Render only when shared state changes

Add shared-data and bundle invalidation signals, and have handles publish them automatically for SAB and graph mutations.

Document the raw core worker protocol in a dedicated VitePress site and simplify the glTF import and picking example.

Amp-Thread-ID: https://ampcode.com/threads/T-01a01ff8-b91f-724f-8952-f07c6b5042fd
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

coredocs/index.md

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+---
+layout: home
+hero:
+  name: Yawn raw core
+  text: Worker, shared memory, and render graphs
+  tagline: The protocol reference for building an alternative handles layer or editor without YawnCore or @yawn/handles.
+  actions:
+    - theme: brand
+      text: Boot from scratch
+      link: /guide/boot
+    - theme: alt
+      text: Worker reference
+      link: /reference/worker
+features:
+  - title: Raw transport
+    details: Start core/worker.js, correlate replies, and handle profiler events.
+  - title: Shared rows
+    details: Build typed views, allocate slots, and follow the dirty-lane protocol.
+  - title: Graph wire format
+    details: Encode, compile, and activate complete WebGPU render and compute graphs.
+---
+
+## Contract at a glance
+
+The browser main thread owns the HTML canvas and starts the module worker. The worker initializes the WASM core and WebGPU against an `OffscreenCanvas`. All control operations are structured-clone messages. Bulk numeric state lives in one returned `SharedArrayBuffer`; graphs describe how named row arrays become GPU resources.
+
+The application is responsible for three important contracts:
+
+1. Correlate each reply by its `request` value; profiler messages are unsolicited.
+2. Finish shared-memory writes before setting `signals[5]` (`sabDirty`).
+3. Before a mutation that invalidates compiled render bundles, set `signals[6]` (`bundleDirty`), make the mutation, compile and switch a replacement graph, then let successful `switch-loadout` clear lane 6.
+
+This site describes the current wire API, not the higher-level wrapper API.