[tool search] support namespaced deferred dynamic tools (#18413)

Deferred dynamic tools need to round-trip a namespace so a tool returned
by `tool_search` can be called through the same registry key that core
uses for dispatch.

This change adds namespace support for dynamic tool specs/calls,
persists it through app-server thread state, and routes dynamic tool
calls by full `ToolName` while still sending the app the leaf tool name.
Deferred dynamic tools must provide a namespace; non-deferred dynamic
tools may remain top-level.

It also introduces `LoadableToolSpec` as the shared
function-or-namespace Responses shape used by both `tool_search` output
and dynamic tool registration, so dynamic tools use the same wrapping
logic in both paths.

Validation:
- `cargo test -p codex-tools`
- `cargo test -p codex-core tool_search`

---------

Co-authored-by: Sayan Sisodiya <sayan@openai.com>

codex-rs/protocol/src/dynamic_tools.rs

@@ -8,6 +8,8 @@ use ts_rs::TS;
 #[derive(Debug, Clone, Serialize, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 pub struct DynamicToolSpec {
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub namespace: Option<String>,
     pub name: String,
     pub description: String,
     pub input_schema: JsonValue,
@@ -20,6 +22,8 @@ pub struct DynamicToolSpec {
 pub struct DynamicToolCallRequest {
     pub call_id: String,
     pub turn_id: String,
+    #[serde(default)]
+    pub namespace: Option<String>,
     pub tool: String,
     pub arguments: JsonValue,
 }
@@ -44,6 +48,7 @@ pub enum DynamicToolCallOutputContentItem {
 #[derive(Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct DynamicToolSpecDe {
+    namespace: Option<String>,
     name: String,
     description: String,
     input_schema: JsonValue,
@@ -57,6 +62,7 @@ impl<'de> Deserialize<'de> for DynamicToolSpec {
         D: Deserializer<'de>,
     {
         let DynamicToolSpecDe {
+            namespace,
             name,
             description,
             input_schema,
@@ -65,6 +71,7 @@ impl<'de> Deserialize<'de> for DynamicToolSpec {
         } = DynamicToolSpecDe::deserialize(deserializer)?;
 
         Ok(Self {
+            namespace,
             name,
             description,
             input_schema,
@@ -99,6 +106,7 @@ mod tests {
         assert_eq!(
             actual,
             DynamicToolSpec {
+                namespace: None,
                 name: "lookup_ticket".to_string(),
                 description: "Fetch a ticket".to_string(),
                 input_schema: json!({

codex-rs/protocol/src/protocol.rs

@@ -2441,6 +2441,9 @@ pub struct DynamicToolCallResponseEvent {
     pub call_id: String,
     /// Turn ID that this dynamic tool call belongs to.
     pub turn_id: String,
+    /// Dynamic tool namespace, when one was provided.
+    #[serde(default)]
+    pub namespace: Option<String>,
     /// Dynamic tool name.
     pub tool: String,
     /// Dynamic tool call arguments.