feat: expose provider capability bounds to app server clients (#20049)

follow up of #19442. The app server now exposes provider-derived bounds
through a new v2 `modelProvider/read` method. The response reports the
configured provider map key as `modelProvider` and returns the effective
capability booleans so clients can align their UI with the same
provider-owned limits used by core.

codex-rs/app-server-protocol/schema/json/ClientRequest.json

@@ -1896,6 +1896,9 @@
       },
       "type": "object"
     },
+    "ModelProviderCapabilitiesReadParams": {
+      "type": "object"
+    },
     "NetworkAccess": {
       "enum": [
         "restricted",
@@ -5478,6 +5481,30 @@
       "title": "Model/listRequest",
       "type": "object"
     },
+    {
+      "properties": {
+        "id": {
+          "$ref": "#/definitions/RequestId"
+        },
+        "method": {
+          "enum": [
+            "modelProvider/capabilities/read"
+          ],
+          "title": "ModelProvider/capabilities/readRequestMethod",
+          "type": "string"
+        },
+        "params": {
+          "$ref": "#/definitions/ModelProviderCapabilitiesReadParams"
+        }
+      },
+      "required": [
+        "id",
+        "method",
+        "params"
+      ],
+      "title": "ModelProvider/capabilities/readRequest",
+      "type": "object"
+    },
     {
       "properties": {
         "id": {

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

@@ -1266,6 +1266,30 @@
           "title": "Model/listRequest",
           "type": "object"
         },
+        {
+          "properties": {
+            "id": {
+              "$ref": "#/definitions/v2/RequestId"
+            },
+            "method": {
+              "enum": [
+                "modelProvider/capabilities/read"
+              ],
+              "title": "ModelProvider/capabilities/readRequestMethod",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/definitions/v2/ModelProviderCapabilitiesReadParams"
+            }
+          },
+          "required": [
+            "id",
+            "method",
+            "params"
+          ],
+          "title": "ModelProvider/capabilities/readRequest",
+          "type": "object"
+        },
         {
           "properties": {
             "id": {
@@ -11035,6 +11059,32 @@
         "title": "ModelListResponse",
         "type": "object"
       },
+      "ModelProviderCapabilitiesReadParams": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "ModelProviderCapabilitiesReadParams",
+        "type": "object"
+      },
+      "ModelProviderCapabilitiesReadResponse": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "properties": {
+          "imageGeneration": {
+            "type": "boolean"
+          },
+          "namespaceTools": {
+            "type": "boolean"
+          },
+          "webSearch": {
+            "type": "boolean"
+          }
+        },
+        "required": [
+          "imageGeneration",
+          "namespaceTools",
+          "webSearch"
+        ],
+        "title": "ModelProviderCapabilitiesReadResponse",
+        "type": "object"
+      },
       "ModelRerouteReason": {
         "enum": [
           "highRiskCyberActivity"

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

@@ -1972,6 +1972,30 @@
           "title": "Model/listRequest",
           "type": "object"
         },
+        {
+          "properties": {
+            "id": {
+              "$ref": "#/definitions/RequestId"
+            },
+            "method": {
+              "enum": [
+                "modelProvider/capabilities/read"
+              ],
+              "title": "ModelProvider/capabilities/readRequestMethod",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/definitions/ModelProviderCapabilitiesReadParams"
+            }
+          },
+          "required": [
+            "id",
+            "method",
+            "params"
+          ],
+          "title": "ModelProvider/capabilities/readRequest",
+          "type": "object"
+        },
         {
           "properties": {
             "id": {
@@ -7689,6 +7713,32 @@
       "title": "ModelListResponse",
       "type": "object"
     },
+    "ModelProviderCapabilitiesReadParams": {
+      "$schema": "http://json-schema.org/draft-07/schema#",
+      "title": "ModelProviderCapabilitiesReadParams",
+      "type": "object"
+    },
+    "ModelProviderCapabilitiesReadResponse": {
+      "$schema": "http://json-schema.org/draft-07/schema#",
+      "properties": {
+        "imageGeneration": {
+          "type": "boolean"
+        },
+        "namespaceTools": {
+          "type": "boolean"
+        },
+        "webSearch": {
+          "type": "boolean"
+        }
+      },
+      "required": [
+        "imageGeneration",
+        "namespaceTools",
+        "webSearch"
+      ],
+      "title": "ModelProviderCapabilitiesReadResponse",
+      "type": "object"
+    },
     "ModelRerouteReason": {
       "enum": [
         "highRiskCyberActivity"

