feat: show runtime metrics in console (#10278)

Summary of changes:

- Adds a new feature flag: runtime_metrics
  - Declared in core/src/features.rs
  - Added to core/config.schema.json
  - Wired into OTEL init in core/src/otel_init.rs

- Enables on-demand runtime metric snapshots in OTEL
  - Adds runtime_metrics: bool to otel/src/config.rs
  - Enables experimental custom reader features in otel/Cargo.toml
  - Adds snapshot/reset/summary APIs in:
    - otel/src/lib.rs
    - otel/src/metrics/client.rs
    - otel/src/metrics/config.rs
    - otel/src/metrics/error.rs

- Defines metric names and a runtime summary builder
  - New files:
    - otel/src/metrics/names.rs
    - otel/src/metrics/runtime_metrics.rs
  - Summarizes totals for:
    - Tool calls
    - API requests
    - SSE/streaming events

- Instruments metrics collection in OTEL manager
  - otel/src/traces/otel_manager.rs now records:
    - API call counts + durations
    - SSE event counts + durations (success/failure)
    - Tool call metrics now use shared constants

- Surfaces runtime metrics in the TUI
  - Resets runtime metrics at turn start in tui/src/chatwidget.rs
- Displays metrics in the final separator line in
tui/src/history_cell.rs

- Adds tests
  - New OTEL tests:
    - otel/tests/suite/snapshot.rs
    - otel/tests/suite/runtime_summary.rs
  - New TUI test:
- final_message_separator_includes_runtime_metrics in
tui/src/history_cell.rs

Scope:
- 19 files changed
- ~652 insertions, 38 deletions


<img width="922" height="169" alt="Screenshot 2026-01-30 at 4 11 34 PM"
src="https://github.com/user-attachments/assets/1efd754d-a16d-4564-83a5-f4442fd2f998"
/>

codex-rs/core/src/features.rs

@@ -101,6 +101,8 @@ pub enum Feature {
     RemoteModels,
     /// Experimental shell snapshotting.
     ShellSnapshot,
+    /// Enable runtime metrics snapshots via a manual reader.
+    RuntimeMetrics,
     /// Persist rollout metadata to a local SQLite database.
     Sqlite,
     /// Append additional AGENTS.md guidance to user instructions.
@@ -437,6 +439,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         },
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::RuntimeMetrics,
+        key: "runtime_metrics",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::Sqlite,
         key: "sqlite",

codex-rs/core/src/otel_init.rs

@@ -2,6 +2,7 @@ use crate::config::Config;
 use crate::config::types::OtelExporterKind as Kind;
 use crate::config::types::OtelHttpProtocol as Protocol;
 use crate::default_client::originator;
+use crate::features::Feature;
 use codex_otel::config::OtelExporter;
 use codex_otel::config::OtelHttpProtocol;
 use codex_otel::config::OtelSettings;
@@ -77,6 +78,7 @@ pub fn build_provider(
 
     let originator = originator();
     let service_name = service_name_override.unwrap_or(originator.value.as_str());
+    let runtime_metrics = config.features.enabled(Feature::RuntimeMetrics);
 
     OtelProvider::from(&OtelSettings {
         service_name: service_name.to_string(),
@@ -86,6 +88,7 @@ pub fn build_provider(
         exporter,
         trace_exporter,
         metrics_exporter,
+        runtime_metrics,
     })
 }