diff --git a/codex-rs/analytics/src/analytics_client_tests.rs b/codex-rs/analytics/src/analytics_client_tests.rs
index ba9d172353..b3ed451e43 100644
--- a/codex-rs/analytics/src/analytics_client_tests.rs
+++ b/codex-rs/analytics/src/analytics_client_tests.rs
@@ -4536,6 +4536,7 @@ async fn turn_event_counts_completed_tool_items() {
         }),
         mcp_app_resource_uri: None,
         plugin_id: Some("sample@test".to_string()),
+        read_only_hint: None,
         result: None,
         error: None,
         duration_ms,
diff --git a/codex-rs/app-server-protocol/schema/json/ServerNotification.json b/codex-rs/app-server-protocol/schema/json/ServerNotification.json
index ab02038e41..0d96710c28 100644
--- a/codex-rs/app-server-protocol/schema/json/ServerNotification.json
+++ b/codex-rs/app-server-protocol/schema/json/ServerNotification.json
@@ -4373,6 +4373,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
index 194cf085b3..512c7346ef 100644
--- a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
+++ b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
@@ -19261,6 +19261,12 @@
                   "null"
                 ]
               },
+              "readOnlyHint": {
+                "type": [
+                  "boolean",
+                  "null"
+                ]
+              },
               "result": {
                 "anyOf": [
                   {
diff --git a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
index 2506b97869..af02ed4da9 100644
--- a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
+++ b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
@@ -17025,6 +17025,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ItemCompletedNotification.json b/codex-rs/app-server-protocol/schema/json/v2/ItemCompletedNotification.json
index 4cc31d75f1..b80ab71aae 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ItemCompletedNotification.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ItemCompletedNotification.json
@@ -900,6 +900,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ItemStartedNotification.json b/codex-rs/app-server-protocol/schema/json/v2/ItemStartedNotification.json
index 5dc869ee6c..70f46ed222 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ItemStartedNotification.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ItemStartedNotification.json
@@ -900,6 +900,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ReviewStartResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ReviewStartResponse.json
index 411d345c68..0169150eee 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ReviewStartResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ReviewStartResponse.json
@@ -1045,6 +1045,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadForkResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadForkResponse.json
index f3410c1460..beb11fc042 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadForkResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadForkResponse.json
@@ -1594,6 +1594,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadListResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadListResponse.json
index 154d698066..020258690f 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadListResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadListResponse.json
@@ -1385,6 +1385,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadMetadataUpdateResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadMetadataUpdateResponse.json
index 84893b059d..d759eab1ce 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadMetadataUpdateResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadMetadataUpdateResponse.json
@@ -1385,6 +1385,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadReadResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadReadResponse.json
index c035ef8271..17ebd74b14 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadReadResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadReadResponse.json
@@ -1385,6 +1385,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadResumeResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadResumeResponse.json
index fab346d49d..16bcc27f91 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadResumeResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadResumeResponse.json
@@ -1594,6 +1594,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadRollbackResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadRollbackResponse.json
index 68471bcdd8..56ca9d6091 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadRollbackResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadRollbackResponse.json
@@ -1385,6 +1385,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json
index 6145520bbb..a8f9f373d7 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json
@@ -1594,6 +1594,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadStartedNotification.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadStartedNotification.json
index e3c26033cf..bea9304afc 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadStartedNotification.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadStartedNotification.json
@@ -1385,6 +1385,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ThreadUnarchiveResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ThreadUnarchiveResponse.json
index b37937c395..b693425bdb 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ThreadUnarchiveResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ThreadUnarchiveResponse.json
@@ -1385,6 +1385,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/TurnCompletedNotification.json b/codex-rs/app-server-protocol/schema/json/v2/TurnCompletedNotification.json
index 1a29812139..5c08f256c7 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/TurnCompletedNotification.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/TurnCompletedNotification.json
@@ -1045,6 +1045,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/TurnStartResponse.json b/codex-rs/app-server-protocol/schema/json/v2/TurnStartResponse.json
index 31519649c0..6ec43412ef 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/TurnStartResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/TurnStartResponse.json
@@ -1045,6 +1045,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/json/v2/TurnStartedNotification.json b/codex-rs/app-server-protocol/schema/json/v2/TurnStartedNotification.json
index 0281c28ced..18f79d4406 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/TurnStartedNotification.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/TurnStartedNotification.json
@@ -1045,6 +1045,12 @@
                 "null"
               ]
             },
+            "readOnlyHint": {
+              "type": [
+                "boolean",
+                "null"
+              ]
+            },
             "result": {
               "anyOf": [
                 {
diff --git a/codex-rs/app-server-protocol/schema/typescript/v2/ThreadItem.ts b/codex-rs/app-server-protocol/schema/typescript/v2/ThreadItem.ts
index 0a8ab88519..f7932106b6 100644
--- a/codex-rs/app-server-protocol/schema/typescript/v2/ThreadItem.ts
+++ b/codex-rs/app-server-protocol/schema/typescript/v2/ThreadItem.ts
@@ -69,7 +69,7 @@ durationMs: number | null, } | { "type": "fileChange", id: string, changes: Arra
 /**
  * Deprecated: use `appContext.resourceUri` instead.
