feat(addon): add com.basis.addon.snapcontrols package

[towneh]

Summary

Adds a new addon package, com.basis.addon.snapcontrols, with a small set of components for building things that snap between positions — knobs, levers, switches, and so on. The idea is to drop a few markers into a scene and have an object click between them when you grab it.

What's in the box:

• BasisSnapPathInteractable — the abstract base. Give it a list of markers (transforms); when grabbed it tracks your hand or laser, finds the marker you're closest to, and tweens itself into place. Fires OnSnapIndexChanged whenever it moves to a new one.
• BasisRotarySnapInteractable — the concrete subclass for rotary motion. Lay the markers along an arc and the object swings between them around a pivot, rotating to match. The swing axis is worked out from where you put the markers so you don't have to align anything by hand.
• BasisActivationTarget — a little companion you stick on a marker. Flips GameObjects on/off (or fires UnityEvents) whenever that marker becomes the active one. Handy for "the lamp lights up when the dial points at it" type setups.
• BasisRotarySnapMarkerTint — paints a marker in a different material while a snap interactable is sitting on it. Can listen to multiple sources (e.g. a clock's hour and minute hands), and the most recent one wins when they overlap.
• Sample scene "Rotational Snap Example" — a throw lever opening a swing door, a rotary selector picking which of three sliding doors opens, and a flip switch on a wall. Importable from the Package Manager's Samples panel.

The asmdef autoreferences Basis Framework, BasisSDK, BasisCommon, and BasisDebug.

Required checks

All boxes below must be ticked before this PR can merge. If a check is genuinely N/A, tick it anyway and explain under Notes.

• Tested — I built and ran this locally. The change works in the editor and (where relevant) in a built player.
• Transform access is combined and limited — In hot paths, transform reads/writes go through TransformAccessArray or are otherwise batched. I have not added per-frame transform.position / transform.rotation / transform.localPosition calls inside loops. Whenever I need both position and rotation, I use the combined APIs — SetPositionAndRotation / SetLocalPositionAndRotation for writes, GetPositionAndRotation / GetLocalPositionAndRotation for reads — instead of two separate property accesses; the combined call does one local-to-world matrix traversal instead of two.
• Addressables used for asset/memory loading — Any new asset loads go through Addressables. No new Resources.Load, no direct asset references that pull large content into memory on scene load.
• No new GetComponent / AddComponent where avoidable — Where unavoidable, the result is cached on a field, and any GetComponent<T> is replaced with TryGetComponent<T>(out var x) — bare GetComponent will be denied. TryGetComponent is the modern API (Unity 2019.2+) and skips the Editor-only GC allocation GetComponent causes when a component is missing: Unity wraps the null return in a managed "fake null" object so its overloaded == operator can still detect destroyed C++ objects, and constructing that wrapper allocates; TryGetComponent returns a bool plus out parameter and never builds the wrapper. None of these calls run inside Update, LateUpdate, FixedUpdate, jobs, or other per-frame code paths.
• Per-frame work is scheduled through BasisEventDriver — Any new per-frame work hooks into BasisEventDriver rather than adding standalone Update / LateUpdate / FixedUpdate callbacks on a MonoBehaviour.
• Considered jobification — I asked whether this work can be moved to a Unity Job (Burst-compiled where possible). If it can, it is. If it cannot, the reason is in Notes.
• No needless { get; set; } properties or access lockdowns — Public fields are fine; Basis is meant to be read and modified freely, so don't wall things off private/internal without a real reason. Don't wrap a field in { get; set; } when the accessors do nothing — property accessors have a real performance cost vs direct field access, and the lead maintainer prefers plain fields (or a method / setter-only property when only the setter needs logic) over a noop-getter pair. For .Instance singletons, callers reassigning Type.Instance is allowed; if that would break your code, log a warning or throw — don't block the assignment. Locking down access is not your call.
• Camera access goes through BasisLocalCameraDriver — Code that needs the local camera (transform, projection, rig data, etc.) pulls it from BasisLocalCameraDriver rather than looking one up itself. Don't roll a separate camera discovery path.
• Logging uses BasisDebug — All new logging calls go through BasisDebug.Log / BasisDebug.LogWarning / BasisDebug.LogError (with an appropriate LogTag) instead of UnityEngine.Debug.Log / Debug.LogWarning / Debug.LogError. BasisDebug routes through Basis's tagged, color-coded logger and respects the project-wide LoggingDisabled toggle so logging can be killed at runtime; bare Debug.Log calls bypass that and will be denied.
• No scene-wide discovery for dependencies — New code is architected so it does not need FindObjectOfType / FindObjectsOfType / GameObject.Find / FindGameObjectsWithTag to locate what it depends on. References are wired in — registered through an existing manager/driver, injected at init, or passed in by the caller — rather than discovered by scanning the scene at runtime. If a scene scan is genuinely unavoidable, justify it under Notes.
• No allocations in hot paths — Per-frame code (Update / LateUpdate / FixedUpdate, simulation loops, jobs, anything called once per frame or more) does not allocate. No new on reference types, no LINQ, no string concatenation/interpolation, no boxing, no foreach over interface-typed collections. Allocate once at init and reuse the buffer.
• No debugging in hot paths — No log calls of any kind on per-frame paths, including BasisDebug. Hot-path logging floods the console and incurs cost on every frame regardless of whether the message is filtered out downstream. If a hot-path log is needed while iterating, gate it behind #if UNITY_EDITOR and remove (or leave gated) before merge.
• Hot-path collection access is optimized — Cache .Count (lists) / .Length (arrays) into a local int before the loop instead of re-reading the property each iteration. Prefer T[] (with a separate length int when the array is over-sized) over List<T> where the data is hot — Unity's mono BCL doesn't expose CollectionsMarshal.AsSpan(List<T>), so a list can't be fed into Span<T> / unsafe paths cleanly. Where the perf justifies it, drop into Span<T> / ref locals / Unsafe.As / unsafe pointer code to skip bounds checks and copies, and call out the invariants you're relying on under Notes so reviewers can sanity-check them.

