[AZ-455] Decompose Step 3 — test task specs (AZ-457..AZ-482)

Adds 26 blackbox-test task specs under epic AZ-455 plus the matching
rows in _dependencies_table.md. Each task depends on AZ-456 (test
infrastructure). Advances autodev existing-code flow Step 5 → Step 6
(Implement Tests, cycle 1) ready for batch implementation.

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

_docs/02_tasks/todo/AZ-471_test_canvas_bbox.md

@@ -0,0 +1,70 @@
+# Test — Canvas Editor (Bounding-Box + Multi-Select + Zoom + Pan)
+
+**Task**: AZ-471_test_canvas_bbox
+**Name**: CanvasEditor manual draw + 8-handle resize + Ctrl+click multi-select + Ctrl+wheel zoom + Ctrl+drag pan
+**Description**: Implement the 5 blackbox tests covering the core canvas interactions: draw bbox, resize via 8 handles, multi-select via Ctrl+click, zoom-around-cursor via Ctrl+wheel, pan via Ctrl+drag.
+**Complexity**: 5 points
+**Dependencies**: AZ-456_test_infrastructure
+**Component**: 06_annotations (CanvasEditor) (Blackbox Tests)
+**Tracker**: AZ-471
+**Epic**: AZ-455
+
+## Problem
+
+The canvas editor is the SPA's most-interactive surface; canvas-pixel coordinates introduce floating-point + DPR gotchas that have caused subtle off-by-pixel regressions. The 5 scenarios pin geometry, modifier-key semantics, and viewport transformation.
+
+## Outcome
+
+- 5 scenarios pass with deterministic numeric fixtures (no `getBoundingClientRect` flakiness across viewport sizes).
+
+## Scope
+
+### Included
+
+| Scenario | Profile | Source file |
+|----------|---------|-------------|
+| FT-P-39 — manual bounding-box draw on `<CanvasEditor>` | fast + e2e | blackbox-tests.md |
+| FT-P-40 — 8-handle bbox resize | fast | blackbox-tests.md |
+| FT-P-41 — Ctrl+click multi-select on canvas | fast | blackbox-tests.md |
+| FT-P-42 — Ctrl+wheel zoom-around-cursor | fast | blackbox-tests.md |
+| FT-P-43 — Ctrl+drag pan on empty canvas | fast | blackbox-tests.md |
+
+### Excluded
+
+- Tile-split interaction (covered in 19_test_tile_split_zoom).
+- Annotation overlay membership (covered in 07_test_overlay_membership).
+- Save-on-change (covered in 05_test_annotations_endpoint).
+
+## Acceptance Criteria
+
+**AC-1: Manual draw geometry**
+Draw a bbox at `(x1,y1)→(x2,y2)`; resulting annotation carries the canonical canvas-coordinate quad. Floating-point compare within ±0.5 px tolerance.
+
+**AC-2: 8-handle resize**
+Drag each of the 8 handles independently; assert resulting bbox geometry per handle. Each handle's anchor (opposite corner / edge midpoint) is invariant during the drag.
+
+**AC-3: Ctrl+click multi-select**
+Ctrl+click on a second bbox adds it to the selection; selection set contains both bboxes (asserted via DOM rendering — selection ring style).
+
+**AC-4: Zoom-around-cursor**
+Ctrl+wheel at cursor `(cx, cy)`: the canvas pixel under `(cx, cy)` BEFORE the wheel equals the canvas pixel under `(cx, cy)` AFTER (within ±0.5 px).
+
+**AC-5: Empty-canvas pan**
+Ctrl+drag on an empty canvas region: viewport offset shifts by `(dx, dy)`; bbox positions in canvas coords are invariant.
+
+## System Under Test Boundary
+
+- System under test: `<CanvasEditor>` + its pointer/mouse handlers + the canvas-coordinate ↔ viewport transform.
+- Allowed stubs: MSW for annotation load.
+- Disallowed: stubbing the canvas component or asserting on React state. Pointer events are dispatched via RTL `user-event` (or Playwright `dispatchEvent` for e2e).
+- Expected observables per `results_report.md` rows 73-78 (Group 16).
+
+## Constraints
+
+- Use fixed-size canvas (640×480) so coordinate math is deterministic.
+
+## Risks & Mitigation
+
+**Risk 1 — DPR + retina display flakiness**
+- *Risk*: Test runner on a retina display reports different physical pixels than the e2e Docker container.
+- *Mitigation*: Playwright config forces `deviceScaleFactor: 1`; Vitest+jsdom defaults to DPR 1.