        if (error instanceof AnalysisCancelledError) return evidence;
+      }
+    }
+    return err(keepIncompleteObservation(error, operation, nonJsonReason));
+  }
+
   private evidence(
     operation: string,
     input:
diff --git a/src/application/javascript/ElectronObservationService.test.ts b/src/application/javascript/ElectronObservationService.test.ts
index 0d055e1f09..01e9e8c0e2 100644
--- a/src/application/javascript/ElectronObservationService.test.ts
+++ b/src/application/javascript/ElectronObservationService.test.ts
@@ -1,6 +1,5 @@
 import { expect, it } from "vitest";
 
-import { classifyBrowserCompleteness } from "../../domain/browserCompleteness.js";
 import {
   AnalysisCancelledError,
   AnalysisOutputError,
@@ -12,14 +11,27 @@ import {
   electronTargetListSchema,
   inspectElectronPageInputSchema,
 } from "../../domain/javascript/electronObservation.js";
+import { emptyElectronPageCoverage } from "../../domain/javascript/electronPageInspection.fixture.js";
+import type { AnalysisError } from "../../domain/analysisErrorBase.js";
 import { err, ok } from "../../domain/result.js";
 import type { ElectronObservationPort } from "./ElectronObservationPort.js";
 import {
   inspectElectronPage,
   listElectronTargets,
 } from "./ElectronObservationService.js";
+import {
+  expectDroppedPartial,
+  expectKeptPartial,
+  expectOwnerError,
+} from "../ownerObservationExpectation.fixture.js";
 
 const identity = { id: "electron-fixture", name: "Fixture", version: "1" };
+const pageProvider = (failure: AnalysisError): ElectronObservationPort => ({
+  identity: () => identity,
+  listTargets: async () =>
+    err(new AnalysisCancelledError("list_electron_targets")),
+  inspectPage: async () => err(failure),
+});
 const input = inspectElectronPageInputSchema.parse({
   cdp_endpoint: "http://127.0.0.1:9222",
   target_id: "electron-page",
@@ -40,33 +52,7 @@ const inspection = electronPageInspectionSchema.parse({
     file_path: "/app/index.html",
     attached: false,
   },
-  capture_window: {
-    started_at: "2026-01-01T00:00:00.000Z",
-    ended_at: "2026-01-01T00:00:00.000Z",
-    observation_ms: 0,
-  },
-  completeness: classifyBrowserCompleteness({
-    policyFilteredSections: new Set(),
-    attachLimitedSections: new Set(),
-    truncatedSections: new Set(),
-    unavailableSections: new Set(),
-    excluded: [],
-    droppedEvents: {
-      scripts: 0,
-      network_requests: 0,
-      console_events: 0,
-      websocket_connections: 0,
-      websocket_frames: 0,
-      webmcp_tools: 0,
-      timeline_events: 0,
-    },
-  }),
-  frames: [],
-  dom: { total_nodes: 0, nodes: [] },
-  scripts: { total: 0, items: [] },
-  resources: [],
-  workers: [],
-  limitations: [],
+  ...emptyElectronPageCoverage(),
 });
 
