fix(gsd): suppress workflow stderr during /gsd

src/resources/extensions/gsd/commands/index.ts

@@ -8,7 +8,13 @@ export function registerGSDCommand(pi: ExtensionAPI): void {
     getArgumentCompletions: getGsdArgumentCompletions,
     handler: async (args: string, ctx: ExtensionCommandContext) => {
       const { handleGSDCommand } = await import("./dispatcher.js");
-      await handleGSDCommand(args, ctx, pi);
+      const { setStderrLoggingEnabled } = await import("../workflow-logger.js");
+      const previousStderrSetting = setStderrLoggingEnabled(false);
+      try {
+        await handleGSDCommand(args, ctx, pi);
+      } finally {
+        setStderrLoggingEnabled(previousStderrSetting);
+      }
     },
   });
 }

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

@@ -18,6 +18,7 @@ import {
   summarizeLogs,
   formatForNotification,
   setLogBasePath,
+  setStderrLoggingEnabled,
   _resetLogs,
 } from "../workflow-logger.ts";
 
@@ -375,5 +376,20 @@ describe("workflow-logger", () => {
       logError("tool", "failed", { cmd: "complete_task" });
       assert.ok(written[0].includes('"cmd":"complete_task"'));
     });
+
+    test("suppresses stderr when disabled", (t) => {
+      const written: string[] = [];
+      const orig = process.stderr.write.bind(process.stderr);
+      const previous = setStderrLoggingEnabled(false);
+      // @ts-ignore — patching for test
+      process.stderr.write = (chunk: string) => { written.push(chunk); return true; };
+      t.after(() => {
+        process.stderr.write = orig;
+        setStderrLoggingEnabled(previous);
+      });
+
+      logWarning("engine", "hidden warning");
+      assert.deepEqual(written, []);
+    });
   });
 });

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

@@ -67,6 +67,7 @@ export interface LogEntry {
 const MAX_BUFFER = 100;
 let _buffer: LogEntry[] = [];
 let _auditBasePath: string | null = null;
+let _stderrEnabled = true;
 
 /**
  * Set the base path for persistent audit log writes.
@@ -77,6 +78,16 @@ export function setLogBasePath(basePath: string): void {
   _auditBasePath = basePath;
 }
 
+/**
+ * Enable or disable immediate stderr writes for workflow logs.
+ * Returns the previous setting so callers can restore it.
+ */
+export function setStderrLoggingEnabled(enabled: boolean): boolean {
+  const previous = _stderrEnabled;
+  _stderrEnabled = enabled;
+  return previous;
+}
+
 // ─── Public API ─────────────────────────────────────────────────────────
 
 /**
@@ -245,7 +256,7 @@ function _push(
   // Always forward to stderr so terminal watchers see it (see module header for policy)
   const prefix = severity === "error" ? "ERROR" : "WARN";
   const ctxStr = context ? ` ${JSON.stringify(context)}` : "";
-  process.stderr.write(`[gsd:${component}] ${prefix}: ${message}${ctxStr}\n`);
+  _writeStderr(`[gsd:${component}] ${prefix}: ${message}${ctxStr}\n`);
 
   // Persist to notification store (both warnings and errors)
   try {
@@ -255,7 +266,7 @@ function _push(
       "workflow-logger",
     );
   } catch (notifErr) {
-    process.stderr.write(`[gsd:workflow-logger] notification-store append failed: ${(notifErr as Error).message}\n`);
+    _writeStderr(`[gsd:workflow-logger] notification-store append failed: ${(notifErr as Error).message}\n`);
   }
 
   // Buffer for auto-loop to drain
@@ -275,11 +286,16 @@ function _push(
       appendFileSync(join(auditDir, "audit-log.jsonl"), JSON.stringify(sanitized) + "\n", "utf-8");
     } catch (auditErr) {
       // Best-effort — never let audit write failures bubble up
-      process.stderr.write(`[gsd:audit] failed to persist log entry: ${(auditErr as Error).message}\n`);
+      _writeStderr(`[gsd:audit] failed to persist log entry: ${(auditErr as Error).message}\n`);
     }
   }
 }
 
+function _writeStderr(message: string): void {
+  if (!_stderrEnabled) return;
+  process.stderr.write(message);
+}
+
 /**
  * Sanitize a log entry before persisting to the audit JSONL file.
  * Strips potentially sensitive context (raw paths, cwd, full error text)