Snap — vector geometry

Placeholder. This page reserves the vector member of the snap family; its details and implementation are deferred with the vector-edit implementation. The mode itself — and the summary of what its snapping must cover — is now specified in vector-edit.md; this page will hold the source/threshold/chrome details when they are authored.

Vector snapping is a distinct system, not a variant of the rect snaps: the agents are points (dragged anchors, curve control points, pen-tool candidates), and the targets are the shape's own geometry — other anchors, segment midpoints/intersections, the shape's frame — plus the usual neighborhood. That changes every layer the rect family settled: the session freezes point sets instead of nine-point rects, thresholds capture point-to-point, and the chrome marks points and connecting hairlines rather than edge rules or gap labels. The pipeline placement does not change: it is interpretation (SNAP-1 applies unchanged), gated by the same geometry toggle and disable modifier.

Doctrine sources, when this gets specified: the web's vector content edit mode (event-target.cem-vector.reducer.ts, the path tool + curve/translate-vector-controls gestures) and @grida/svg-editor's core/vector-edit/; the engine seam is cmath's point-anchor snapping (snapToPoints / by_points in @grida/cmath/_snap), which math2::snap does not yet port — that port is the named engine gap in snap.md's Engine notes.

Contracts will be authored with the feature (reserved prefix: VSNAP-*); until then the deferral is tracked in snap.md's deferred list.