 it("converts a retained raw Electron inspection into partial Evidence", async () => {
@@ -77,13 +63,7 @@ it("converts a retained raw Electron inspection into partial Evidence", async ()
       cleanup: "transport-closed",
     },
   });
-  const provider: ElectronObservationPort = {
-    identity: () => identity,
-    listTargets: async () =>
-      err(new AnalysisCancelledError("list_electron_targets")),
-    inspectPage: async () => err(failure),
-  };
-  const result = await inspectElectronPage(provider, input);
+  const result = await inspectElectronPage(pageProvider(failure), input);
   expect(result.ok).toBe(false);
   if (!result.ok) {
     expect(result.error).toBe(failure);
@@ -116,13 +96,7 @@ it("converts a raw inspection retained by provider cleanup failure", async () =>
       },
     },
   );
-  const provider: ElectronObservationPort = {
-    identity: () => identity,
-    listTargets: async () =>
-      err(new AnalysisCancelledError("list_electron_targets")),
-    inspectPage: async () => err(failure),
-  };
-  const result = await inspectElectronPage(provider, input);
+  const result = await inspectElectronPage(pageProvider(failure), input);
   expect(result.ok).toBe(false);
   if (!result.ok) {
     expect(result.error).toBe(failure);
@@ -244,3 +218,43 @@ it.each(["list", "inspect"] as const)(
     expect(providerCalls).toBe(0);
   },
 );
+
+it("keeps cancellation when the retained Electron inspection is incomplete", async () => {
+  const reason = { requested: "stop before page inspection completed" };
+  const partial = {
+    kind: "electron-page-observation",
+    inspection: { target_id: "electron-page" },
+    cleanup: "incomplete",
+  };
+  const failure = new AnalysisCancelledError("inspect_electron_page", {
+    cause: reason,
+    partialObservation: partial as never,
+  });
+  const result = await inspectElectronPage(pageProvider(failure), input);
+  expectKeptPartial(expectOwnerError(result, failure, reason), partial);
+});
+
+it.each([
+  { inspection: { requests: Number.NaN }, cleanup: "incomplete" as const },
+  {
+    inspection: { scripts: [undefined] },
+    cleanup: "transport-closed" as const,
+  },
+])(
+  "drops a non-JSON Electron inspection and keeps cancellation primary",
+  async (unsafe) => {
+    const reason = { requested: "stop before page inspection completed" };
+    const failure = new AnalysisCancelledError("inspect_electron_page", {
+      cause: reason,
+      partialObservation: {
+        kind: "electron-page-observation",
+        ...unsafe,
+      } as never,
+    });
+    const result = await inspectElectronPage(pageProvider(failure), input);
+    expectDroppedPartial(
+      expectOwnerError(result, failure, reason),
+      "Electron provider retained a non-JSON incomplete observation.",
+    );
+  },
+);
diff --git a/src/application/javascript/ElectronObservationService.ts b/src/application/javascript/ElectronObservationService.ts
index 67a0776cb4..ead41e418f 100644
--- a/src/application/javascript/ElectronObservationService.ts
+++ b/src/application/javascript/ElectronObservationService.ts
@@ -18,7 +18,10 @@ import {
   electronPageInspectionSchema,
   electronTargetListSchema,
 } from "../../domain/javascript/electronObservation.js";
-import { completeProviderEvidence } from "../ProviderOperationExecution.js";
+import {
+  completeProviderEvidence,
+  keepIncompleteObservation,
+} from "../ProviderOperationExecution.js";
 
 /** List local file pages exposed by the explicitly selected endpoint. */
 export const listElectronTargets = async (
@@ -79,34 +82,32 @@ export const inspectElectronPage = async (
       partial.kind === "electron-page-observation"
     ) {
       const report = electronPageInspectionSchema.safeParse(partial.inspection);
-      if (!report.success) {
-        if (result.error instanceof AnalysisCancelledError)
-          return err(
-            new AnalysisOutputError(
-              "inspect_electron_page",
-              "Electron provider retained a malformed completed page inspection.",
-              { cause: report.error },
-            ),
-          );
+      if (report.success) {
+        const inspection = {
+          ...report.data,
+          limitations: [
+            ...report.data.limitations,
+            partial.cleanup === "transport-closed"
+              ? "REA closed its CDP transport; this does not imply target shutdown."
+              : "CDP transport cleanup remains incomplete.",
+          ],
+        } satisfies ElectronPageInspection;
+        result.error.partialObservation = createElectronEvidence(
+          "inspect_electron_page",
+          input,
+          inspection,
+          ready.value.identity(),
+        );
         return result;
       }
-      const inspection = {
-        ...report.data,
-        limitations: [
-          ...report.data.limitations,
-          partial.cleanup === "transport-closed"
-            ? "REA closed its CDP transport; this does not imply target shutdown."
-            : "CDP transport cleanup remains incomplete.",
-        ],
-      } satisfies ElectronPageInspection;
-      result.error.partialObservation = createElectronEvidence(
-        "inspect_electron_page",
-        input,
-        inspection,
-        ready.value.identity(),
-      );
     }
-    return result;
+    return err(
+      keepIncompleteObservation(
+        result.error,
+        "inspect_electron_page",
+        "Electron provider retained a non-JSON incomplete observation.",
+      ),
+    );
   }
   const report = electronPageInspectionSchema.safeParse(result.value);
   if (!report.success)
diff --git a/src/application/javascript/JavaScriptRuntimeObservationService.test.ts b/src/application/javascript/JavaScriptRuntimeObservationService.test.ts
index b9351db166..6ef97ff4c2 100644
--- a/src/application/javascript/JavaScriptRuntimeObservationService.test.ts
+++ b/src/application/javascript/JavaScriptRuntimeObservationService.test.ts
@@ -14,6 +14,35 @@ import {
   listJavaScriptRuntimeTargets,
   observeJavaScriptRuntime,
 } from "./JavaScriptRuntimeObservationService.js";
+import {
+  expectDroppedPartial,
+  expectKeptPartial,
+  expectOutputError,
+  expectOwnerError,
+  expectPreemptedCancellation,
+} from "../ownerObservationExpectation.fixture.js";
+
+const observeCancelled = async (partial: unknown) => {
+  const reason = { requested: "stop before runtime observation completed" };
+  const failure = new AnalysisCancelledError("observe_javascript_runtime", {
+    cause: reason,
+    partialObservation: partial as never,
+  });
+  const result = await observeJavaScriptRuntime(
+    {
+      identity: () => ({ id: "test", name: "Test", version: "1" }),
+      listTargets: async () =>
+        err(new AnalysisCancelledError("list_javascript_runtime_targets")),
+      observe: async () => err(failure),
+    },
+    {
+      inspector_endpoint: "http://127.0.0.1:9229",
+      target_id: "target",
+      observation_ms: 0,
+    },
+  );
+  return { result, failure, reason };
+};
 
