A /steer redirect during a thinking phase serialized the streamed
reasoning into the persisted assistant checkpoint ('Reasoning shown
before the interruption: ...'). An assistant turn exposing its own
chain-of-thought reads to Anthropic's output classifier as
reasoning-injection/prefill jailbreak, so every subsequent call on the
session deterministically returned 'Provider returned an empty
response' — and because the checkpoint is persisted and replayed, no
retry, nudge, or empty-recovery branch could ever escape it. Four
sessions were permanently bricked this way in the week of Jul 21-27
(42+ blocked calls; every reasoning-free checkpoint that week was
untouched — same mechanism as the prefill.json incident).
Class fix: streamed reasoning is now display-only state. The
_current_streamed_reasoning_text accumulator is removed entirely
(producer in _fire_reasoning_delta, resets, and init), so no future
path can serialize CoT into replayable content. The checkpoint keeps
only the visible response text; the model regenerates its reasoning on
the retried turn. Invariant documented in _apply_active_turn_redirect.
Regression tests: CoT never appears in either checkpoint shape,
reasoning-only interrupts produce a bare checkpoint, reasoning deltas
stay display-only.
teknium1
cf0c42fa0b