Shader assets: graph-built shaders, the Shader tab and sprite rows from the graph (#62)

A shader is an asset carrying a node graph (Texture color, Output, Property,
Color, Add/Subtract/Multiply/Divide, Mix, Luminance) that compiles to the GLSL
fragment of a Pixi filter. The Shader tab reuses the Behavior canvas; a sprite
wears a shader through its Shader picker, and the rows below it are the
graph's Property nodes. Property schema, resolution and deviation take the
project because a sprite's rows now live in another asset. The built-in
registry of the prototype is gone; "Adjust colors" ships as a graph in the
fixture and the three example games.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/viewport/ShaderLibrary.ts

@@ -0,0 +1,39 @@
+import type { ShaderAsset } from '../core/model/Asset';
+import { findAssetOf, type Project } from '../core/model/Project';
+import { compileShader, type ShaderBuild } from '../core/shader/compile';
+import type { ShaderSource } from './shaders';
+
+/**
+ * Compiled shader graphs, one per asset, recompiled when the graph's content changes. A graph is
+ * edited in place, so the cache keys on its serialized form rather than on its identity.
+ */
+export class ShaderLibrary {
+  private readonly builds = new Map<string, { fingerprint: string; build: ShaderBuild }>();
+
+  buildFor(asset: ShaderAsset): ShaderBuild {
+    const fingerprint = JSON.stringify(asset.graph);
+    const cached = this.builds.get(asset.id);
+    if (cached && cached.fingerprint === fingerprint) return cached.build;
+    const build = compileShader(asset.graph);
+    this.builds.set(asset.id, { fingerprint, build });
+    return build;
+  }
+
+  /** For one redraw: each asset is looked up and fingerprinted once, however many sprites wear it. */
+  source(project: Project): ShaderSource {
+    const seen = new Map<string, ShaderBuild | null>();
+    return {
+      compiled: (assetId) => {
+        let build = seen.get(assetId);
+        if (build === undefined) {
+          const asset = findAssetOf(project, assetId, 'shader');
+          build = asset ? this.buildFor(asset) : null;
+          seen.set(assetId, build);
+        }
+        return build?.compiled ?? null;
+      },
+    };
+  }
+}
+
+export const shaderLibrary = new ShaderLibrary();