feat: Wave C pivot - steer markers, not follow-ups

Owner correction (2026-09-26, later): a real lesson is ONE continuous
teach->quiz->teach run - there are no run-would-stop moments mid-lesson,
and the run ends that DO exist are quiz stopper exits where delivery
must not fire. Subagent results must land BETWEEN messages INSIDE the
run, never splitting a toolCall from its toolResult.

Vehicle 1 now hands markers to agent.steer() - pi's STEERING queue:
the loop drains it at TURN BOUNDARIES (after a completed assistant
message AND its tool results - the bonded pair survives injection) and
again at RUN START (a continuation drains before its first LLM call),
then CONTINUES the run with the marker in context.
steeringMode "all" replaces followUpMode.

registerLiveAgent moved BEFORE runPiTurn and now hands pending markers
itself: the start poll drains the queue SYNCHRONOUSLY inside the
runPiTurn call, so a later registration would miss it. A marker
stranded by a quiz-terminated run therefore rides the ANSWER run's
first LLM call - the native replacement for the old continuation
coalescing.

Settlement reconciliation, the idle wake, probe-handoff exclusion,
and the registry-as-truth design are UNCHANGED; stranding is now
exactly the stopper-exit case.

Tests: jobs 45/45 (fakeAgent.steer; new pin - registration steers
pending markers into the new run, parked wake never fires); chat-flow
24/24 (new e2e through the real composition - a gated mid-run turn, a
marker delivered while the turn streams, record shape
[call, result, MARKER, response] with the marker adjacent to the
completed unit, the model SEES the marker in its next prompt, zero
wakes); full suite 999/999, tsc/lint/build green.

Live smoke (PORT=3004): research dispatched in the probe turn parked
behind the dangling quiz; on the quiz answer the marker injected at
the answer run's START poll - record [answer result, marker, teacher
response], job flipped done/delivered at settlement, brief card
rendered with its sources toggle.

Plan doc: docs/PI-NATIVE-MIGRATION-PLAN.md gains the pivot section.
Deferred (owner list): thinking blocks rendering after messages;
vanishing tool-call output tokens.

docs/PI-NATIVE-MIGRATION-PLAN.md

@@ -589,3 +589,36 @@ again — Wave C is the structural migration onto pi's own delivery seams.
 2. Client `applyWireEvent` non-assistant appends.
 3. Pump simplification + `claimSteers` deletion + handler cleanup.
 4. Test migration (jobs, chat-flow, session-core) + live smoke.
+
+## Wave C pivot (owner correction, later 2026-09-26): follow-ups → STEERING
+
+The owner re-examined the follow-ups-only ruling and overturned it: a real
+learning session is ONE continuous run — teach a thing, verify it with a
+quiz tool call, begin teaching the next thing. There are no "run would
+otherwise stop" moments mid-lesson, and the few run ends that do exist are
+exactly the ones where delivery must NOT happen (the question stopper). So
+subagent results must be delivered MID-RUN, BETWEEN messages.
+
+The pivot (all in the same two-vehicle skeleton):
+
+- Vehicle 1 hands markers to `agent.steer()` — pi's STEERING queue. The
+  loop drains it at TURN BOUNDARIES: after a completed assistant message
+  AND its tool results (never between a toolCall and its toolResult — the
+  bonded pair survives injection), and again at RUN START (a continuation
+  drains the queue BEFORE its first LLM call). The run CONTINUES with the
+  marker in context.
+- `steeringMode: "all"` (was `followUpMode`) — every handed marker joins
+  one boundary injection.
+- `registerLiveAgent` moved BEFORE `runPiTurn` in the handler and now
+  hands pending markers itself: the loop's start poll drains the queue
+  SYNCHRONOUSLY inside the `runPiTurn` call, so a later registration would
+  miss it. A marker stranded by a quiz-terminated run therefore rides the
+  ANSWER run's first LLM call — the native replacement for the old
+  continuation coalescing.
+- Settlement reconciliation, the idle wake, probe-handoff exclusion, and
+  the registry-as-truth design are UNCHANGED (stranding is now exactly the
+  stopper-exit case; the wake still covers a cold-and-idle queue).
+
+Deferred after the pivot (owner's list): thinking blocks sometimes
+rendering after messages; output tokens of certain tool calls vanishing
+with no tool call actually happening.