conformance: reject duplicate evidence ids

[team-humaki]

Fixes #14.

Adds conformance/v0.1/invalid/duplicate-id for the SPEC §4.3 / §7 rule that evidence id values must be unique. Two items share id: a with otherwise valid locators and digests; aegisproof verify reports INVALID / SCHEMA and exits 1.

Also covers the fixture from internal/verify so the path cannot rot.

go test ./internal/verify
go run ./cmd/aegisproof verify ./conformance/v0.1/invalid/duplicate-id; echo $?

[new-world-coder]

Validation vs issue #14 + contribution rules

Looks good — this is a clean first contribution.

Check	Status
Issue #14: fixture under conformance/v0.1/invalid/	✅ invalid/duplicate-id
Issue #14: README row	✅
Issue #14: verify exits 1	✅ (INVALID / SCHEMA)
SPEC §4.3 / §7 uniqueness	✅ exercised correctly
DCO (Signed-off-by)	✅
Scope (no LLM/cloud/compliance verdict language)	✅
Digests match file bytes	✅
Local go test ./...	✅
GitHub Actions CI (after first-time fork approval)	✅

Extra credit beyond the issue acceptance criteria: the in-package unit test + conformance path test is exactly the right hardening so the fixture cannot rot.

Non-blocking follow-ups (maintainer or optional follow-on PR)

1. .github/workflows/ci.yml still only smoke-checks bad-digest and path-traversal under “Conformance invalid must fail”. Worth adding duplicate-id (and eventually the other invalid fixtures) so CI mirrors the README table — not a blocker since go test already covers this case.
2. Optional: assert SCHEMA + the duplicate-id message in TestConformanceInvalidDuplicateID the same way TestDuplicateEvidenceID already does.

Welcome — and thank you for being AegisProof’s first external contributor. 🙌

[new-world-coder]

Nit (non-blocking): identical file bytes + identical digests correctly isolate the failure to duplicate id (not digest). Nice choice.

Optional hardening for this test only: also assert a SCHEMA error mentioning duplicate evidence id, matching TestDuplicateEvidenceID above — so a future regression that fails for the wrong reason still fails the test.

[new-world-coder]

Thank you for AegisProof’s first external contribution — and for going beyond the issue with the unit + conformance path tests so the fixture can’t rot. Welcome, and we hope you’ll stick around for more good-first-issue work when you’re free.