The desktop `/title <name>` command 404s with "Session not found" on
every platform (reported on Windows in #38508).
Root cause: `session.create` returns two distinct ids — a *runtime*
session id (held in `activeSessionIdRef`) and a `stored_session_id` (the
DB `sessions.id`) — and deliberately does NOT persist a DB row until the
first turn. Routing `/title` through the REST `PATCH /api/sessions/{id}`
endpoint (as #38576 proposed) resolves the id against the `sessions`
table, so the runtime id — or any brand-new, not-yet-persisted session —
never resolves and returns 404. This is an id-type mismatch, not a
Windows file-locking quirk, so it fails on macOS and Linux too.
Fix: route `/title <name>` through the gateway's `session.title` RPC —
the exact path the TUI already uses (`ui-tui/.../slash/commands/core.ts`).
The RPC maps the runtime id to the in-memory session, writes through the
gateway's own DB connection, and queues the title (`pending: true`) when
the row isn't persisted yet, so it works for a fresh chat. The sidebar is
then refreshed via the existing `refreshSessions()` plumbing.
Keeps the sidebar-refresh wiring and `refreshSessions` threading from
#38576; replaces only the broken REST/slash-worker write path. A bare
`/title` (no arg) still falls through to the worker to show the current
title.
Tests rewritten to assert `session.title` routing with the runtime-vs-
stored id distinction (which the original mock collapsed), plus the
queued/`pending` fresh-chat case and the error path.
Supersedes #38576. Fixes#38508.
Co-authored-by: xxxigm <54813621+xxxigm@users.noreply.github.com>
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