Forward caller metadata on MCP resource reads (#59509)

## What changed

Accept an optional `_meta` object on `mcpServer/resource/read` and forward it to MCP `resources/read`, including reads bound to an originating tool call. Update the protocol schemas and generated TypeScript and Python types.

Reject caller metadata containing host-owned `threadId`, `x-codex-turn-metadata`, or `codex/connectionLease` keys. For `codex_apps`, also reserve `connector_id`, `link_id`, and `_codex_apps.resource_uri` to preserve app and account routing.

## Testing

Add integration coverage for metadata forwarding through stdio, hosted app reads with and without a thread, and origin-bound widget reads. Cover rejection of reserved keys and non-object metadata.

GitOrigin-RevId: 227ee0fb5fe15fa2ff2ec66d4d5ae16de8935a8c

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

@@ -2569,6 +2569,7 @@ mod tests {
         let mcp_resource_read = ClientRequest::McpResourceRead {
             request_id: request_id(),
             params: v2::McpResourceReadParams {
+                meta: None,
                 thread_id: Some("thread-1".to_string()),
                 origin_call_id: None,
                 server: "server-a".to_string(),
@@ -2763,6 +2764,7 @@ mod tests {
         let mcp_resource_read = ClientRequest::McpResourceRead {
             request_id: request_id(),
             params: v2::McpResourceReadParams {
+                meta: None,
                 thread_id: None,
                 origin_call_id: None,
                 server: "server-a".to_string(),

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

@@ -112,6 +112,10 @@ pub struct ListMcpServerStatusResponse {
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]
 pub struct McpResourceReadParams {
+    /// Additional MCP request metadata. Account and turn routing keys are reserved.
+    #[serde(rename = "_meta")]
+    #[ts(rename = "_meta", optional = nullable)]
+    pub meta: Option<serde_json::Map<String, JsonValue>>,
     #[ts(optional = nullable)]
     pub thread_id: Option<String>,
     /// Originating MCP tool call used to select the resource's app.