Fixes#2549 (P0 data loss). Every drain exit previously truncated the WHOLE
queue (six `: > "$QUEUE"` sites), which (a) destroyed privacy/mode-held
entries while misattributing them as "no allowlisted changes", (b) destroyed
entries enqueued concurrently during the drain, and (c) left push-failed
commits stranded locally with nothing ever re-pushing them until unrelated
new work arrived.
Now: compute_paths_to_stage classifies every entry (stageable / retained
privacy-held / dropped skipped-invalid-unmatched-missing); rewrite_queue
re-reads the LIVE queue at mv time and removes only this drain's processed
paths (retained + concurrent appends + unparseable lines survive; atomic
tmp+mv); an unpushed-commit detector at run start re-pushes stranded local
commits (receipted fail-closed; a receipt refusal skips the retry rather
than wedging the drain; guards missing origin/<branch>; runs inside the
existing lock). Status lines carry counts; full drop paths go to a 0600
sidecar (.brain-sync-drops.json) so filenames stay out of transcripts.
--drop-queue remains the one intentional truncation.
Matrix added: privacy retention, unmatched/missing counted drops + sidecar
mode, unparseable-line preservation, surgical same-drain retention, push-fail
commit retention + detector re-delivery on an EMPTY queue, receipt-refusal
skip. 35/35 in test/brain-sync.test.ts.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
