test: add repo fixture semantic fact assertion helpers #329

Summary

Add assertion helpers that compare a repo fixture's expected.semanticFacts against bootstrap output or graph state.

The fixture builder can already carry expected semantic facts. The next step is making those facts executable so Hill 1 tests read like product statements rather than manual graph assertions.

Why

Upcoming bootstrap slices need to prove that artifact inventory, entity extraction, and relationship inference satisfy the design intent. Tests should be able to say: given this fixture, assert these semantic facts were found with the expected edge type, confidence band, and provenance.

Scope

• Add helpers for asserting expected semantic facts against bootstrap JSON summaries, graph exports, or direct graph reads.
• Support exact facts and partial matching for confidence/provenance metadata.
• Produce clear failure messages that name missing, extra, and mismatched facts.
• Keep helpers fixture-local; do not add production graph behavior.

Acceptance Criteria

• A bootstrap acceptance test can compose a fixture and assert expected facts in a few readable lines.
• Failures include source, type, target, and metadata mismatch details.
• Helpers work with the canonical fixture builder from test: build canonical repo fixture builder with base repos and overlays #311.

Related

• test: translate Hill 1 bootstrap acceptance criteria into failing tests #310
• bootstrap: implement first-pass entity extraction for files docs ADRs and modules #304
• bootstrap: implement repo-local artifact inventory and classification #306
• bootstrap: implement first-pass relationship inference with provenance and confidence #307
• PR Add canonical repo fixture builder #327