[codex] Add Hegel property bench suite

[fireharp]

Summary

Adds an opt-in Hegel verifier layer for chant without changing recipe schema or the default verifier-first trust path. This now reports Hegel evidence per property instead of collapsing the suite into one aggregate result.

Changes

• Adds chant bench --suite=properties as an explicit opt-in suite.
• Keeps chant bench --suite=all as the fast compatibility gate: retrieval + e2e only.
• Emits five property-level bench results with cases counts.
• Writes the latest property report to .chant/hegel/properties-report.json.
• Writes generated failure payloads to .chant/hegel/failures/<property-id>.json when a property fails.
• Adds build-tagged Hegel property tests for retrieval invariants, runner trust gates, spell hash stability, and the CSV recipe oracle.
• Pins hegel.dev/go/hegel v0.5.3 and keeps Hegel state under .chant/hegel/.
• Documents hermetic CI usage with HEGEL_SERVER_COMMAND.

Property coverage

• PROP-retrieval-stale-penalty: 50 cases
• PROP-retrieval-signal-monotonicity: 50 cases
• PROP-runner-trust-gate: 50 cases
• PROP-spell-hash-stability: 50 cases
• PROP-csv-recipe-oracle: 25 cases

Validation

• go test ./...
• go test -tags hegel ./internal/bench -run TestRunProperties_AllPass -count=1
• go run ./cmd/chant bench --suite=properties --json -> total: 5, passed: 5, failed: 0
• go run ./cmd/chant bench --suite=all --json -> retrieval + e2e only, failed: 0
• git diff --check

Notes

Left unrelated untracked repomix-output.xml out of the commits.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/hegel-verifier-mvp

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