Batch merge reliability roadmap coverage

[adamziel]

What it does

Adds three focused merge-reliability slices in one PR:

• Retires old AUTOINCREMENT ID bands after branch reset so explicit imports into a previously published band stay review-held.
• Adds WordPress semantic validator coverage for stale wp_term_taxonomy.count after relationship changes.
• Automatically plans one safe schema dependency case: a source-changed view can apply when the only invalidating target trigger was also dropped by source.

Rationale

These are independent roadmap gaps, but grouping them avoids three more open PRs and lets CI validate them through the faster COW-only path.

ID bands need reset/reuse protection because IDs can be embedded in JSON and serialized data. Term counts are a common WordPress cached invariant that generic row merging cannot infer. The schema planner should resolve narrow safe dependency cases instead of sending every dependent view/trigger situation to manual review.

Implementation

merge.php now records retired band state during reset-safe band allocation and excludes retired bands from active explicit-ID validation. The schema planner drops unchanged target triggers first when source both rewrites the view and drops the trigger that would make validation fail.

The semantic fixture creates custom taxonomy relationships with stale cached counts, then verifies the WordPress-scoped audit conflict, logical identity, and preserved candidate state.

Testing instructions

php -l scripts/cow/merge.php
php -l tests/cow/id_bands.php
php -l tests/cow/wp_semantic_validator.php
php -l tests/cow/schema_review.php
php tests/cow/id_bands.php
TMPDIR="$PWD/.tmp" php tests/cow/wp_semantic_validator.php
php tests/cow/schema_review.php
git diff --check origin/trunk...HEAD

Local focused results: id_bands.php passed 46 assertions, wp_semantic_validator.php passed 522 assertions, and schema_review.php passed 288 assertions.