diff --git a/src/agents/pi-embedded-runner/run.overflow-compaction.fixture.ts b/src/agents/pi-embedded-runner/run.overflow-compaction.fixture.ts
index ce8e80e030a..6f4dea234e7 100644
--- a/src/agents/pi-embedded-runner/run.overflow-compaction.fixture.ts
+++ b/src/agents/pi-embedded-runner/run.overflow-compaction.fixture.ts
@@ -112,8 +112,8 @@ export function queueOverflowAttemptWithOversizedToolOutput(
       promptError: overflowError,
       messagesSnapshot: [
         {
-          role: "assistant",
-          content: "big tool output",
+          role: "toolResult",
+          content: [{ type: "text", text: "x".repeat(80_000) }],
         } as unknown as EmbeddedRunAttemptResult["messagesSnapshot"][number],
       ],
     }),
diff --git a/src/agents/pi-embedded-runner/run.overflow-compaction.harness.ts b/src/agents/pi-embedded-runner/run.overflow-compaction.harness.ts
index 88ae95f34ed..3f32edeed85 100644
--- a/src/agents/pi-embedded-runner/run.overflow-compaction.harness.ts
+++ b/src/agents/pi-embedded-runner/run.overflow-compaction.harness.ts
@@ -69,6 +69,19 @@ export const mockedPrepareProviderRuntimeAuth = vi.fn(async () => undefined);
 export const mockedRunEmbeddedAttempt =
   vi.fn<(params: unknown) => Promise<EmbeddedRunAttemptResult>>();
 export const mockedRunContextEngineMaintenance = vi.fn(async () => undefined);
+export const mockedSessionLikelyHasOversizedToolResults = vi.fn(() => false);
+type MockTruncateOversizedToolResultsResult = {
+  truncated: boolean;
+  truncatedCount: number;
+  reason?: string;
+};
+export const mockedTruncateOversizedToolResultsInSession = vi.fn<
+  () => Promise<MockTruncateOversizedToolResultsResult>
+>(async () => ({
+  truncated: false,
+  truncatedCount: 0,
+  reason: "no oversized tool results",
+}));
 
 type MockFailoverErrorDescription = {
   message: string;
@@ -203,6 +216,14 @@ export function resetRunOverflowCompactionHarnessMocks(): void {
   mockedRunEmbeddedAttempt.mockReset();
   mockedRunContextEngineMaintenance.mockReset();
   mockedRunContextEngineMaintenance.mockResolvedValue(undefined);
+  mockedSessionLikelyHasOversizedToolResults.mockReset();
+  mockedSessionLikelyHasOversizedToolResults.mockReturnValue(false);
+  mockedTruncateOversizedToolResultsInSession.mockReset();
+  mockedTruncateOversizedToolResultsInSession.mockResolvedValue({
+    truncated: false,
+    truncatedCount: 0,
+    reason: "no oversized tool results",
+  });
 
   mockedCoerceToFailoverError.mockReset();
   mockedCoerceToFailoverError.mockReturnValue(null);
@@ -375,6 +396,11 @@ export async function loadRunOverflowCompactionHarness(): Promise<{
     runEmbeddedAttempt: mockedRunEmbeddedAttempt,
   }));
 