 it("preserves failed Inspector cleanup when cancellation occurs during observation", async () => {
   const controller = new AbortController();
@@ -126,11 +155,7 @@ it("does not let late cancellation hide an invalid completed Inspector report",
     },
     { inspector_endpoint: "http://127.0.0.1:9229" },
   );
-  expect(output).toMatchObject({
-    ok: false,
-    error: { _tag: "AnalysisOutputError" },
-  });
-  if (!output.ok) expect(output.error).toBeInstanceOf(AnalysisOutputError);
+  expectOutputError(output);
 
   const controller = new AbortController();
   const late = await listJavaScriptRuntimeTargets(
@@ -147,11 +172,7 @@ it("does not let late cancellation hide an invalid completed Inspector report",
     { inspector_endpoint: "http://127.0.0.1:9229" },
     { signal: controller.signal },
   );
-  expect(late).toMatchObject({
-    ok: false,
-    error: { _tag: "AnalysisOutputError" },
-  });
-  if (!late.ok) expect(late.error).toBeInstanceOf(AnalysisOutputError);
+  expectOutputError(late);
 });
 
 it("converts a raw runtime observation retained by cleanup failure", async () => {
@@ -309,11 +330,23 @@ it.each(["list", "observe"] as const)(
             { signal: controller.signal },
           );
 
