fix(coding-agent): clarify truncated recovery failure

closes #8130

packages/coding-agent/CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - Fixed `pi.registerFlag()` accepting default values that do not match the declared flag type ([#8064](https://github.com/earendil-works/pi/issues/8064)).
 - Fixed Z.AI Coding Plan defaults referencing the removed GLM-5.1 model ([#8096](https://github.com/earendil-works/pi/issues/8096)).
+- Fixed repeated ambiguous truncated-response recovery being mislabeled as context overflow ([#8130](https://github.com/earendil-works/pi/issues/8130)).
 
 ## [0.84.2] - 2026-08-14
 

packages/coding-agent/src/core/agent-session.ts

@@ -2008,8 +2008,9 @@ export class AgentSession {
 		// Automatic cases 1 and 2: context overflow.
 		// A length stop is recoverable when output ended below the model's original desired limit,
 		// independent of the configured context size or any context-clamped provider request limit.
+		const contextOverflow = sameModel && isContextOverflow(assistantMessage, contextWindow);
 		const recoverableLength = sameModel && isRecoverableLength(assistantMessage, this.model?.maxTokens ?? 0);
-		if (sameModel && (isContextOverflow(assistantMessage, contextWindow) || recoverableLength)) {
+		if (contextOverflow || recoverableLength) {
 			const willRetry = assistantMessage.stopReason !== "stop";
 
 			// Case 2: the response completed successfully. Compact, but do not retry because
@@ -2019,14 +2020,16 @@ export class AgentSession {
 			}
 
 			if (this._overflowRecoveryAttempted) {
+				const errorMessage = contextOverflow
+					? "Context overflow recovery failed after one compact-and-retry attempt. Try reducing context or switching to a larger-context model."
+					: "Truncated response recovery failed after one compact-and-retry attempt.";
 				this._emit({
 					type: "compaction_end",
 					reason: "overflow",
 					result: undefined,
 					aborted: false,
 					willRetry: false,
-					errorMessage:
-						"Context overflow recovery failed after one compact-and-retry attempt. Try reducing context or switching to a larger-context model.",
+					errorMessage,
 				});
 				return false;
 			}

packages/coding-agent/test/suite/agent-session-compaction.test.ts

@@ -353,6 +353,34 @@ describe("AgentSession compaction characterization", () => {
 		expect(harness.faux.state.callCount).toBe(2);
 		expect(harness.eventsOfType("compaction_start").filter((event) => event.reason === "overflow")).toHaveLength(1);
 		expect(harness.eventsOfType("compaction_end").at(-1)?.errorMessage).toBe(
+			"Truncated response recovery failed after one compact-and-retry attempt.",
+		);
+	});
+
+	it("keeps overflow wording when a repeated length stop fills the context window", async () => {
+		const harness = await createHarness({
+			models: [{ id: "faux-1", contextWindow: 100, maxTokens: 100 }],
+		});
+		harnesses.push(harness);
+		const sessionInternals = harness.session as unknown as SessionWithCompactionInternals;
+		const lengthOverflowMessage = createAssistant(harness, {
+			stopReason: "length",
+			totalTokens: 100,
+			timestamp: Date.now(),
+		});
+		const runAutoCompactionSpy = vi.spyOn(sessionInternals, "_runAutoCompaction").mockResolvedValue(false);
+		const compactionErrors: string[] = [];
+		harness.session.subscribe((event) => {
+			if (event.type === "compaction_end" && event.errorMessage) {
+				compactionErrors.push(event.errorMessage);
+			}
+		});
+
+		await sessionInternals._checkCompaction(lengthOverflowMessage);
+		await sessionInternals._checkCompaction({ ...lengthOverflowMessage, timestamp: Date.now() + 1 });
+
+		expect(runAutoCompactionSpy).toHaveBeenCalledTimes(1);
+		expect(compactionErrors).toContain(
 			"Context overflow recovery failed after one compact-and-retry attempt. Try reducing context or switching to a larger-context model.",
 		);
 	});