Testing details

Tick the platforms you actually tested on. Leave the rest unticked — these are informational and do not block merge.

• Windows
• Linux
• Android
• iOS
• macOS

Input / control mode coverage:

• Tested in VR (note headset under Notes)
• Tested in desktop / non-VR mode
• Tested with phone controls (mobile touch input)
• N/A — change does not touch player/XR/input code

Where applicable, confirm these flows still work after your changes:

• Hot-switching (desktop ↔ VR mode swap at runtime)
• Avatar swapping
• Server swapping (joining / leaving / changing servers)
• N/A — change does not touch any of the above

Notes

N/A boxes. A few of the required checks are ticked only because they don't apply here, not because the code does the thing:

• Addressables — nothing in the package loads assets at runtime.
• Considered jobification — one held interactable doing a tiny bit of vector math against ≤12 markers; the job overhead would dwarf the work.
• Camera access — package doesn't touch the camera rig.

Where the rest land in the code.

• Combined transform access / no per-frame transform reads in loops: tween writes use SetPositionAndRotation. The one loop that does read marker positions sits in BasisRotarySnapInteractable.FindNearestIndex, runs only while the interactable is held, and walks the marker list once per frame (typical 3–12 entries). I didn't reach for TransformAccessArray for that — happy to revisit if you'd rather see it batched.
• GetComponent / AddComponent: two component lookups in total (BasisActivationTarget from the snap-path base, Renderer from the marker tint). Both use TryGetComponent and both run at Awake, never per-frame.
• Per-frame work via BasisEventDriver: hooks into the existing interaction system's InputUpdate callback. No new MonoBehaviour Update methods.
• No needless properties: CurrentIndex and IsActive use restricted setters ({ get; protected set; } and { get; private set; }) because outside writes would corrupt internal state. Everything else is plain fields.
• Logging: one BasisDebug.LogError for misconfigured snap points, no UnityEngine.Debug anywhere.
• No scene-wide discovery: everything is wired through Inspector references — no FindObjectOfType, no Find calls.
• Hot-path allocations: InputUpdate and FindNearestIndex are struct-only. The marker tint's listener delegates are allocated once at Start and cached, not per-frame.
• Hot-path collection access: .Length is cached to a local int before every loop in the hot paths.

Other things worth knowing.

• The rotary subclass works out its swing axis from where the markers actually are (cross product of two chords) rather than from anything you set on the pivot. That way authors can drop markers wherever they want and the rotation just follows along.
• Haven't tested in VR yet — desktop is solid but the headset path still needs a pass before merge. It uses the same input pipeline as the existing pickup interactables, so it should be fine, but worth confirming.