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

@@ -0,0 +1,5 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "ModelProviderCapabilitiesReadParams",
+  "type": "object"
+}

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

@@ -0,0 +1,21 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "properties": {
+    "imageGeneration": {
+      "type": "boolean"
+    },
+    "namespaceTools": {
+      "type": "boolean"
+    },
+    "webSearch": {
+      "type": "boolean"
+    }
+  },
+  "required": [
+    "imageGeneration",
+    "namespaceTools",
+    "webSearch"
+  ],
+  "title": "ModelProviderCapabilitiesReadResponse",
+  "type": "object"
+}

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

@@ -0,0 +1,5 @@
+// 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.
+
+export type ModelProviderCapabilitiesReadParams = Record<string, never>;

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

@@ -0,0 +1,5 @@
+// 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.
+
+export type ModelProviderCapabilitiesReadResponse = { namespaceTools: boolean, imageGeneration: boolean, webSearch: boolean, };

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

@@ -234,6 +234,8 @@ export type { Model } from "./Model";
 export type { ModelAvailabilityNux } from "./ModelAvailabilityNux";
 export type { ModelListParams } from "./ModelListParams";
 export type { ModelListResponse } from "./ModelListResponse";
+export type { ModelProviderCapabilitiesReadParams } from "./ModelProviderCapabilitiesReadParams";
+export type { ModelProviderCapabilitiesReadResponse } from "./ModelProviderCapabilitiesReadResponse";
 export type { ModelRerouteReason } from "./ModelRerouteReason";
 export type { ModelReroutedNotification } from "./ModelReroutedNotification";
 export type { ModelUpgradeInfo } from "./ModelUpgradeInfo";

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

@@ -642,6 +642,11 @@ client_request_definitions! {
         serialization: None,
         response: v2::ModelListResponse,
     },
+    ModelProviderCapabilitiesRead => "modelProvider/capabilities/read" {
+        params: v2::ModelProviderCapabilitiesReadParams,
+        serialization: None,
+        response: v2::ModelProviderCapabilitiesReadResponse,
+    },
     ExperimentalFeatureList => "experimentalFeature/list" {
         params: v2::ExperimentalFeatureListParams,
         serialization: global("config"),
@@ -2243,6 +2248,23 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn serialize_model_provider_capabilities_read() -> Result<()> {
+        let request = ClientRequest::ModelProviderCapabilitiesRead {
+            request_id: RequestId::Integer(7),
+            params: v2::ModelProviderCapabilitiesReadParams {},
+        };
+        assert_eq!(
+            json!({
+                "method": "modelProvider/capabilities/read",
+                "id": 7,
+                "params": {}
+            }),
+            serde_json::to_value(&request)?,
+        );
+        Ok(())
+    }
+
     #[test]
     fn serialize_list_collaboration_modes() -> Result<()> {
         let request = ClientRequest::CollaborationModeList {

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

@@ -2355,6 +2355,20 @@ pub struct GetAccountResponse {
     pub requires_openai_auth: bool,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, Default, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ModelProviderCapabilitiesReadParams {}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ModelProviderCapabilitiesReadResponse {
+    pub namespace_tools: bool,
+    pub image_generation: bool,
+    pub web_search: bool,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Default, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]

