refactor(capture-kit): move screenshot-diff beside its pixel worker and overlays

docs/adr/0019-request-bound-platform-runtime.md

@@ -990,10 +990,11 @@ anchor, not as a proposed commitment.
   `interaction-targeting` and the android UI-hierarchy fixtures) and
   `src/__tests__/snapshot-desktop-surface.test.ts` (pinned to the root
   eager-import-closure fixtures).
-- `src/screenshot-diff/*.ts` (region split/overlay/summarization/component composition) —
-  pixel-diff computation and PNG decode/encode already call capture-kit's `png`/
-  `png-worker-client`; the root files remain for daemon/CLI diff-report composition.
-  Equivalent: none (built atop already-migrated capture-kit mechanics).
+- `src/screenshot-diff/*.ts` (region split/overlay/summarization/component composition, with its
+  test) — **migrated to `packages/capture-kit/src/`** beside the pixel worker and screenshot
+  overlays it was built on. The CLI and command output consume it through
+  `@agent-device/capture-kit/screenshot-diff`, `/screenshot-diff-regions`, and
+  `/screenshot-diff-overlay-matches`.
 - `src/provider-device-runtime.ts`, `src/provider-device-runtimes.ts`,
   `src/provider-limrun-runtime.ts`, `src/provider-webdriver.ts`. Mostly already thin: the bulk of
   WebDriver and Limrun provider logic lives in `packages/provider-webdriver/src/` and

packages/capture-kit/package.json

@@ -238,10 +238,22 @@
       "types": "./src/screenshot-density.ts",
       "default": "./src/screenshot-density.ts"
     },
+    "./screenshot-diff": {
+      "types": "./src/screenshot-diff.ts",
+      "default": "./src/screenshot-diff.ts"
+    },
+    "./screenshot-diff-overlay-matches": {
+      "types": "./src/screenshot-diff-overlay-matches.ts",
+      "default": "./src/screenshot-diff-overlay-matches.ts"
+    },
     "./screenshot-diff-pixels": {
       "types": "./src/screenshot-diff-pixels.ts",
       "default": "./src/screenshot-diff-pixels.ts"
     },
+    "./screenshot-diff-regions": {
+      "types": "./src/screenshot-diff-regions.ts",
+      "default": "./src/screenshot-diff-regions.ts"
+    },
     "./screenshot-overlay": {
       "types": "./src/screenshot-overlay.ts",
       "default": "./src/screenshot-overlay.ts"

src/screenshot-diff/screenshot-diff-region-overlay.ts → packages/capture-kit/src/screenshot-diff-region-overlay.ts

@@ -1,4 +1,4 @@
-import type { PNG } from '@agent-device/capture-kit/png';
+import type { PNG } from './png.ts';
 import type { ScreenshotDiffRegion } from './screenshot-diff-regions.ts';
 
 const REGION_BORDER_COLOR = [0, 187, 255, 255] as const;

src/screenshot-diff/screenshot-diff-region-split.ts → packages/capture-kit/src/screenshot-diff-region-split.ts

@@ -1,4 +1,4 @@
-import type { PNG } from '@agent-device/capture-kit/png';
+import type { PNG } from './png.ts';
 import type { MutableDiffRegion } from './screenshot-diff-region-types.ts';
 
 // Region splitting is based on screen-relative heights so it works on phone,

src/screenshot-diff/screenshot-diff-regions.ts → packages/capture-kit/src/screenshot-diff-regions.ts

@@ -1,5 +1,5 @@
 import type { Rect } from '@agent-device/kernel/snapshot';
-import type { PNG } from '@agent-device/capture-kit/png';
+import type { PNG } from './png.ts';
 import { normalizedRect, type NormalizedRect } from '@agent-device/kernel/screenshot-geometry';
 import { findConnectedMaskComponents } from './screenshot-diff-components.ts';
 import { splitLargeDiffRegions } from './screenshot-diff-region-split.ts';

src/screenshot-diff/__tests__/screenshot-diff.test.ts → packages/capture-kit/src/screenshot-diff.test.ts

@@ -2,10 +2,10 @@ import { test } from 'vitest';
 import assert from 'node:assert/strict';
 import fs from 'node:fs';
 import path from 'node:path';
-import { mkdtempForTestSync } from '@agent-device/test-kit';
+import { mkdtempForTestSync } from './tmp-dir.fixtures.ts';
 
-import { hasPngSignature, PNG } from '@agent-device/capture-kit/png';
-import { compareScreenshots } from '../screenshot-diff.ts';
+import { hasPngSignature, PNG } from './png.ts';
+import { compareScreenshots } from './screenshot-diff.ts';
 
 function tmpDir(): string {
   return mkdtempForTestSync('agent-device-screenshot-diff-');

src/screenshot-diff/screenshot-diff.ts → packages/capture-kit/src/screenshot-diff.ts

