feat: add pixelmatch pre-filter with tiered classification (Phase 2)

Implements the pre-filter layer that gates AI analysis:
- SHA-256 hash check for instant SKIP (byte-identical screenshots)
- pixelmatch comparison with configurable threshold (0.05 default)
- Spatial cluster detection via 8-connectivity flood-fill
- Three tiers: SKIP (0 cost), FAST_CHECK (scattered), FULL_ANALYSIS (clustered)
- Diff overlay PNG generation for visual debugging
- Standalone CLI with JSON report output

Zero false-negative guarantee: only byte-identical or zero-diff
screenshots skip analysis. Tiers control depth, not whether analysis
occurs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 2 people

.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "dojowatch",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "description": "AI-native visual regression testing — capture, diff, and analyze UI changes with LLM vision",
   "author": {
     "name": "Dojo Coding LLC",

CHANGELOG.md

@@ -1,6 +1,19 @@
 # Changelog
 
-## [0.1.0] — Unreleased
+## [0.2.0] — Unreleased
+
+### Added
+- **Pre-filter engine** (`scripts/prefilter.ts`): pixelmatch-based tiered classification
+  - SHA-256 hash comparison for instant SKIP detection
+  - pixelmatch with configurable threshold (default 0.05) and anti-alias filtering
+  - Spatial cluster detection using 8-connectivity flood-fill
+  - Three tiers: SKIP (0 tokens), FAST_CHECK (~600 tokens), FULL_ANALYSIS (~2400 tokens)
+  - Diff overlay PNG generation for visual inspection
+  - Standalone CLI entrypoint with JSON report output
+- **Type declaration** for pixelmatch v6 (`scripts/pixelmatch.d.ts`)
+- **Prefilter tests** with fixture PNG pairs covering all tier scenarios
+
+## [0.1.0]
 
 ### Added
 - Initial project structure as Claude Code plugin + standalone scripts

package.json

@@ -1,6 +1,6 @@
 {
   "name": "dojowatch",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "private": true,
   "type": "module",
   "scripts": {

scripts/pixelmatch.d.ts

@@ -0,0 +1,22 @@
+declare module "pixelmatch" {
+  interface PixelmatchOptions {
+    threshold?: number;
+    includeAA?: boolean;
+    alpha?: number;
+    aaColor?: [number, number, number];
+    diffColor?: [number, number, number];
+    diffColorAlt?: [number, number, number];
+    diffMask?: boolean;
+  }
+
+  function pixelmatch(
+    img1: Buffer | Uint8Array | Uint8ClampedArray,
+    img2: Buffer | Uint8Array | Uint8ClampedArray,
+    output: Buffer | Uint8Array | Uint8ClampedArray | null,
+    width: number,
+    height: number,
+    options?: PixelmatchOptions
+  ): number;
+
+  export default pixelmatch;
+}