fix(desktop): recover session after sleep/wake gateway restart

[bpasquini]

Problem

When a laptop running the Hermes desktop app sleeps and wakes, the TUI gateway's WebSocket reconnects but the in-memory session table (_sessions dict in tui_gateway/server.py) is cleared. The desktop app still holds the old activeSessionId, so the next message send calls prompt.submit with a stale session ID. The gateway returns error code 4001 (session not found), which surfaces to the user as an inline error bubble:

Prompt failed: session not found

The only workaround is to manually start a new chat or relaunch the app.

Root Cause

requestGateway in use-gateway-request.ts retries on transport-level errors ("not connected", "connection closed") but not on gateway-level errors like "session not found". So after a sleep/wake reconnect, the first prompt always fails.

Fix

Wrap prompt.submit in a try/catch inside usePromptActions. On a "session not found" error:

1. Call session.resume with selectedStoredSessionIdRef.current — the durable SQLite session ID that survives gateway restarts
2. Update activeSessionIdRef.current to the fresh live session_id returned by the gateway
3. Retry prompt.submit once with the recovered ID

If recovery fails or the error is something else, the original error is re-thrown and surfaces normally. This is a one-shot retry (no infinite loop risk).

Testing

Repro steps:

1. Open Hermes desktop app, start a chat
2. Close the laptop lid / sleep the machine
3. Wake it up and wait for the gateway WebSocket to reconnect
4. Type a message and send

Before: "Prompt failed: session not found" error bubble appears, message not sent
After: Message sends transparently on the first attempt after wake

Files Changed

• apps/desktop/src/app/session/hooks/use-prompt-actions.ts — added session recovery block around prompt.submit (~32 lines)

[teknium1]

Merged via #42688. Your fix commit was cherry-picked onto current main with your authorship preserved in git log (72f522d) — it had to be re-merged under the attachment-sync text rewrite that landed since you opened this, and we added a vitest covering the recovery path on top. Thanks for the clean diagnosis and one-shot retry design.