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>

app/androidApp/src/main/kotlin/com/example/aiapp/Events.kt

@@ -108,6 +108,28 @@ sealed class SessionEvent {
         val turnStart: Long? = null,
     ) : SessionEvent()
 
+    /**
+     * A task the session started in the background reporting back: a subagent that has finished, or
+     * a backgrounded command.
+     *
+     * It is a message the session *received*, and the turn it wakes up and runs follows it. Without
+     * a row for it, that turn's reply met the previous one with nothing in between and the two were
+     * folded into a single message -- one answer running straight into the next mid-sentence.
+     */
+    data class TaskNote(
+        /** The tool call it belongs to; a subagent is named by that id. */
+        val about: String,
+        /**
+         * What the reader knows the task as -- a subagent's title. Null for a backgrounded command,
+         * which its own summary names; the row says so rather than inventing a title.
+         */
+        val title: String?,
+        /** How it ended, in the CLI's word: "completed", "failed", "cancelled". */
+        val status: String,
+        /** What it said on the way out, where it said anything. */
+        val summary: String?,
+    ) : SessionEvent()
+
     /**
      * A command the session was asked to run on itself and cannot run yet. Resolved by
      * [CommandSent] with the same id; a command that ran straight away has only that one.
@@ -252,6 +274,13 @@ fun parseSeqEvent(json: String): SeqEvent {
                     body.getString("text"),
                     if (body.has("turnStart")) body.getLong("turnStart") else null,
                 )
+            "taskNote" ->
+                SessionEvent.TaskNote(
+                    about = body.getString("about"),
+                    title = body.optString("title").ifEmpty { null },
+                    status = body.getString("status"),
+                    summary = body.optString("summary").ifEmpty { null },
+                )
             "commandQueued" ->
                 SessionEvent.CommandQueued(body.getString("id"), body.getString("text"))
             "commandSent" -> SessionEvent.CommandSent(body.getString("id"), body.getString("text"))