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/schema/json/ClientRequest.json

@@ -2173,6 +2173,14 @@
     },
     "McpResourceReadParams": {
       "properties": {
+        "_meta": {
+          "additionalProperties": true,
+          "description": "Additional MCP request metadata. Account and turn routing keys are reserved.",
+          "type": [
+            "object",
+            "null"
+          ]
+        },
         "connectorId": {
           "type": [
             "string",

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -15299,6 +15299,14 @@
       "McpResourceReadParams": {
         "$schema": "http://json-schema.org/draft-07/schema#",
         "properties": {
+          "_meta": {
+            "additionalProperties": true,
+            "description": "Additional MCP request metadata. Account and turn routing keys are reserved.",
+            "type": [
+              "object",
+              "null"
+            ]
+          },
           "connectorId": {
             "type": [
               "string",

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -11260,6 +11260,14 @@
     "McpResourceReadParams": {
       "$schema": "http://json-schema.org/draft-07/schema#",
       "properties": {
+        "_meta": {
+          "additionalProperties": true,
+          "description": "Additional MCP request metadata. Account and turn routing keys are reserved.",
+          "type": [
+            "object",
+            "null"
+          ]
+        },
         "connectorId": {
           "type": [
             "string",

codex-rs/app-server-protocol/schema/json/v2/McpResourceReadParams.json

@@ -22,6 +22,14 @@
     }
   },
   "properties": {
+    "_meta": {
+      "additionalProperties": true,
+      "description": "Additional MCP request metadata. Account and turn routing keys are reserved.",
+      "type": [
+        "object",
+        "null"
+      ]
+    },
     "connectorId": {
       "type": [
         "string",

codex-rs/app-server-protocol/schema/typescript/v2/McpResourceReadParams.ts

@@ -1,9 +1,14 @@
 // GENERATED CODE! DO NOT MODIFY BY HAND!
 
 // This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
+import type { JsonValue } from "../serde_json/JsonValue";
 import type { McpResourceReadTarget } from "./McpResourceReadTarget";
 
-export type McpResourceReadParams = { threadId?: string | null,
+export type McpResourceReadParams = {
+/**
+ * Additional MCP request metadata. Account and turn routing keys are reserved.
+ */
+_meta?: { [key in string]?: JsonValue } | null, threadId?: string | null,
 /**
  * Originating MCP tool call used to select the resource's app.
  */

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.