[Refactor] Consolidate code-mode turn lifecycle state

[roomote-roomote]

​Created by Roomote. View the task or mention @roomote-roomote for follow-up asks.

What changed

• Replaced five independently mutable code-mode turn fields with one turn-scoped lifecycle owner.
• Modeled inactive, awaiting-server, and server-bound phases explicitly so capability, directory, mounted integration IDs, and leased-server state move together.
• Moved same-turn mounting and retry bookkeeping behind that owner, with focused coverage for inactive turns, server binding, duplicate suppression, and next-turn retry after a rejected live mount.

Why this change was made

Code-mode integration activation and mid-turn refresh depended on partial state spread across the Fast orchestration service. Keeping those invariants in one owner reduces invalid combinations and makes the lifecycle safer to extend.

Impact

There is no intended user-facing behavior change. Same-turn connection refresh, next-turn durability, and collision fallback are preserved, while the orchestration service carries less mutable lifecycle state. The change was kept narrow around the active per-tool approvals work in #3001 to reduce merge overlap.

[roomote-community]

No code issues found. See task

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