Let the driver say it started, so both screens agree

The session list reads the manager's status; the session screen replays the
transcript. Correcting a relaunched session's stale `exited` by writing the
manager's view directly left those two saying different things about one
session -- which showed up as a stop button that turned into a play button a
moment after the screen opened, and a status row that disagreed with the row
it was opened from.

So the correction goes through the event sink instead, from the driver that
started the process: `EchoDriver::new` and `LlamaDriver::attached` already
announce the state they start in, and `ClaudeDriver` was the one starting a
process silently. It says idle only when it started one -- adopting says
nothing, since a process that was already running may be mid-turn. Coming
from the driver also orders it against the exit `follow` reports for a
process that dies immediately, which a status written from the manager could
not be.

Verified against a stand-in CLI: stop, restart the backend, and the list and
the transcript's last status both say idle, with the relaunch recorded.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

PLAN.md

@@ -332,10 +332,24 @@ Three decisions worth not undoing:
 That last rule found a real bug in the launch path, which is where the phone
 would have hit it: a relaunched session took its status from the transcript,
 so one whose process had died before a backend restart reported `Exited`
-while the launch it had just gone through was starting a new process. The
-status now says `Idle` when a launch leaves a process running — `Exited`
-there is not merely stale, it is the word that refuses every command and
-invites somebody to start a second process against a live conversation.
+while the launch it had just gone through was starting a new process —
+`Exited` there is not merely stale, it is the word that refuses every command
+and invites somebody to start a second process against a live conversation.
+
+**Who says so matters as much as what is said.** The first fix wrote `Idle`
+straight into the manager's view, and that produced a second bug on the
+phone: the session list reads the manager's status and the session screen
+replays the transcript, so a status written in one and not the other is two
+screens disagreeing about one session — visible as a stop button that turned
+into a play button a moment after the screen opened. So the rule is that
+**a driver announces the state it starts in, through the event sink**, which
+is what `EchoDriver::new` and `LlamaDriver::attached` already did;
+`ClaudeDriver` was the one that started a process silently. It says `Idle`
+only when it *started* one — adopting says nothing, because a process that
+was already running may be mid-turn and the transcript's last word is the
+better answer until its output says otherwise. Coming from the driver also
+orders it against the exit `follow` reports, which a status written from the
+manager could not be.
 
 On the phone this is one button in the composer, left of Send, whose mark and
 colour say what pressing it would do now: an orange pause while a turn is