Audit: detect_track, masks, and multiplex Stage A/B/C commit history

[Copilot]

User suspected an unintended force-push overwrote changes to Stage A, B, and C in the multiplex pipeline. This PR is a pure audit — no code was modified.

Findings

detect_track/ — 6 commits total

• 7e3a6e0 (Feb 24, 2026) is the critical change — bundled inside a Stage E commit, processor.py quietly changed Stage A mask-writing from unconditional to config-gated (default False):

  -  # Always write a canonical mask
  -  mask_ref = self.writer.write_mask_npz(...)
  +  write_yolo_masks = _cfg_get(cfg, "stages.stage_A.masks.write_yolo_masks", False)
  +  mask_ref = self.writer.write_mask_npz(...) if write_yolo_masks else None

• Other detect_track changes (dc65ae2, 542d20b, 9029ada, 80cc446) were intentional Stage A buildout through Jan 18.

masks/ — 2 commits total

• Stable since 9029ada (Jan 16, 2026). Only change was schema-correct empty DataFrame in Stage B run.py.

multiplex_runner.py — 11 commits, stable since Jan 23

• 64faf3d (Jan 16) was the major structural change: renamed run_multiplex_ABC → run_multiplex_AC, dropped Stage B from the active multiplex window, and redesigned Stage C placeholder outputs.
• Commits 3b3a76b through 80cc446 (Jan 17–18) added real Stage C processing: C0Scheduler, gating, AprilTag decode, C2 identity registry.
• eacc5e6 (Jan 23) was the last touch — fps single-source-of-truth fix. No changes for 2+ months after that.

Rollback Guidance

Area	Last stable commit	Date
multiplex_runner.py	eacc5e6	Jan 23, 2026
processor.py (mask behavior)	80cc446	Jan 18, 2026
masks/run.py	9029ada	Jan 16, 2026

To restore the old always-on mask writing in Stage A:

git checkout 80cc446 -- src/bjj_pipeline/stages/detect_track/processor.py

The multiplex orchestration wiring itself is intact — multiplex_runner.py has not changed since Jan 23.

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