Successor test-harness fix on governed source 5cf20128 (tree c5368428).
Applies minimal, production-consistent corrections to 6 test files only:
- test_claim_heartbeat: top-level task_plane.* -> app.task_plane.* (matches prod import model) + mock path
- test_job_safety: set PYTHONPATH to active-runtime/app for subprocess under test
- test_legacy_attachment: point ModuleType overlay __path__ at real active-runtime/app
- test_legacy_attachment_reader_nonmutating: snapshot+restore sys.modules[app.*] to stop global pollution
- test_terminal_proof_importer: supply purpose/required_evidence to acceptance conditions (mission contract)
- test_g7_web_surface_negative: replace hardcoded C:/ path with repo-relative path
No production source changes. Task: V2R2C3 successor harness repair (governed).
task/V2R2C3-succ-harness-20260915