diff --git a/src/agents/pi-embedded-runner/run.overflow-compaction.e2e.test.ts b/src/agents/pi-embedded-runner/run.overflow-compaction.e2e.test.ts
index 594f5e6d2..dbb561316 100644
--- a/src/agents/pi-embedded-runner/run.overflow-compaction.e2e.test.ts
+++ b/src/agents/pi-embedded-runner/run.overflow-compaction.e2e.test.ts
@@ -1,27 +1,37 @@
 import "./run.overflow-compaction.mocks.shared.js";
 import { beforeEach, describe, expect, it, vi } from "vitest";
+import { isCompactionFailureError, isLikelyContextOverflowError } from "../pi-embedded-helpers.js";
 
 vi.mock("../../utils.js", () => ({
   resolveUserPath: vi.fn((p: string) => p),
 }));
 
-vi.mock("../pi-embedded-helpers.js", async () => {
-  return {
-    isCompactionFailureError: (msg?: string) => {
+import { log } from "./logger.js";
+import { runEmbeddedPiAgent } from "./run.js";
+import { makeAttemptResult, mockOverflowRetrySuccess } from "./run.overflow-compaction.fixture.js";
+import {
+  mockedCompactDirect,
+  mockedRunEmbeddedAttempt,
+  mockedSessionLikelyHasOversizedToolResults,
+  mockedTruncateOversizedToolResultsInSession,
+  overflowBaseRunParams as baseParams,
+} from "./run.overflow-compaction.shared-test.js";
+import type { EmbeddedRunAttemptResult } from "./run/types.js";
+
+const mockedIsCompactionFailureError = vi.mocked(isCompactionFailureError);
+const mockedIsLikelyContextOverflowError = vi.mocked(isLikelyContextOverflowError);
+
+describe("overflow compaction in run loop", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockedIsCompactionFailureError.mockImplementation((msg?: string) => {
       if (!msg) {
         return false;
       }
       const lower = msg.toLowerCase();
       return lower.includes("request_too_large") && lower.includes("summarization failed");
-    },
-    isContextOverflowError: (msg?: string) => {
-      if (!msg) {
-        return false;
-      }
-      const lower = msg.toLowerCase();
-      return lower.includes("request_too_large") || lower.includes("request size exceeds");
-    },
-    isLikelyContextOverflowError: (msg?: string) => {
+    });
+    mockedIsLikelyContextOverflowError.mockImplementation((msg?: string) => {
       if (!msg) {
         return false;
       }
@@ -32,52 +42,12 @@ vi.mock("../pi-embedded-helpers.js", async () => {
         lower.includes("context window exceeded") ||
         lower.includes("prompt too large")
       );
-    },
-    isFailoverAssistantError: vi.fn(() => false),
-    isFailoverErrorMessage: vi.fn(() => false),
-    isAuthAssistantError: vi.fn(() => false),
-    isRateLimitAssistantError: vi.fn(() => false),
-    isBillingAssistantError: vi.fn(() => false),
-    classifyFailoverReason: vi.fn(() => null),
-    formatAssistantErrorText: vi.fn(() => ""),
-    parseImageSizeError: vi.fn(() => null),
-    pickFallbackThinkingLevel: vi.fn(() => null),
-    isTimeoutErrorMessage: vi.fn(() => false),
-    parseImageDimensionError: vi.fn(() => null),
-  };
-});
-
-import { compactEmbeddedPiSessionDirect } from "./compact.js";
-import { log } from "./logger.js";
-import { runEmbeddedPiAgent } from "./run.js";
-import { makeAttemptResult, mockOverflowRetrySuccess } from "./run.overflow-compaction.fixture.js";
-import { runEmbeddedAttempt } from "./run/attempt.js";
-import type { EmbeddedRunAttemptResult } from "./run/types.js";
-import {
-  sessionLikelyHasOversizedToolResults,
-  truncateOversizedToolResultsInSession,
-} from "./tool-result-truncation.js";
-
-const mockedRunEmbeddedAttempt = vi.mocked(runEmbeddedAttempt);
-const mockedCompactDirect = vi.mocked(compactEmbeddedPiSessionDirect);
-const mockedSessionLikelyHasOversizedToolResults = vi.mocked(sessionLikelyHasOversizedToolResults);
-const mockedTruncateOversizedToolResultsInSession = vi.mocked(
-  truncateOversizedToolResultsInSession,
-);
-
-const baseParams = {
-  sessionId: "test-session",
-  sessionKey: "test-key",
-  sessionFile: "/tmp/session.json",
-  workspaceDir: "/tmp/workspace",
-  prompt: "hello",
-  timeoutMs: 30000,
-  runId: "run-1",
-};
-
-describe("overflow compaction in run loop", () => {
-  beforeEach(() => {
-    vi.clearAllMocks();
+    });
+    mockedCompactDirect.mockResolvedValue({
+      ok: false,
+      compacted: false,
+      reason: "nothing to compact",
+    });
     mockedSessionLikelyHasOversizedToolResults.mockReturnValue(false);
     mockedTruncateOversizedToolResultsInSession.mockResolvedValue({
       truncated: false,
diff --git a/src/agents/pi-embedded-runner/run.overflow-compaction.shared-test.ts b/src/agents/pi-embedded-runner/run.overflow-compaction.shared-test.ts
new file mode 100644
index 000000000..45bab82e1
--- /dev/null
+++ b/src/agents/pi-embedded-runner/run.overflow-compaction.shared-test.ts
@@ -0,0 +1,26 @@
+import { vi } from "vitest";
+import { compactEmbeddedPiSessionDirect } from "./compact.js";
+import { runEmbeddedAttempt } from "./run/attempt.js";
+import {
+  sessionLikelyHasOversizedToolResults,
+  truncateOversizedToolResultsInSession,
+} from "./tool-result-truncation.js";
+
+export const mockedRunEmbeddedAttempt = vi.mocked(runEmbeddedAttempt);
+export const mockedCompactDirect = vi.mocked(compactEmbeddedPiSessionDirect);
+export const mockedSessionLikelyHasOversizedToolResults = vi.mocked(
+  sessionLikelyHasOversizedToolResults,
+);
+export const mockedTruncateOversizedToolResultsInSession = vi.mocked(
+  truncateOversizedToolResultsInSession,
+);
+
+export const overflowBaseRunParams = {
+  sessionId: "test-session",
+  sessionKey: "test-key",
+  sessionFile: "/tmp/session.json",
+  workspaceDir: "/tmp/workspace",
+  prompt: "hello",
+  timeoutMs: 30000,
+  runId: "run-1",
+} as const;
diff --git a/src/agents/pi-embedded-runner/run.overflow-compaction.test.ts b/src/agents/pi-embedded-runner/run.overflow-compaction.test.ts
index db299e8ed..56dc31edd 100644
--- a/src/agents/pi-embedded-runner/run.overflow-compaction.test.ts
+++ b/src/agents/pi-embedded-runner/run.overflow-compaction.test.ts
@@ -1,23 +1,17 @@
 import "./run.overflow-compaction.mocks.shared.js";
 import { beforeEach, describe, expect, it, vi } from "vitest";
 import { pickFallbackThinkingLevel } from "../pi-embedded-helpers.js";
-import { compactEmbeddedPiSessionDirect } from "./compact.js";
 import { runEmbeddedPiAgent } from "./run.js";
 import { makeAttemptResult, mockOverflowRetrySuccess } from "./run.overflow-compaction.fixture.js";
 import { mockedGlobalHookRunner } from "./run.overflow-compaction.mocks.shared.js";
-import { runEmbeddedAttempt } from "./run/attempt.js";
-import type { EmbeddedRunAttemptResult } from "./run/types.js";
 import {
-  sessionLikelyHasOversizedToolResults,
-  truncateOversizedToolResultsInSession,
-} from "./tool-result-truncation.js";
-
-const mockedRunEmbeddedAttempt = vi.mocked(runEmbeddedAttempt);
-const mockedCompactDirect = vi.mocked(compactEmbeddedPiSessionDirect);
-const mockedSessionLikelyHasOversizedToolResults = vi.mocked(sessionLikelyHasOversizedToolResults);
-const mockedTruncateOversizedToolResultsInSession = vi.mocked(
-  truncateOversizedToolResultsInSession,
-);
+  mockedCompactDirect,
+  mockedRunEmbeddedAttempt,
+  mockedSessionLikelyHasOversizedToolResults,
+  mockedTruncateOversizedToolResultsInSession,
+  overflowBaseRunParams,
+} from "./run.overflow-compaction.shared-test.js";
+import type { EmbeddedRunAttemptResult } from "./run/types.js";
 const mockedPickFallbackThinkingLevel = vi.mocked(pickFallbackThinkingLevel);
 
