Thread briefly becomes inactive while a turn starts

[D3OXY]

Problem

When a provider session starts a turn, the thread can briefly transition from Connecting to inactive before becoming Working. This makes status-grouped thread lists jump between sections during startup.

The lifecycle currently exposes provider readiness between session connection and turn start as an idle-ready state, even though a turn-start request is still pending.

Expected behavior

A pending turn should remain Connecting through provider readiness and transition directly to Working when the turn starts. A failed start should still settle to ready or error, and genuinely idle sessions should remain inactive.

Acceptance criteria

• New and restarted sessions do not expose an inactive frame during turn startup.
• Provider readiness preserves Connecting while a turn start is pending.
• Turn start transitions directly from Connecting to Working.
• Failed starts and genuinely idle sessions keep their existing terminal states.
• Lifecycle coverage includes successful startup, failed startup, and idle readiness.