desktop: opening URL-style path resolves to C:\static, /api/fs/read returns 500 (UnexpectedStatus) #50913

Summary

Opening a backend-served URL path (/static/render/xxx.mp4) in the desktop app triggers GET /api/fs/read/... with a drive-root-relative Windows path (\static\render\xxx.mp4), which resolves to C:\static\render\xxx.mp4 (does not exist) → ENOENT → HTTP 500 → user-facing toast "加载文件失败 / UnexpectedStatus".

Environment

• opencode version: 2.0.13 (from runtime diagnostics; opencode CLI not on PATH so opencode --version is Unavailable)
• OS: Windows_NT 10.0.26200.7462 (win32 x64)
• Terminal: Unavailable: desktop app, TERM=xterm-256color, TERM_PROGRAM unset
• Shell: C:\Windows\system32\cmd.exe
• Install/channel: OpenCode Desktop (%LOCALAPPDATA%\Programs\@opencodedesktop), channel: latest
• Active plugins: none found (no opencode.json(c) project or global; only ~/.config/opencode/service.json)

Reproduction

1. A local backend serves a file at URL path /static/render/task_x_composed.mp4; the same file exists on disk at <project>\static\render\task_x_composed.mp4.
2. In the desktop app, open/click this path as presented (string /static/render/task_x_composed.mp4).
3. The app requests GET /api/fs/read/... with path \static\render\task_x_composed.mp4.
4. FileSystem.realPath resolves the drive-root-relative path against C:\ → lstat 'C:\static' → ENOENT.
5. Server returns 500; desktop shows the toast "加载文件失败 / UnexpectedStatus".

Reproduced twice consecutively (2026-09-23 00:22:39 and 00:23:02 local time).

Expected Behavior

The file reader should resolve the path against the project/workspace root (where <project>\static\render\... exists), or a URL-style input should not be treated as a filesystem path at all. A genuinely missing file should surface as a not-found result, not a generic 500 → UnexpectedStatus.

Actual Behavior

cause="PlatformError: NotFound: FileSystem.realPath (\static\render\)
 [cause]: Error: ENOENT: no such file or directory, lstat 'C:\static'"
http.method=GET http.url=/api/fs/read/task_..._composed.mp4 http.status=500

Both attempts failed identically (role=server, HTTP 500).

Additional Context

• Log source: ~/.local/share/opencode/log/opencode.log, two identical entries at 2026-09-22T16:22:39.433Z and 2026-09-22T16:23:02.120Z.
• The target file is fine: it exists at <project>\static\render\task_..._composed.mp4 and serves correctly over HTTP (200, video/mp4, 1,597,924 bytes).
• Likely path derivation: the URL /static/render/... had / normalized to \, leaving a drive-root-relative path; Windows resolves \static\... against the current drive root (C:\).
• Frequency: consistent (2/2 attempts).
• Workaround: open the same content via its HTTP URL in a browser, or pass the absolute filesystem path; both avoid the toast.
• Screenshot of the toast and full redacted log lines available on request.