[P2] Synthetic mutation harness for CI ground truth (B2-008)

[stranske]

Why

R6 requires deterministic mutations for CI ground truth without proprietary docs. Verified: tests/test_main.py:1-33 is the only functional test module — no tests/mutations/ directory. Missing behavior: no labeled mutation pairs for diff gates.

Scope

tests/mutations/ generator applying labeled edits to synthetic LPA fixtures.

Non-Goals

• Do NOT use real manager documents.
• Scaffold-only completion does NOT count.

Tasks

• Add tools/generate_mutations.py producing paired before/after JSON segment trees.
• Add tests/mutations/test_mutation_pair_known_diff.py asserting expected change classes.
• Add tests/blackline/test_mutation_pairs.py wiring mutation pairs to blackline diff (depends on B2-005).

Acceptance Criteria

• Named test: tests/mutations/test_mutation_pair_known_diff.py::test_gate_provision_change_detected passes.
• Deliberate-break gate: skip one mutation → test must FAIL → revert.

Implementation Notes

Mutation pairs feed the clause blackline engine in B2-005.

Surfaced by B2-008.

[github-actions]

This issue is not yet agent-processable. See docs/AGENT_ISSUE_FORMAT.md.

• Tasks item must name a concrete file, symbol, path, config key, job, or command: Wire mutation pairs into blackline tests (B2-005)..
• None of the 3 paths this issue cites exist in this repository (clones/Doc-Lineage/tests/test_main.py, tests/mutations/, before/after). An agent cloning this repo has nothing to act on. File it against the repo that holds the code, or cite the evidence here.

Recommended but absent: Implementation Notes

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