[AZ-447] autodev Steps 1-4 baseline: docs, tests, refactor specs

Captures the full output of autodev existing-code Phase A through
Step 4 (Code Testability Revision) for the Azaion UI workspace:

- Step 1 Document: _docs/02_document/ (FINAL_report, architecture,
  glossary, components/, modules/, diagrams/, system-flows,
  module-layout) plus _docs/00_problem/ + _docs/01_solution/ +
  _docs/legacy/ + _docs/how_to_test + README.
- Step 2 Architecture Baseline: architecture_compliance_baseline.md.
- Step 3 Test Spec: _docs/02_document/tests/ (environment,
  test-data, blackbox/performance/resilience/security/
  resource-limit tests, traceability-matrix), enum_spec_snapshot,
  expected_results/results_report.md (98 rows), plus the
  run-tests.sh + run-performance-tests.sh runners.
- Step 4 Code Testability Revision: 01-testability-refactoring/
  run dir (list-of-changes C01-C07, deferred_to_refactor,
  analysis/research_findings + refactoring_roadmap) and the 7
  child task specs AZ-448..AZ-454 under _docs/02_tasks/todo/
  plus _dependencies_table.md.
- _docs/_autodev_state.md pins the cursor at Step 4 / refactor
  Phase 4 entry so /autodev resumes cleanly.

Epic AZ-447 (UI testability gates) tracks the 7 child tasks that
will land in subsequent commits.

