fix(models): retry pre-request WebSocket handshake failures

[CoralGarden52]

Summary

OpenAIResponsesWSModel could fail immediately when the peer closed during the WebSocket HTTP upgrade. With the supported websockets>=15 client, a close before a valid HTTP 101 response is reported as websockets.exceptions.InvalidMessage. That exception was raised before _ensure_websocket_connection returned, so the existing pre-event retry path never handled it.

This change:

• includes connection acquisition in the existing cleanup/retry boundary;
• recognizes the exact pre-upgrade InvalidMessage case;
• retries at most once, only before any request frame can have been sent;
• marks that handshake failure as replay-safe for retry advice;
• preserves the existing no-replay behavior for send/receive failures after a request may have been transmitted.

Test plan

• Reproduced with a local raw TCP WebSocket server that closes the first connection before HTTP 101, then completes a valid handshake on the second connection.
• The production model completed with 2 handshakes, exactly one response.create frame, and response_id=resp_local_probe.
• make tests: 9292 passed, 29 skipped; serial tests: 77 passed, 4 skipped.
• .agents/skills/code-change-verification/scripts/run.sh: passed (format, lint, typecheck, and tests).
• Added regression coverage for handshake retry and replay-safe retry advice.
• Searched open upstream PRs for InvalidMessage, websocket handshake, pre-event websocket, and websocket retry; no duplicate open PR was found.

Issue number

No existing issue found; the failure was reproduced locally against the real websockets handshake path.

Checks

• I've added new tests, if relevant
• I've run .agents/skills/code-change-verification/scripts/run.sh
• I've confirmed all verification steps pass
• If using Codex, I've run a read-only code review before submitting this PR

This PR is intentionally opened as a draft pending maintainer review.