Update docs for DC-1 testing, fix toolbar clipping

- Updated DESIGN.md: rendering strategy (no backing bitmap, screen-space
  grid, viewport clamping), added line snap and box tool documentation
- Updated PROGRESS.md: DC-1 testing results and fixes applied
- Updated CLAUDE.md: key conventions for rendering
- Fix toolbar overlap: use clipToBounds on canvas AndroidView to prevent
  it from drawing over the toolbar area

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -81,7 +81,10 @@ eng-pad/
 
 - Stroke points are packed as little-endian float BLOBs: `[x0,y0,x1,y1,...]`
 - All coordinates are in canonical space (300 DPI). Screen transform via `Matrix`.
-- Grid spacing: 60pt (~5 squares/inch). Grid is drawn on screen, excluded from exports.
+- Grid drawn in **screen space** with pixel-snapped positions (not canonical space) for uniform squares.
 - Pen widths: 0.38mm = 4.49pt, 0.5mm = 5.91pt (at 300 DPI).
-- Two pen sizes only, no pressure sensitivity.
+- Anti-aliasing disabled on all paint objects for crisp e-ink rendering.
+- No backing bitmap — strokes draw directly as paths.
+- Viewport: page always fills screen, pan clamped to edges, dynamic min zoom.
+- Line snap: hold pen still 1.5s to snap to straight line (60pt movement threshold).
 - Hardware palm rejection only (EMR digitizer).

DESIGN.md

@@ -181,20 +181,39 @@ The editor toolbar controls the active mode:
 | Draw     | Create strokes with the active pen size               |
 | Erase    | Touch a stroke to delete it (stroke-level eraser)     |
 | Select   | Draw a rectangle to select strokes, then move/copy/delete |
+| Box      | Drag corner-to-corner to draw rectangles              |
+
+### Line Snap
+
+When drawing in pen mode, holding the stylus still for 1.5 seconds
+activates line snap mode. The stroke is replaced with a straight line
+from the original pen-down point to the current position. Moving the
+pen continues the straight line. The snap timer is canceled if the pen
+moves more than ~5mm (60pt at 300 DPI) from the origin before the
+timer fires. This allows drawing straight lines for diagrams without
+a separate ruler tool.
 
 ## Rendering Strategy
 
 ### On-Screen
 
-1. **Completed strokes** are rendered to a backing `Bitmap`. This bitmap is
-   redrawn only when strokes change (add, delete, move).
-2. **In-progress stroke** (pen is down) is drawn directly to the canvas on
-   each `onDraw` call, on top of the backing bitmap.
-3. **Grid** is drawn as a separate pass — thin gray lines at 60pt intervals.
-4. The view `Matrix` transforms everything from canonical to screen space.
+1. **Completed strokes** are drawn directly as `Path` objects on each
+   `onDraw` call. No backing bitmap — direct path rendering avoids the
+   resolution loss that caused blurry strokes on e-ink displays.
+2. **In-progress stroke** (pen is down) is drawn on top of completed strokes.
+3. **Grid** is drawn in screen pixel space (not canonical space) with
+   pixel-snapped line positions. This ensures perfectly uniform square
+   spacing regardless of zoom level. Grid uses 1px screen-space lines.
+4. **Strokes** are drawn in canonical space via the view `Matrix`.
+   Anti-aliasing is disabled on all paint objects for crisp e-ink rendering.
 
-This approach means `onDraw` is fast for the common case (pen moving):
-draw the cached bitmap + one active path + grid.
+### Viewport
+
+The page always fills the entire visible canvas area:
+- Minimum zoom is computed dynamically so the page never appears smaller
+  than the viewport in either dimension.
+- Pan is clamped so page edges stay at or beyond viewport edges.
+- Background is white to eliminate any visible non-page area.
 
 ### PDF Export
 
@@ -220,6 +239,7 @@ Command pattern with a depth limit of 50:
 | `DeleteStrokeAction` | Delete stroke     | Re-insert stroke   |
 | `MoveStrokesAction`  | Offset points     | Offset back        |
 | `DeleteMultipleAction`| Delete strokes   | Re-insert strokes  |
+| `CopyStrokesAction`  | Duplicate strokes | Delete copies      |
 
 The `UndoManager` maintains two stacks. Performing a new action clears the
 redo stack. Each action also persists or deletes from Room as part of
@@ -244,7 +264,6 @@ Stroke-level eraser (not pixel-level):
 2. Hit test: check stroke bounding box first (fast reject), then check
    point-by-point distance (threshold: ~42 canonical points / ~3.5mm).
 3. Hit strokes are deleted immediately (with undo support).
-4. Backing bitmap is rebuilt after deletion.
 
