feat(core): serialize bounded WebDriver BiDi locateNodes commands

[seonghobae]

Stacked on exact PR #174 head ec6293eb86666a5de335d0a71674215a8953db33.

Buyer gap

#174 closes protocol-proof and node-admission confusion, but its current truth boundary explicitly stops before serializing or transmitting a WebDriver BiDi command. This child owns the next bounded boundary: deterministic, fail-closed serialization of the reviewed browsingContext.locateNodes accessibility query into an exact WebDriver BiDi command envelope. It performs no transport I/O and grants no browser, policy, destination, or typed-input authority.

Implemented contract

Current exact head d28836ae8c0f2096f214d681f001d60e9fcb780b:

• accepts only WebDriver BiDi js-uint command IDs, including 0 and 9007199254740991, and rejects larger u64 values;
• validates the browsing-context identifier against the existing external browser identifier budget and protocol-text injection policy;
• JSON-escapes reviewed string values while preserving ordinary Unicode text;
• serializes the exact accessibility locator, finite maxNodeCount, and fixed minimal serialization options already carried by WebDriverBiDiAccessibilityQuery;
• exposes source-free typed validation errors;
• records the implemented boundary in CHANGELOG.md; and
• grounds the command envelope and locateNodes parameter shape in the W3C WebDriver BiDi Editor’s Draft dated 20 July 2026 in docs/doctoring/browser-agent-protocols.md.

This remains an inert transport value: it does not authenticate a browser or adapter, perform transport I/O, bind the command to current OriginWeave session/context/origin authority, correlate a response, admit returned nodes, or authorize policy/typed input.

Exact-head evidence

For unchanged exact head d28836ae8c0f2096f214d681f001d60e9fcb780b:

• repository CI run 32058217738: success;
• Manifest V3 Compatibility run 32058217732: success;
• no formal review or unresolved review thread is currently present.

These checks are head-specific; no predecessor evidence is transferred.

Stack discipline

Keep Draft while #174 and its prerequisites remain active. PR #182 owns the next response-correlation slice and is stacked on this head. No predecessor check/review/coverage evidence transfers. This scheduled actor does not merge, self-approve, alter workflows, add secrets, weaken checks, tag, or publish.

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