[hsliuustc0106]

Summary

Adds a repeatable unit-test baseline for the canvas interaction surface and for src/backend/rules.ts derivation, so later refactors (#174, #175) can fail on regressions. Product behavior is unchanged.

Canvas selection, drag authoring, connection drops, node placement, keyboard actions, and image/video/audio/text generation submission were inline in CanvasWorkspace. Those decisions now live in pure helpers (workspaceInteraction.ts, generationSettings.ts) that the workspace calls. The helpers are what the new tests exercise.

Coverage

• Selection: flow select-changes merge in place; select-all skips folded stack members.
• Dragging: click-slop and cancelled gestures author nothing; a real drag is one undo step; a resize keeps its compensating position.
• Connections: unfinished drops open the creation menu only after leaving the handle, and only on the pane or an unlocked group. New nodes sit on the dropped port, then inside the group.
• History and shortcuts: undo/redo, reorder, paste, group, import, and arrow nudges map to the existing commands. A nudge is one undo step.
• Generation submission: service and text requests, context-only inputs, audio run count, voice ids, and missing pinned metadata.
• Import/export: a placed node, its reference edge, and its prompt survive a .canvas archive round trip.
• Rules derivation: model labels and lookup, voice ids, music/speech normalization, model-change cleanup, reference rejection, video mode and aspect derivation, submission blockers, and reference budgets (byte dedup, counts, agent images, continuation clips).

New files are picked up by the existing CI step npm test (node --test tests/*.test.ts). No workflow change.

Validation

Run:

• node --test tests/canvasInteraction.test.ts tests/rulesDerivation.test.ts
• npm test — 601 passed
• npx tsc --noEmit
• npm run check:i18n — 2864 keys, 168 Chinese source lines (legacy model names moved with getNodeGenerationSettings; total unchanged)

Not run:

• npm run build (Vite production bundle)
• python -m pytest
• isolated browser workflows
• real model or media generation

Intentional gaps

• [refactor] Split the CanvasWorkspace mega-component #174 is not started. React Flow DOM guards (focus, elementFromPoint, marquee) stay in CanvasWorkspace; tests cover the decisions those guards call.
• [refactor] Remove duplicated business rules between frontend and backend #175 is not started. Frontend and Python rules are still separate. Parameter round-trip through CreationProjection stays covered by the existing tests/creationParameters.test.ts.

Fixes #172