-    expect(result.ok).toBe(false);
-    if (!result.ok) {
-      expect(result.error).toBeInstanceOf(AnalysisCancelledError);
-      expect(result.error.cause).toBe(reason);
-    }
-    expect(providerCalls).toBe(0);
+    expectPreemptedCancellation(result, reason, providerCalls);
+  },
+);
+
+it("keeps cancellation when the retained runtime observation is incomplete", async () => {
+  const partial = { runtime: "partial", scripts: [] };
+  const { result, failure, reason } = await observeCancelled(partial);
+  expectKeptPartial(expectOwnerError(result, failure, reason), partial);
+});
+
+it.each([{ scripts: [undefined] }, { elapsed_ms: Number.NaN }])(
+  "drops a non-JSON runtime partial and keeps cancellation primary",
+  async (partial) => {
+    const { result, failure, reason } = await observeCancelled(partial);
+    expectDroppedPartial(
+      expectOwnerError(result, failure, reason),
+      "Inspector retained a non-JSON incomplete observation.",
+    );
   },
 );
diff --git a/src/application/javascript/JavaScriptRuntimeObservationService.ts b/src/application/javascript/JavaScriptRuntimeObservationService.ts
index 398995f139..0eedaff93b 100644
--- a/src/application/javascript/JavaScriptRuntimeObservationService.ts
+++ b/src/application/javascript/JavaScriptRuntimeObservationService.ts
@@ -13,7 +13,10 @@ import type {
   ObserveJavaScriptRuntimeInput,
 } from "../../domain/javascript/javascriptRuntimeObservation.js";
 import { err, ok, type Result } from "../../domain/result.js";
-import { completeProviderEvidence } from "../ProviderOperationExecution.js";
+import {
+  completeProviderEvidence,
+  keepIncompleteObservation,
+} from "../ProviderOperationExecution.js";
 import {
   javascriptRuntimeObservationSchema,
   javascriptRuntimeTargetListSchema,
@@ -76,15 +79,7 @@ export const observeJavaScriptRuntime = async (
       !("kind" in partial)
     ) {
       const report = javascriptRuntimeObservationSchema.safeParse(partial);
-      if (!report.success && result.error instanceof AnalysisCancelledError)
-        return err(
-          new AnalysisOutputError(
-            "observe_javascript_runtime",
-            "Inspector retained a malformed completed runtime observation.",
-            { cause: report.error },
-          ),
-        );
-      if (report.success)
+      if (report.success) {
         result.error.partialObservation =
           createJavaScriptRuntimeObservationEvidence(
             "observe_javascript_runtime",
@@ -92,8 +87,16 @@ export const observeJavaScriptRuntime = async (
             report.data,
             ready.value.identity(),
           );
+        return result;
+      }
     }
-    return result;
+    return err(
+      keepIncompleteObservation(
+        result.error,
+        "observe_javascript_runtime",
+        "Inspector retained a non-JSON incomplete observation.",
+      ),
+    );
   }
   const report = javascriptRuntimeObservationSchema.safeParse(result.value);
   if (!report.success)
diff --git a/src/application/ownerObservationExpectation.fixture.ts b/src/application/ownerObservationExpectation.fixture.ts
new file mode 100644
index 0000000000..609edb0f48
--- /dev/null
+++ b/src/application/ownerObservationExpectation.fixture.ts
@@ -0,0 +1,72 @@
+import { expect } from "vitest";
+import type { AnalysisError } from "../domain/analysisErrorBase.js";
+import {
+  AnalysisCancelledError,
+  AnalysisOutputError,
+} from "../domain/analysisErrorCore.js";
+import { projectAnalysisError } from "../domain/analysisErrorProjection.js";
+import type { Result } from "../domain/result.js";
+
+/** Assert the service returned the same owner error and its cause. */
+export const expectOwnerError = <T>(
+  result: Result<T, AnalysisError>,
+  failure: AnalysisError,
+  cause: unknown,
+): AnalysisError => {
+  expect(result.ok).toBe(false);
+  if (result.ok) throw new Error("Expected the owner failure");
+  expect(result.error).toBe(failure);
+  expect(result.error.cause).toBe(cause);
+  return result.error;
+};
+
+/** A JSON-safe incomplete observation stays on the owner error. */
+export const expectKeptPartial = (
+  error: AnalysisError,
+  partial: unknown,
+  code: "cancelled" | "provider_timeout" = "cancelled",
+): void => {
+  expect(error.partialObservation).toEqual(partial);
+  expect(error.secondaryFailures).toHaveLength(0);
+  expect(projectAnalysisError(error)).toMatchObject({
+    code,
+    details: { partial_observation: partial },
+  });
+};
+
