fix(agents): preserve precheck after context assembly failure

jalehman · jalehman · commit 63059958a06c · 2026-06-30T00:30:46.000-07:00
diff --git a/src/agents/embedded-agent-runner/run/attempt.spawn-workspace.context-engine.test.ts b/src/agents/embedded-agent-runner/run/attempt.spawn-workspace.context-engine.test.ts
@@ -2106,6 +2106,46 @@ describe("runEmbeddedAttempt context engine sessionKey forwarding", () => {
     expect(hoisted.preemptiveCompactionCalls).toHaveLength(0);
   });
 
+  it("keeps the generic precheck active when owning context engine assembly fails", async () => {
+    const lockEvents = trackSessionWriteLocks();
+    let sawPrompt = false;
+    const hugeHistory = "large raw history ".repeat(2_000);
+
+    const result = await createContextEngineAttemptRunner({
+      contextEngine: createTestContextEngine({
+        info: {
+          id: "test-context-engine",
+          name: "Test Context Engine",
+          version: "0.0.1",
+          ownsCompaction: true,
+        },
+        assemble: async () => {
+          throw new Error("assembly failed");
+        },
+      }),
+      sessionKey,
+      tempPaths,
+      sessionMessages: [{ role: "user", content: hugeHistory, timestamp: 1 }] as AgentMessage[],
+      attemptOverrides: {
+        contextTokenBudget: 500,
+      },
+      sessionPrompt: async (session) => {
+        sawPrompt = true;
+        session.messages = [
+          ...session.messages,
+          { role: "assistant", content: "done", timestamp: 2 },
+        ];
+      },
+    });
+
+    expect(sawPrompt).toBe(false);
+    expect(result.promptErrorSource).toBe("precheck");
+    expect(result.preflightRecovery?.route).toBe("compact_only");
+    expect(hoisted.preemptiveCompactionCalls).toHaveLength(1);
+    expect(hoisted.preemptiveCompactionCalls.at(-1)).not.toHaveProperty("unwindowedMessages");
+    expectInitialLockReleasedBeforePostTurnWrite(lockEvents);
+  });
+
   it("repairs tool-result pairing after context engine assembly", async () => {
     let promptMessages: AgentMessage[] = [];
 
diff --git a/src/agents/embedded-agent-runner/run/attempt.ts b/src/agents/embedded-agent-runner/run/attempt.ts
@@ -2577,6 +2577,7 @@ export async function runEmbeddedAttempt(
       let unwindowedContextEngineMessagesForPrecheck: AgentMessage[] | undefined;
       let contextEnginePromptAuthority: NonNullable<AssembleResult["promptAuthority"]> =
         "assembled";
+      let contextEngineAssemblySucceeded = false;
       const inFlightPromptSettlePromises = new Set<Promise<void>>();
       const inFlightAbortSettlePromises = new Set<Promise<void>>();
       const trackSettlePromise = (
@@ -3334,6 +3335,7 @@ export async function runEmbeddedAttempt(
               activeSession.agent.state.messages = assembledMessages;
             }
             contextEnginePromptAuthority = assembled.promptAuthority ?? "assembled";
+            contextEngineAssemblySucceeded = true;
             if (contextEnginePromptAuthority === "preassembly_may_overflow") {
               unwindowedContextEngineMessagesForPrecheck =
                 preassemblyContextEngineMessagesForPrecheck;
@@ -4604,7 +4606,8 @@ export async function runEmbeddedAttempt(
           let preemptiveCompaction = null;
           const shouldSkipPrecheck =
             skipPromptSubmission ||
-            (activeContextEngine?.info.ownsCompaction &&
+            (contextEngineAssemblySucceeded &&
+              activeContextEngine?.info.ownsCompaction &&
               contextEnginePromptAuthority !== "preassembly_may_overflow");
 
           if (shouldSkipPrecheck && !skipPromptSubmission) {
