A terminal panel beside an agent chat

A real shell on the chat's own connection, opened and closed like the
inspector and never beside it. The modes govern the model; what a person
types is theirs, since they hold the credential and could open the same
shell with an ssh client. The model cannot see the panel -- a button
copies the output you choose into the composer.

The session outlives the socket: closing the panel leaves a build
running, and coming back reattaches with the scrollback. Two tabs share
one shell and the smaller window decides the size. It ends on an idle
timeout, on deleting the chat, on disabling, moving or deleting the
connection, and on a restart -- which says why rather than quietly
opening a fresh shell that has lost the working directory.

The nginx template's `Connection ""` is right for SSE and fails every
WebSocket handshake, so `location /` now uses a `map $http_upgrade`;
update.sh grows a drift check for it, because the only symptom on a
stale vhost is a panel that cannot connect.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/main.py

@@ -31,6 +31,7 @@ from lembas.api import (
     library,
     pages,
     preferences,
+    terminal,
 )
 from lembas.api.deps import RedirectToLogin, is_htmx, login_redirect
 from lembas.config import settings
@@ -90,9 +91,14 @@ async def lifespan(app: FastAPI) -> AsyncIterator[None]:
 
     # Replies still being written are cancelled and persisted with whatever
     # they have, rather than left as permanently unfinished rows.
+    from lembas.services.agent.terminal import shutdown as stop_terminals
     from lembas.services.generation import shutdown as stop_generations
 
     await stop_generations()
+    # Open shells have nothing to persist: whatever was running on the far side
+    # is cut off mid-command. Every deploy does this, and the panel is told why
+    # rather than left to guess -- see deploy/README.md.
+    await stop_terminals()
     log.info("LLeMbas stopped")
 
 
@@ -112,6 +118,7 @@ def create_app() -> FastAPI:
     app.include_router(auth.router)
     app.include_router(preferences.router)
     app.include_router(chats.router)
+    app.include_router(terminal.router)
     app.include_router(audio.router)
     app.include_router(files.router)
     app.include_router(folders.router)