feat(app-server): add ThreadItem::DynamicToolCall (#12732)

Previously, clients would call `thread/start` with dynamic_tools set,
and when a model invokes a dynamic tool, it would just make the
server->client `item/tool/call` request and wait for the client's
response to complete the tool call. This works, but it doesn't have an
`item/started` or `item/completed` event.

Now we are doing this:
- [new] emit `item/started` with `DynamicToolCall` populated with the
call arguments
- send an `item/tool/call` server request
- [new] once the client responds, emit `item/completed` with
`DynamicToolCall` populated with the response.

Also, with `persistExtendedHistory: true`, dynamic tool calls are now
reconstructable in `thread/read` and `thread/resume` as
`ThreadItem::DynamicToolCall`.

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

@@ -3057,6 +3057,19 @@ pub enum ThreadItem {
     },
     #[serde(rename_all = "camelCase")]
     #[ts(rename_all = "camelCase")]
+    DynamicToolCall {
+        id: String,
+        tool: String,
+        arguments: JsonValue,
+        status: DynamicToolCallStatus,
+        content_items: Option<Vec<DynamicToolCallOutputContentItem>>,
+        success: Option<bool>,
+        /// The duration of the dynamic tool call in milliseconds.
+        #[ts(type = "number | null")]
+        duration_ms: Option<i64>,
+    },
+    #[serde(rename_all = "camelCase")]
+    #[ts(rename_all = "camelCase")]
     CollabAgentToolCall {
         /// Unique identifier for this collab tool call.
         id: String,
@@ -3105,6 +3118,7 @@ impl ThreadItem {
             | ThreadItem::CommandExecution { id, .. }
             | ThreadItem::FileChange { id, .. }
             | ThreadItem::McpToolCall { id, .. }
+            | ThreadItem::DynamicToolCall { id, .. }
             | ThreadItem::CollabAgentToolCall { id, .. }
             | ThreadItem::WebSearch { id, .. }
             | ThreadItem::ImageView { id, .. }
@@ -3285,6 +3299,15 @@ pub enum McpToolCallStatus {
     Failed,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub enum DynamicToolCallStatus {
+    InProgress,
+    Completed,
+    Failed,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]