fix(network): restore bounded BiDi opening-response validation

[seonghobae]

Repair boundary

Restores and hardens the RFC 6455 WebDriver BiDi server opening-response boundary that had already existed in the historical transport stack but was dropped when PR #195 was reconstructed onto its retained prerequisite base. This dependency-root repair is stacked directly on current PR #195 exact head 5c111d0db6c363f9d1786c21cc01c5c7398007bd; no predecessor checks, reviews, approvals, or synthetic merge evidence are transferred.

Current implementation

The branch validates the bounded HTTP/1.1 WebSocket opening response on the exact peer-verified stream, including 101 Switching Protocols, tokenized Upgrade: websocket / Connection: Upgrade, a single client-key-correlated Sec-WebSocket-Accept, response-size and monotonic-deadline ceilings, typed read/cleanup failures, and fail-closed malformed-header handling. It rejects the malformed status-line form HTTP/1.1 101\r\n...: RFC status code parsing requires the mandatory separator before the reason phrase.

It now also preserves HTTP/WebSocket extension interoperability at the correct authority boundary. RFC 9110 permits obs-text (%x80-FF) in field values, while RFC 6455 requires unknown opening-handshake header fields to be ignored. The parser therefore no longer rejects a valid handshake solely because an ignored extension field contains opaque non-UTF-8 octets. Required handshake fields remain fail closed: an Upgrade, Connection, or Sec-WebSocket-Accept value containing such replacement material cannot satisfy the reviewed ASCII token or exact accept-value contract. The standards decision and APA 7 references are recorded in docs/doctoring.md.

It performs no DNS/reconnect/proxy fallback, Chromium-process authentication, browser action, TLS-authority widening, unrestricted JavaScript execution, or browser/Agent authority grant.

Test-first / exact-head evidence

A realistic loopback status-line regression was added on exact test-only head cb24998c62fda3b2f885ee4f1425569dd4a17598. Exact CI run 33243277333 reached the regression and failed semantically because the malformed no-separator status line was accepted.

The ignored-extension compatibility defect was independently reproduced on exact test-only head 3c52466d1cd3978e1bb0a8f48a82c0c0e846fd43. Exact CI run 33246054621 checked out that head, passed repository contracts, formatting, and workspace compilation, then failed the full test step because a standards-valid unknown header containing 0x80 was rejected by the whole-response UTF-8 decoder.

The smallest root-cause repair produced behavioral GREEN head 70cab65592c21d7d1008b467c7810eeae382e427: whole-response decoding is loss-tolerant for parsing/ignoring opaque extension-field content, while a dedicated hostile regression confirms non-ASCII replacement material still cannot turn an invalid required Upgrade value into websocket. Exact CI run 33246188780 passed Rust contracts, full tests, strict Clippy, rustdoc, and exact owned-production function/line/region/branch coverage on that behavioral head.

The subsequent standards-only documentation commit changed only docs/doctoring.md. The current unchanged exact head is 7ea14fd486706f7599e8e9f3919141a722e36ed4. Exact CI run 33246431722 is GREEN on this current head:

• Rust contracts job 99084590721 checked out exact head and passed repository contracts, canonical formatting, workspace/all-target check, full tests, strict Clippy, and API documentation/rustdoc;
• Production coverage job 99084590826 checked out exact head and passed exact owned-production function, line, region, and branch measurement/diagnostics/enforcement.

GitHub currently reports this Draft mergeable. No independent approval is claimed. Central required workflows that are absent on this Draft are not promoted as passing evidence.

Authority boundary

Protected-main AGENTS.md remains authoritative. This scheduled branch does not merge, self-approve, force-push, destructively rebase, alter workflows/rulesets/secrets, weaken checks, tag, release, or publish.

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