tui(v2): /cd tilde expansion uses client home for remote servers #55171

Summary

/cd ~ in the TUI expands ~ against the client's home directory before
sending it to the server. When a macOS client attaches to a Linux server, the
tilde becomes /Users/<user>, which does not exist server-side, so the
directory change fails with Location not found: /Users/<user>.

Same class as #47665 (client-side path resolution while attached to a remote
server), but hit through the /cd slash command's tilde expansion rather than
the positional directory argument.

Environment

• opencode version: 2.0.26 (branch v2)
• OS: macOS client → Linux server
• Attach: opencode --server https://<server> (TUI attached to remote opencode serve)
• Active plugins: none

Reproduction

1. Start the server on Linux: opencode serve (reachable from the client).
2. Attach from the macOS client: opencode --server https://<server>.
3. On the TUI home screen (no session yet), run: /cd ~
4. Observe failure: "Failed to change directory — Location not found:
   /Users/". The tilde was expanded to the client's home.

Expected Behavior

~ expands according to the server's home (e.g. /home/<user>), since the
server owns the filesystem the location refers to.

Actual Behavior

• No active session: the client pre-expands ~ → /Users/<user> and sends
  that absolute path in location.get. The server uses the query parameter
  verbatim (no server-side tilde expansion on this endpoint), so Linux tries to
  boot a location at /Users/<user> and fails.
• With an active session: session.move sends the raw ~ and the server
  expands it correctly with its own home — the move works. But the client still
  records its locally-expanded /Users/... path into directory recents.
• Autocomplete is also affected: typing /cd ~/ lists the client's home
  (via file.list on the wrong absolute path), producing empty/failed results.

Additional Context

Root cause — packages/tui/src/component/prompt/index.tsx (~line 279), the
session.cd command handler:

const expanded =
  value === "~" ? paths.home : value.startsWith("~/") ? path.join(paths.home, value.slice(2)) : value

paths.home resolves through TuiPathsProvider (packages/tui/src/app.tsx,
home: global.home) to os.homedir() of the client process
(packages/util/src/global.ts). The expanded path is then sent to
location.get, whose server-side middleware (requestRef in
packages/server/src/location.ts) performs no tilde expansion of its own.
The session flow shows the intended split: SessionMove.resolveDestination
(packages/core/src/session/move.ts) expands ~ server-side using the
server's Global.home. location.get lacks the equivalent, and the TUI
expands too early regardless.
Secondary affected sites (same client-home source):

• directory autocomplete: packages/tui/src/component/prompt/autocomplete.tsx
  passes paths.home into directoryAutocomplete, whose
  directoryAutocompleteSearch (packages/tui/src/prompt/directory-completion.ts)
  maps //x to the client home before calling file.list
• recents: the session branch of the /cd handler records the
  client-computed path via directoryRecents.touch
  A structural blocker for a clean client-side fix: the server never reports its
  home directory. Location.Info (packages/schema/src/location.ts) carries only
  directory/project, so clients have no authoritative home to expand against.
  Possible directions:

1. Expand ~ server-side in the location middleware (mirroring
   SessionMove.resolveDestination), letting the TUI send raw input on the
   no-session path — consistent with how session.move already behaves.
2. Expose the server's home (e.g. a home field on location.get) so TUI
   autocomplete and display can use the correct root client-side.
   Related: cli(v2): positional directory resolved locally even with --server, fails on remote-only paths #47665 (same class, CLI positional directory), Desktop: project picker sends host paths to a remote server, and the resulting failure is silent #44150 (Desktop project
   picker sends host paths), TUI referencing local directory when using attach --dir to connect to a remote server. #5380 / TUI sends absolute local paths causing ENOENT on server side #4686 / attach: @ file mentions use client-local path instead of remote directory #13732 (closed V1 cousins of the
   family).