Stage every artifact a promotion manifest binds

[DavidBakerEffendi]

The v0.3.1 legacy freeze
(32954887242)
ran all eleven candidate shards green — roslyn included, so #171 worked —
and then failed in aggregation:

Error: canonicalize promotion artifact docs/legacy-promotion-selection-policy.md
Caused by: No such file or directory (os error 2)

freeze-manifest resolves a promotion manifest's bound artifacts relative to
the staged corpus. The legacy manifest binds its eligibility policy under
docs/, and stage-release-bundle.sh copies benchmarks fixtures adapters schema src containers scripts plus a few root files — never docs/. So the
bundle could not canonicalize an artifact its own manifest hash-binds, which is
exactly the self-verifying property the tier exists to provide.

It is the only such artifact: sweeping every file reference in
benchmarks/promotion/** yields one path outside the staged prefixes, bound by
both manifest.json and cohort.json.

The fix

Copy exactly the bound files, derived by reading the promotion manifests
rather than naming docs/ here, so a newly bound artifact is staged without
editing this script. Not all of docs/ — that carries node_modules and build
output, which would bloat the bundle and hand the analyzer a large unrelated
tree to index.

Verification, against the failed run's own evidence

• Staging emits the policy at the manifest's expected path, sha256
  1ac2968892c97af5… — matching the binding — and docs/ contributes that
  one file and nothing else.
• Downloaded all eleven shard reports from that run and re-ran the exact
  aggregation: succeeds, satisfies the workflow's
  snapshotKind == "legacy_promoted" and balancedCoreCaseCount == 110 and (.corpus | length == 30) gate, and generate-results produces both pages.

That run's Bifrost report also confirms the expected set from #160 exactly:

110 cases: 106 passed, 1 improved, 3 failed, 0 errors   (bifrost 6624e883)
  improved  cpp-parity-function-like-macro-expanded-call
  failed    rust-struct-construction                                  (#170)
  failed    rust-parity-module-declaration-definition                 (#170)
  failed    scala-parity-case-class-generated-construction-and-copy

Regression cover

Adds a test asserting the derivation is present and that every artifact bound
outside the staged prefixes actually exists. unittest discover runs 40 tests
green; reproduction contract exits 0.

🤖 Generated with Claude Code