Look around the machine before deciding to talk about it

The terminal and the canvas both needed a Chat, so they were missing from the
one screen where you are choosing which machine to work on. A draft is the
smallest thing that fixes it: an id, and the three facts behind it.

The trick is that a draft resolves to a *transient* Chat -- constructed, never
added to a session. `canvas.agent_ready`, `_executor`, `_load_agent`, `_save_agent`
and `agent_session.resolve` read exactly four attributes between them and none
of them queries or writes the row, so all of it works unchanged and nothing had
to learn what a draft is. Proven against a real sshd rather than a stub: a
transient chat opens and saves a project file over the same SFTP path a real one
uses, and the database stays empty throughout.

Chats are still created lazily. A draft is not a chat and never becomes one;
when the first prompt makes the real one, the shell is re-keyed into it and the
open tabs are copied across. `terminal.rekey` moves the registry key *and*
`session.chat_id`, because close_for_profile, close_for_owner and the reaper all
pop by the field -- a stale one would leave a dead session that `get` keeps
handing out. The shell is only adopted when its profile and directory match the
chat as finally resolved, since `_new_chat` settles an empty directory to the
connection's own; otherwise it is left alone rather than transplanted onto a
chat that says it runs elsewhere.

Two canvas sources are refused on a draft, by name, and one of them is a hole
rather than an inconvenience. `_load_file` authorises with
`attachment.chat_id != chat.id`, and an upload made on the new-chat screen is
stored with `chat_id=None` -- so a draft whose chat carried no id would make that
comparison `None != None`, which is False, and open every unclaimed attachment
its owner has. `as_chat` does set an id, so it already fails; the refusal is
stated anyway, because a guarantee that lives in an id-shaped coincidence is one
the next change breaks without noticing.

Adoption needed almost no JavaScript: start_chat already answers with
HX-Redirect, so the page reloads and the canvas adopts by construction while the
terminal reconnects to the re-keyed session and replays its scrollback -- the "a
reload is indistinguishable from a second tab" property working for us. What
re-points them mid-screen is a `lembas:agent-target` event, dispatched from
`setDir` and the connection select because assigning to a hidden field's value
fires nothing on its own. Driven under a DOM stub before committing.

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

src/lembas/web/static/js/terminal.js

@@ -463,6 +463,26 @@
     document.addEventListener("lembas:theme", function () {
       if (term) term.options.theme = readTheme();
     });
+
+    /* The panel now belongs to a different shell: the new-chat screen changed
+       connection or directory, so `dataset.url` has been rewritten and the
+       socket is pointed at the wrong machine. Closing is deliberate -- hence
+       the flag, which is what stops "Disconnected" being reported for something
+       nobody lost -- and the screen is cleared because this really is a
+       different shell, unlike a reconnect to the same one.
+
+       Reconnecting is left to the panel being opened, so a target changed while
+       the terminal is shut costs nothing. */
+    window.lembas = window.lembas || {};
+    window.lembas.repointTerminal = function () {
+      if (socket) {
+        closedOnPurpose = true;
+        socket.close();
+        socket = null;
+      }
+      if (term) term.reset();
+      if (panel && !panel.hidden && panel.dataset.url) connect();
+    };
   }
 
   if (document.readyState === "loading") {