chore: c6 docs-hygiene from cumulative_review_batches_28-30

Land F1+F2+F3 from the PASS_WITH_WARNINGS cumulative review of
batches 28-30 (AZ-305 / AZ-307 / AZ-308) before continuing to
batch 31. All three are bounded by the c6_tile_cache component;
no public API contract change beyond the new error re-export.

F1 (Medium / Architecture):
  Re-export CacheBudgetExhaustedError from c6_tile_cache package
  __init__ so consumers can catch the AZ-308 budget-exhaustion
  variant without widening to TileCacheError (which drops the
  needed_bytes / available_bytes / evicted_count diagnostics).

F2 (Medium / Architecture):
  Refresh the c6_tile_cache section of module-layout.md so the
  Public API line and the Internal-files list reflect what is
  actually on disk after batches 28-30 (drop the stale
  Tile / TileRecord / connection.py entries; add the AZ-305
  postgres_filesystem_store + tools.py, AZ-307 freshness_gate,
  AZ-308 cache_budget_enforcer entries; pivot the Public API
  bullet to the __init__.__all__ as canonical, mirroring the
  c7_inference section format).

F3 (Low / Maintainability):
  Promote the triplicate intra-module _iso_ts_now() helper into
  a single c6_tile_cache._timestamp.iso_ts_now and import it
  from postgres_filesystem_store, freshness_gate, and
  cache_budget_enforcer. FDR record envelope ts format now has
  one source of truth.

Test impact:
  tests/unit/c6_tile_cache: 105 passed, 57 skipped (pre-existing
  Docker-compose skip markers). No new tests required for F1/F2
  (re-export + doc) and F3 (pure refactor; existing tests assert
  FDR record shape, not the helper symbol).

Autodev state advanced to awaiting-invocation; next session
resumes greenfield Step 7 at batch 31 (AZ-298 TensorrtRuntime).

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/02_document/module-layout.md

@@ -137,17 +137,26 @@ Bootstrap reference: `_docs/02_tasks/todo/AZ-263_initial_structure.md`. Architec
 
 - **Epic**: AZ-250 (E-C6 Tile Cache & Vector Index)
 - **Directory**: `src/gps_denied_onboard/components/c6_tile_cache/`
-- **Public API**:
-  - `__init__.py` (re-exports `TileStore`, `Tile`, `TileQualityMetadata`, `TileRecord`, `SectorClassification`)
-  - `interface.py` (`TileStore` Protocol — query/get/put surface; concrete impls swappable)
+- **Public API** (`__init__.py` `__all__`; consult the module for the canonical list):
+  - `interface.py` (three Protocols: `TileStore`, `TileMetadataStore`, `DescriptorIndex` — query/get/put surface; concrete impls swappable)
+  - DTOs: `TileId`, `TileMetadata`, `TileMetadataPersistent`, `TileQualityMetadata`, `Bbox`, `SectorBoundary`, `HnswParams`, `IndexMetadata`
+  - Enums: `TileSource`, `FreshnessLabel`, `VotingStatus`, `SectorClassification`
+  - ABC: `TilePixelHandle`
+  - Config block: `C6TileCacheConfig` (registered on import)
+  - Error family rooted at `TileCacheError` with documented subtypes (`TileNotFoundError`, `TileFsError`, `TileMetadataError`, `ContentHashMismatchError`, `FreshnessRejectionError`, `CacheBudgetExhaustedError`, `IndexUnavailableError`) + sibling `IndexBuildError` (offline build envelope, not in the `TileCacheError` family)
 - **Internal**:
-  - `postgres_filesystem_store.py` (Postgres mirror + filesystem mmap + FAISS HNSW; production-default)
-  - `_native/` (`cpp/faiss_index/` wrapper)
-  - `migrations.py` (`apply_migrations(config) -> MigrationResult` runner invoked by the composition root at startup; AZ-304 + later)
-  - `_uuid_namespace.py` (pinned `TILE_NAMESPACE_UUID` + `derive_tile_id` / `derive_location_hash` helpers; cross-repo coordinated with `satellite-provider`; AZ-304)
-  - `connection.py` (planned — `psycopg_pool` ConnectionPool helper; AZ-305, not landed yet)
+  - `_native/` (FAISS C++ wrapper, planned)
+  - `_tile_pixel_handle.py` (`TilePixelHandle` ABC)
+  - `_types.py` (DTOs / enums; consumed via the Public API re-exports)
+  - `_uuid_namespace.py` (AZ-304 — pinned `TILE_NAMESPACE_UUID` + `derive_tile_id` / `derive_location_hash` helpers; cross-repo coordinated with `satellite-provider`)
+  - `migrations.py` (AZ-304 — `apply_migrations(config) -> MigrationResult` runner invoked by the composition root at startup)
+  - `postgres_filesystem_store.py` (AZ-305 — production-default `TileStore` + `TileMetadataStore` impl over Postgres mirror + filesystem; `PostgresFilesystemStore.from_config` opens its own `psycopg_pool.ConnectionPool` and constructs an `AZ-307 FreshnessGate`)
+  - `freshness_gate.py` (AZ-307 — `ACTIVE_CONFLICT` reject + `STABLE_REAR` downgrade per `freshness_gate.md` v1.0.0)
+  - `cache_budget_enforcer.py` (AZ-308 — RESTRICT-SAT-2 10 GiB hard cap; `CacheBudgetEnforcer.reserve_headroom` + `BudgetEnforcedTileStore` write-decorator)
+  - `tools.py` (AZ-305 — operator dump CLI invoked via `python -m gps_denied_onboard.components.c6_tile_cache.tools ...`)
+  - `errors.py`, `config.py` (component plumbing)
 - **Owns**: `src/gps_denied_onboard/components/c6_tile_cache/**`, `cpp/faiss_index/**`, `tests/unit/c6_tile_cache/**`, `db/migrations/**` (project-level Alembic env owned by c6 — `alembic.ini` at repo root points here; `0001_initial.py` shipped by AZ-263 bootstrap, `0002_c6_tile_identity_and_lru.py` and forward owned by AZ-304+ migrations)
-- **Imports from**: `_types`, `helpers.sha256_sidecar`, `helpers.wgs_converter`, `config`, `logging`, `fdr_client`
+- **Imports from**: `_types`, `helpers.sha256_sidecar`, `helpers.wgs_converter`, `clock`, `config`, `logging`, `fdr_client`
 - **Consumed by**: `c2_vpr`, `c2_5_rerank`, `c3_matcher`, `c10_provisioning`, `c11_tile_manager`, `runtime_root`
 
 ### Component: c7_inference