  */
-mcpAppResourceUri?: string, pluginId: string | null, result: McpToolCallResult | null, error: McpToolCallError | null,
+mcpAppResourceUri?: string, pluginId: string | null, readOnlyHint: boolean | null, result: McpToolCallResult | null, error: McpToolCallError | null,
 /**
  * The duration of the MCP tool call in milliseconds.
  */
diff --git a/codex-rs/app-server-protocol/src/protocol/thread_history.rs b/codex-rs/app-server-protocol/src/protocol/thread_history.rs
index b50d376c39..57103f8049 100644
--- a/codex-rs/app-server-protocol/src/protocol/thread_history.rs
+++ b/codex-rs/app-server-protocol/src/protocol/thread_history.rs
@@ -787,6 +787,7 @@ impl ThreadHistoryBuilder {
                 }),
             mcp_app_resource_uri: payload.mcp_app_resource_uri.clone(),
             plugin_id: payload.plugin_id.clone(),
+            read_only_hint: payload.read_only_hint,
             result: None,
             error: None,
             duration_ms: None,
@@ -839,6 +840,7 @@ impl ThreadHistoryBuilder {
                 }),
             mcp_app_resource_uri: payload.mcp_app_resource_uri.clone(),
             plugin_id: payload.plugin_id.clone(),
+            read_only_hint: payload.read_only_hint,
             result,
             error,
             duration_ms,
@@ -2782,6 +2784,7 @@ mod tests {
                 app_name: None,
                 action_name: None,
                 plugin_id: None,
+                read_only_hint: None,
                 duration: Duration::from_millis(8),
                 result: Err("boom".into()),
             }),
@@ -2840,6 +2843,7 @@ mod tests {
                 app_context: None,
                 mcp_app_resource_uri: None,
                 plugin_id: None,
+                read_only_hint: None,
                 result: None,
                 error: Some(McpToolCallError {
                     message: "boom".into(),
@@ -2872,6 +2876,7 @@ mod tests {
                 app_name: Some("Calendar".into()),
                 action_name: Some("lookup".into()),
                 plugin_id: Some("sample@test".into()),
+                read_only_hint: Some(false),
                 duration: Duration::from_millis(8),
                 result: Ok(CallToolResult {
                     content: vec![serde_json::json!({
@@ -2910,6 +2915,7 @@ mod tests {
                 }),
                 mcp_app_resource_uri: Some("ui://widget/lookup.html".into()),
                 plugin_id: Some("sample@test".into()),
+                read_only_hint: Some(false),
                 result: Some(Box::new(McpToolCallResult {
                     content: vec![serde_json::json!({
                         "type": "text",
diff --git a/codex-rs/app-server-protocol/src/protocol/v2/item.rs b/codex-rs/app-server-protocol/src/protocol/v2/item.rs
index f3a3a65d20..009b7275d4 100644
--- a/codex-rs/app-server-protocol/src/protocol/v2/item.rs
+++ b/codex-rs/app-server-protocol/src/protocol/v2/item.rs
@@ -317,6 +317,7 @@ pub enum ThreadItem {
         /// Deprecated: use `appContext.resourceUri` instead.
         mcp_app_resource_uri: Option<String>,
         plugin_id: Option<String>,
+        read_only_hint: Option<bool>,
         result: Option<Box<McpToolCallResult>>,
         error: Option<McpToolCallError>,
         /// The duration of the MCP tool call in milliseconds.
