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/otel/tests/suite/runtime_summary.rs

@@ -0,0 +1,77 @@
+use codex_app_server_protocol::AuthMode;
+use codex_otel::OtelManager;
+use codex_otel::RuntimeMetricTotals;
+use codex_otel::RuntimeMetricsSummary;
+use codex_otel::metrics::MetricsClient;
+use codex_otel::metrics::MetricsConfig;
+use codex_otel::metrics::Result;
+use codex_protocol::ThreadId;
+use codex_protocol::protocol::SessionSource;
+use eventsource_stream::Event as StreamEvent;
+use opentelemetry_sdk::metrics::InMemoryMetricExporter;
+use pretty_assertions::assert_eq;
+use std::time::Duration;
+
+#[test]
+fn runtime_metrics_summary_collects_tool_api_and_streaming_metrics() -> Result<()> {
+    let exporter = InMemoryMetricExporter::default();
+    let metrics = MetricsClient::new(
+        MetricsConfig::in_memory("test", "codex-cli", env!("CARGO_PKG_VERSION"), exporter)
+            .with_runtime_reader(),
+    )?;
+    let manager = OtelManager::new(
+        ThreadId::new(),
+        "gpt-5.1",
+        "gpt-5.1",
+        Some("account-id".to_string()),
+        None,
+        Some(AuthMode::ApiKey),
+        true,
+        "tty".to_string(),
+        SessionSource::Cli,
+    )
+    .with_metrics(metrics);
+
+    manager.reset_runtime_metrics();
+
+    manager.tool_result(
+        "shell",
+        "call-1",
+        "{\"cmd\":\"echo\"}",
+        Duration::from_millis(250),
+        true,
+        "ok",
+    );
+    manager.record_api_request(1, Some(200), None, Duration::from_millis(300));
+    let sse_response: std::result::Result<
+        Option<std::result::Result<StreamEvent, eventsource_stream::EventStreamError<&str>>>,
+        tokio::time::error::Elapsed,
+    > = Ok(Some(Ok(StreamEvent {
+        event: "response.created".to_string(),
+        data: "{}".to_string(),
+        id: String::new(),
+        retry: None,
+    })));
+    manager.log_sse_event(&sse_response, Duration::from_millis(120));
+
+    let summary = manager
+        .runtime_metrics_summary()
+        .expect("runtime metrics summary should be available");
+    let expected = RuntimeMetricsSummary {
+        tool_calls: RuntimeMetricTotals {
+            count: 1,
+            duration_ms: 250,
+        },
+        api_calls: RuntimeMetricTotals {
+            count: 1,
+            duration_ms: 300,
+        },
+        streaming_events: RuntimeMetricTotals {
+            count: 1,
+            duration_ms: 120,
+        },
+    };
+    assert_eq!(summary, expected);
+
+    Ok(())
+}