# Interaction Scope *The authoritative interaction state machine ("the spine") — one scope describes "what the user is currently doing".* Applies to: `packages/editor/src/lib/interaction/**`, `packages/editor/src/store/use-interaction-scope.ts`. Before this, "what is the user doing right now?" was re-derived from 7+ independent `useEditor` flags (`movingNode`, `placementDragMode`, `activeHandleDrag`, `curvingWall`, `curvingFence`, `editingHole`, `movingWallEndpoint`, `movingFenceEndpoint`). Every overlay and pick site re-derived its behaviour from a different subset, so the flags could drift into illegal combinations (moving + curving at once; a stale `movingNode` after a drag ended). The scope collapses them into one discriminated union, making those combinations unrepresentable: a scope is exactly one interaction at a time, and `idle` carries no payload. --- ## The model `InteractionScope` (`lib/interaction/scope.ts`) is a discriminated union on `kind`: | `kind` | Payload | What | |---|---|---| | `idle` | — | Nothing in flight. The only state where selection/hover picking is meaningful. | | `placing` | `nodeId`, `nodeType`, `view`, `pressDrag` | Placing a fresh node (catalog/preset/build tool). `pressDrag` = gizmo press-drag (commit on release) vs click-to-place. | | `moving` | `nodeId`, `nodeType`, `view` | Moving an existing node. | | `handle-drag` | `nodeId`, `handle` | Dragging a resize/translate/rotate handle of a selected node. | | `drafting` | `tool` | Click-to-click drafting of a polyline/polygon kind (wall/fence/slab/…). | | `reshaping` | `nodeId`, `reshape`, `holeIndex?` | Reshaping a selected node's geometry. `reshape` is `curve \| hole \| endpoint \| boundary`. | | `box-select` | — | Marquee selection drag. | | `painting` | — | Material paint application. | `reshaping` groups endpoint/curve/hole/boundary edits as sub-states of one scope (rather than four sibling kinds) — there is one node and one in-flight reshape, so "curving and hole-editing at once" stays unrepresentable. `view` is `'2d' | '3d'`. ### Helpers - `isIdle(scope)` / `isActive(scope)` — `idle` vs anything else (`ActiveInteractionScope`). - `scopeNodeId(scope)` — the node a scope acts on, or `null`. `drafting`/`box-select`/`painting`/`idle` target no single existing node. - `selectionEnabled(scope)` — true only while `idle`. During any active interaction the pointer belongs to that interaction's body, not to selecting a different object; the picking choke point must not route a hover/click to selection while this is false. --- ## The store contract `useInteractionScope` (default export of `store/use-interaction-scope.ts`) is the single owner. Exactly one scope at a time; the only writable shape is `InteractionScope`, so there is no setter that can leave a half-state. | Method | Behaviour | |---|---| | `begin(scope: ActiveInteractionScope)` | Enter an interaction. If one is already active it is replaced (single owner, no producer races). | | `update(patch)` | Patch the current scope's payload. **Ignored when idle, and ignored when the patch's `kind` differs from the active kind** — payload updates must not change which interaction is running (use `begin` for that). | | `end()` | Return to idle atomically. Both commit and cancel call it; the write-vs-revert distinction lives in the interaction body, not here. | | `endIf(match)` | Return to idle only if the active scope satisfies `match`. | **Atomic-end invariant.** `end()` sets the scope back to `IDLE_SCOPE` in one write — no interaction payload can leak past the end of its interaction (no stale `nodeId`, no half-cleared flags). `endIf` exists because scope is currently driven from independent legacy flag clears (below): clearing one flag (e.g. a fence curve) must not stomp an unrelated active scope (e.g. a wall move), so the clear only ends the scope if it owns it. --- ## Hot-set: what is raycast-eligible during an interaction `lib/interaction/hot-set.ts` answers "which scene objects can the active interaction target?" It is never hand-authored per interaction — it falls out of the node's `asset.attachTo` plus whether a candidate exposes a top surface. `attachClassOf(attachTo)` collapses attachment to three `AttachClass` values: - `wall` — `attachTo` of `wall` or `wall-side`. - `ceiling` — `attachTo` of `ceiling`. - `surface` — everything else ("floor item" really means *surface-resting*: rests on the floor **or** any host's top surface). `isPickableForAttach(placed, candidate)` decides, for a node of attach class `placed`, whether a `HotSetCandidate` is a valid host/surface: - `wall` → only `wall` candidates. - `ceiling` → only `ceiling` candidates. - `surface` → the floor (`isFloorLike`), or any candidate that `exposesTop` (registry `capabilities.surfaces.top`) — but **never** a ceiling-mounted host. A floor lamp must not land on a ceiling fan; a ceiling fan's `attachClass` is `ceiling` and is excluded as a host top (Track E). `isCandidateInHotSet(scope, placedAttachClass, candidate)` lifts this to a whole scope: - `idle` → `true` (selection/phase filtering stays in the selection manager; the hot-set only narrows what an *active* interaction can target). - `placing` / `moving` → `isPickableForAttach`, or `true` when `placedAttachClass` is `null`. - every other active scope → `false`: nothing in the scene is a placement target, so the interaction body's own raycast owns the pointer. `HotSetCandidate` (`type`, `isFloorLike`, `exposesTop`, `attachClass`) is derived from the candidate node + its registry definition by the caller, keeping this module pure and unit-testable without the scene