Merge pull request #605: fix(uploads): probe the workspace bounded before a prompt upload

Conflict resolved in test/routes/session-routes.test.ts: #602's
remote-pane-history mock and #605's bounded-path-probe mock are both kept.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/routes/session-routes.ts

@@ -377,7 +377,9 @@ export function imageMagicMatchesExt(data: Buffer, ext: string): boolean {
  * touched, and a file already there is theirs and stays as it is.
  */
 async function ensureUploadDir(workingDir: string): Promise<string | null> {
-  // workingDir is guaranteed to exist (live session).
+  // workingDir exists (live session) and the caller bounded-probed its mount, so
+  // the lstat/mkdir below normally start on a reachable path; a mount that dies
+  // after that probe is the same residual race POST /api/sessions accepts.
   const uploadDir = join(workingDir, UPLOADS_DIR);
   try {
     const dirStat = await fs.lstat(uploadDir);
@@ -5354,6 +5356,20 @@ export function registerSessionRoutes(
       );
     }
 
+    // The upload is written under session.workingDir (ensureUploadDir below), and
+    // a live session's workspace can sit on a network mount that stopped answering.
+    // Probe it bounded before the first disk touch, as #516 requires for a path the
+    // user named, so one dead mount cannot freeze a libuv threadpool worker per
+    // upload. Only "unknown" (the mount is not answering) is refused here, the way
+    // the create route does; absent / not-a-directory keep ensureUploadDir's own
+    // errors, since a live session's workspace should be neither.
+    if ((await probePathKind(session.workingDir, { pastCap: true })) === 'unknown') {
+      return createErrorResponse(
+        ApiErrorCode.OPERATION_FAILED,
+        describeUnknownPath('Workspace', session.workingDir, { pastCap: true })
+      );
+    }
+
     if (!req.isMultipart()) {
       reply.code(400);
       return createErrorResponse(ApiErrorCode.INVALID_INPUT, 'Expected multipart/form-data');