## Why
Model settings can change between steps in the same turn. Token-budget defaults,
context-window limits, and model-visible guidance need to stay aligned with the
model captured for each step.
## What changed
- Preserve the turn's original token-budget preferences and resolve model-owned
defaults when each `StepContext` is created.
- Use the step's model to determine context-window availability and token-budget
guidance, while keeping explicit user settings unchanged.
- Emit one-time replacement or removal notices when context-window guidance
changes, including compatibility with previously persisted world-state
snapshots.
- Add `ModelInfo::usable_context_window()` to distinguish reserved-headroom
capacity from the resolved context window and auto-compaction limit.
## Testing
- Cover mid-turn model switches with model defaults, explicit settings, config
reloads, missing context windows, and missing destination guidance.
- Cover unchanged, replaced, removed, blank, and legacy guidance transitions.
GitOrigin-RevId: 91100a9f3625bef8a79ecd158eb028051c309eee
## What changed
- Add optional Browser Use and Computer Use confirmation-policy Markdown to model catalog messages.
- Send the configured documents verbatim in `openai/confirmation_policies` metadata for `node_repl` and `cua_repl` tool calls. Send an empty object when the issuing model has no policies so runtime defaults are cleared.
- Use the issuing step's model snapshot across approval waits, and omit the metadata for other MCP servers and Guardian sessions.
## Testing
- Cover policy serialization, configuration overrides, model changes, approval waits, partial or empty policies, eligible server filtering, and Guardian exclusion.
GitOrigin-RevId: 038c4c262a31fc71986e4a2a947fe9bcbd407acc
## What changed
- Add bundled proactivity and follow-up guidance when `ReasoningEffort::Persistent` is selected.
- Allow model metadata to override or disable the guidance with `persistent_instructions`.
- Track the instructions as world state so effort and model changes replace or retire stale guidance without duplicating unchanged context.
- Tailor approval guidance to `send_user_message_async` availability, rebuild it for forked agents and rolled-back history, and exclude Guardian sessions.
## Testing
- Cover default, overridden, disabled, replaced, and retired instructions.
- Cover model changes, history transitions, agent forks, Guardian sessions, and asynchronous-message tool availability.
GitOrigin-RevId: 78e05d0335a70b385bd069b45edcd4ba570cef91
## What changed
- Add a feature-gated `TurnSettings` operation that can update the model,
reasoning effort, reasoning summary, and service tier for subsequent steps of
a named running turn without changing future thread settings.
- Report whether an update was applied, rejected, or lost its live target.
- Revalidate managed constraints and preserve the turn's admitted approval and
Guardian safety properties before publishing an updated settings snapshot.
## Testing
- Cover sparse updates, step capture and ordering, target replacement, managed
policy changes, model metadata safety, and separation from future settings.
GitOrigin-RevId: ecaaaa95b4fd4ec9d62265bef551582dddb36d78
Abhinav