Ephemeral empty-response/prefill recovery scaffolding (the synthetic
assistant "(empty)" turn, the user nudge, the terminal "(empty)"
sentinel, and the thinking-only prefill placeholder) exists only to
drive the next API retry; the in-memory loop pops it before appending
the real response. The append-only flush did not mirror that, so a
mid-turn persist could commit scaffolding to the SQLite session store
(and JSON log), and a resumed session would replay synthetic
"(empty)"/nudge turns as genuine context — re-poisoning the empty-retry
boundary forever.
Filter ephemeral scaffolding at both durable-write sites
(_flush_messages_to_session_db + _save_session_log), by flag not
position, so buried scaffolding (an answered nudge leaves the synthetic
pair mid-list) is skipped too. Covers all three flags including
_thinking_prefill.
Adapted onto current main's identity-tracking flush.
Cherry-picked from #41281 by petrichor-op.
state.db now stores every message field the JSON snapshot stored. Removed
the method, all 7 call-sites, and ~13 test stubs that suppressed its file I/O.
Body is in git history if it ever needs to come back.
When empty-response terminal scaffolding fires on a tool-result turn,
_drop_trailing_empty_response_scaffolding left the live history ending at
a bare 'tool' message. The next user input then landed as [...tool, user],
a protocol-invalid sequence that OpenRouter/Opus and other providers
silently fail on (returns empty content). That retriggered the empty-retry
recovery every turn, and recovery flags never hit SQLite (no column for
them), so history kept looking broken on every reload.
Two fixes:
1. Scaffolding strip rewinds the orphan assistant(tool_calls)+tool pair
after popping sentinels. Only fires when scaffolding flags were
actually present, so mid-iteration tool loops are untouched.
2. _repair_message_sequence runs right before every API call as a
defensive belt: drops stray tool messages with unknown tool_call_ids,
merges consecutive user messages so no user input is lost. Does NOT
rewind assistant(tool_calls)+tool+user — that pattern is valid when
the user redirected before the model got its continuation turn.
Repro: session 20260507_044111_fa7e65. Opus-4.7/OpenRouter returned
content-less response after a 42KB execute_code output, nudge+retry
chain exhausted (no fallback configured), terminal sentinel appended,
scaffolding stripped leaving bare tool tail, user typed 'wtf happened..'
and landed as tool→user violation. Every subsequent turn collapsed in
<50ms with the same 3-retry empty chain because the API request itself
was malformed.
Verified live via HTTP mock: pre-fix reproduced 5 api_calls/0.15s exit
'empty_response_exhausted'; post-fix 1 api_call/0.10s exit
'text_response(finish_reason=stop)'. Three-turn session flows cleanly
through the scenario. Full run_agent suite: 1242 passed (0 regressions,
2 pre-existing concurrent_interrupt failures unrelated).