+  vi.doMock("./tool-result-truncation.js", () => ({
+    sessionLikelyHasOversizedToolResults: mockedSessionLikelyHasOversizedToolResults,
+    truncateOversizedToolResultsInSession: mockedTruncateOversizedToolResultsInSession,
+  }));
+
   vi.doMock("./context-engine-maintenance.js", () => ({
     runContextEngineMaintenance: mockedRunContextEngineMaintenance,
   }));
diff --git a/src/agents/pi-embedded-runner/run.overflow-compaction.loop.test.ts b/src/agents/pi-embedded-runner/run.overflow-compaction.loop.test.ts
index a476f76eb82..6c645359b6d 100644
--- a/src/agents/pi-embedded-runner/run.overflow-compaction.loop.test.ts
+++ b/src/agents/pi-embedded-runner/run.overflow-compaction.loop.test.ts
@@ -4,6 +4,7 @@ import {
   makeCompactionSuccess,
   makeOverflowError,
   mockOverflowRetrySuccess,
+  queueOverflowAttemptWithOversizedToolOutput,
 } from "./run.overflow-compaction.fixture.js";
 import {
   loadRunOverflowCompactionHarness,
@@ -13,6 +14,8 @@ import {
   mockedIsLikelyContextOverflowError,
   mockedLog,
   mockedRunEmbeddedAttempt,
+  mockedSessionLikelyHasOversizedToolResults,
+  mockedTruncateOversizedToolResultsInSession,
   overflowBaseRunParams as baseParams,
 } from "./run.overflow-compaction.harness.js";
 
@@ -26,6 +29,8 @@ describe("overflow compaction in run loop", () => {
   beforeEach(() => {
     mockedRunEmbeddedAttempt.mockReset();
     mockedCompactDirect.mockReset();
+    mockedSessionLikelyHasOversizedToolResults.mockReset();
+    mockedTruncateOversizedToolResultsInSession.mockReset();
     mockedContextEngine.info.ownsCompaction = false;
     mockedLog.debug.mockReset();
     mockedLog.info.mockReset();
@@ -57,6 +62,12 @@ describe("overflow compaction in run loop", () => {
       compacted: false,
       reason: "nothing to compact",
     });
+    mockedSessionLikelyHasOversizedToolResults.mockReturnValue(false);
+    mockedTruncateOversizedToolResultsInSession.mockResolvedValue({
+      truncated: false,
+      truncatedCount: 0,
+      reason: "no oversized tool results",
+    });
   });
 
   it("retries after successful compaction on context overflow promptError", async () => {
@@ -129,6 +140,37 @@ describe("overflow compaction in run loop", () => {
     expect(mockedLog.warn).toHaveBeenCalledWith(expect.stringContaining("auto-compaction failed"));
   });
 
+  it("falls back to tool-result truncation and retries when oversized results are detected", async () => {
+    queueOverflowAttemptWithOversizedToolOutput(mockedRunEmbeddedAttempt, makeOverflowError());
+    mockedRunEmbeddedAttempt.mockResolvedValueOnce(makeAttemptResult({ promptError: null }));
+
+    mockedCompactDirect.mockResolvedValueOnce({
+      ok: false,
+      compacted: false,
+      reason: "nothing to compact",
+    });
+    mockedSessionLikelyHasOversizedToolResults.mockReturnValue(true);
+    mockedTruncateOversizedToolResultsInSession.mockResolvedValueOnce({
+      truncated: true,
+      truncatedCount: 1,
+    });
+
+    const result = await runEmbeddedPiAgent(baseParams);
+
+    expect(mockedCompactDirect).toHaveBeenCalledTimes(1);
+    expect(mockedSessionLikelyHasOversizedToolResults).toHaveBeenCalledWith(
+      expect.objectContaining({ contextWindowTokens: 200000 }),
+    );
+    expect(mockedTruncateOversizedToolResultsInSession).toHaveBeenCalledWith(
+      expect.objectContaining({ sessionFile: "/tmp/session.json" }),
+    );
+    expect(mockedRunEmbeddedAttempt).toHaveBeenCalledTimes(2);
+    expect(mockedLog.info).toHaveBeenCalledWith(
+      expect.stringContaining("Truncated 1 tool result(s)"),
+    );
+    expect(result.meta.error).toBeUndefined();
+  });
+
   it("retries compaction up to 3 times before giving up", async () => {
     const overflowError = makeOverflowError();
 
