docs(snapshots): clarify that threshold defines which pixels are different

[Dmitry Gozman (dgozman)]

Summary

• maxDiffPixels and maxDiffPixelRatio docs now point to threshold, which defines which pixels are considered different.
• The "Visual comparisons" guide section covers both maxDiffPixels and threshold.

Fixes #42959

[github-actions]

Test results for "tests 1"

5 flaky

⚠️ [chromium-library] › library/browsercontext-page-event.spec.ts:173 › should work with Ctrl-clicking `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-page] › page/workers.spec.ts:191 › should attribute network activity for worker inside iframe to the iframe `@chromium-ubuntu-22.04-node22`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:257 › third party 'Partitioned;' cookies `@firefox-ubuntu-22.04-node20`
⚠️ [firefox-library] › library/browsercontext-cookies-third-party.spec.ts:470 › top level 'Partitioned;' cookie and same origin iframe `@firefox-ubuntu-22.04-node20`
⚠️ [webkit-library] › library/video.spec.ts:152 › screencast › should continue recording main page after popup closes `@webkit-ubuntu-22.04-node20`

52383 passed, 1243 skipped

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Merge workflow run.

[github-actions]

Test results for "MCP"

1 failed
❌ [chromium] › mcp/sse.spec.ts:196 › sse transport browser lifecycle (persistent) @mcp-ubuntu-latest-chromium

8828 passed, 1480 skipped

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Merge workflow run.

[github-actions]

Hi, I'm the Playwright bot and I took a first look at the CI failures.

🟢 The one failure is a pre-existing flake, not caused by this PR

mcp/sse.spec.ts:196 fails the same way on main, and this PR only changes docs and the generated test.d.ts comments.

Details

This PR (b3e4abc) edits the docs for the threshold snapshot option and regenerates the JSDoc in packages/playwright/types/test.d.ts. No runtime code changes, so the MCP SSE transport can't be affected.

Pre-existing flake / infra

• [chromium] › mcp/sse.spec.ts:196 › sse transport browser lifecycle (persistent) (mcp-ubuntu-latest-chromium): pre-existing flake. The test-results DB shows the same expect(received).toEqual(expected) deep-equality failure on commits this PR didn't touch:

  • main: 35785203077, 36070734686, 36118130299
  • other PRs: feat(test-runner): add --shuffle to run tests in random order #42877 (35810822373), feat(chromium): roll to r1247 #42915 (36045564131)

  Across 737 recorded runs, it had a failing attempt in 5, on both Ubuntu and Windows, and passed in the rest.

_{Triaged by the Playwright bot - agent run}