## Why
Thread settings can change while a turn is running, and delegated review or
compaction steps can select a different model. Each request needs a consistent
set of settings resolved against the model that will execute it.
## What changed
- Capture immutable resolved settings for each model step, including model
metadata, reasoning options, service tier, approvals, and personality.
- Keep in-flight steps on their captured settings while applying thread updates
to subsequent work.
- Resolve inherited reasoning summaries and filter service tiers against the
selected model and feature configuration for review and compaction steps.
## Testing
Added coverage for settings updates during paused turns, model changes,
previous-model compaction, review-model defaults, and service-tier filtering.
GitOrigin-RevId: fca4b3b305379f1bf26a5cac75ee0dd1747ac1f6