codex-rs/app-server/README.md

@@ -191,6 +191,7 @@ Example with notification opt-out:
 - `fs/unwatch` — stop sending notifications for a prior `fs/watch`; returns `{}`.
 - `fs/changed` — notification emitted when watched paths change, including the `watchId` and `changedPaths`.
 - `model/list` — list available models (set `includeHidden: true` to include entries with `hidden: true`), with reasoning effort options, `additionalSpeedTiers`, optional legacy `upgrade` model ids, optional `upgradeInfo` metadata (`model`, `upgradeCopy`, `modelLink`, `migrationMarkdown`), and optional `availabilityNux` metadata.
+- `modelProvider/capabilities/read` — read provider-level capabilities for the currently configured model provider.
 - `experimentalFeature/list` — list feature flags with stage metadata (`beta`, `underDevelopment`, `stable`, etc.), enabled/default-enabled state, and cursor pagination. For non-beta flags, `displayName`/`description`/`announcement` are `null`.
 - `experimentalFeature/enablement/set` — patch the in-memory process-wide runtime feature enablement for the currently supported feature keys (`apps`, `memories`, `plugins`, `remote_control`, `tool_search`, `tool_suggest`, `tool_call_mcp_elicitation`). For each feature, precedence is: cloud requirements > --enable <feature_name> > config.toml > experimentalFeature/enablement/set (new) > code default.
 - `collaborationMode/list` — list available collaboration mode presets (experimental, no pagination). This response omits built-in developer instructions; clients should either pass `settings.developer_instructions: null` when setting a mode to use Codex's built-in instructions, or provide their own instructions explicitly.

codex-rs/app-server/src/codex_message_processor.rs

@@ -1275,6 +1275,11 @@ impl CodexMessageProcessor {
             ClientRequest::ConfigRequirementsRead { .. } => {
                 warn!("ConfigRequirementsRead request reached CodexMessageProcessor unexpectedly");
             }
+            ClientRequest::ModelProviderCapabilitiesRead { .. } => {
+                warn!(
+                    "ModelProviderCapabilitiesRead request reached CodexMessageProcessor unexpectedly"
+                );
+            }
             ClientRequest::ExternalAgentConfigDetect { .. }
             | ClientRequest::ExternalAgentConfigImport { .. } => {
                 warn!("ExternalAgentConfig request reached CodexMessageProcessor unexpectedly");

codex-rs/app-server/src/message_processor.rs

@@ -56,6 +56,7 @@ use codex_app_server_protocol::JSONRPCErrorError;
 use codex_app_server_protocol::JSONRPCNotification;
 use codex_app_server_protocol::JSONRPCRequest;
 use codex_app_server_protocol::JSONRPCResponse;
+use codex_app_server_protocol::ModelProviderCapabilitiesReadResponse;
 use codex_app_server_protocol::ServerNotification;
 use codex_app_server_protocol::ServerRequestPayload;
 use codex_app_server_protocol::experimental_required_message;
@@ -76,6 +77,7 @@ use codex_login::default_client::USER_AGENT_SUFFIX;
 use codex_login::default_client::get_codex_user_agent;
 use codex_login::default_client::set_default_client_residency_requirement;
 use codex_login::default_client::set_default_originator;
+use codex_model_provider::create_model_provider;
 use codex_models_manager::collaboration_mode_presets::CollaborationModesConfig;
 use codex_protocol::ThreadId;
 use codex_protocol::protocol::SessionSource;
@@ -938,6 +940,13 @@ impl MessageProcessor {
                     )
                     .await;
             }
+            ClientRequest::ModelProviderCapabilitiesRead {
+                request_id,
+                params: _,
+            } => {
+                self.handle_model_provider_capabilities_read(request_id_for_connection(request_id))
+                    .await;
+            }
             other => {
                 // Box the delegated future so this wrapper's async state machine does not
                 // inline the full `CodexMessageProcessor::process_request` future, which
@@ -957,6 +966,24 @@ impl MessageProcessor {
         Ok(())
     }
 
