fix: steer-delivery starvation — continuation coalescing (claimSteers)

The bug (seen live): a teacher that ends every turn with a new pending quiz
keeps the wake pipeline's idle gates permanently closed — the steer sits in
'delivering result' forever while the learner answers check after check.

- claimSteers (server/jobs.ts): the chat-handler claims every queued,
  undelivered steer the instant a client turn wins the turn registry, and
  appends it after the learner's answer — conversion-safe, the answered
  quiz carries its output. Every answer flushes pending steers immediately.
- The pump keeps its post-idle duplicate-guard (re-check steerDelivered
  before firing), so a claim racing the pump converges to exactly one
  delivery either way.
- The stale-job sweep now skips chats with a turn in flight (a healthy but
  slow wake no longer gets falsely re-queued as 'recovering').
- Out-of-lane surgical touch (flagged for master review): the 3-line
  handleChatRequest seam (claim after beginTurn, persist+stream 'outgoing').
- Verified live end-to-end on the stuck session: answering the pending quiz
  fired the steer + wake turn within a second; job flipped done/delivered.

src/core/contracts/jobs.ts

@@ -73,6 +73,17 @@ export interface JobRecord {
  *     a polling client that sees the flip re-syncs once and gets the
  *     finished record.
  *
+ *     CONTINUATION COALESCING: the idle window above can starve — a
+ *     quiz-chaining teacher ends every turn with a new pending check, so
+ *     the gates never stay open long enough for a wake to fire. The fix:
+ *     when a client turn wins the turn registry, the handler CLAIMS every
+ *     queued, undelivered steer (jobs.ts claimSteers) and appends it after
+ *     the learner's answer in that very turn — conversion-safe, because the
+ *     answered quiz carries its output. Every answer flushes pending
+ *     steers immediately; the wake pump remains for turns that end with no
+ *     pending question. The pump re-checks steerDelivered right before
+ *     firing, so a claim racing the pump converges to exactly one delivery.
+ *
  *  5. No pending job parts ever exist, so the composer never gates on jobs
  *     (the learner can interject mid-job; the steer queues behind their
  *     turn) and job tool outputs never trigger the client-side