fix(in-flight-compaction): persist steering messages + use live messages array for compaction

Fix two critical bugs found in code review:

Bug A — Permanent loss of mid-turn steering messages:
drainSteering injected queued messages into the kernel's in-memory messages
array but never persisted them, so a user could never see them and in-flight
compaction (which loaded the store) scrubbed them. Fix: drainSteering now
persists the steering message to the store as part of the same critical section
as the injection (await store.append). This required making drainSteering async
— the kernel now awaits it (contract: return type allows Promise; backward-
compatible with sync callbacks). Fire-and-forget was unsafe: the conversation-
store append reads the seq counter then writes chunks across multiple awaits,
so a concurrent steering append + next-step onStepComplete append would both
read the same seq counter and collide (the msgIdx-collision class of bug).

Bug B — Index misalignment (DB <-> LLM divergence):
keepLastN was sliced independently from the store's array (no steering) and
the kernel's array (with steering), so the slices dropped DIFFERENT messages.
Fix (follows from A): performCompaction accepts the kernel's LIVE messages
array instead of reloading the stale store; the SAME recentKept slice is used
for both the store write (replaceHistory) and the value returned to the kernel
(compactedMessages), so they stay byte-aligned by construction. The post-seal/
manual compact() path still loads the store (the turn has ended, so it is
stable).

Tests: kernel async-drainSteering-await contract test; orchestrator steering-
persisted + store/LLM-alignment regression test; queue.test.ts asserts the
steering is persisted; its fake runTurn now awaits drainSteering.

Verification: typecheck clean; 2014 tests pass (was 2012; +2 new + 1 assertion);
biome 0 errors (12 pre-existing warnings in untouched files).

1 files changed, 4 insertions, 2 deletions

diff --git a/packages/kernel/src/runtime/run-turn.ts b/packages/kernel/src/runtime/run-turn.ts
index 76e2edf..8f68865 100644
--- a/packages/kernel/src/runtime/run-turn.ts
+++ b/packages/kernel/src/runtime/run-turn.ts
@@ -720,8 +720,10 @@ export async function runTurn(input: RunTurnInput): Promise<RunTurnResult> {
         // and append them after the tool results, before the next call.
         // The kernel owns no queue and names no feature — it just calls
         // the callback and appends. Emits nothing (caller emits the
-        // `steering` AgentEvent in its own wrapper).
-        const steering = input.drainSteering?.() ?? [];
+        // `steering` AgentEvent in its own wrapper). The callback MAY
+        // return a Promise (the shell persists the injected messages
+        // before returning) — `await` handles both sync and async.
+        const steering = (await input.drainSteering?.()) ?? [];
         for (const msg of steering) {
           messages.push(msg);
         }