@@ -2,12 +2,12 @@ import { promises as fs } from 'node:fs';
 import path from 'node:path';
 import { AppError } from '@agent-device/kernel/errors';
 import type { Rect } from '@agent-device/kernel/snapshot';
-import { PNG } from '@agent-device/capture-kit/png';
+import { PNG } from './png.ts';
 import {
   computeScreenshotDiffPixelsAsync,
   decodeScreenshotImageAsync,
   encodePngAsync,
-} from '@agent-device/capture-kit/png-worker-client';
+} from './png-worker-client.ts';
 import { annotateDiffRegions } from './screenshot-diff-region-overlay.ts';
 import { summarizeDiffRegions, type ScreenshotDiffRegion } from './screenshot-diff-regions.ts';
 import type { ImageDimensions } from '@agent-device/kernel/screenshot-geometry';

scripts/layering/model.test.ts

@@ -521,7 +521,6 @@ test('classifyZone separates the ranked spine from intentionally-unranked zones'
   assert.equal(classifyZone('(root)'), 'ranked');
   assert.equal(classifyZone('platform-runtime'), 'ranked');
   assert.equal(classifyZone('mcp'), 'ranked');
-  assert.equal(classifyZone('screenshot-diff'), 'ranked');
   // A zone that is neither ranked nor listed peripheral must be flagged, never
   // silently treated as back-edge-free.
   assert.equal(classifyZone('not-a-real-zone'), 'unclassified');

scripts/layering/model.ts

@@ -55,7 +55,6 @@ const TARGET_DAG_RANK = new Map([
   ['maestro', 1],
   ['replay-port', 1],
   ['replay-test', 1],
-  ['screenshot-diff', 1],
   ['selectors', 1],
   ['session-journal', 1],
   ['core', 2],

scripts/layering/package-boundaries.test.ts

@@ -529,7 +529,10 @@ test('the real tree parses, declares, and passes R11', () => {
     '@agent-device/capture-kit/screen-recording-stop-recovery',
     '@agent-device/capture-kit/screen-recording-transport',
     '@agent-device/capture-kit/screenshot-density',
+    '@agent-device/capture-kit/screenshot-diff',
+    '@agent-device/capture-kit/screenshot-diff-overlay-matches',
     '@agent-device/capture-kit/screenshot-diff-pixels',
+    '@agent-device/capture-kit/screenshot-diff-regions',
     '@agent-device/capture-kit/screenshot-overlay',
     '@agent-device/capture-kit/scroll-edge-state',
     '@agent-device/capture-kit/snapshot-baseline',

src/cli/commands/screenshot.ts

@@ -1,6 +1,6 @@
 import { localCommandPolicy } from '@agent-device/contracts/command-policy';
 import { formatScreenshotDiffText, formatSnapshotDiffText } from '../../commands/output/diff.ts';
-import type { ScreenshotDiffResult } from '../../screenshot-diff/screenshot-diff.ts';
+import type { ScreenshotDiffResult } from '@agent-device/capture-kit/screenshot-diff';
 import { AppError } from '@agent-device/kernel/errors';
 import { isNonDefaultResponseLevel } from '@agent-device/kernel/contracts';
 import { resolveUserPath } from '@agent-device/host-kit/file';

src/commands/capture/runtime/diff-screenshot.ts

@@ -16,8 +16,8 @@ import { AppError } from '@agent-device/kernel/errors';
 import {
   compareScreenshots,
   type ScreenshotDiffResult,
-} from '../../../screenshot-diff/screenshot-diff.ts';
-import { attachCurrentOverlayMatches } from '../../../screenshot-diff/screenshot-diff-overlay-matches.ts';
+} from '@agent-device/capture-kit/screenshot-diff';
+import { attachCurrentOverlayMatches } from '@agent-device/capture-kit/screenshot-diff-overlay-matches';
 import type { RuntimeCommand } from '../../runtime-types.ts';
 import {
   createCommandTempFile,

src/commands/output/diff.ts

@@ -1,8 +1,8 @@
 import path from 'node:path';
 import { colorize, supportsColor } from './color.ts';
 import { readSnapshotWarnings } from './snapshot.ts';
-import type { ScreenshotDiffResult } from '../../screenshot-diff/screenshot-diff.ts';
-import type { ScreenshotDiffRegion } from '../../screenshot-diff/screenshot-diff-regions.ts';
+import type { ScreenshotDiffResult } from '@agent-device/capture-kit/screenshot-diff';
+import type { ScreenshotDiffRegion } from '@agent-device/capture-kit/screenshot-diff-regions';
 type SnapshotDiffLine = {
   kind?: 'added' | 'removed' | 'unchanged';
   text?: string;