feat(clients): reload provider sessions per thread without restarting T3 Code

[DavidIlie]

What changed

Provider processes load MCP servers and runtime configuration when they start. Existing threads therefore required a full T3 Code restart to pick up changes such as enabling Computer Use.

This adds Reload agent session to thread actions and the command palette on web/desktop, plus thread controls on mobile. It stops only that thread's provider process; the next message starts a new process and resumes the stored provider conversation with current configuration. Other threads and the environment keep running.

Reload reuses the existing stop/resume lifecycle and works across Codex, Claude Code, Cursor, Grok, and OpenCode. An idle-only precondition is checked atomically by the decider, so a stale client cannot interrupt a turn started elsewhere.

Closes #5437.

Screenshots

Before	After

Validation

• 107 focused client, orchestration, reactor, and provider tests passed
• Contracts, client-runtime, web, mobile, and server typechecks passed
• Targeted lint, formatting, and git diff --check
• Isolated web pass confirmed reload followed by a successful resumed turn through a fresh provider process

Model: GPT-5.6 Sol · Harness: Codex in T3 Code

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a new user-facing feature (reload agent session) with UI controls across mobile and web, backend decider logic changes, and contract modifications. New features introducing user-facing behavior warrant human review.

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[theophile-wallez]

Hi! Any news on this?

[juliusmarminge]

Thanks for the PR. We're not taking changes to the orchestration and provider layers right now: that part of the server is being rewritten for V2, and merging into the current code would either conflict with or be thrown away by that work.

Closing for now. If this is still an issue once V2 lands, please reopen (or open a fresh PR against the new code) and we'll take a proper look.