fix(gsd): wire setLogBasePath into engine init to resurrect audit log (#2745)

* fix: wire setLogBasePath into engine init to resurrect audit log

_auditBasePath was always null — setLogBasePath() existed but was never
called from any production code path. Every logWarning/logError call hit
the if (_auditBasePath) guard as false, so nothing was ever written to
.gsd/audit-log.jsonl.

Two independent fixes:
1. Remove _auditBasePath = null from _resetLogs() — the base path must
   survive unit resets, it's stable for process lifetime
2. Call setLogBasePath(base) after s.basePath = base in both the fresh-
   start path (bootstrapAutoSession) and the resume path (startAuto)

Adds two tests verifying disk persistence and that _resetLogs doesn't
kill the audit path.

Fixes #2722

* refactor: clean up audit log tests and avoid redundant mkdirSync

- Use makeTempDir/cleanup from test-utils.ts instead of inline mkdtempSync/rmSync
- Add afterEach in audit describe block to reset _auditBasePath via
  setLogBasePath("") — prevents state bleed into subsequent tests since
  _resetLogs() no longer clears it
- Drop four raw imports (mkdtempSync, rmSync, tmpdir — join was already used)
- Guard mkdirSync in _push() with _auditDirEnsured flag — was calling
  mkdirSync on every log entry; now called once per base path

* revert: remove _auditDirEnsured flag

mkdirSync({ recursive: true }) on an existing dir is a cheap stat, not
meaningful overhead on a low-frequency warn/error path. The flag added
mutable state for no real gain.

src/resources/extensions/gsd/auto-start.ts

@@ -67,6 +67,7 @@ import {
   getDebugLogPath,
 } from "./debug-logger.js";
 import { parseUnitId } from "./unit-id.js";
+import { setLogBasePath } from "./workflow-logger.js";
 import type { AutoSession } from "./auto/session.js";
 import {
   existsSync,
@@ -461,6 +462,7 @@ export async function bootstrapAutoSession(
     s.verbose = verboseMode;
     s.cmdCtx = ctx;
     s.basePath = base;
+    setLogBasePath(base);
     s.unitDispatchCount.clear();
     s.unitRecoveryCount.clear();
     s.lastBudgetAlertLevel = 0;

src/resources/extensions/gsd/auto.ts

@@ -114,6 +114,7 @@ import {
   formatCost,
   formatTokenCount,
 } from "./metrics.js";
+import { setLogBasePath } from "./workflow-logger.js";
 import { join } from "node:path";
 import { readFileSync, existsSync, mkdirSync, writeFileSync, unlinkSync } from "node:fs";
 import { atomicWriteSync } from "./atomic-write.js";
@@ -1102,6 +1103,7 @@ export async function startAuto(
     s.stepMode = requestedStepMode;
     s.cmdCtx = ctx;
     s.basePath = base;
+    setLogBasePath(base);
     s.unitDispatchCount.clear();
     s.unitLifetimeDispatches.clear();
     if (!getLedger()) initMetrics(base);

src/resources/extensions/gsd/tests/workflow-logger.test.ts

@@ -1,8 +1,11 @@
 // GSD Extension — Workflow Logger Tests
 // Tests for the centralized warning/error accumulator.
 
-import { describe, test, beforeEach } from "node:test";
+import { describe, test, beforeEach, afterEach } from "node:test";
 import assert from "node:assert/strict";
+import { existsSync, readFileSync } from "node:fs";
+import { join } from "node:path";
+import { makeTempDir, cleanup } from "./test-utils.ts";
 import {
   logWarning,
   logError,
@@ -14,6 +17,7 @@ import {
   hasAnyIssues,
   summarizeLogs,
   formatForNotification,
+  setLogBasePath,
   _resetLogs,
 } from "../workflow-logger.ts";
 
@@ -222,6 +226,44 @@ describe("workflow-logger", () => {
     });
   });
 
+  describe("audit log persistence", () => {
+    let dir: string;
+
+    beforeEach(() => {
+      dir = makeTempDir("wl-audit-");
+    });
+
+    afterEach(() => {
+      setLogBasePath("");
+      cleanup(dir);
+    });
+
+    test("writes entry to .gsd/audit-log.jsonl after setLogBasePath", () => {
+      setLogBasePath(dir);
+      logWarning("engine", "audit test entry");
+
+      const auditPath = join(dir, ".gsd", "audit-log.jsonl");
+      assert.ok(existsSync(auditPath), "audit-log.jsonl should exist");
+      const content = readFileSync(auditPath, "utf-8");
+      const entry = JSON.parse(content.trim());
+      assert.equal(entry.severity, "warn");
+      assert.equal(entry.component, "engine");
+      assert.equal(entry.message, "audit test entry");
+    });
+
+    test("_resetLogs does not clear the audit base path", () => {
+      setLogBasePath(dir);
+      _resetLogs();
+      logWarning("engine", "post-reset entry");
+
+      const auditPath = join(dir, ".gsd", "audit-log.jsonl");
+      assert.ok(existsSync(auditPath), "audit-log.jsonl should exist after _resetLogs");
+      const content = readFileSync(auditPath, "utf-8");
+      const entry = JSON.parse(content.trim());
+      assert.equal(entry.message, "post-reset entry");
+    });
+  });
+
   describe("buffer limit", () => {
     test("caps at MAX_BUFFER entries, dropping oldest", () => {
       const OVER = 110;

src/resources/extensions/gsd/workflow-logger.ts

@@ -199,7 +199,6 @@ export function readAuditLog(basePath?: string): LogEntry[] {
  */
 export function _resetLogs(): void {
   _buffer = [];
-  _auditBasePath = null;
 }
 
 // ─── Internal ───────────────────────────────────────────────────────────