fix(files): a workspace whose folder was deleted leaves the Files places

The lane payload carries folder_missing (ENOENT/ENOTDIR only). Files hides
such a workspace and never reopens it as the default place; the Workspace
sidebar strikes its name through with a hint to remove it from its menu.
A folder that cannot be read no longer keeps the previous folder's entries
under its error, and a change in Files re-reads the workspace list.

server/__tests__/lanes-lib.test.js

@@ -337,6 +337,16 @@ describe("lanes lib", () => {
     );
   });
 
+  it("payload says folder_missing only when the folder is gone", () => {
+    const fs = require("node:fs");
+    const dir = fs.mkdtempSync(pathMod.join(os.tmpdir(), "lane-gone-"));
+    const l = lanes.createLane({ cwd: dir });
+    assert.equal(lanes.lanePayload(lanes.getLane(l.id)).folder_missing, false);
+    fs.rmSync(dir, { recursive: true });
+    assert.equal(lanes.lanePayload(lanes.getLane(l.id)).folder_missing, true);
+    lanes.deleteLane(l.id);
+  });
+
   it("payload carries node states and progress", () => {
     const l = lanes.createLane({ cwd: "/tmp/wt/d" });
     lanes.setStage(l.id, { stage: "review" });

server/lib/lanes.js

@@ -9,6 +9,7 @@
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
+const fs = require("node:fs");
 const path = require("node:path");
 const { db } = require("../db");
 const aiTools = require("./ai-tools");
@@ -749,6 +750,17 @@ function ownerNames(id) {
   };
 }
 
+/** True only when the folder is GONE (ENOENT/ENOTDIR) — a folder this
+ *  process may not read is still there, so it never counts as deleted. */
+function folderMissing(cwd) {
+  try {
+    fs.statSync(cwd);
+    return false;
+  } catch (err) {
+    return err.code === "ENOENT" || err.code === "ENOTDIR";
+  }
+}
+
 function lanePayload(lane, ageSec = null) {
   const pipeline = getPipeline(lane.pipeline);
   const since = lane.stage_since ? Date.parse(lane.stage_since) : NaN;
@@ -775,6 +787,9 @@ function lanePayload(lane, ageSec = null) {
       : Math.max(0, Math.round((Date.now() - since) / 1000)),
     last_event_seconds: ageSec,
     liveness: classifyLiveness({ status: lane.status, stage: lane.stage, ageSec }, DEAD_SEC),
+    // The folder was deleted under the workspace (from Files, a shell): the
+    // record stays — its sessions are history — but nothing can open in it.
+    folder_missing: folderMissing(lane.cwd),
   };
 }