[codex-analytics] add extensible feature thread sources (#27063)

## Why
- `ThreadSource` currently defines a closed set of core-owned values
- Product features also create threads for background or scheduled work
- Adding every product-specific value to the core enum would require
repeated `codex-rs` protocol changes
- Feature-backed values let product callers provide precise attribution
while preserving the existing core classifications

## What Changed
- Adds `ThreadSource::Feature(String)` for app-owned thread source
values
- Represents all app-server v2 thread sources as scalar strings, so a
feature source is supplied as `"automation"`
- Persists and emits the feature's plain string label, so `"automation"`
produces `thread_source="automation"` in analytics
- Keeps `user`, `subagent`, and `memory_consolidation` as explicit
core-owned values and regenerates the app-server schemas and TypeScript
bindings

## Verification
- `just write-app-server-schema`
- `cargo check --workspace`
- `just test -p codex-protocol
feature_thread_source_serializes_as_its_app_owned_label`
- `just test -p codex-app-server-protocol
thread_sources_round_trip_as_scalar_labels`
- `cargo test -p codex-analytics
thread_initialized_event_serializes_expected_shape`
- `just fmt`

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -57,6 +57,30 @@ fn test_absolute_path() -> AbsolutePathBuf {
     absolute_path("readable")
 }
 
+#[test]
+fn thread_sources_round_trip_as_scalar_labels() {
+    for (source, label) in [
+        (ThreadSource::User, "user"),
+        (ThreadSource::Subagent, "subagent"),
+        (
+            ThreadSource::Feature("automation".to_string()),
+            "automation",
+        ),
+        (ThreadSource::MemoryConsolidation, "memory_consolidation"),
+    ] {
+        let value = serde_json::to_value(&source).expect("serialize thread source");
+
+        assert_eq!(value, json!(label));
+        assert_eq!(
+            serde_json::from_value::<ThreadSource>(value).expect("deserialize thread source"),
+            source
+        );
+
+        let core_source: codex_protocol::protocol::ThreadSource = source.clone().into();
+        assert_eq!(ThreadSource::from(core_source), source);
+    }
+}
+
 #[test]
 fn approvals_reviewer_serializes_auto_review_and_accepts_legacy_guardian_subagent() {
     assert_eq!(

codex-rs/app-server-protocol/src/protocol/v2/thread_data.rs

@@ -7,6 +7,8 @@ use codex_protocol::protocol::SubAgentSource as CoreSubAgentSource;
 use codex_protocol::protocol::ThreadSource as CoreThreadSource;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use schemars::JsonSchema;
+use schemars::r#gen::SchemaGenerator;
+use schemars::schema::Schema;
 use serde::Deserialize;
 use serde::Serialize;
 use std::path::PathBuf;
@@ -61,20 +63,47 @@ impl From<SessionSource> for CoreSessionSource {
     }
 }
 
-#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, JsonSchema, TS)]
-#[serde(rename_all = "snake_case")]
-#[ts(rename_all = "snake_case", export_to = "v2/")]
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, TS)]
+#[serde(try_from = "String", into = "String")]
+#[ts(type = "string")]
+#[ts(export_to = "v2/")]
 pub enum ThreadSource {
     User,
     Subagent,
+    Feature(String),
     MemoryConsolidation,
 }
 
+impl JsonSchema for ThreadSource {
+    fn schema_name() -> String {
+        "ThreadSource".to_string()
+    }
+
+    fn json_schema(generator: &mut SchemaGenerator) -> Schema {
+        String::json_schema(generator)
+    }
+}
+
+impl TryFrom<String> for ThreadSource {
+    type Error = String;
+
+    fn try_from(value: String) -> Result<Self, Self::Error> {
+        value.parse::<CoreThreadSource>().map(Into::into)
+    }
+}
+
+impl From<ThreadSource> for String {
+    fn from(value: ThreadSource) -> Self {
+        CoreThreadSource::from(value).into()
+    }
+}
+
 impl From<CoreThreadSource> for ThreadSource {
     fn from(value: CoreThreadSource) -> Self {
         match value {
             CoreThreadSource::User => ThreadSource::User,
             CoreThreadSource::Subagent => ThreadSource::Subagent,
+            CoreThreadSource::Feature(feature) => ThreadSource::Feature(feature),
             CoreThreadSource::MemoryConsolidation => ThreadSource::MemoryConsolidation,
         }
     }
@@ -85,6 +114,7 @@ impl From<ThreadSource> for CoreThreadSource {
         match value {
             ThreadSource::User => CoreThreadSource::User,
             ThreadSource::Subagent => CoreThreadSource::Subagent,
+            ThreadSource::Feature(feature) => CoreThreadSource::Feature(feature),
             ThreadSource::MemoryConsolidation => CoreThreadSource::MemoryConsolidation,
         }
     }