Simplify-pass folds on the #23254 salvage:
- REUSE (HIGH): append_messages_batch now delegates row serialization to
the pre-existing _insert_message_rows helper (already shared by
replace_messages / archive_and_compact / portability import) instead
of adding a third serialization path (_prepare_message_row +
_MESSAGE_INSERT_SQL are gone). One row-writer for every multi-row
path; the row-ID return was consumed by no production caller, so the
batch returns the inserted count.
- QUALITY (HIGH): the compression-lock + compression-closed admission
guards are extracted into _check_transcript_write_guards, shared by
append_message and append_messages_batch (previously duplicated 23
lines that had already needed targeted fixes, #74478). The role-gated
reasoning filtering is no longer duplicated in run_agent.py — it
lives at its one site inside _insert_message_rows.
- EFFICIENCY (MEDIUM, measured): unbounded seed copies hold one BEGIN
IMMEDIATE for seconds (10k rows ~= 2.4s; FTS triggers dominate) and
monopolize the in-process write lock. append_messages_batch grows a
chunk_rows param; all seed/copy call sites use chunk_rows=500. Same
recovery semantics as the old per-row loops, bounded lock holds.
- REUSE (MEDIUM): the two remaining per-row branch-copy loops found by
the pass (gateway/slash_commands.py /branch, hermes_cli
cli_commands_mixin.py branch) are converted to chunked batches too
(AsyncSessionDB's generic to_thread forwarder covers the async site).
Turn-flush benchmark unchanged after the refactor: 2.43 -> 0.87 ms
median per 5-message flush (64% faster).
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