A steering message confirmed to the user as injected:true could still be
lost: after the loop's last HasPending check it runs out and the chain
finalizes (done event + final messages still streaming — the "few extra
messages" the user sees), then the finally block called Clear() and threw
the queue away. A message arriving in that window was accepted
(IsStreaming still true, Stop runs only in finally) but never drained and
never persisted, so it vanished after F5. Platform-independent; Windows
only widened the window via slower CLI teardown.
Replace the queue with a per-session gated state: Open() at chain start,
Close() at chain end. TryEnqueue() and Close() are mutually exclusive via
a per-session lock, so a confirmed injection can no longer be lost — the
loop either drains it or Close() returns it as leftover. The endpoint now
opens the gate at chain start, uses TryEnqueue as the authoritative check
(false → client resends as a normal message), and in finally closes the
gate and persists any leftover as Type="steer" instead of discarding it,
so it survives F5 and the model sees it on the next message.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