or registry. --- ## Overlay policy: the scope matrix `resolveOverlayPolicy(scope)` (`lib/interaction/overlay-policy.ts`) returns the "Sims-light" overlay behaviour: default-off, opt-in for the active action. During any non-idle scope, scene objects stay visible but non-pickable, and DOM/HUD overlays step back differentiated by how distracting they are. | Overlay | Idle | Any active scope | |---|---|---| | Zone labels | shown | hidden (not a primary editing concern) | | Context badges (hover name pills) | shown | faded + `pointer-events: none` | | Conflicting controls (other objects' handles, floating action menu) | shown | hidden | | Scene objects pickable | yes | no (the hot-set owns targeting; context preserved, can't grab the wrong thing) | | Active affordances (ghost, snap guides, dimension labels, the active handle) | shown | shown | | Contextual control HUD interactive | yes | yes (it *is* the active interaction's own controls — exempt from the pointer-events step-back) | The policy is binary (`IDLE_POLICY` vs `ACTIVE_POLICY`) keyed on `isActive`. --- ## Snapping mode & modifiers (the unified model) Snapping is a persistent, **per-context**, always-visible mode — not a held-Shift bypass. The active scope selects the *context*; the context's current mode selects the *behaviour*. There is no per-kind snapping switch. - **Contexts** (`lib/snapping-mode.ts`, `SNAP_PROFILES`): `wall` (grid/lines/angles/off, default grid), `item` (lines/grid/off, default lines), `polygon` (grid/lines/off, default grid). A kind opts in by declaring `NodeDefinition.snapProfile` (`'item' | 'structural'`); `snapContextOf(scope × profile)` maps it — `structural` while **setting direction** (drafting / endpoint drag) → `wall` (angle-bearing), `structural` otherwise (translate / curve) → `polygon` (no angle), `item` → `item`. No profile → no chip. - **Single read path.** Tools read `isGridSnapActive()` / `isMagneticSnapActive()` / `isAngleSnapActive()` (`store/use-editor`); the grid step is `useEditor.getState().gridSnapStep` gated on `isGridSnapActive()`. These resolve the mode from the scope via `getActiveSnapContext()` → `snappingModeByContext[context]`. - **Modifiers.** Shift (tap) cycles the mode for the active context; Ctrl (tap) cycles the grid step; Alt (hold) is force / free (raw cursor + commit past invalid; for MEP runs, the vertical-riser carve-out). Shift is **not** a snap bypass and Alt is **not** a toggle. - **The chip is the scope's.** The contextual HUD shows the active context's mode and is the only place the mode is cycled — so a tool that wants its chip must run inside a scope whose `snapContextOf` resolves (a build tool, `drafting`, `placing`/`moving`, or `reshaping`). **Known-legacy (migrate on touch).** A few bespoke movers predate this model and still read `event.shiftKey` as a snap bypass with hardcoded steps: the MEP move/endpoint tools (`packages/nodes/src/{duct-segment,pipe-segment,liquid-line,lineset,duct-fitting}/{move-tool,selection}.tsx`), tracked in `plans/editor-placement-interaction-overhaul.md`. A PR that **touches** one must migrate it to the model above, not extend the legacy path. Note: opening a `moving` scope from a bespoke mover is **not** the migration — `useMovingNode()` reads the scope, so `tool-manager` re-mounts the generic `MoveRegistryNodeTool` alongside it (the dual-path FPS/teleport bug). Resolve the mode without a global `moving`/`reshaping` scope; see the plan's dual-path note. --- ## Migration status (strangler fig) The scope is the target source of truth, but the legacy `useEditor` flags still exist as a mirror and are being retired reader-by-reader. Today the scope is **driven from** the central `useEditor` setters — `setMovingNode`, `setActiveHandleDrag`, `setCurvingWall`/`setCurvingFence`, `setEditingHole`, `setMovingWallEndpoint`/`setMovingFenceEndpoint`, `setMode` (for painting) — and from the box-select tool. Each setter calls `begin`/`end` (and `endIf`, so an independent flag clear can't stomp an unrelated scope) to keep the scope in sync. **Contributors:** - Add a new interaction by calling `begin(...)` / `end()` on `useInteractionScope`, **not** by adding a new `useEditor` flag. - Read "what the user is doing" through the scope and its helpers (`isActive`, `scopeNodeId`, `selectionEnabled`), not by recombining flags. New readers should consume the scope so the legacy flag can be deleted once it has no readers. - Add a new attach behaviour by setting `attachTo` on the asset — the hot-set follows with zero per-kind wiring. --- ## Rules - **One owner, one scope.** Only `useInteractionScope` writes the scope, and only via `begin`/`update`/`end`/`endIf`. Never reconstruct interaction state from a private combination of flags. - **`end` is atomic and payload-free.** Never leave a `nodeId`/payload behind on idle; commit-vs-revert logic belongs in the interaction body before `end`. - **`update` cannot change `kind`.** Switching interactions is a `begin`, not a patch. - **Hot-set and overlay policy are pure derivations of the scope** (and, for the hot-set, the candidate metadata). Don't branch overlay/picking behaviour on legacy flags — branch on the scope. - **Don't add new `useEditor` interaction flags.** New interactions go through the scope. - **Snapping is mode-driven.** Read snap state through `isGridSnapActive` / `isMagneticSnapActive` / `isAngleSnapActive` (gate any grid step on the first); never bypass snapping via `event.shiftKey` / `modifiers.shiftKey`, and never hardcode an ungated grid step. Snappable kinds declare `snapProfile`. Shift cycles the mode; Alt is force/free.