Never run two turns into one, and say when a session waits on its own work

A turn started by something with no row of its own -- a subagent reporting
back, a peer message the CLI only owns up to at the end -- met the previous
reply with nothing between it, and the fold grew that reply rather than
starting a new one. Two answers were drawn as one paragraph, running together
mid-sentence with not even a space between them. The fold now refuses to grow
a settled reply, and `joinPages` carries the same rule across a page boundary.

The other half is the row. `Event::TaskNote` records a background task
reporting back -- a subagent that finished, or a backgrounded command -- with
its title, how it ended and what it said; `TaskNoteRow` draws it as a card,
since somebody said this, and its own row rather than an update to the Task
call's, which is above everything the session has said since. Reported once
however many of the CLI's two lifecycle shapes arrive.

`SessionStatus::Waiting` is a session whose own turn is over while work it
started is not. `Idle` means "waiting for a person" and this means the
opposite, so reporting it as idle sent a "finished" notification at the one
moment that was untrue. Drawn as "waiting" in `waitingColor`; the queue and
the held-command boundary release on either end-of-turn status, so a message
sent while a subagent runs is not held until it finishes.

And a usage limit the account hits inside a subagent now reaches the session
as well as the subagent's transcript. `resume.rs` can only schedule against a
session, and a background Task outliving its parent's turn is the ordinary
case, so auto-resume was doing nothing at all for it.

The status word and its colour were two `when`s on two screens, and the second
missed `waiting` silently; they are `sessionStatusWord`/`sessionStatusColour`
now. Echo's `/subagent n` reproduces the whole shape, staggered a second
apart. Verified on the emulator against the sandbox: 169 server tests, ktfmt,
clippy, rustfmt, Android lint and the JVM unit tests all clean.

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

AGENTS.md

@@ -228,6 +228,33 @@ PLAN.md's "Auto-resume" is the design; day to day:
   backend restart. A day after the limit was hit it gives up and says so in
   the transcript.
 
+## A session waiting on its own work
+
+Since 2026-09-06 a session whose turn ended with a **backgrounded subagent or
+command still running** reports `waiting` rather than `idle` — its own status,
+drawn as the word "waiting" in `waitingColor` on both screens. `idle` means
+"waiting for a person" and this means the opposite, so it also suppresses the
+"finished" notification, which used to arrive at the one moment it was untrue.
+Two things fall out of it and are easy to get wrong again: the queue and the
+held-command boundary release on **either** end-of-turn status, so a message
+sent while a subagent runs is not held until the subagent finishes; and
+`sessionWorking("waiting")` is deliberately **false** — nothing is being
+written, and the fold uses that same predicate to decide a reply is settled.
+
+- **A task reporting back is a row** (`Event::TaskNote`, `TaskNoteRow`), and
+  the reply that answers it is a **new** message. The fold refuses to grow a
+  settled reply; without that, two turns with nothing recorded between them
+  were folded into one and ran together mid-sentence. `./ui-sandbox.sh` plus
+  `/subagent 8` in an echo session is the whole rig — the helpers stagger a
+  second apart so each report and the reply to it are legible.
+- **A usage limit a subagent hits reaches the session**, not just the
+  subagent's own transcript; auto-resume can only schedule against a session.
+  That is the case where the main agent is idle and a background Task is
+  still burning quota.
+- **The status word and its colour are `sessionStatusWord` /
+  `sessionStatusColour`**, shared by the list and the session screen. They
+  were two `when`s, and the second one silently missed `waiting`.
+
 ## Shared appearance
 
 - **A row something is happening to is dimmed, drained of colour, and says