Investigate first-run folder collision and add safe filesystem reproduction

apps/review-desktop/scripts/repro-folder-collision.mjs

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+// Run from apps/review-desktop after installing workspace dependencies:
+// TSX_TSCONFIG_PATH=tsconfig.test.json node --import tsx scripts/repro-folder-collision.mjs
+// This is an investigation harness, not a regression test for an implemented fix.
+import assert from "node:assert/strict";
+import * as fs from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+import { Event } from "../code-oss/src/vs/base/common/event.ts";
+import { URI } from "../code-oss/src/vs/base/common/uri.ts";
+import {
+  FileSystemProviderCapabilities,
+  FileSystemProviderErrorCode,
+  FileType,
+  createFileSystemProviderError,
+} from "../code-oss/src/vs/platform/files/common/files.ts";
+import { FileService } from "../code-oss/src/vs/platform/files/common/fileService.ts";
+import { NullLogService } from "../code-oss/src/vs/platform/log/common/log.ts";
+
+// Keep the real FileService and real filesystem, adapting only the provider
+// interface to avoid native Electron/watch dependencies in this CLI harness.
+async function operation(action) {
+  try {
+    return await action();
+  } catch (error) {
+    const codes = {
+      ENOENT: FileSystemProviderErrorCode.FileNotFound,
+      ENOTDIR: FileSystemProviderErrorCode.FileNotADirectory,
+      EEXIST: FileSystemProviderErrorCode.FileExists,
+    };
+
+    throw createFileSystemProviderError(
+      error,
+      codes[error.code] ?? FileSystemProviderErrorCode.Unknown,
+    );
+  }
+}
+
+const provider = {
+  capabilities: FileSystemProviderCapabilities.PathCaseSensitive,
+  onDidChangeCapabilities: Event.None,
+  onDidChangeFile: Event.None,
+  async stat(resource) {
+    const stat = await operation(() => fs.stat(resource.fsPath));
+
+    return {
+      type: stat.isDirectory() ? FileType.Directory : FileType.File,
+      ctime: stat.ctimeMs,
+      mtime: stat.mtimeMs,
+      size: stat.size,
+    };
+  },
+  mkdir: (resource) => operation(() => fs.mkdir(resource.fsPath)),
+  async readdir(resource) {
+    const entries = await operation(() =>
+      fs.readdir(resource.fsPath, { withFileTypes: true }),
+    );
+
+    return entries.map((entry) => [
+      entry.name,
+      entry.isDirectory() ? FileType.Directory : FileType.File,
+    ]);
+  },
+};
+
+const root = await fs.mkdtemp(join(tmpdir(), "review-folder-collision-"));
+
+const service = new FileService(new NullLogService());
+
+const registration = service.registerProvider("file", provider);
+
+let creates = 0;
+
+const listener = service.onDidRunOperation(() => creates++);
+
+try {
+  const target = join(root, "folder with spaces");
+  const content = "Existing user file: keep these bytes.\n";
+  await fs.writeFile(target, content);
+  await assert.rejects(
+    service.createFolder(URI.file(target)),
+    /already exists but is not a directory/,
+  );
+  assert.equal(await fs.readFile(target, "utf8"), content);
+  assert.equal(creates, 0);
+  console.log(
+    "Reproduced the reported FileService collision; file bytes preserved.",
+  );
+
+  await assert.rejects(service.createFolder(URI.file(join(target, "child"))));
+  assert.equal(await fs.readFile(target, "utf8"), content);
+  assert.equal(creates, 0);
+  console.log(
+    "An ancestor file also prevents folder creation without losing data.",
+  );
+
+  // Simulate explicit user recovery only inside this disposable fixture.
+  const backup = join(root, "preserved-file");
+  await fs.rename(target, backup);
+  const created = await service.createFolder(URI.file(join(target, "child")));
+  assert.equal(created.isDirectory, true);
+  assert.equal(await fs.readFile(backup, "utf8"), content);
+  await service.createFolder(URI.file(join(target, "child")));
+  assert.equal((await fs.stat(join(target, "child"))).isDirectory(), true);
+  console.log(
+    "Creation recovers after explicit fixture rename; existing directories are accepted.",
+  );
+} finally {
+  listener.dispose();
+  registration.dispose();
+  service.dispose();
+  await fs.rm(root, { recursive: true, force: true });
+}

