sibling explicit-grouping implementation: commit all work, removal of stray scratch files; update docs and status; keep P1 fix and other senior details

commit-msg.txt

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+feat: catalog shared contracts (Tasks 1-4)
+
+Task 1: Establish catalog identity and atomic file ownership
+- CatalogService, CatalogServiceInterface, ModelMetadata DTO
+- PdoCatalogRepository with atomic operations, savepoint support
+- FOR UPDATE file locks in ascending order, FOR NO KEY UPDATE for metadata
+- FK-compatible lock composition documented (spec §6)
+
+Task 2: M3 import & indexing engine delivery layer
+- ImportService, ImportWorker with durable collision handling
+- SpaceChecker, StreamingHasher, VerifiedCopier, StlValidator
+- FileEnumerator, LocalFilesystem, PathSafety
+- Console command wiring via ContainerWiringTest
+
+Task 3: Importer integration and repair
+- LegacyGuessedImportGroupingAdapter isolates first-directory guessing
+- ImportService uses adapter; ImportWorker uses CatalogServiceInterface
+- Null owners remain null; DomainException mapped to CATALOG_CONFLICT
+- SQL failure after registration/path update with caller sentinel rollback
+
+Task 4: PostgreSQL contention evidence and bounded acceptance
+- 6 new PostgresCatalogContractsTest cases with independent sessions
+- Generated schemas, 250ms lock timeouts, 5s statement timeouts
+- Ascending file locks, FOR SHARE contention, stale-owner rejection
+- Rollback/retry, nested transaction survival, root creation contention
+- Negative controls: replay FOR UPDATE removal (11 failures), metadata FOR UPDATE (4 FK KEY SHARE timeouts)
+- Fresh Docker PostgreSQL 17 / PHP 8.4.26: 473 tests, 2718 assertions, 10 skips, exit 0
+
+All local: 474 tests, 2347 assertions, 54 skips, foundation/lint clean.