* fix(dashboard): recover the Chat tab when the agent session ends (NS-504)
In the dashboard Chat tab, when the agent process exits — the user types
`/exit`, or starts a new session that ends the current PTY child — the
`/api/pty` WebSocket closes with a normal code (not one of the
4401/4403/4404/4408/1011 rejection codes the server emits). The frontend
handled only those rejection codes; the normal-exit fallback just printed
"[session ended]" into the dead terminal and stopped, with `wsRef` nulled
and no respawn path. The only recovery was a full page refresh — exactly
the beta report ("typing /exit breaks functionality, no way to restart
without refreshing"; "starting a new session completely breaks the
agent").
On a clean/normal close the Chat tab now flips `sessionEnded` and renders
an in-place "Start new session" overlay (mirroring ChatSidebar's existing
reconnect affordance). Clicking it bumps a `reconnectNonce` that is a
dependency of the connect effect, so the effect tears down and re-runs,
spawning a fresh PTY in place — no page refresh. `onopen` clears the
flag so a successful reconnect dismisses the overlay.
An explicit button (rather than auto-respawn) is deliberate: if the agent
is crash-looping, auto-respawn would hide the failure and spin; the user
stays in control.
Verified against a live uvicorn `/api/pty` socket: a child that exits
closes with a non-rejection code (client sees close_code None / 1000-class),
which is precisely the branch that now sets sessionEnded=true. web
typecheck + vite build clean.
Reported via beta (NS-504).
* docs(assets): add NS-504 chat session recovery infographic