diff --git a/src/agents/pi-embedded-runner/run.ts b/src/agents/pi-embedded-runner/run.ts
index f4099086e70..1598cbc9758 100644
--- a/src/agents/pi-embedded-runner/run.ts
+++ b/src/agents/pi-embedded-runner/run.ts
@@ -64,6 +64,10 @@ import { runContextEngineMaintenance } from "./context-engine-maintenance.js";
 import { resolveGlobalLane, resolveSessionLane } from "./lanes.js";
 import { log } from "./logger.js";
 import { resolveModelAsync } from "./model.js";
+import {
+  sessionLikelyHasOversizedToolResults,
+  truncateOversizedToolResultsInSession,
+} from "./tool-result-truncation.js";
 import { handleAssistantFailover } from "./run/assistant-failover.js";
 import { runEmbeddedAttempt } from "./run/attempt.js";
 import { createEmbeddedRunAuthController } from "./run/auth-controller.js";
@@ -316,6 +320,7 @@ export async function runEmbeddedPiAgent(
       const MAX_OVERFLOW_COMPACTION_ATTEMPTS = 3;
       const MAX_RUN_LOOP_ITERATIONS = resolveMaxRunRetryIterations(profileCandidates.length);
       let overflowCompactionAttempts = 0;
+      let toolResultTruncationAttempted = false;
       let bootstrapPromptWarningSignaturesSeen =
         params.bootstrapPromptWarningSignaturesSeen ??
         (params.bootstrapPromptWarningSignature ? [params.bootstrapPromptWarningSignature] : []);
@@ -922,6 +927,38 @@ export async function runEmbeddedPiAgent(
                 `auto-compaction failed for ${provider}/${modelId}: ${compactResult.reason ?? "nothing to compact"}`,
               );
             }
+            if (!toolResultTruncationAttempted) {
+              const contextWindowTokens = ctxInfo.tokens;
+              const hasOversized = attempt.messagesSnapshot
+                ? sessionLikelyHasOversizedToolResults({
+                    messages: attempt.messagesSnapshot,
+                    contextWindowTokens,
+                  })
+                : false;
+
+              if (hasOversized) {
+                toolResultTruncationAttempted = true;
+                log.warn(
+                  `[context-overflow-recovery] Attempting tool result truncation for ${provider}/${modelId} ` +
+                    `(contextWindow=${contextWindowTokens} tokens)`,
+                );
+                const truncResult = await truncateOversizedToolResultsInSession({
+                  sessionFile: params.sessionFile,
+                  contextWindowTokens,
+                  sessionId: params.sessionId,
+                  sessionKey: params.sessionKey,
+                });
+                if (truncResult.truncated) {
+                  log.info(
+                    `[context-overflow-recovery] Truncated ${truncResult.truncatedCount} tool result(s); retrying prompt`,
+                  );
+                  continue;
+                }
+                log.warn(
+                  `[context-overflow-recovery] Tool result truncation did not help: ${truncResult.reason ?? "unknown"}`,
+                );
+              }
+            }
             if (
               (isCompactionFailure || overflowCompactionAttempts >= MAX_OVERFLOW_COMPACTION_ATTEMPTS) &&
               log.isEnabled("debug")
diff --git a/src/agents/pi-embedded-runner/tool-result-truncation.ts b/src/agents/pi-embedded-runner/tool-result-truncation.ts
index f5a6bc10d68..c8fcb78a851 100644
--- a/src/agents/pi-embedded-runner/tool-result-truncation.ts
+++ b/src/agents/pi-embedded-runner/tool-result-truncation.ts
@@ -1,5 +1,10 @@
 import type { AgentMessage } from "@mariozechner/pi-agent-core";
 import type { TextContent } from "@mariozechner/pi-ai";
+import { SessionManager } from "@mariozechner/pi-coding-agent";
+import { emitSessionTranscriptUpdate } from "../../sessions/transcript-events.js";
+import { acquireSessionWriteLock } from "../session-write-lock.js";
+import { log } from "./logger.js";
+import { rewriteTranscriptEntriesInSessionManager } from "./transcript-rewrite.js";
 
