[fix] 15-D mesh-edit correctness & input (weld/indexed, outside-click, hotkeys, contrast wire)

[AlexZ005]

Roadmap #15 mesh lane, batch D (plan: cloud plans-core/pending/15-d-editmesh-correctness.md). First of D -> E -> F.

D1 — weld fix + vertex session refresh

• Weld snapshots are now INDEX-EXPANDED (trisToPositions(readTriangles())): applyMeshGeo rebuilds a NON-indexed geometry, so snapshotting the raw position attribute of a fresh INDEXED Box (24 positions / 36 indices) mangled the mesh and undo replayed the same wrong representation. The committed suite only passed because its box had been de-indexed by earlier insets.
• New refreshVertexEditSession(): rebuilds handles + InstancedMesh + wireframe overlay from the live geometry WITHOUT exit/enter (no re-lock, no selection-stash churn). applyMeshGeo reaches it via registerVertexSessionRefresher — registered at meshEdit module eval, because a dynamic import('./meshEdit') back binds a SECOND module instance under vite's ?t= HMR stamps (its editingObject is always null; caught live in this batch).
• No toNonIndexed() at enterEditMode — the live verts channel replicates attribute indices, both peers must agree on the layout; only the meshgeo commit changes representation.

D2 — outside-click deselect

A viewport miss clears the vertex multi-pick / face multi-pick; the edit session, object selection and single-handle gizmo deliberately stay.

D3 — hotkeys toggle + "?" popup + camera-fly guard

• New local pref meshEditHotkeys (default ON) + toolbar keyboard-toggle button and a "?" popover listing the bindings.
• While a session is active AND the pref is on: shortcuts.js skips bare mesh-edit keys (F also fired focusObject), and updateEditorNavigation parks W/A/S/D/Q/E fly (per-frame gate — the popup's preventDefault can't stop the fly key set). Deliberately NOT claimInput('keys'): the claim set isn't refcounted and possess/car would drop it mid-session.
• Quiz 15-D3 resolved with the user: the pref itself is the escape hatch (toggle off -> camera keys return); a dedicated "allow camera keys during edit" setting stays backlog.
• One bundled display-only row in Settings ▸ Shortcuts (E I G S B F X / W, group "Mesh edit") — registerShortcut dedupes exact keys, so a bare F row would collide.

D4 — contrast-aware edit wireframe

Wire color picked at build time from the material's relative luminance (light material -> dark #1f2937; else the existing blue). Rebuilds on every geometry swap pick up material changes incidentally.

Verification

• mesh-ops 29/29 (+7: weld on a truly INDEXED box keeps 12 tris / drops one welded key / no NaN; undo restores exactly; the session survives undo with handles rebuilt 7->8)
• mesh-edit-popup 21/21 (+12: outside-click both modes; hotkeys A/B incl. a camera-fly proof — 0.00000 moved suppressed vs 1.500 with the pref off; "?" popover; pref persists across reload)
• Regressions green: faces-toolbar, mesh-sculpt, undo, vr-face-edit, vr-face-polygon, vr-mesh-undo, collider-custom
• npm run build green; svelte-check 419/62 (the release.yml gate, unchanged)

🤖 Generated with Claude Code

[AlexZ005]

+ D5 (user report, commit 7188d48): unified vertex selection. The weld flow exposed two parallel selection models — the gizmo's selectedHandle vs the ctrl-click vertexSelection set: the gizmo stayed on a vertex that wasn't in the weld set, a multi-selection left the gizmo moving one vertex, and a gizmo-picked vertex read "0 sel".

Now ONE model (Blender-style): plain click = selection {A} + gizmo ("1 sel"); ctrl-click toggles; the anchor rides the last pick and carries the gizmo (removal promotes another member, empty parks it); a gizmo drag moves the whole selection rigidly — single drags keep the verts undo entry, multi-drags record ONE meshgeo entry (weld precedent), live replication streams the existing per-handle verts messages (no new wire types). Weld/create-face read the same set, so plain click + one ctrl-click now welds. VR untouched (isVRMode guard on the gizmo seat).

e2e: mesh-ops 35/35 (+6), mesh-edit-popup 22/22 (+1 counter check); vr-face-weld / vr-face-edit / vr-mesh-undo green; build green; 419/62 held.