+/** A completed value failed output validation, including after a late abort. */
+export const expectOutputError = (
+  result: Result<unknown, AnalysisError>,
+): void => {
+  expect(result).toMatchObject({
+    ok: false,
+    error: { _tag: "AnalysisOutputError" },
+  });
+  if (!result.ok) expect(result.error).toBeInstanceOf(AnalysisOutputError);
+};
+
+/** Cancellation won before the provider ran. */
+export const expectPreemptedCancellation = (
+  result: Result<unknown, AnalysisError>,
+  cause: unknown,
+  providerCalls: number,
+): void => {
+  expect(result.ok).toBe(false);
+  if (result.ok) throw new Error("Expected cancellation");
+  expect(result.error).toBeInstanceOf(AnalysisCancelledError);
+  expect(result.error.cause).toBe(cause);
+  expect(providerCalls).toBe(0);
+};
+
+/** A non-JSON partial is cleared and recorded as a secondary output failure. */
+export const expectDroppedPartial = (
+  error: AnalysisError,
+  reason: string,
+  code: "cancelled" | "provider_timeout" = "cancelled",
+): void => {
+  expect(error.partialObservation).toBeUndefined();
+  expect(error.secondaryFailures).toMatchObject([
+    { _tag: "AnalysisOutputError", reason },
+  ]);
+  expect(projectAnalysisError(error).code).toBe(code);
+};
diff --git a/src/domain/javascript/electronPageInspection.fixture.ts b/src/domain/javascript/electronPageInspection.fixture.ts
new file mode 100644
index 0000000000..e5fe9d0dcb
--- /dev/null
+++ b/src/domain/javascript/electronPageInspection.fixture.ts
@@ -0,0 +1,34 @@
+import { classifyBrowserCompleteness } from "../browserCompleteness.js";
+
+/** Empty coverage tail shared by Electron page fixtures. */
+export const emptyElectronPageCoverage = (observationMs = 0) => ({
+  capture_window: {
+    started_at: "2026-01-01T00:00:00.000Z",
+    ended_at: new Date(
+      Date.parse("2026-01-01T00:00:00.000Z") + observationMs,
+    ).toISOString(),
+    observation_ms: observationMs,
+  },
+  completeness: classifyBrowserCompleteness({
+    policyFilteredSections: new Set(),
+    attachLimitedSections: new Set(),
+    truncatedSections: new Set(),
+    unavailableSections: new Set(),
+    excluded: [],
+    droppedEvents: {
+      scripts: 0,
+      network_requests: 0,
+      console_events: 0,
+      websocket_connections: 0,
+      websocket_frames: 0,
+      webmcp_tools: 0,
+      timeline_events: 0,
+    },
+  }),
+  frames: [],
+  dom: { total_nodes: 0, nodes: [] },
+  scripts: { total: 0, items: [] },
+  resources: [],
+  workers: [],
+  limitations: [],
+});
diff --git a/tests/boundary/mcp/electronMcp.test.ts b/tests/boundary/mcp/electronMcp.test.ts
index 9842407fa0..1d6a8fb318 100644
--- a/tests/boundary/mcp/electronMcp.test.ts
+++ b/tests/boundary/mcp/electronMcp.test.ts
@@ -29,7 +29,7 @@ import { parseMcpToolError } from "../../fixtures/mcpToolError.js";
 import { AsarArtifactReader } from "../../../src/artifacts/AsarArtifactReader.js";
 import { toolAvailabilityInventory } from "../../../src/contracts/toolOutputSchemaPrimitives.js";
 import { AnalysisCancelledError } from "../../../src/domain/analysisErrorCore.js";
-import { classifyBrowserCompleteness } from "../../../src/domain/browserCompleteness.js";
+import { emptyElectronPageCoverage } from "../../../src/domain/javascript/electronPageInspection.fixture.js";
 import type { ElectronPageInspection } from "../../../src/domain/javascript/electronObservation.js";
 import { err } from "../../../src/domain/result.js";
 
@@ -115,33 +115,7 @@ it("records completed Electron facts after final detach as server Evidence", asy
       file_path: "/tmp/index.html",
       attached: true,
     },
-    capture_window: {
-      started_at: "2026-01-01T00:00:00.000Z",
-      ended_at: "2026-01-01T00:00:00.001Z",
-      observation_ms: 1,
-    },
-    completeness: classifyBrowserCompleteness({
-      policyFilteredSections: new Set(),
-      attachLimitedSections: new Set(),
-      truncatedSections: new Set(),
-      unavailableSections: new Set(),
-      excluded: [],
-      droppedEvents: {
-        scripts: 0,
-        network_requests: 0,
-        console_events: 0,
-        websocket_connections: 0,
-        websocket_frames: 0,
-        webmcp_tools: 0,
-        timeline_events: 0,
-      },
-    }),
-    frames: [],
-    dom: { total_nodes: 0, nodes: [] },
-    scripts: { total: 0, items: [] },
-    resources: [],
-    workers: [],
-    limitations: [],
+    ...emptyElectronPageCoverage(1),
   };
   const provider: ElectronObservationPort = {
     identity: () => ({