Fix WebMCP results for forms and navigation

[rgarcia]

Summary

• return awaiting_submission with structured form state as soon as Chromium populates a non-autosubmit declarative form
• keep terminal WebMCP invocations alive across frame navigation so late toolResponded events are preserved
• add CDP fixtures covering a form that never emits a terminal response and a result delivered after navigation commits
• document and type the new invocation status

Why

Non-autosubmit declarative forms intentionally remain active after Chromium fills them, so waiting for a terminal event turns successful form population into a timeout. Separately, navigation can begin before Chromium emits a valid terminal tool result. These states should not be reported as unknown outcomes.

Validation

• go vet ./...
• go test -race ./lib/webmcpclient ./cmd/api/api ./lib/oapi
• full non-e2e race suite passed across the run; lib/devtoolsproxy required one retry after a transient Chromium TempDir cleanup failure
• bun test runtime/*.test.ts
• rebuilt the headful image from head commit e022a44 and exercised the full public Stripe checkout from one /playwright/execute request using webmcp.invokeTool: form fill returned awaiting_submission with form_populated: true and submitted: false in 8.9ms, submission returned completed in 80.0ms, and the confirmation page loaded successfully

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