feat: add metric to track the number of turns with memory usage (#18662)

Add a metric `codex.turn.memory` to know if a turn used memories or not.
This is not part of the other turn metrics as a label to limit
cardinality

codex-rs/core/src/tasks/mod.rs

@@ -35,6 +35,7 @@ use codex_login::AuthManager;
 use codex_models_manager::manager::ModelsManager;
 use codex_otel::SessionTelemetry;
 use codex_otel::TURN_E2E_DURATION_METRIC;
+use codex_otel::TURN_MEMORY_METRIC;
 use codex_otel::TURN_NETWORK_PROXY_METRIC;
 use codex_otel::TURN_TOKEN_USAGE_METRIC;
 use codex_otel::TURN_TOOL_CALL_METRIC;
@@ -96,6 +97,29 @@ fn emit_turn_network_proxy_metric(
     );
 }
 
+fn emit_turn_memory_metric(
+    session_telemetry: &SessionTelemetry,
+    feature_enabled: bool,
+    config_enabled: bool,
+    has_citations: bool,
+) {
+    let read_allowed = feature_enabled && config_enabled;
+    session_telemetry.counter(
+        TURN_MEMORY_METRIC,
+        /*inc*/ 1,
+        &[
+            ("read_allowed", bool_tag(read_allowed)),
+            ("feature_enabled", bool_tag(feature_enabled)),
+            ("config_use_memories", bool_tag(config_enabled)),
+            ("has_citations", bool_tag(has_citations)),
+        ],
+    );
+}
+
+fn bool_tag(value: bool) -> &'static str {
+    if value { "true" } else { "false" }
+}
+
 /// Thin wrapper that exposes the parts of [`Session`] task runners need.
 #[derive(Clone)]
 pub(crate) struct SessionTaskContext {
@@ -409,6 +433,7 @@ impl Session {
         let mut pending_input = Vec::<ResponseInputItem>::new();
         let mut should_clear_active_turn = false;
         let mut token_usage_at_turn_start = None;
+        let mut turn_had_memory_citation = false;
         let mut turn_tool_calls = 0_u64;
         let turn_state = {
             let mut active = self.active_turn.lock().await;
@@ -428,6 +453,7 @@ impl Session {
         if let Some(turn_state) = turn_state {
             let mut ts = turn_state.lock().await;
             pending_input = ts.take_pending_input();
+            turn_had_memory_citation = ts.has_memory_citation;
             turn_tool_calls = ts.tool_calls;
             token_usage_at_turn_start = Some(ts.token_usage_at_turn_start.clone());
         }
@@ -531,6 +557,12 @@ impl Session {
                 &[("token_type", "reasoning_output"), tmp_mem],
             );
         }
+        emit_turn_memory_metric(
+            &self.services.session_telemetry,
+            turn_context.features.enabled(Feature::MemoryTool),
+            turn_context.config.memories.use_memories,
+            turn_had_memory_citation,
+        );
         let (completed_at, duration_ms) = turn_context
             .turn_timing_state
             .completed_at_and_duration_ms()