Auto-stamp bcfp baseline in run_provincial_parity.R

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Problem

data-raw/logs/bcfp_baselines.csv records the bcfp comparison baseline (model_run_id + SHA) each link comparison was computed against. The CSV's existing rows are compare-flavoured: (link_schema, bcfp_model_run_id) pairs. Currently hand-maintained — the goal is auto-stamping.

Stamping must happen where comparisons actually occur. The trifecta orchestrator (data-raw/trifecta_provincial.sh) dispatches builds; it does not compare. Comparison happens one layer down inside run_provincial_parity.R (per-WSG via compare_bcfishpass_wsg()).

Where bcfp is touched

Script	Queries bcfp?	Stamp here?
data-raw/trifecta_provincial.sh	No (dispatch only)	No
data-raw/run_provincial_parity.R	Yes — per-WSG via compare_bcfishpass_wsg()	Yes — once per invocation
data-raw/compare_bcfishpass_wsg.R	Yes — single WSG	Sub-call (not stamped per-WSG)
data-raw/compare_rollups.R	No — link-vs-link RDS delta	No (no bcfp involved)

Proposed Solution

1. Wire the stamp at the top of run_provincial_parity.R, once per invocation (not per-WSG). The same script handles single-host runs and trifecta-dispatched per-host runs, so single wiring covers both call patterns automatically.
2. CSV schema migration: add host column. Trifecta runs produce 3 rows (m4 / m1 / cypher) all with the same bcfp_model_run_id but different host context. Backfill existing rows to m4 (they were single-host runs).
3. Tunnel-tolerance: reuse compare_bcfishpass_wsg()'s existing tunnel where possible; warn-and-continue if the tunnel can't open. Stamp failure must not block a build.
4. Idempotency: if (host, link_schema, bcfp_model_run_id, run_started_pdt) row already exists, skip — supports resume-safe retries.

Final CSV columns: run_started_pdt, host, run_label, link_schema, bcfp_model_run_id, bcfp_model_version, bcfp_date_completed, notes.

Verification

• Run trifecta_provincial.sh --config=default_rearbreaks --schema=fresh_default_rearbreaks.
• Confirm three rows in bcfp_baselines.csv (host = m4, m1, cypher) all with matching bcfp_model_run_id.
• Confirm [bcfp-baseline] stamped: ... line in each host's run_provincial_parity.R log.
• Re-running with the same run_started_pdt does not double-stamp.

Out of scope

• Mid-run bcfp build collision detection (Tuesday rebuilds shifting bcfp build mid-trifecta). Separate enhancement.
• Stamping on compare_rollups.R (link-vs-link methodology delta, no bcfp involved).