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

_docs/02_document/modules/src__features__dataset__DatasetPage.md

@@ -0,0 +1,69 @@
+# Module: `src/features/dataset/DatasetPage.tsx`
+
+> Compact module doc. Spec: `_docs/ui_design/README.md` (Dataset Explorer Layout) and parent suite `../../../../_docs/09_dataset_explorer.md` (API contract). Imports `CanvasEditor` from `../annotations/` — see cross-feature edge in `00_discovery.md §8`.
+
+## Purpose
+
+Owns the `/dataset` route. Read-side surface for the `Annotations` table: paginated thumbnail grid, date / class / status / objects-only / name filters, inline editing through the Annotations Tab's `CanvasEditor`, and a class-distribution chart. Mirrors the legacy `Azaion.Dataset.DatasetExplorer` window (`_docs/legacy/wpf-era.md §5`).
+
+## Public interface
+
+Default-exported page component, no props. Mounts under `/dataset` in `App.tsx`.
+
+## Internal logic
+
+- **Tabs**: `'annotations'` (grid, default) | `'editor'` (hidden until a thumbnail is double-clicked) | `'distribution'` (bar chart). State held in component.
+- **Filters**: `fromDate`, `toDate`, `statusFilter` (`AnnotationStatus`), `selectedClassNum` (from `DetectionClasses`), `objectsOnly` (boolean), `search` (400 ms debounced via `useDebounce`).
+- **Pagination**: client `page` state, server `pageSize` fixed at 20, `totalPages = ceil(totalCount / pageSize)`.
+- **Selection**: `Set<annotationId>`. Plain click replaces; Ctrl+click toggles. Validate button appears when set is non-empty.
+- **Validate**: `POST /api/annotations/dataset/bulk-status` with `{ annotationIds[], status: Validated }`.
+- **Distribution**: lazy-loaded on tab switch via `GET /api/annotations/dataset/class-distribution`.
+- **Editor tab** mounts `<CanvasEditor>` with a synthesised `Media` stub built from `editorAnnotation.mediaId` (most fields blank). Used so `CanvasEditor` can fetch the image via `/api/annotations/annotations/{id}/image`.
+
+## Dependencies
+
+- Internal: `api/client`, `useDebounce`, `useResizablePanel` (left panel 250 / 200–400), `FlightContext`, `DetectionClasses`, `ConfirmDialog` (imported but not used here — see Findings), `features/annotations/CanvasEditor`, `types/index`.
+- External: `react`, `react-i18next`.
+
+## External integrations
+
+| Endpoint | Where | Notes |
+|---|---|---|
+| `GET /api/annotations/dataset?...` | `fetchItems` | Filters: `page`, `pageSize`, `fromDate`, `toDate`, `flightId`, `status`, `classNum`, `hasDetections`, `name`. |
+| `GET /api/annotations/dataset/{id}` | `handleDoubleClick` | Loads full `AnnotationListItem` for the editor tab. |
+| `POST /api/annotations/dataset/bulk-status` | `handleValidate` | Body: `{ annotationIds, status }`. |
+| `GET /api/annotations/dataset/class-distribution` | `loadDistribution` | Class histogram. |
+| `GET /api/annotations/annotations/{id}/thumbnail` | grid tile `<img src=>` | One HTTP per visible tile. |
+| `GET /api/annotations/annotations/{id}/image` | `CanvasEditor` (delegated) | When the editor is open. |
+
+Spec contract is in parent suite `_docs/09_dataset_explorer.md`.
+
+## Findings carried into Step 4 / 6 / 8
+
+1. **No keyboard shortcuts implemented**: spec demands `1–9` (class), Enter (save), Del (delete), X (delete all), Esc (close editor), V (validate selected), Up/Down/PageUp/PageDown (navigate). Only Ctrl+click for multi-select works. The editor tab has no Save / Delete buttons either. Step 6 problem extraction.
+2. **`Refresh thumbnails` button is missing** — spec calls for a status-bar action to regenerate the thumbnail database with progress. Step 6.
+3. **No virtualisation in the grid**: spec says "virtualized grid" — current code renders all `items` returned by the page (max 20 due to `pageSize`). For larger pages performance would degrade. Today not a problem because `pageSize=20`. Step 8.
+4. **Editor tab does not Save**: opening an annotation in the editor lets the user edit `editorDetections` locally but there's no Save / Cancel control wired up. Edits are discarded when the user changes tab. Step 6.
+5. **`editorMedia` synthetic stub** — `mediaType: 1` is a magic number (`MediaType.Image = 1`); should reuse the enum import already present. Step 4.
+6. **`ConfirmDialog` imported but never used** — dead import. Step 4 cleanup.
+7. **`fetchItems` does `catch {}`** silently — same `coderule.mdc` violation as elsewhere. Step 4.
+8. **Empty-state**: when `items.length === 0` the grid renders nothing; no "No matches" message. Step 4.
+9. **`thumbnail` URL does not include a cache-buster**; if a thumbnail is regenerated server-side, the browser will keep the stale image. Step 4 / Step 8.
+10. **`isSeed` red-ring is correctly rendered**, but `isSeed` is not in `AnnotationStatus` filters — the user can't filter to seeds-only. Step 6 if intended.
+11. **Date inputs accept any `<input type="date">` string**; no validation that `fromDate ≤ toDate`. Step 4.
+12. **Status filter buttons skip status `None`** (spec lists None as one of the four buttons) — current code shows `All`, `Created`, `Edited`, `Validated`, conflating `All` with "include None". Step 4.
+13. **`selectedClassNum=0` is the "no filter" sentinel** but also a real class number (class 0 exists per `_docs/ui_design/README.md` → military vehicle). Selecting class 0 in `DetectionClasses` is indistinguishable from "no filter". Step 6.
+14. **Inherits one cross-cutting UI fix and one cross-repo parent-doc fix** (resolved with user 2026-05-10):
+    - **[STEP 4 — UI FIX]** `AnnotationStatus` values must change from UI `0/1/2` to spec `0/10/20/30/40` (`src/types/index.ts:23`). Every status filter button in this page (`null`/`null`/`Created`/`Edited`/`Validated`) currently sends a wrong integer. The "All" button is value `null` (no filter) — keep, but also expose a real "None" filter using the new `AnnotationStatus.None=0`. **PRIORITY** for Step 4. See annotations doc finding #27.
+    - **[RESOLVED 2026-05-10]** `DatasetItem.isSplit` is correct on UI; parent `../../../../_docs/09_dataset_explorer.md §1` response schema now includes it. See annotations doc finding #33.
+
+## Tests
+
+None.
+
+## Cross-doc references
+
+- Parent suite Dataset Explorer API: `../../../../_docs/09_dataset_explorer.md`
+- UI spec: `../../ui_design/README.md` (Dataset Explorer Layout, Keyboard Shortcuts).
+- Imports `CanvasEditor` from `features/annotations/` — see `00_discovery.md §8` cross-feature edge.
+- Legacy WPF reference: `../../legacy/wpf-era.md §5` (Dataset Explorer window).