 ## E-ink Considerations
 

PROGRESS.md

@@ -44,9 +44,10 @@ See PROJECT_PLAN.md for the full step list.
 ### Phase 3: Canvas — Basic Drawing (2026-03-24)
 
 - [x] 3.1–3.4: PadCanvasView — stylus input with historical points, Path/Paint
-  stroke rendering, backing bitmap at 1/4 resolution, 60pt grid, Matrix
-  coordinate transform (canonical ↔ screen)
-- [x] 3.5: CanvasState — tool enum (PEN_FINE, PEN_MEDIUM, ERASER, SELECT),
+  stroke rendering, direct path drawing (no backing bitmap), 60pt grid
+  drawn in screen space with pixel-snapped positions, Matrix coordinate
+  transform (canonical ↔ screen)
+- [x] 3.5: CanvasState — tool enum (PEN_FINE, PEN_MEDIUM, ERASER, SELECT, BOX),
   zoom/pan state, pen width constants (4.49pt, 5.91pt)
 - [x] 3.6: EditorViewModel — loads strokes from Room, saves on completion
 - [x] 3.7: EditorScreen + Toolbar — Compose wrapper with AndroidView,
@@ -58,18 +59,19 @@ See PROJECT_PLAN.md for the full step list.
 
 ### Phase 4: Zoom and Pan (2026-03-24)
 
-- [x] 4.1: ScaleGestureDetector with focal-point zoom (0.5×–4×)
-- [x] 4.2: Finger drag for pan with multi-pointer tracking (handles finger
-  swaps during pinch gestures)
+- [x] 4.1: ScaleGestureDetector with focal-point zoom (dynamic min–4×)
+- [x] 4.2: Finger drag for pan with multi-pointer tracking, pan clamped
+  so page always fills viewport
 - [x] 4.3: Input routing by tool type already in place from Phase 3
 - Zoom/pan state managed locally in PadCanvasView for responsiveness,
   synced to ViewModel on gesture end
+- Minimum zoom computed dynamically from page/view dimensions
 
 ### Phase 5: Eraser (2026-03-24)
 
 - [x] 5.1–5.3: Stroke-level eraser with bounding box hit test (42pt radius),
   processes historical touch points for thorough erasing, deletes from
-  view + Room DB, rebuilds backing bitmap
+  view + Room DB
 
 ### Phase 6: Undo/Redo (2026-03-24)
 
@@ -110,12 +112,29 @@ See PROJECT_PLAN.md for the full step list.
 - [x] 10.3: Empty states and delete confirmations already in place from Phase 2
 - [ ] 10.4: Performance profiling — requires on-device testing
 
+### On-Device Testing — Daylight DC-1 (2026-03-24)
+
+Tested on DC-1, identified and fixed rendering issues:
+
+- **Grid**: original grid drawn in canonical space had uneven spacing due to
+  sub-pixel positioning when scaled. Fixed by drawing grid in screen space
+  with pixel-snapped line positions. Now uniform squares.
+- **Stroke quality**: original backing bitmap at 1/4 resolution caused blurry
+  strokes. Fixed by removing backing bitmap entirely and drawing paths directly.
+  Anti-aliasing disabled on all paint for crisp e-ink lines.
+- **Viewport**: dark gray background was visible around page edges. Fixed by
+  clamping pan to page edges, computing dynamic min zoom, and white background.
+- **Box tool**: works correctly on device.
+- **PDF export**: correctly elides grid — confirmed on device.
+- **Line snap**: increased threshold to 60pt (~5mm) and switched to max-distance
+  tracking to handle EMR stylus hand tremor.
+
 ## Status
 
 All implementation phases complete. Remaining work:
-- On-device testing on Supernote Manta and Daylight DC-1
-- Performance profiling (stroke rendering, page load times)
-- Manual verification of PDF export fidelity
+- Test on Supernote Manta
+- Verify line snap behavior on device
+- Performance profiling with heavily annotated pages
 
 ## Decisions & Deviations
 

app/src/main/kotlin/net/metacircular/engpad/ui/editor/EditorScreen.kt

@@ -3,6 +3,7 @@ package net.metacircular.engpad.ui.editor
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.ui.draw.clipToBounds
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
@@ -114,8 +115,9 @@ fun EditorScreen(
         AndroidView(
             factory = { canvasView },
             modifier = Modifier
-                .fillMaxSize()
-                .weight(1f),
+                .fillMaxWidth()
+                .weight(1f)
+                .clipToBounds(),
         )
     }
 }