fix(story-mode): read how current Claude Code builds deliver prompts and end turns

Found by replaying round-2 review transcripts while the reviews ran, then
surveyed across 150 local transcripts:

- A prompt typed while Claude works writes no user line in current builds,
  only a queued_command attachment where Claude took it in (602 of them
  locally, 485 of those background-task reports). It now joins the running
  turn; a report that lands mid-turn is a notice on the wire, not a new
  mission panel, and a background helper's answer joins back from it.
- Some sessions never write turn_duration (13 of 135 locally): the Stop
  hook's stop_hook_summary (never preventedContinuation in 815 seen) now
  ends the turn, timed by its own span. Before, such a session's turns
  never ended.
- A helper started as a teammate (teammate_spawned) is a background helper;
  its <teammate-message> reports (text or a JSON idle notification) join it
  by name, and the turn they start reads "readme-writer: README done".
- A <cross-session-message> names its sender; pasted text loses Claude
  Code's <pasted_content> wrapper (it showed in balloons and the picker).
- The mission panel, its balloon and its drawer follow who sent each
  prompt (you, a background job, another session), not who started the turn.
- A caption names a script by its first line that says something, not
  `set -e`, a bare `cd` or `S=/tmp/...`.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/api-reference.md

@@ -1067,7 +1067,7 @@ Responses carry a weak `ETag` with `Cache-Control: no-cache`; a request with a m
 
 A `page` carries the turn's summary fields plus `events` (one per prompt, sentence Claude wrote and tool call, with `intent`, `ok` when the call returned, `edit` hunks in Claude Code's own `structuredPatch` shape, the tail of `output`, `helper`, `tests` counts, and `files` for the files a Bash call printed with `cat`/`head`/`tail`, as the command named them), `panels` (each `{ kind, events, caption: { story, director }, balloon?, files?, ... }`, at most 12 per page, indices into `events`), `filesChanged`, `added`, `removed`, `helpers`, `helpersRunning`, `partial` (the turn began before the part that was read) and `truncated` (older outputs were dropped to keep the page small). A transcript that cannot be read is a `500` with `OPERATION_FAILED`.
 
-A helper started in the background (`helper.background`) carries `helper.running: true` until its `<task-notification>` arrives; that notification starts a turn of its own (origin `task`), whose prompt event carries the helper's answer as `output`, and the answer, tool count and duration are joined back onto the helper in the turn that started it. Claude Code times such a turn from the prompt that started the chain; Story Mode caps a turn's `durationMs` at the turn's own span.
+A helper started in the background (`helper.background`) carries `helper.running: true` until its `<task-notification>` arrives; that notification starts a turn of its own (origin `task`), whose prompt event carries the helper's answer as `output`, and the answer, tool count and duration are joined back onto the helper in the turn that started it. Claude Code times such a turn from the prompt that started the chain; Story Mode caps a turn's `durationMs` at the turn's own span. A helper started as a teammate (`status: teammate_spawned`) is a background helper too, and its `<teammate-message>` reports join it by name. A prompt that arrives while Claude works (typed, a background job's report, a message from another session) is written by current Claude Code builds as a `queued_command` attachment, not a user line; it joins the running turn, a prompt event carrying `origin` (`human`, `task`, `peer`, `system`), and a report that lands mid-turn is an event with intent `notice` rather than a new mission panel. A turn ends at `turn_duration`, or at the Stop hook's `stop_hook_summary` (unless it prevented the stop) in sessions that never write `turn_duration`, timed then by its own span.
 
 ## Git worktrees of a case