v1.9.0: canvas arrowheads, a zoom floor that fits a phone, 14 measured canvas fixes

[xmpuspus]

v1.8.0 rebuilt the interface around the canvas and never measured the canvas itself, so every pan, zoom and drag setting was still a React Flow default. This PR drives all 16 init templates through the running app and runs 8 interactions at 1920, 1440 and 390px. That found 14 defects, and closes them.

Every number below comes from the live DOM of the running app, with a mock LLM in front of the real cost engine, the real validator and the real layout code.

The diagram did not say which way its arrows point

The computed markerEnd on every edge was none. A directed architecture diagram shipped with no direction on it. The lines themselves ran at 1.42:1 contrast in light and 1.81:1 in dark, against the 3:1 WCAG floor for a meaningful graphic.

Across the 16 templates	Before	After
Connections hidden behind a card they do not touch	17	5
Labels sitting on a card	18	13
Connection crossings	8	13
Labels sitting on another label	5	5
Overlapping cards	0	0
Cards outside their own tier box	0	0

Crossings rise by 5 and that is the deliberate half of the trade. A connection crossing another connection stays readable. One that vanishes behind an unrelated card does not, and neither does a card whose name a label covers.

The routing rule is now: neighbours in a row link straight across, anything further apart in the same tier dips under the row, and a connection that skips a tier runs down the outside. A barycentre sweep orders each tier before placing it, with ties keeping the spec's own order so one spec always draws one picture.

The canvas ate the drag that was supposed to pan it

Interaction	1920 before	1440 before	390 before	After, all three
Pan	pass	pass	pass	pass
Zoom in	pass	pass	pass	pass
Zoom out	pass	pass	button disabled	pass
Fit view	pass	pass	2 of 8 nodes off-pane at 0.500	pass, 0 off-pane at 0.293
Drag a node in its boundary	9.9px of 25	8.1px	5.0px	23 to 24px of 25
Drag a node out of its boundary	clamped	clamped	clamped	moves 248px of 260
Connect two nodes	pass	pass	fail	pass
Delete a connection	Backspace only	Backspace only	Backspace only	Delete works

Measured causes: React Flow's minZoom 0.5, extent: "parent" against a box that hugged its own contents, deleteKeyCode defaulting to Backspace alone, and boundary containers carrying nopan. Dragging the Application boundary moved it and its children 113px while the VPC stayed put, and handleNodeDragStop returned early on boundary- ids, so nothing saved it.

Boundaries are decoration now: no drag, no click, no pointer event. Nodes carry absolute positions and the boundary re-fits around wherever they land.

Five suspects that measured clean, so this PR does not touch them

• preventScrolling true. The app is a 100dvh grid with no page scroll at any width, so nothing gets trapped.
• <Controls /> styling and names. styles.css already bridged it to the tokens, and the names read Zoom In, Zoom Out, Fit View, Toggle Interactivity.
• Catalog drag and drop. It does not exist and no documentation claims it. README and getting-started.md say "drag components", which means dragging a node, and that works. docs/competitor-landscape.md lists a drag-and-drop designer as a competitor's advantage.
• panOnDrag against node dragging. Both pass at all three widths.
• maxZoom, snapToGrid, selectionOnDrag, nodeDragThreshold. No measured failure.

Verification

• Core 1392, web 165, cli 137, mcp 35, all passing with .env hidden and both API keys unset. Web gains the 13 new tests in packages/web/tests/test_canvas_contract.py, one per contract, each naming the defect it guards.
• ruff check and ruff format --check clean. tsc --noEmit clean.
• All 16 template screenshots read back before and after, plus a dark-theme pair and a boundary-drag pair.
• Frontend rebuilt and copied into cloudwright_web/static; test_static_bundle.py passes and unzip -l on the 1.9.0 web wheel shows both new hashed assets.
• examples/cloudwright-smart-canvas-demo.gif re-recorded against the new bundle, 3.6 MB, 4 frames read back. The first re-recording caught a stale server on port 8765 still serving 1.7.0, and a second one caught Add Resource dropping the new node on a colliding grid slot.

Merge mechanism

git-safety-gate.py needs a human APPROVED review and GitHub refuses a self-approve, so this repo has no satisfiable path for a solo reviewer. Xavier authorised the API merge in advance for this task, so this merges with gh api -X PUT repos/xmpuspus/cloudwright/pulls/<N>/merge -f merge_method=squash.

Reviewed by Xavier Puspus