docs: add contributing & style guidance

[towneh]

Summary

Add contributing.md and style.md files

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

This is supporting guidance and documentation only