test: pin TODO-002 retirement contract (depends on #432)

[FileSystemGuy]

Summary

Adds a tripwire-style contract test that locks in the retirement plan for the three deferred-runtime-cross-check stubs tagged TODO-002:

Rule	Owner	Method
3.3.5 trainingDistributedDataAccessibility	TrainingCheck	distributed_data_accessibility_check
3.3.7 trainingNodeCapabilityConsistency	TrainingCheck	node_capability_consistency_check
4.7.4 checkpointSimultaneousRwSupport	CheckpointingCheck	simultaneous_rw_support

Each stub currently emits an INFO-level note containing the marker TODO-002, returns True, and contributes no violation, because summary.json doesn't expose the per-host data the real cross-check would need. For 4.7.4 the structural anchor is SystemYamlSchemaCheck.SCHEMA_ERROR_RULE_MAP's three field-level entries (simultaneous_write, simultaneous_read, multi_host); 3.3.5 / 3.3.7 have no schema anchor and rely entirely on the deferred runtime stub.

What the test pins

Five parametrized assertions (11 cases total) covering both the runtime side and the schema-anchor side:

1. Decoration survives — @rule(...) is still on the method and discover_rules() still lists the ID. Catches "I deleted the method" or "I forgot to redecorate after upgrading the body" — without this, mlpstorage rules-coverage silently drops the rule.
2. TODO-002 marker is present in the method source — the marker is the deferral signal. Removing it is the explicit retirement act; when it disappears, the failure message walks the retirer through the 7-point retirement checklist in the module docstring.
3. No log_violation while deferred — catches the half-retirement: violation call added but TODO-002 marker still present.
4. Schema anchors remain for rules that declare them — locks the three 4.7.4 SCHEMA_ERROR_RULE_MAP entries in place so retiring the runtime stub can't accidentally take the schema-anchor coverage with it.
5. No silent anchor additions — forward-looking: 3.3.5 / 3.3.7 have no anchor today; if someone adds one as defense in depth, the test fails until they register it in EXPECTED_SCHEMA_ANCHORS, making it part of the contract.

Why a separate file from the existing pin tests

The existing per-method pin tests (TestChkpt05DeferredFollowUp in test_checkpointing_check_phase2.py, test_3_3_5_* / test_3_3_7_* in test_training_check_retrofit.py) test that the current body emits info. This file tests the contract across all three rules, so partial retirement still trips one of the cross-rule invariants. The split is intentional — anyone touching a stub has to come through this file, which doubles as the retirement checklist.

Dependency on PR #432

This PR is intentionally a draft. The test imports symbols (rule_registry, system_yaml_schema_checks.SCHEMA_ERROR_RULE_MAP) that don't exist on main yet — they land with PR #432 (FileSystemGuy-rules-validator). Until that merges, CI on this branch will fail at import time.

Sequencing:

1. PR Submission checker: complete Rules.md coverage + 'mlpstorage validate' subcommand #432 merges to main → rule_registry, SystemYamlSchemaCheck, and the three deferred stubs all land.
2. Rebase this branch onto the new main, mark Ready for review, merge.

Test plan

• On FileSystemGuy-rules-validator (which has all dependencies): python3 -m pytest mlpstorage_py/tests/test_todo_002_retirement_contract.py -v → 11 passed, 0 failed.
• Full suite on the dependency branch: 517 passed, 1 xfailed (up from 506).
• Re-run on main once PR Submission checker: complete Rules.md coverage + 'mlpstorage validate' subcommand #432 lands.

[github-actions]

MLCommons CLA bot All contributors have signed the MLCommons CLA ✍️ ✅