## Why
Interrupting a turn while MCP tools were still starting could abort before the
submitted user input was recorded in conversation history.
## What changed
- Build and retain the MCP tool list and tool router as part of each step
snapshot, using the turn cancellation token during tool discovery.
- Record turn hooks and submitted input when cancellation occurs during startup
prewarming, pre-sampling compaction, or first-step capture.
- Reuse the captured router for sampling, compaction, and prompt debugging so
advertised and executable tools share the same request-scoped view.
## Testing
Add coverage that interrupts each affected MCP startup phase and verifies that
the user prompt remains in history before the turn-aborted marker.
GitOrigin-RevId: 6e96c6814357a55545d69b580e28f35933cfadf7
## Why
Remote compaction can process large histories. Repeatedly estimating and replacing the full history, and cloning it when tracing is disabled, adds avoidable CPU and memory overhead.
## What changed
- Estimate each history item's token count once, update the total as trailing tool outputs are rewritten, and replace history only after all rewrites are selected.
- Preserve unclamped token totals while calculating removed tokens so saturated estimates do not hide overflow.
- Snapshot compaction input history only when rollout tracing is enabled.
- Reuse the v2 request input instead of cloning it before adding the compaction trigger.
## Testing
- Cover enabled and disabled compaction trace contexts through `is_enabled()` assertions.
GitOrigin-RevId: 8de9c9704ba29532fba05430eb204bbae2e8bf83
## Why
This PR is a behavior-preserving refactor only. It does not add a
fallback, change which model is used for compaction, or otherwise change
compaction behavior. The behavioral change is implemented in the stacked
follow-up, #30319.
Pre-sampling compaction deliberately uses the previous turn's context
when the compaction compatibility hash changes or when switching to a
model with a smaller context window. That preserves the model settings
that produced the history being compacted, but the previous context is
not always usable. For example, a resumed thread can still reference a
model slug that has since been retired, causing compaction to fail
before the currently selected model can sample.
#30319 addresses that failure mode by retrying compaction with the
current turn's selected model when the backend rejects the
previous-model attempt. This PR performs only that preparatory refactor.
## What changed
- Extracted one legacy `/responses/compact` request attempt into
`compact_remote_request.rs`.
- Extracted one Responses-based remote compaction request attempt into
`compact_remote_v2_attempt.rs`.
- Kept hooks, lifecycle events, analytics, window advancement, history
processing and installation, and error behavior unchanged in the
existing orchestration paths.
- Preserved standalone Responses-based compaction's owned client-session
lifetime through lifecycle completion.
## Testing
- `just test -p codex-core -E 'test(remote_compact)'` (22 tests)
Ahmed Ibrahim