 /**
  * Maximum share of the context window a single tool result should occupy.
@@ -245,6 +250,80 @@ export function truncateOversizedToolResultsInMessages(
   return { messages: result, truncatedCount };
 }
 
+export async function truncateOversizedToolResultsInSession(params: {
+  sessionFile: string;
+  contextWindowTokens: number;
+  sessionId?: string;
+  sessionKey?: string;
+}): Promise<{ truncated: boolean; truncatedCount: number; reason?: string }> {
+  const { sessionFile, contextWindowTokens } = params;
+  const maxChars = calculateMaxToolResultChars(contextWindowTokens);
+  let sessionLock: Awaited<ReturnType<typeof acquireSessionWriteLock>> | undefined;
+
+  try {
+    sessionLock = await acquireSessionWriteLock({ sessionFile });
+    const sessionManager = SessionManager.open(sessionFile);
+    const branch = sessionManager.getBranch();
+
+    if (branch.length === 0) {
+      return { truncated: false, truncatedCount: 0, reason: "empty session" };
+    }
+
+    const oversizedIndices: number[] = [];
+    for (let i = 0; i < branch.length; i += 1) {
+      const entry = branch[i];
+      if (entry.type !== "message") {
+        continue;
+      }
+      const msg = entry.message;
+      if ((msg as { role?: string }).role !== "toolResult") {
+        continue;
+      }
+      if (getToolResultTextLength(msg) > maxChars) {
+        oversizedIndices.push(i);
+      }
+    }
+
+    if (oversizedIndices.length === 0) {
+      return { truncated: false, truncatedCount: 0, reason: "no oversized tool results" };
+    }
+
+    const replacements = oversizedIndices.flatMap((index) => {
+      const entry = branch[index];
+      if (!entry || entry.type !== "message") {
+        return [];
+      }
+      return [{ entryId: entry.id, message: truncateToolResultMessage(entry.message, maxChars) }];
+    });
+
+    const rewriteResult = rewriteTranscriptEntriesInSessionManager({
+      sessionManager,
+      replacements,
+    });
+    if (rewriteResult.changed) {
+      emitSessionTranscriptUpdate(sessionFile);
+    }
+
+    log.info(
+      `[tool-result-truncation] Truncated ${rewriteResult.rewrittenEntries} tool result(s) in session ` +
+        `(contextWindow=${contextWindowTokens} maxChars=${maxChars}) ` +
+        `sessionKey=${params.sessionKey ?? params.sessionId ?? "unknown"}`,
+    );
+
+    return {
+      truncated: rewriteResult.changed,
+      truncatedCount: rewriteResult.rewrittenEntries,
+      reason: rewriteResult.reason,
+    };
+  } catch (err) {
+    const errMsg = err instanceof Error ? err.message : String(err);
+    log.warn(`[tool-result-truncation] Failed to truncate: ${errMsg}`);
+    return { truncated: false, truncatedCount: 0, reason: errMsg };
+  } finally {
+    await sessionLock?.release();
+  }
+}
+
 /**
  * Check if a tool result message exceeds the size limit for a given context window.
  */
@@ -255,3 +334,22 @@ export function isOversizedToolResult(msg: AgentMessage, contextWindowTokens: nu
   const maxChars = calculateMaxToolResultChars(contextWindowTokens);
   return getToolResultTextLength(msg) > maxChars;
 }
+
+export function sessionLikelyHasOversizedToolResults(params: {
+  messages: AgentMessage[];
+  contextWindowTokens: number;
+}): boolean {
+  const { messages, contextWindowTokens } = params;
+  const maxChars = calculateMaxToolResultChars(contextWindowTokens);
+
+  for (const msg of messages) {
+    if ((msg as { role?: string }).role !== "toolResult") {
+      continue;
+    }
+    if (getToolResultTextLength(msg) > maxChars) {
+      return true;
+    }
+  }
+
+  return false;
+}