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

[thymikee]

Summary

Moves the seven src/screenshot-diff/ modules (961 LOC) and their test into packages/capture-kit/src/, next to screenshot-diff-pixels, the PNG worker and the screenshot overlays they already depended on. Every outgoing edge already targeted kernel/capture-kit, so no new package or dependency is needed. The screenshot-diff layering zone is removed.

• Consumers (src/cli/commands/screenshot.ts, src/commands/capture/runtime/diff-screenshot.ts, src/commands/output/diff.ts) now import @agent-device/capture-kit/screenshot-diff, /screenshot-diff-regions and /screenshot-diff-overlay-matches.
• The test uses capture-kit's local tmp-dir.fixtures.ts (capture-kit cannot depend on test-kit, which depends on it).
• 15 files; ADR 0019 inventory updated. No behavior change.

Validation

Tested at 05c664543:

• pnpm check:affected --run passed (layering, production-exports, package).
• vitest run packages/capture-kit/src/screenshot-diff.test.ts: 22/22.
• git diff -M90% shows renames with only import-specifier edits.
• Fresh-context adversarial review: no findings.

Not run: device lanes (no runtime path change). CI pending.

[cubic-dev-ai]

No issues found across 16 files

_{View guided diff | Turn on auto-fix | Re-trigger cubic}

[github-actions]

Size Report

Metric	Base	Current	Diff
Installed (including dependencies)	5.29 MB	5.29 MB	0 B
Package (unpacked)	5.29 MB	5.29 MB	0 B
Package (download)	1.59 MB	1.59 MB	+10 B

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	27.6 ms	26.2 ms	-1.4 ms
CLI --help	77.3 ms	76.6 ms	-0.8 ms

[thymikee]

I reviewed 05c6645 and found no problems. The move of screenshot-diff beside its pixel worker and overlays keeps the same logic and only updates import paths, and the code looks good.

Smoke Tests is still running, so CI has not finished. The diff only moves a CLI-side diff-report module, so a failure there would be unlikely to come from this change. The only overlap is with the screenshot-diff CLI route. I did not run the eager-closure ceiling gate, fallow, or the test suite, and I did not check whether any consumer besides the three listed sees a changed import closure.

This can merge once Smoke Tests finishes green.

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-10-16 13:05 UTC