## Why
Tool router construction rebuilds the deferred-tool BM25 index during
session initialization and before each sampling continuation, even when
the searchable tool metadata is unchanged. Local profiling measured
`append_tool_search_executor` at roughly 113 ms per continuation, making
repeated index construction the largest measured router-building cost.
## What changed
- Add a session-scoped `ToolSearchHandlerCache` so continuations and
user turns can reuse the existing handler.
- Key reuse on the complete ordered `Vec<ToolSearchInfo>`, rebuilding
when searchable text, loadable tool specs, source metadata, or ordering
changes.
- Build handlers outside the cache lock and recheck before publishing
them, avoiding holding the mutex during index construction.
## Verification
- `cache_reuses_identical_search_infos_and_rebuilds_changed_inputs`
covers exact cache reuse and invalidation when the ordered search
metadata changes.
- Local rollout profiling showed the initial router build populating the
cache and unchanged later continuations reusing it:
- uncached: 118 ms median across 14 spans from 3 rollouts
- cached: 4 ms median across 12 spans from 3 rollouts
## Why
Codex app-server latency traces do not granularly cover turn task
startup and inter-request handoffs. These spans help attribute time
across task execution, startup prewarm, in-flight tool completion, and
rollout persistence.
## What changed
- Add `session_task.run` spans around task execution and
`session_task.flush_rollout` around flushing pending conversation
transcript writes to durable storage
- Add `regular_task.prepare_run_turn` around regular-turn startup (Send
the `TurnStarted` event, reset turn-specific reasoning state, and
resolve any startup prewarm)
- Add `startup_prewarm.resolve` around waiting for background session
prewarming to finish, fail, time out, or be cancelled
- Add a function-level trace span around draining in-flight tool calls
(Wait for tool calls to complete, record tool result in conversation
history, and other bookkeeping)
## Verification
Trigger Codex rollout and observe new spans are included
## Why
Codex app-server latency traces do not granularly cover turn
orchestration, sampling-request preparation, and tool-loading work.
These spans help separate local coordination/setup costs from model
streaming and tool execution.
## What changed
- Add `run_turn.*` spans around sampling-request input preparation and
post-sampling state collection
- Add function-level trace spans around turn setup, hook execution,
compaction, prompt construction, and MCP tool exposure
- Add `built_tools.*` spans around plugin loading and discoverable-tool
loading
## Verification
Trigger Codex rollout and observe new spans are included
## Why
- Local profiling shows `append_tool_search_executor` averages ~113ms
per call. Adding a span lets us track this cost as we optimize in
follow-up PRs, either by reducing the work or avoiding repeated rebuilds
when inputs have not changed.
- While we're here, we can add spans to `build_tool_router` and other
sub-calls which code analysis shows may have additional opportunities
for improvement.
## What changed
Add function-level trace spans around `build_tool_router`,
`build_tool_specs_and_registry`, `add_tool_sources`,
`append_tool_search_executor`, and
`build_model_visible_specs_and_registry`
## Verification
Trigger Codex rollout and observe new spans are included
## Why
[Recent PR](https://github.com/openai/codex/pull/22709) removed
`trace_id` from `TurnContextItem`.
## What changed
- Add to `TurnStartedEvent` so rollout consumers can correlate turns
with telemetry traces.
- Note that the branch name is out of date because I originally re-added
to `TurnContextItem`, but we decided to move it to `TurnStartedEvent`.
## Verification
- `cargo test -p codex-protocol`
- `cargo test -p codex-core --lib
regular_turn_emits_turn_started_without_waiting_for_startup_prewarm`
- `cargo test -p codex-core --test all
emits_warning_when_resumed_model_differs`
- `cargo test -p codex-rollout`
- `cargo test -p codex-state`
## Why
- Similar change as https://github.com/openai/codex/pull/21219
- Without change: MCP tool calls receive
`_meta["x-codex-turn-metadata"]` with various key values.
- Issue: MCP servers currently do not know if user input was requested
during the turn (Ex: Model decides to prompt the user for approval
mid-turn before making a possibly risky tool call). MCP servers may want
to know this when tracking latency metrics because these instances are
inflated.
## What Changed
- With change: MCP turn metadata now includes
`user_input_requested_during_turn` when a model-visible
`request_user_input` call happened earlier in the turn, propagated in
`_meta["x-codex-turn-metadata"]`.
- `mark_turn_user_input_requested()` is called when user input is
requested through either MCP elicitation (`mcp.rs`) or the
`request_user_input` tool (`mod.rs`).
- MCP tool call `_meta` is now built immediately before execution
(`mcp_tool_call.rs`) so user input requested earlier in the same turn,
including within the same tool call via elicitation, is reflected in the
metadata.
- Normal `/responses` turn metadata headers are unchanged.
## Verification
- `codex-rs/core/src/session/mcp_tests.rs`
- `codex-rs/core/src/tools/handlers/request_user_input_tests.rs`
- `codex-rs/core/src/turn_metadata_tests.rs`
- `codex-rs/core/tests/suite/search_tool.rs`
## Why
- Similar change as https://github.com/openai/codex/pull/19473.
- Without change: MCP tool calls receive
`_meta["x-codex-turn-metadata"]` with `session_id`, `turn_id`, and
`turn_started_at_unix_ms`.
- Issue: MCP servers may want the model and reasoning effort to better
understand tool-call behavior and latency relative to turn start.
## What Changed
- With change: MCP turn metadata now includes `model` and
`reasoning_effort`, propagated in `_meta["x-codex-turn-metadata"]`.
- Normal `/responses` turn metadata headers are unchanged.
## Verification
- `codex-rs/core/src/mcp_tool_call_tests.rs`
- `codex-rs/core/src/turn_metadata_tests.rs`
- `codex-rs/core/tests/suite/search_tool.rs`
## Why
- Without change: MCP tool call spans include request-side details such
as server, tool, call ID, connector, session, and turn.
- Issue: Some useful telemetry is only known by the MCP server after it
handles the tool call, such as target identity or whether the call
triggered a user-facing flow.
## What Changed
- With change: Codex reads allowlisted telemetry from
`_meta["codex/telemetry"]["span"]` and records it on the
`mcp.tools.call` span.
- Adds span fields for `codex.mcp.target.id` and
`codex.mcp.user_flow.triggered`, with strict type checks and bounded
target ID length.
## Verification
`codex-rs/core/src/mcp_tool_call_tests.rs`
## Why
- Without change: MCP tool calls receive
`_meta["x-codex-turn-metadata"]` with `session_id` and `turn_id`.
- Issue: MCP servers may want the turn start timestamp to measure
internal latency relative to turn start.
## What Changed
- With change: turn metadata now includes `turn_started_at_unix_ms`,
which is propagated to MCP tool calls in
`_meta["x-codex-turn-metadata"]`.
## Verification
- `codex-rs/core/src/mcp_tool_call_tests.rs`
- `codex-rs/core/src/turn_metadata_tests.rs`
- `codex-rs/core/src/turn_timing_tests.rs`
- `codex-rs/core/tests/responses_headers.rs`
- `codex-rs/core/tests/suite/search_tool.rs`
mchen-oai