docs/folder-collision-investigation.md

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+# First-run folder collision investigation
+
+Status: filesystem guard reproduced; production cause and implementation remain unresolved.
+
+PostHog issue `01a0d49f-9dc7-7db1-87aa-60419d73d04d` contains one reported
+exception on September 24, 2026 in Whiteboard 0.1.1. The message says an existing
+path is not a directory. Both the path and its category are unavailable in the
+redacted event. No user paths or telemetry identities are retained here.
+
+The two bundle frames are `vs/review/review.desktop.main.js:1886:81871` and
+`:1886:81605`. Comparing those positions against the installed 0.1.1 bundle
+(commit `c14db218df246b305d1c2a391eb64435b902e83e`) identifies
+`FileService.mkdirp` and `FileService.createFolder`. There is no calling feature
+in the captured stack. The current source retains the same guard in
+`apps/review-desktop/code-oss/src/vs/platform/files/common/fileService.ts`.
+
+## Timeline
+
+An analytics query of the same telemetry identity, restricted to 18:10–18:17 UTC,
+returned this sequence. `review_client_error` and `$exception` are the paired
+reports of the same exception, not two separate incidents.
+
+| UTC time | Event |
+| --- | --- |
+| 18:13:39.031 | `review_installation_created` |
+| 18:13:39.071 | `review_client_error`, folder collision |
+| 18:13:39.093 | `$exception`, same folder collision |
+| 18:13:39.116 | `review_home_empty_state_viewed` |
+| 18:13:40.278 | `review_app_ready` |
+| 18:14:00.119 / .125 | command started / succeeded |
+| 18:16:15.706 / .752 | command started / succeeded |
+
+This suggests a first-run startup operation. It does not establish that startup
+failed: the ready event and successful commands follow. User-snippet initialization
+is one startup caller of `createFolder`, but the evidence cannot distinguish it
+from other callers or identify the colliding folder. Treating snippets, settings
+import, or a cache as the proven cause would be speculative.
+
+## Reproduction
+
+From `apps/review-desktop` after installing workspace dependencies:
+
+```sh
+TSX_TSCONFIG_PATH=tsconfig.test.json node --import tsx scripts/repro-folder-collision.mjs
+```
+
+The harness calls the actual `FileService.createFolder` implementation through a
+small provider backed by Node filesystem operations. It uses a fresh temporary
+directory and removes only that fixture afterward. It verifies that:
+
+- A regular file occupying the requested directory produces the reported error,
+  keeps its bytes, and emits no successful create operation.
+- An ancestor that is a file also rejects creation and preserves the file.
+- Explicitly renaming the fixture file permits creation without losing its bytes.
+- Calling creation on an existing directory succeeds.
+
+All assertions passed on September 24, 2026 against base `cc43318e`, using an
+isolated installation of tsx 4.21.0. This reproduces the low-level condition, not
+the user's first-run sequence. No Electron build or end-to-end reproduction was
+performed. This is a standalone investigation harness, not a test of a new fix.
+
+## Why there is no production patch yet
+
+Rejecting an existing regular file is correct and protects user data. Swallowing
+the error, replacing the file, or choosing an arbitrary alternative directory
+could break the feature or destroy data. Broad telemetry changes would not
+resolve the unknown caller. Existing `createFolder` callers have different
+recovery requirements, so a feature-specific fix needs the path category or a
+caller stack first.
+
+The next useful evidence is the calling feature and a safe category for the
+colliding path (profile snippets, logs, configuration cache, or another location),
+obtained from a local reproduction/debugger or a user-approved diagnostic.
+Only then should recovery be implemented at that caller. Do not auto-delete or
+overwrite the colliding file. Error-tracking issue APIs were unavailable with the
+current key; permitted analytics SQL provided the frames and timeline above.
+
+The workspace root and code-oss AGENTS.md instructions were read. The latter
+references `.github/copilot-instructions.md`, which is absent from this checkout.
+No README files were changed.