 describe("runEmbeddedPiAgent overflow compaction trigger routing", () => {
@@ -61,15 +55,7 @@ describe("runEmbeddedPiAgent overflow compaction trigger routing", () => {
       compactDirect: mockedCompactDirect,
     });
 
-    await runEmbeddedPiAgent({
-      sessionId: "test-session",
-      sessionKey: "test-key",
-      sessionFile: "/tmp/session.json",
-      workspaceDir: "/tmp/workspace",
-      prompt: "hello",
-      timeoutMs: 30000,
-      runId: "run-1",
-    });
+    await runEmbeddedPiAgent(overflowBaseRunParams);
 
     expect(mockedCompactDirect).toHaveBeenCalledTimes(1);
     expect(mockedCompactDirect).toHaveBeenCalledWith(
@@ -124,15 +110,7 @@ describe("runEmbeddedPiAgent overflow compaction trigger routing", () => {
       truncatedCount: 1,
     });
 
-    const result = await runEmbeddedPiAgent({
-      sessionId: "test-session",
-      sessionKey: "test-key",
-      sessionFile: "/tmp/session.json",
-      workspaceDir: "/tmp/workspace",
-      prompt: "hello",
-      timeoutMs: 30000,
-      runId: "run-1",
-    });
+    const result = await runEmbeddedPiAgent(overflowBaseRunParams);
 
     expect(mockedCompactDirect).toHaveBeenCalledTimes(3);
     expect(mockedTruncateOversizedToolResultsInSession).toHaveBeenCalledTimes(1);
@@ -149,15 +127,7 @@ describe("runEmbeddedPiAgent overflow compaction trigger routing", () => {
     );
     mockedPickFallbackThinkingLevel.mockReturnValue("low");
 
-    const result = await runEmbeddedPiAgent({
-      sessionId: "test-session",
-      sessionKey: "test-key",
-      sessionFile: "/tmp/session.json",
-      workspaceDir: "/tmp/workspace",
-      prompt: "hello",
-      timeoutMs: 30000,
-      runId: "run-1",
-    });
+    const result = await runEmbeddedPiAgent(overflowBaseRunParams);
 
     expect(mockedRunEmbeddedAttempt).toHaveBeenCalledTimes(32);
     expect(mockedCompactDirect).not.toHaveBeenCalled();