fix(I-25): --workload is bound to the prompt corpus — receipt.workload only with corpus_sha256 of a prompts file whose _meta.corpus equals the label; --workload W1 --profile short is refused with one line (PMAT-973, #2888, #2756)

[noahgift]

PP-066 DAG row I-25 (issue #2888; defect #2756; epic #2873; ticket PMAT-973; owner perf-gate; receipt docs/audits/impl-PMAT-973-receipt.md, status: partial until merged).

The defect (#2756): --workload was a free-text label with no connection to the prompts sent; apr test llm band --workload W1 --profile short sent one prompt thirty times and the receipt recorded workload: W1 — the W1 corpus's own _meta.distinctness_rationale says identical prompts let prefix caching, not the scheduler, drive Arm A's number. A label the receipt cannot falsify is not provenance.

What lands: bind_workload(label, prompts_file) -> WorkloadBinding { label, corpus_sha256, prompt_count } — accepted only when the file's first-line _meta.corpus equals the label (refused naming both labels, or "not a labelled corpus"); the band receipt carries corpus_sha256 (sha256 of the file bytes); --workload <corpus label> with no prompts file is refused before the first request with one line naming the corpus. Test module workload_corpus_binding (RED first at 24b077a): the real W1 corpus binds (256 prompts), a W2-labelled file refuses W1, a header-less file refuses, a receipt with a label and no digest is refused. Contract contracts/apr-workload-corpus-binding-v1.yaml (kind: pattern); README 1812 contracts.

Acceptance, re-run by the orchestrator on e925fc0

A_i	rc
cargo test -p apr-cli --lib workload_corpus_binding	0 (4 passed)
cargo test -p apr-cli --lib test_llm_band (65 tests)	0
cargo fmt --all -- --check · cargo clippy -p apr-cli --lib -- -D warnings · pv validate · pv lint · check_contract_test_binding.sh · check_contract_enforcement.sh · check_readme_claims.sh · check_no_claim_literals.sh · check_roadmap_diff_additive.sh	0 each

Mutation — RED, then restored GREEN: the _meta.corpus comparison removed (any file accepted) → a_corpus_labelled_w2_refuses_the_w1_label and a_prompt_set_with_no_meta_header_is_not_a_labelled_corpus FAILED (2/4) → restored 4/4.

Recorded: the card's --test workload_corpus_binding is a #[cfg(test)] module of commands::test_llm_band (crate-private tree; the lib.rs seam is blocked by the pre-commit gate on pre-existing debt — same as R-3/T-2); the --profile short refusal is the unit-tested branch, not a live server run. Receipt for this PR itself: advisory, not produced (driver A1).

[github-actions]

§13.11 rung 1 — quorum shadow verdict

S13-SHADOW pr=3008 head=b73c5e96eb2d26c5fc4d4a8b855ca96817fbbf1c verdict=REFUSE class=Q1 arm_rc=1

Shadow mode: this records a verdict and merges nothing. A refusal
to arm is not a block (§13 adds zero rows to §7) — the pull request is
exactly as green as it was.