Settle camera + simulation presets: fix the first-load feel

[aaltshuler]

Problem (measured)

Storybook made it obvious: every fresh force-layout graph renders tiny and jittery. Two mechanisms, quantified on an 800-node clustered protocol:

1. Distant blob — fitViewOnFirstData frames the seed ring; the simulation then contracts the graph to 5–17% viewport fill across the entire parameter space (12-combo sweep; physics cannot fix this, only the camera can).
2. Endless jitter — the engine's default cooling (decay 5000, friction 0.85) never reaches visible stillness inside 20s. A damped profile (friction 0.6, decay 1000) is visually still in ~5s with a clean exponential cooldown.

Fix

• Settle camera — fitViewOnSettle: 'follow' (default) | 'once' | false. 'follow' keeps the settling graph framed with periodic animated refits riding the engine frame fan-out (frame-counted: no timers, no rAF of its own — it dies with the frames it rides, honoring the quiescence invariant), plus one final fit at first quiescence. Any user camera input (pointer/wheel on the container, or any public camera call) cancels it. Fixed layouts never arm.
• Simulation presets — simulation accepts 'calm' | 'spread' | 'tight' | 'lively' alongside a full config; SIMULATION_PRESETS and resolveSimulation exported. Values chosen by measured time-to-stillness, not vibes.
• Default changed — omitted simulation now resolves to 'calm'; the previous engine-default feel is one prop away (simulation="lively").

Result (live, same fixture)

	before	after
viewport fill at settle	0.07 × 0.12	0.50 × 0.80
visible stillness	never (>20s)	~5s

Tests

Nine new pinning tests (settle-camera.test.ts): default-calm config reaches the engine, preset identity no-ops, follow cadence + quiescence finale + post-settle silence, 'once'/false modes, frame cap, user-camera cancellation, fixed-layout never arms. One existing assertion updated (sim-controls): the mount replay now legitimately carries the default simulation config. Full check green: 1,794 tests.

🤖 Generated with Claude Code

https://claude.ai/code/session_018SeFxK217ZrHSERqK6kjcb

Greptile Summary

This PR improves first-load force-layout behavior by adding a settle-aware camera mode and named simulation presets, with calm simulation behavior as the new default.

• Adds periodic and final settle-camera fitting with cancellation on explicit camera input.
• Adds and exports simulation presets and preset resolution.
• Exposes the settle-camera option through the React binding.
• Adds regression coverage for settle modes, cancellation, and simulation preset propagation.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
packages/core/src/instance.ts	Implements settle-camera lifecycle and simulation preset resolution; the previously reported restored-camera overwrite is now addressed on both restore completion paths.
packages/core/src/types.ts	Defines the simulation preset names, immutable preset configurations, resolver, and widened host-update input.
packages/react/src/Graph.tsx	Exposes the construction-time settle-camera option and forwards widened simulation inputs to the core instance.
packages/core/test/settle-camera.test.ts	Pins settle cadence, quiescence behavior, cancellation paths, fixed-layout behavior, and simulation preset propagation.

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