workflow-fix: verify_task_body Context-row provenance vs epm:followup-scope cross-check

Overview / Motivation

Auto-filed by the workflow-fix-on-bug protocol from a clean-result-critic prose follow-up on task #1426 (fold round r1, Lens 5b, mechanizable: yes).

Goal

Add a verify_task_body.py check that cross-checks the body **Context:** row's follow-up clause cost_class/source tokens against the latest epm:followup-scope v1 note fields for the same followup_label; FAIL on contradiction.

Workflow gap

• Bug observed: the #1426 fold's Context row said "proposer cost_class free-analysis" while the round's epm:followup-scope marker recorded source: proposer-9b-cheap, est_gpu_hours: 14 (GPU cheap band) — a provenance contradiction only the adversarial critic caught.
• Why it is a workflow gap: the Context row is the run-provenance record the clean-result ships forward (SPEC.md § footer, check 17); the followup-scope marker is machine-readable ground truth in events.jsonl, so the contradiction is mechanically checkable but no check exists.
• Confidence (emitter): high
• verified-at-filing: grep -n 'followup-scope' scripts/verify_task_body.py → 4 hits (lines 4261, 4389, 12161, 12236), all in OTHER checks' contexts (origin-prompt informational note, provenance-source enumeration, armed-label dispatchability helpers); none compares Context-row cost_class/source tokens to the marker fields (2026-07-18).

Proposed change (candidate diff sketch — refine in planning)

+ new check: when the **Context:** row names a follow-up round (followup_label
+   or source/cost_class tokens), parse the latest matching epm:followup-scope
+   note via task_workflow.parse_followup_note_field; FAIL when the body's
+   source/cost_class contradicts the marker's (missing tokens = skip, not FAIL)

Provenance

• workflow_fix_target: scripts/verify_task_body.py
• fingerprint: fb694bc00379

Surfaced prose (clean-result-critic #1426 fold r1): "mechanizable: yes — cross-check the body Context: follow-up clause's cost_class/source tokens against the latest epm:followup-scope v1 note fields; FAIL on contradiction."