fix: hold the wording path to the same bar as the sentinel path

[cannabinoids]

Rebased onto current main. 1782034 covers the case that killed the four-agent
research team — raised idle thresholds plus CONTINUATION_PATTERNS for progress
reports — so this is now scoped to three things that fix does not reach. Reproductions
are in #4.

What changes

The wording path still ends a run on two agents, whatever the team size.
hasTwoRecentCompletionSignals returns true for any two distinct agents, so once a
trio is quiet past TWO_SIGNAL_IDLE_THRESHOLD_MS the third can still be cut off by the
other two — which is what the comment directly above that call warns about. It becomes
hasRecentCompletionSignalsFromAll: same sliding window, every active agent must appear
in it. The sentinel path already holds this bar.

Two guards on the heuristic path, inside isCompletionStatement and placed after
the CLOSING_PATTERNS check, so an unambiguous sign-off still wins outright:

• a sign-off is short — a 600-character analysis containing "done" is an agent working
• a sign-off does not quote the machinery

The second came from a review task pointed at scripts/collab-poll.sh: both agents
quoted its own ---STATUS:{ACTIVE,QUIET,DONE,WAITING} sentinel and the run ended
mid-analysis. CONTINUATION_PATTERNS doesn't catch those, because nothing in them
announces further work — they aren't progress reports, they're descriptions of the
protocol.

Completion counts only from the last user message. ensemble steer exists so a user
can redirect a running team, but a sentinel sent before the redirect still counted, so a
team could disband while an agent was answering the new instruction — observed with a 15
second gap between the sentinel and the interjection. "Wrap it up" followed by sentinels
still disbands.

Tests

Nine specs: five in premature-disband.test.ts (machinery-quoting, DONE-protocol talk,
team-say announcements, the long-analysis case, and a genuine short sign-off still
counting), four in ensemble.test.ts (trio needs all three; sentinels before a user
interjection are void; sentinels after it still disband). All nine fail on main and
pass with this change.

tsc --noEmit and eslint clean. The whole suite passes except
onboarding-smoke.test.ts, which times out on my machine at the default 5s and is
untouched here — it's green in your CI, so it looked like my hardware rather than
something to change in your repo.

Not included

Deliberately narrow. A separate branch carries user-interjection ergonomics (durable
per-agent inbox, idle-gated delivery, pause/resume), agent-transcript isolation via
--append-system-prompt-file and a pinned --session-id, and ollama-backed agents via
ollama launch. Those change behaviour rather than fixing defects, so they stay out
unless you want them.

[cannabinoids]

Closing this one myself — I'd rather not leave a PR sitting against a function you're actively iterating on, and your threshold raise in 1782034 already covers most of what prompted it.

The three changes live on my fork if they're ever useful: the wording path held to every active agent (matching the sentinel path, and what the comment above that call already describes), two guards so an agent quoting a script's own DONE sentinel isn't read as finishing, and completion counted only from the last user redirect. Reproductions are in #4 and stand on their own.

Thanks for ensemble — it's a genuinely nice thing to work in.