fix(tui_gateway): tolerate deleted cwd in slash worker and path completion

[Dusk1e]

What & why

os.getcwd() raises FileNotFoundError when the process's working directory is deleted out from under it (e.g. a scratch workspace cleaned up mid-session). The TUI gateway called it unguarded in three spots:

• _SlashWorker.__init__ → subprocess.Popen(cwd=os.getcwd())
• _completion_cwd() → the raw-chain fallback and the final return

So a deleted launch directory crashed slash commands, path completion, and — because _completion_cwd() feeds the unguarded session.create handler — new-session creation.

Fix

Add a small _safe_getcwd() helper that mirrors the existing tools.terminal_tool._safe_getcwd (fall back to TERMINAL_CWD, then the home directory) and route the three callsites through it. Behavior is unchanged when the CWD exists; only the error path changes.

How to test

tests/test_tui_gateway_server.py adds 3 focused tests covering the helper and both surfaces under a deleted CWD:

• test_safe_getcwd_falls_back_when_cwd_deleted
• test_completion_cwd_tolerates_deleted_cwd
• test_slash_worker_tolerates_deleted_cwd

Test results

• tests/test_tui_gateway_server.py + tests/tools/test_terminal_task_cwd.py → 218 passed
• tests/tui_gateway/ → 103 passed
• ruff check → clean

[teknium1]

Thanks for identifying a real deleted-CWD failure path. Current main still passes cwd=os.getcwd() when spawning _SlashWorker (tui_gateway/server.py:321) and retains both unguarded _completion_cwd() fallbacks (tui_gateway/server.py:1520, tui_gateway/server.py:1528). The proposed helper matches the established terminal behavior in tools/terminal_tool.py:1196-1207.

Problems

• Current main also has a later-added unguarded fallback in _default_session_cwd() (tui_gateway/server.py:1116). A deleted launch CWD can still fail that default/resume route after this PR's three substitutions.

Suggested changes

• During salvage, apply the safe resolver to _default_session_cwd() and add coverage for that path alongside the slash-worker and completion cases.
• Preserve the current _SlashWorker subprocess setup at tui_gateway/server.py:295-324, including profile-home environment scoping and platform process flags.

Automated hermes-sweeper review.

[teknium1]

When salvaging this helper onto current main, also route the later-added _default_session_cwd() fallback through it (tui_gateway/server.py:1116). Otherwise a deleted launch CWD still fails the default/resume session path.