handle_turn() (and stream_turn) decided "did the handler append its
reply?" by snapshotting the assistant-message count before kickoff and
appending the stringified result when the count came back unchanged. A
handler that appends its reply and then trims state.messages to a cap —
a normal bounded-context pattern — left the count unchanged, so the
fallback appended the reply a second time on every turn once trimming
engaged, and the duplicates then crowded real turns out of the capped
window.
Replace the count heuristic with an explicit per-turn flag:
append_assistant_message() sets _assistant_reply_appended, handle_turn
and stream_turn clear it before kickoff and only fall back when no
assistant message was appended during the turn. The now-unused
_assistant_message_count() helper is removed.
Fixes EPD-181.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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