…-window race

The steer queue was only drained mid-loop (after tool-call batches). Two
gaps allowed steer messages to be silently dropped:

1. Idle-window race: a Steer call lands between two RunStream invocations;
   the queue holds the message but nothing drains it when the next
   RunStream starts.
2. First-turn miss: when a RunStream turn produces a plain-text response
   with no tool calls, res.Stopped fires before the mid-loop drain is
   reached; the pending steer message is never injected.

Fix: drain steerQueue at the top of the for-loop body (before the first
model call) using the same pattern as the existing mid-loop drain.

Also extract the duplicate system-reminder wrap string into wrapSteerMessage
so the two drain sites cannot drift apart.

Also handles the empty-session bootstrap case: a RunStream started with
zero messages but steer messages already queued injects those messages
before the first model call, giving the model its initial context.

Tests added:
- TestSteer_IdleWindowIsConsumedOnNextTurn
- TestSteer_EmptySessionBootstrap

Fixes docker#2491

Assisted-By: docker-agent

The system-reminder envelope is only appropriate when the agent is
actively working (mid-loop, between tool calls). At the top of a new
turn the runtime is idle, so steer messages are injected as plain
user messages — no wrapping needed.

Assisted-By: docker-agent

- Move top-of-turn drain to after AgentInfo and contextLimit init so
  compactIfNeeded can be called immediately after injection (S1, S2).
- Extract appendSteerAndEmit helper (wrap bool) to eliminate the
  duplicated add-message+emit-event idiom at both drain sites (S3).
- Tighten both steer tests to assert the stored session message and the
  message seen by the model contain raw content with NO system-reminder
  envelope for the top-of-turn path (B1).
- Document messageRecordingProvider fallback behaviour for unexpected
  extra model calls (N4).

Assisted-By: docker-agent

A Steer() call arriving in the narrow window between the mid-loop drain
and the res.Stopped break was stranded until the next RunStream call.

Fix: re-check steerQueue inside the res.Stopped block before breaking.
Any message that enqueued successfully is now guaranteed to be consumed
within the current RunStream. Messages injected here use the
system-reminder envelope (matching mid-turn semantics: the agent just
finished a turn).

T1: both existing top-of-turn steer tests already assert
NotContains(<system-reminder>) in firstCallMsgs — confirmed present.

Test added: TestSteer_EndOfIterationRaceIsConsumedInCurrentRunStream
Uses a provider hook to inject a Steer() synchronously during
CreateChatCompletionStream on the first call, simulating the race.
Asserts: steer UserMessageEvent emitted within the same RunStream,
exactly 2 model calls made, and stored session message carries the
system-reminder envelope.

Assisted-By: docker-agent

… test

At res.Stopped the current turn is ending and a new one is about to
begin — the agent is not mid-task — so steer messages injected there
should be plain user messages, same as the top-of-turn drain.

Changes:
- loop.go: appendSteerAndEmit(wrap=false) at the end-of-iteration drain
  (inside res.Stopped block); update comment accordingly.
- runtime_test.go: add hookStream type that fires a callback on the
  FinishReasonStop Recv, giving a deterministic injection point;
  rewrite TestSteer_EndOfIterationRaceIsConsumedInCurrentRunStream to
  use hookStream and assert consumed-in-same-RunStream invariant (2
  model calls, UserMessageEvent present, steer content in session).

Assisted-By: docker-agent

….Contains

- hookStream: add blank line separating embedded *mockStream from
  onStop field (embeddedstructfieldcheck)
- TestSteer_EndOfIterationRaceIsConsumedInCurrentRunStream: replace
  assert.True(strings.Contains(...)) with assert.Contains (testifylint)

Assisted-By: docker-agent

All three steer drain sites now inject plain user messages.
Remove wrapSteerMessage helper and the wrap bool parameter from
appendSteerAndEmit — there is no wrapping anywhere.

Update code comments and PR body to reflect the simplified semantics.
Tighten TestSteer_EndOfIterationRaceIsConsumedInCurrentRunStream to use
assert.Equal + assert.NotContains now that the mid-loop drain no longer
wraps, removing the stale wrap=true/wrap=false caveat comment.

Assisted-By: docker-agent

Cut multi-line explanations to one short line each at all three
drain sites and on appendSteerAndEmit.

Assisted-By: docker-agent