feat: add session source as otel metadata tag (#9720)

Add session.source and user.account_id as global OTEL metric tags to
identify client surface and user.

codex-rs/otel/src/lib.rs

@@ -31,6 +31,7 @@ pub struct OtelEventMetadata {
     pub(crate) auth_mode: Option<String>,
     pub(crate) account_id: Option<String>,
     pub(crate) account_email: Option<String>,
+    pub(crate) session_source: String,
     pub(crate) model: String,
     pub(crate) slug: String,
     pub(crate) log_user_prompts: bool,
@@ -149,8 +150,13 @@ impl OtelManager {
         if !self.metrics_use_metadata_tags {
             return Ok(Vec::new());
         }
-        let mut tags = Vec::with_capacity(5);
+        let mut tags = Vec::with_capacity(6);
         Self::push_metadata_tag(&mut tags, "auth_mode", self.metadata.auth_mode.as_deref())?;
+        Self::push_metadata_tag(
+            &mut tags,
+            "session_source",
+            Some(self.metadata.session_source.as_str()),
+        )?;
         Self::push_metadata_tag(&mut tags, "model", Some(self.metadata.model.as_str()))?;
         Self::push_metadata_tag(&mut tags, "app.version", Some(self.metadata.app_version))?;
         Ok(tags)