refactor(cursor): use shared provider account setup and storage

[juliusmarminge]

Cursor browser login landed in #12948 with its own settings UI and credential persistence. Keeping that separate would duplicate the setup architecture for subsequent providers.

Adapt Cursor to the shared account contracts and settings UI, and persist its SDK credentials through the common provider credential store. Retain the SDK-specific login, verification, cancellation, and rollback behavior at the Cursor adapter boundary.

Depends on #12965.

Validation: focused Cursor authentication, credential persistence, driver, and provider tests passed, including damaged-store recovery. Scoped server and web typechecks passed.

Live Cursor sign-in and before/after UI evidence are pending. The V2 selection-restart CI failure is tracked by #13113. This PR remains a draft.

Implemented with GPT-6 in the Codex harness.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	4.9 KiB	—	6.8 KiB	✅
Codex	Thread snapshot wire	—	3.7 KiB	—	4.9 KiB	✅
Codex	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Codex	Live turn WebSocket decoded	—	20.4 KiB	—	29.3 KiB	✅
Codex	Live turn messages	—	2	—	8	✅
Claude	Total thread wire	—	4.9 KiB	—	6.8 KiB	✅
Claude	Thread snapshot wire	—	3.7 KiB	—	4.9 KiB	✅
Claude	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Claude	Live turn WebSocket decoded	—	20.8 KiB	—	29.3 KiB	✅
Claude	Live turn messages	—	2	—	8	✅

Baseline: unavailable · PR result: ccf168b · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 106.1 KiB
• Claude decoded thread snapshot: 106.4 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This PR changes production authentication behavior and migrates Cursor credentials from a legacy file into shared secret-backed storage, while also changing the account-management UI and auth-state contract. Because it handles sensitive credentials and existing sign-in persistence, human review is required.

Notes:

• All code in this push has already been reviewed. Approvability was decided on eligibility alone.

^{You can add or adjust custom eligibility rules. Learn more.}

[macroscopeapp]

Effect Service Conventions found one blocking namespace-import violation; see the inline review comment.

^{Posted via Macroscope — Effect Service Conventions}