Manual /compress shrinks the model-facing context_messages but keeps the
visible messages[] transcript. The old context returned via two paths (#4836):
(1) append-only state.db reconciliation re-appending pre-compression rows, and
(2) startup .bak recovery treating the intentional shrink as data loss.
Half A (routes.py _handle_session_compress): persist truncation_watermark +
truncation_boundary (= watermark of the compressed context), set
compression_anchor_mode="manual", refresh last_prompt_tokens, stamp missing
timestamps on the compressed context, and delete the now-stale .bak. The
boundary==watermark stamp drives the #4772 reconciliation logic onto its
conservative path (block replay of pre-compression rows) while post-compression
turns still merge once sidecar timestamps advance past the watermark.
Half B (session_recovery.py): the .bak recovery guard. MAINTAINER FIX over the
original PR — the contributor suppressed recovery whenever
compression_anchor_mode=="manual", a flag set once at compress and never
cleared, which PERMANENTLY disabled #1558 crash-recovery for any compressed
session (real data loss). Recovery is now suppressed only when the session was
intentionally compressed AND the .bak is genuinely the pre-compression backup,
discriminated by the compaction marker (the same _context_messages_include_
compression_marker signal reconciliation uses): a marked .bak post-dates the
compression -> recover; an unmarked .bak with a larger context is the
shrink-undoing pre-compression one -> suppress. Fail-open on any error.
Resolves an Opus-gate edge in the first cut (length-only heuristic wrongly
suppressed a loss that shrank BOTH messages and context). Two new non-vacuous
regression tests: post-compression real loss recovers, and the both-shrunk
marked-backup case recovers.
Co-authored-by: hyl-ailab <hyl-ailab@users.noreply.github.com>
nesquena-hermes