@@ -961,6 +962,7 @@ impl From<CoreTurnItem> for ThreadItem {
                     }),
                     mcp_app_resource_uri: mcp.mcp_app_resource_uri,
                     plugin_id: mcp.plugin_id,
+                    read_only_hint: mcp.read_only_hint,
                     result: mcp.result.map(McpToolCallResult::from).map(Box::new),
                     error: mcp.error.map(McpToolCallError::from),
                     duration_ms,
diff --git a/codex-rs/app-server-protocol/src/protocol/v2/tests.rs b/codex-rs/app-server-protocol/src/protocol/v2/tests.rs
index 2bbcde4d6e..4558a59992 100644
--- a/codex-rs/app-server-protocol/src/protocol/v2/tests.rs
+++ b/codex-rs/app-server-protocol/src/protocol/v2/tests.rs
@@ -3144,6 +3144,7 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
         app_name: Some("Calendar".to_string()),
         action_name: Some("create_event".to_string()),
         plugin_id: Some("sample@test".to_string()),
+        read_only_hint: Some(true),
         status: CoreMcpToolCallStatus::InProgress,
         result: None,
         error: None,
@@ -3167,6 +3168,7 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
             }),
             mcp_app_resource_uri: Some("app://connector".to_string()),
             plugin_id: Some("sample@test".to_string()),
+            read_only_hint: Some(true),
             result: None,
             error: None,
             duration_ms: None,
@@ -3184,6 +3186,7 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
         app_name: None,
         action_name: None,
         plugin_id: None,
+        read_only_hint: Some(false),
         status: CoreMcpToolCallStatus::Completed,
         result: Some(CallToolResult {
             content: vec![json!({"type": "text", "text": "ok"})],
@@ -3206,6 +3209,7 @@ fn core_turn_item_into_thread_item_converts_supported_variants() {
             app_context: None,
             mcp_app_resource_uri: None,
             plugin_id: None,
+            read_only_hint: Some(false),
             result: Some(Box::new(McpToolCallResult {
                 content: vec![json!({"type": "text", "text": "ok"})],
                 structured_content: Some(json!({"ok": true})),
@@ -3234,6 +3238,7 @@ fn mcp_tool_call_app_context_serializes_connector_id() {
         }),
         mcp_app_resource_uri: Some("app://connector".to_string()),
         plugin_id: None,
+        read_only_hint: Some(false),
         result: None,
         error: None,
         duration_ms: None,
@@ -3257,6 +3262,7 @@ fn mcp_tool_call_app_context_serializes_connector_id() {
             },
             "mcpAppResourceUri": "app://connector",
             "pluginId": null,
+            "readOnlyHint": false,
             "result": null,
             "error": null,
             "durationMs": null,
diff --git a/codex-rs/app-server/README.md b/codex-rs/app-server/README.md
index a79faecddf..680e223e76 100644
--- a/codex-rs/app-server/README.md
+++ b/codex-rs/app-server/README.md
@@ -1503,7 +1503,7 @@ The app-server streams JSON-RPC notifications while a turn is running. Each turn
 - `reasoning` — `{id, summary, content}` where `summary` holds streamed reasoning summaries (applicable for most OpenAI models) and `content` holds raw reasoning blocks (applicable for e.g. open source models).
 - `commandExecution` — `{id, pluginId?, scriptPath?, command, cwd, status, commandActions, aggregatedOutput?, exitCode?, durationMs?}` for sandboxed commands; `pluginId` is present only for commands attributed to a trusted first-party plugin, newly attributed items also include `scriptPath` as a safe `/`-separated path relative to the trusted plugin root, older history may omit `scriptPath`, and `status` is `inProgress`, `completed`, `failed`, or `declined`.
 - `fileChange` — `{id, changes, status}` describing proposed edits; `changes` list `{path, kind, diff}` and `status` is `inProgress`, `completed`, `failed`, or `declined`.
