Draggable and resizable nodes, persisted to a sidecar — no database

[lex00]

The graph has pan/zoom (ensureZoomControls, web/app.js:1791) but no way to move or resize a node — positions are dagre's, take them or leave them. For screenshots, docs, and just living with a graph daily, hand-placement matters: dagre is a good first draft and a bad final layout.

Scope (deliberately client-first, no database):

1. Drag — pointer-drag a node card (or a containment box) applies a transform delta to its data-node-id group; edges connected to it re-anchor (straight-line fallback is acceptable for a dragged node; full spline re-route is not required).
2. Resize — a corner handle on containment boxes and (later) cards; boxes matter more, cards may be v2.
3. Persistence, no DB — a layout sidecar keyed by node id, two tiers:
   • localStorage per project+lens (free, survives reload, per-browser);
   • optional POST /api/layout writing .behold/layout.json next to the project (shareable, versionable, still not a database). Server applies stored deltas at render time so exports and snapshots honor them.
4. Reset — a "relayout" action that clears the sidecar for the current lens.

Deltas are keyed by stable node id + lens + zoom tier, and a stored delta for a node that no longer exists is silently dropped — the graph is chant's, the layout is yours, and the source of truth ordering never inverts.

Deferral note: this is consciously behind icons/render-coverage in priority. Filing now so the shape (deltas-over-dagre, sidecar-not-DB) is agreed before anyone builds the wrong version.

Acceptance

• Drag a card, reload: it stays put (localStorage tier). Export SVG: it stays put (server tier, if enabled).
• Delete the node from the estate: the stale delta is ignored without error.
• ?logical=1 and the plain graph keep independent layouts.

[lex00]

Follow-up note on the sidecar and .gitignore (from #257, which closes this):

.behold/layout.json is per-user state and should be gitignored in served projects — .gitignore line .behold/. That is the distinction from .behold.json, which is project config (the tier axis) and belongs in the repo: one describes what the project is, the other describes how one person likes to look at it. The README ("The hand-layout sidecar") and the docs site both carry that recommendation now.

Committing it is a legitimate choice, just an explicit one: check .behold/layout.json in when you actually want a reviewed, shared arrangement (a diagram in a runbook, a screenshot everyone reproduces), and accept that a layout conflict is then a merge conflict like any other. behold does not care either way — it reads whatever is on disk, and merges it under whatever this browser has in localStorage, so a committed layout never overrides a placement you can see on your own screen.

No example project's .gitignore was touched by #257 — that is the served project's call, not behold's.