Separate live and restart configure paths

[rgarcia]

Summary

• model /chromium/configure as explicit live and restart execution modes
• extract clearly named helpers for the existing live display path and stop/start path without changing their ordering or error handling
• preserve restart selection for profiles, extensions, nonempty policies, and nonempty Chromium flags
• preserve live behavior for display-only and start_url-only requests
• preserve recording-segment restart ordering after successful navigation and before Chromium recovery on error paths
• add mode/actionable-selection unit coverage and browser WebSocket identity assertions for live and restart e2e cases

Testing

• go vet ./...
• go test -race ./cmd/api/api -count=1
• go test -v -race -timeout 15m ./e2e -run '^TestChromiumConfigureMultipartPowerset$' -count=1
• built images/chromium-headless/image/Dockerfile locally for the e2e run

The full non-e2e race suite was also attempted. All packages passed except the existing lib/devtoolsproxy restart test, which failed during t.TempDir cleanup because Chromium was still writing its profile directory; rerunning that package reproduced the same cleanup failure.

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Note

Medium Risk
Touches Chromium lifecycle, display/recording coordination, and configure error recovery—behavior-preserving refactor but operationally sensitive.

Overview
/chromium/configure is refactored around explicit live vs restart execution modes instead of a single inline needsStop branch.

ChromiumConfigure dispatches via chromiumConfigureModeFor (replacing chromiumNeedsStopCycle) into chromiumConfigureLive (display patch + optional start_url without stopping Chromium) and chromiumConfigureRestart (stop/apply/start). Shared navigation moves to chromiumConfigureNavigate.

On the restart path, recording segment resume is centralized: segments restart after successful navigation on the happy path, and in a defer on errors (before Chromium recovery) instead of only via a display-step defer.

Unit tests cover mode selection and actionables; the configure powerset e2e adds start_url cases and asserts browser WebSocket identity is preserved on live configures and changes on policy/flags/extension restart paths.

^{Reviewed by Cursor Bugbot for commit e7753a2. Bugbot is set up for automated code reviews on this repo. Configure here.}