Interaction

The Interaction capability answers how user input becomes semantic canvas behavior. It sits above the Renderer Runtime and consumes backend-neutral Input and Hit Results. Stable Document changes still go through Command/Kernel, while stable Selection and Viewport changes still go through Session.

Current delivery

Layer	Package	Responsibility
Value contract	@nodebraid/interaction-api	Immutable Node Drag, Viewport Pan, Box Selection, and Connection Preview Projections
Port capability	@nodebraid/plugin-port	Node/domain Contributions resolved into revision-bound Port Snapshots
Runtime behavior	@nodebraid/plugin-interaction	Selection, Box Selection, Delete Selection, Drag, Pan, Zoom, and Port-aware/node-level Connection
Duplicate behavior	@nodebraid/plugin-duplicate-selection	Independent Duplicate Command, ID materialization, subgraph copy, and Ctrl/Cmd+D Binding
Clipboard behavior	@nodebraid/plugin-clipboard	Copy/Paste Commands with application-owned codec/transport and Ctrl/Cmd+C / Ctrl/Cmd+V Bindings
Projection adapter	@nodebraid/plugin-renderer	Exclusive Interaction Projection Binding and Renderer synchronization
Reference backend	@nodebraid/renderer-svg	Preview on real SVG geometry with aligned Hit/Input coordinates

Renderer Input + Hit Result
            │
            ▼
Interaction Runtime
    ├── Preview ─────────▶ Interaction Projection Binding
    ├── Selection/Viewport ▶ Session Service
    └── final Node moves ─▶ Move Nodes Command ─▶ Kernel

Behavioral boundaries

• Pointer move updates only the Projection; it does not continuously write Kernel or Session.
• A primary-pointer drag from empty Canvas space creates a World Rect Box Selection. Pointerup evaluates current Node geometry and updates Session without a Transaction or History entry.
• Node Drag executes interaction.nodes.move once on pointerup. One Transaction naturally creates at most one History Entry.
• Mouse Connection uses Renderer-owned Node-level Anchors, an application Edge materializer, and one interaction.edge.create Transaction.
• When the Renderer owns Focus and no Active Gesture exists, Delete executes interaction.selection.delete: explicit and incident Edges are removed before selected Nodes, naturally forming one undoable and redoable History Entry.
• The independent Duplicate Selection Plugin executes selection.duplicate over the selected-Node induced subgraph. The application provides only a complete ID mapping, while Ctrl/Cmd+D reaches the same Command through an Interaction Shortcut Binding.
• The Clipboard Plugin reuses the same subgraph semantics through @nodebraid/canvas-fragment. Copy captures one committed Fragment; Paste materializes it in one Transaction and then updates Selection. The application explicitly owns the text codec, navigator.clipboard Adapter, and opaque data rules.
• Middle button or Space+primary can establish Pan. Wheel Zoom is anchored to a Screen Point and bounded by explicit configuration.
• One Activation owns one Gesture Pointer. Additional Pointers, Wheel during a Gesture, pointer cancellation, lost capture, and stale evidence all have explicit semantics and diagnostics.
• Dependency loss or Plugin unload stops input, clears Preview, releases Capture, clears local state, and unregisters the Command. Recovery creates a fresh idle Activation.

Non-goals

The first Clipboard version excludes Serialized Document, Persistence, cross-version text promises, HTML/image formats, rich text, and a generic JSON codec. Existing Connection, Box Selection, and Delete Selection non-goals remain unchanged. Pinch/touch tools, HTML overlays, text editing, collaboration presence, product UI, and a generic Tool Registry also remain out of scope.

Verification

The successful path composes the real Plugin Host, Kernel, Command, Session, Renderer, History, and SVG Provider in Chromium. Structural, recovery, and cleanup faults are injected only through public seams; a fake Renderer does not certify successful Selection, Drag, Pan, Zoom, or Capture behavior.