test: validate native select onChange regression (#2975)

[Sion612]

Purpose

This fork-local draft is a staged CI check for the native select notification fix proposed for codex-team#2975.

The validation base branch starts at upstream next commit 30e1f792abac9a29b7d614273ff0f3b36ade2b64.

Validation sequence

1. The first commit adds the SelectTool fixture and four Cypress regression tests while retaining the original core. The new select notification assertions are expected to fail. Dependency, browser, workflow, and unrelated failures do not establish the regression.
2. After verifying that failure, the planned second commit delegates native select change events to the block update path, checks block ownership, and removes the listener during destruction. Existing pull-request workflows can then verify the fix.

The final proposed change is limited to three files: src/components/block/index.ts, test/cypress/tests/onchange.cy.ts, and test/cypress/fixtures/tools/SelectTool.ts.

Local evidence

• Node 18.20.8 / Yarn 1.22.22: lint, production build, and test build passed after a cached offline install with scripts disabled. Lint reported the same 219 warnings in both compared trees.
• The Cypress spec compiled through the repository's Vite preprocessor, but Cypress assertions could not run locally because the Cypress binary download was unavailable.
• An independent Playwright harness, using Node 24.19.0 and Chromium 149.0.7827.0, observed 8 missing-notification failures and 4 passing control checks with the original core. All 12 checks passed with the proposed fix. These results are separate from Cypress.
• The complete final patch passed an application check against the clean baseline.

Pending checks

The staged Cypress failure and pass, the full suite, and the Firefox / Chrome / Edge CI jobs remain to be verified. CI results must be associated with both the PR head commit and the actual checked-out test commit.

Implementation and verification were AI-assisted.