Summary

PATCH /v1/threads/{id} currently accepts only { "archived": true|false }. Whalescale needs per-turn overrides (model, reasoning effort, etc.) and other thread metadata edits without going through a full thread recreate.

Scope

Extend the patch handler in crates/tui/src/runtime_api.rs (currently around update_thread) to accept additional optional fields:

• title (rename)
• model_override (per-thread default)
• reasoning_effort_override
• system_prompt_override (additive)

Each missing in body = no change. Validate inputs and reject unknown fields with a 400.

Tracks

• whalescale#256 — PATCH /v1/threads accepts only archived (workaround: per-turn override)
• Umbrella: whalescale#228

Acceptance

• New fields persisted via runtime_threads.rs (bump schema_version if storage shape changes).
• Updated request shape documented in docs/RUNTIME_API.md.
• Existing { "archived": ... } calls still work unchanged.