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/api/agents.py

@@ -24,6 +24,7 @@ from lembas.api.deps import Db, RequiredUser, require_permission
 from lembas.api.pages import sidebar_context
 from lembas.db.models import AUTH_METHODS, AUTH_PASSWORD, SshProfile
 from lembas.services import settings_store
+from lembas.services.agent import draft as draft_service
 from lembas.services.agent import index as index_service
 from lembas.services.agent import jobs as jobs_service
 from lembas.services.agent import ssh as ssh_service
@@ -276,6 +277,23 @@ def _job_chat(db: Db, user: RequiredUser, chat_id: str):
     return chat, agent_session.resolve(db, chat, user)
 
 
+@router.get("/api/agents/{profile_id}/draft")
+async def draft_target(db: Db, user: RequiredUser, profile_id: str, dir: str = ""):
+    """The id the panels should use for a chat that does not exist yet.
+
+    Hung off the profile rather than the chat for the reason `browse` is: the
+    caller is the *new*-chat composer, where the connection and the directory
+    are the things being chosen. Ownership of the profile is the whole
+    authorisation, as everywhere else in this module.
+
+    Deterministic, so asking twice for the same target gives the same id and
+    finds the shell already running there rather than opening a second one.
+    """
+    profile = _profile(db, user, profile_id)
+    draft = draft_service.remember(user.id, profile.id, dir or profile.default_dir or "")
+    return {"id": draft.id, "dir": draft.project_dir}
+
+
 @router.get("/api/chats/{chat_id}/jobs")
 async def jobs_chip(request: Request, db: Db, user: RequiredUser, chat_id: str):
     """How many jobs are running, as the chip in the composer row.