fix(lint): preserve opening-tag source bounds after multiline closes

[harimkang]

What

Preserve correct opening-tag source bounds in parseHtmlStructure (packages/lint/src/utils.ts) so the unclosed_tag_swallowed_element rule no longer misreports valid siblings after a multiline closing tag.

Fixes #3916.

Why

Reproduced with HyperFrames v0.8.36, official source f86aae655ae5aae7a9a2c124fa016f3bc30ebe52, and htmlparser2@10.1.0.

A closing tag with whitespace before > can leave Parser.startIndex inside that closing tag. The next opening tag then includes the preceding whitespace and > in its raw range, causing a valid sibling to trigger unclosed_tag_swallowed_element:

<span>A</span
    ><span>B</span>

How

Capture the original opening-name bounds in onopentagname, before attributes are scanned. Bound the search using HTML name delimiters while retaining < inside malformed names, and use the original name end for attributes: a lowercased Unicode name can have a different UTF-16 length. Implied opening tags retain their existing parser-reported ranges. The source text and the lint rule/severity remain unchanged.

Test plan

• Unit tests added/updated
• Manual testing performed
• Documentation updated (not applicable)

Validation executed:

• From packages/lint: node ../../node_modules/vitest/vitest.mjs run --config vitest.config.ts — 16 files, 651 tests passed.
• From the repository root: node node_modules/typescript/bin/tsc --project packages/lint/tsconfig.json --noEmit --types node — passed.
• npx --yes oxfmt@0.41.0 --check packages/lint/src/utils.ts packages/lint/src/utils.test.ts packages/lint/src/rules/core.test.ts and npx --yes oxlint@1.64.0 packages/lint/src/utils.ts packages/lint/src/utils.test.ts packages/lint/src/rules/core.test.ts — passed.
• From packages/lint: node ../../node_modules/tsup/dist/cli-default.js — Node and browser lint entrypoints built successfully.

Tests cover adjacent and multiline closing tags, malformed names containing <, quoted < values, ignored markup inside a malformed close, implied p/br opens, Unicode lowercase expansion, and genuine missing->/unquoted-attribute negatives.

[jrusso1020]

Reviewed revision 5721b91. No blocking findings.

The opening-name callback preserves original source boundaries, including Unicode names whose lowercase representation changes length (packages/lint/src/utils.ts:76). Regression tests retain genuine malformed-tag detection alongside the valid multiline-close cases (packages/lint/src/rules/core.test.ts:965).

Validation: all 651 lint tests passed with local workspace-source aliases. An independent adversarial pass compared source ranges with tokenizer offsets across 101,512 HTML inputs without mismatches, covering implied tags, malformed names, raw-text content, and quoted attributes.

— Codex

Verdict: APPROVE
Reasoning: The change fixes the false positive while preserving malformed-input detection; no introduced correctness issues were found.