+    async fn handle_model_provider_capabilities_read(&self, request_id: ConnectionRequestId) {
+        let result = async {
+            let config = self
+                .config_api
+                .load_latest_config(/*fallback_cwd*/ None)
+                .await?;
+            let provider = create_model_provider(config.model_provider, /*auth_manager*/ None);
+            let capabilities = provider.capabilities();
+            Ok::<_, JSONRPCErrorError>(ModelProviderCapabilitiesReadResponse {
+                namespace_tools: capabilities.namespace_tools,
+                image_generation: capabilities.image_generation,
+                web_search: capabilities.web_search,
+            })
+        }
+        .await;
+        self.outgoing.send_result(request_id, result).await;
+    }
+
     async fn handle_config_value_write(
         &self,
         request_id: ConnectionRequestId,

codex-rs/app-server/tests/common/mcp_process.rs

@@ -54,6 +54,7 @@ use codex_app_server_protocol::McpResourceReadParams;
 use codex_app_server_protocol::McpServerToolCallParams;
 use codex_app_server_protocol::MockExperimentalMethodParams;
 use codex_app_server_protocol::ModelListParams;
+use codex_app_server_protocol::ModelProviderCapabilitiesReadParams;
 use codex_app_server_protocol::PluginInstallParams;
 use codex_app_server_protocol::PluginListParams;
 use codex_app_server_protocol::PluginReadParams;
@@ -517,6 +518,16 @@ impl McpProcess {
         self.send_request("model/list", params).await
     }
 
+    /// Send a `modelProvider/capabilities/read` JSON-RPC request.
+    pub async fn send_model_provider_capabilities_read_request(
+        &mut self,
+        params: ModelProviderCapabilitiesReadParams,
+    ) -> anyhow::Result<i64> {
+        let params = Some(serde_json::to_value(params)?);
+        self.send_request("modelProvider/capabilities/read", params)
+            .await
+    }
+
     /// Send an `experimentalFeature/list` JSON-RPC request.
     pub async fn send_experimental_feature_list_request(
         &mut self,

codex-rs/app-server/tests/suite/v2/mod.rs

@@ -26,6 +26,7 @@ mod mcp_server_status;
 mod mcp_tool;
 mod memory_reset;
 mod model_list;
+mod model_provider_capabilities_read;
 mod output_schema;
 mod plan_item;
 mod plugin_install;

codex-rs/app-server/tests/suite/v2/model_provider_capabilities_read.rs

@@ -0,0 +1,69 @@
+use std::time::Duration;
+
+use anyhow::Result;
+use app_test_support::McpProcess;
+use app_test_support::to_response;
+use codex_app_server_protocol::JSONRPCResponse;
+use codex_app_server_protocol::ModelProviderCapabilitiesReadParams;
+use codex_app_server_protocol::ModelProviderCapabilitiesReadResponse;
+use codex_app_server_protocol::RequestId;
+use pretty_assertions::assert_eq;
+use tempfile::TempDir;
+use tokio::time::timeout;
+
+const DEFAULT_TIMEOUT: Duration = Duration::from_secs(30);
+
+#[tokio::test]
+async fn read_default_provider_capabilities() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_TIMEOUT, mcp.initialize()).await??;
+
+    let request_id = mcp
+        .send_model_provider_capabilities_read_request(ModelProviderCapabilitiesReadParams {})
+        .await?;
+    let response: JSONRPCResponse = timeout(
+        DEFAULT_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(request_id)),
+    )
+    .await??;
+    let received: ModelProviderCapabilitiesReadResponse = to_response(response)?;
+
+    let expected = ModelProviderCapabilitiesReadResponse {
+        namespace_tools: true,
+        image_generation: true,
+        web_search: true,
+    };
+    assert_eq!(received, expected);
+    Ok(())
+}
+
+#[tokio::test]
+async fn read_amazon_bedrock_provider_capabilities() -> Result<()> {
+    let codex_home = TempDir::new()?;
+    std::fs::write(
+        codex_home.path().join("config.toml"),
+        r#"model_provider = "amazon-bedrock"
+"#,
+    )?;
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_TIMEOUT, mcp.initialize()).await??;
+
+    let request_id = mcp
+        .send_model_provider_capabilities_read_request(ModelProviderCapabilitiesReadParams {})
+        .await?;
+    let response: JSONRPCResponse = timeout(
+        DEFAULT_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(request_id)),
+    )
+    .await??;
+    let received: ModelProviderCapabilitiesReadResponse = to_response(response)?;
+
+    let expected = ModelProviderCapabilitiesReadResponse {
+        namespace_tools: false,
+        image_generation: false,
+        web_search: false,
+    };
+    assert_eq!(received, expected);
+    Ok(())
+}