fix: propagate max-step failures and unify task transcripts (#874)

Co-authored-by: Letta <noreply@letta.com>

src/tests/agent/subagent-max-steps-propagation.test.ts

@@ -0,0 +1,20 @@
+import { describe, expect, test } from "bun:test";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+
+describe("subagent max_steps error propagation", () => {
+  test("non-zero exit path prefers parsed finalError over generic exit code", () => {
+    const managerPath = fileURLToPath(
+      new URL("../../agent/subagents/manager.ts", import.meta.url),
+    );
+    const source = readFileSync(managerPath, "utf-8");
+
+    expect(source).toContain(
+      "const propagatedError = state.finalError?.trim();",
+    );
+    expect(source).toContain(
+      `const fallbackError = stderr || \`Subagent exited with code \${exitCode}\`;`,
+    );
+    expect(source).toContain("error: propagatedError || fallbackError");
+  });
+});

src/tests/tools/task-foreground-transcript.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, test } from "bun:test";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+
+describe("Task foreground transcript wiring", () => {
+  test("writes foreground transcript start and result output", () => {
+    const taskPath = fileURLToPath(
+      new URL("../../tools/impl/Task.ts", import.meta.url),
+    );
+    const source = readFileSync(taskPath, "utf-8");
+
+    expect(source).toContain("const foregroundTaskId = getNextTaskId();");
+    expect(source).toContain(
+      "const outputFile = createBackgroundOutputFile(foregroundTaskId);",
+    );
+    expect(source).toContain(
+      "writeTaskTranscriptStart(outputFile, description, subagent_type);",
+    );
+    expect(source).toContain(
+      "writeTaskTranscriptResult(outputFile, result, header);",
+    );
+    expect(source).toContain(
+      `return \`\${truncatedOutput}\\nOutput file: \${outputFile}\`;`,
+    );
+    expect(source).toContain(
+      `return \`Error: \${errorMessage}\\nOutput file: \${outputFile}\`;`,
+    );
+  });
+});