The ref leg: conformance verdict becomes legs == REFERENCE where the evaluator judges (TOR-8); 30 selftest scenarios incl. the co-drift class

[O6lvl4]

Second slice of #10: the runner adjudicates against the reference (TOR-8).

• scripts/conformance.py --legs ref (in the default leg set): for every program in spec/wasm_cross + spec/programs, where the reference evaluator produces observables, native and wasm must each equal the reference's — agreement between the two targets is no longer sufficient there. A reference abstain (ledgered class) is counted and skipped, never a pass or fail; a malformed protocol reply or evaluator fault is red. // @ref-allow: <reason> tracks a disagreement under adjudication and goes STALE when healed — grain_functions.almd carries the first one (finding F1, named-argument evaluation order).
• scripts/selftest-conformance.py: 21 → 30 scenarios with a scripted stub als-ref — including the class this whole instrument exists for: co-drift (targets agree with each other, both differ from the reference) is red. proofs/runner-coverage.toml floor 85.1% → 86.3% (--write in this PR, per the gate's ratchet).
• conformance.yml builds ref/ (pinned 1.95.0, cached) and runs the leg by default; the statement records the reference's version beside the binary and wasmtime.
• QUALIFICATION limitation 2 narrows rather than lifts: on the evaluated subset the runner judges truth; on the abstained subset it still judges agreement, bounded by the shrink-only proofs/ref-abstain.toml.

Smoke: --legs ref --limit 40 → 11 judged / 11 pass / 29 abstained. Full-corpus ref runs happen in the conformance workflow (weekly / dispatch), as with every other leg.

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