-- `mcpToolCall` — `{id, server, tool, status, arguments, appContext, mcpAppResourceUri?, pluginId, result?, error?}` describing MCP calls; `appContext` is `{connectorId, linkId, resourceUri, appName, actionName}` for calls through a trusted MCP app, where `connectorId` identifies the connector that owns the tool, `linkId` identifies the app link, `resourceUri` points to the widget template, `appName` is the connector's display name, and `actionName` is the stable connector `Action.name`. `appName` and `actionName` may be null for older rollout entries. The top-level `mcpAppResourceUri` is deprecated and temporarily duplicated for client migration. `tool` identifies the raw MCP tool. `status` is `inProgress`, `completed`, or `failed`.
+- `mcpToolCall` — `{id, server, tool, status, arguments, appContext, mcpAppResourceUri?, pluginId, readOnlyHint, result?, error?}` describing MCP calls; `appContext` is `{connectorId, linkId, resourceUri, appName, actionName}` for calls through a trusted MCP app, where `connectorId` identifies the connector that owns the tool, `linkId` identifies the app link, `resourceUri` points to the widget template, `appName` is the connector's display name, and `actionName` is the stable connector `Action.name`. `readOnlyHint` is `true` for read-only tools, `false` for write-capable tools, and `null` when the annotation is unavailable, including older rollout entries. The hint describes tool capability, not whether an invocation succeeded or performed a write; use `status`, `result`, and `error` to determine the execution outcome. `appName` and `actionName` may be null for older rollout entries. The top-level `mcpAppResourceUri` is deprecated and temporarily duplicated for client migration. `tool` identifies the raw MCP tool. `status` is `inProgress`, `completed`, or `failed`.
 - `collabToolCall` — `{id, tool, status, senderThreadId, receiverThreadId?, newThreadId?, prompt?, agentStatus?}` describing collab tool calls (`spawn_agent`, `send_input`, `resume_agent`, `wait`, `close_agent`); `status` is `inProgress`, `completed`, or `failed`.
 - `webSearch` — `{id, query, action?, results?}` for a web search request issued by the agent; `action` mirrors the Responses API web_search action payload (`search`, `open_page`, `find_in_page`) and may be omitted until completion. For standalone web search, `results` contains the out-of-band structured result DTOs returned by `/v1/alpha/search`; clients should ignore result types and fields they do not understand.
 - `imageView` — `{id, path}` emitted when the agent invokes the image viewer tool.
diff --git a/codex-rs/app-server/src/request_processors/thread_resume_redaction.rs b/codex-rs/app-server/src/request_processors/thread_resume_redaction.rs
index c0fb1d0a6c..1357aeb271 100644
--- a/codex-rs/app-server/src/request_processors/thread_resume_redaction.rs
+++ b/codex-rs/app-server/src/request_processors/thread_resume_redaction.rs
@@ -89,6 +89,7 @@ mod tests {
                 }),
                 mcp_app_resource_uri: Some("ui://widget/lookup.html".to_string()),
                 plugin_id: Some("sample@test".to_string()),
+                read_only_hint: None,
                 result: Some(Box::new(McpToolCallResult {
                     content: vec![serde_json::json!({
                         "type": "text",
@@ -138,6 +139,7 @@ mod tests {
                 }),
                 mcp_app_resource_uri: Some("ui://widget/lookup.html".to_string()),
                 plugin_id: Some("sample@test".to_string()),
+                read_only_hint: None,
                 result: Some(Box::new(redacted_mcp_tool_call_result())),
                 error: None,
                 duration_ms: Some(8),
@@ -156,6 +158,7 @@ mod tests {
             app_context: None,
             mcp_app_resource_uri: None,
             plugin_id: None,
+            read_only_hint: None,
             result: None,
             error: Some(McpToolCallError {
                 message: "secret error".to_string(),
@@ -176,6 +179,7 @@ mod tests {
                 app_context: None,
                 mcp_app_resource_uri: None,
                 plugin_id: None,
+                read_only_hint: None,
                 result: None,
                 error: Some(McpToolCallError {
                     message: REDACTED_PAYLOAD.to_string(),
diff --git a/codex-rs/app-server/tests/suite/v2/mcp_tool.rs b/codex-rs/app-server/tests/suite/v2/mcp_tool.rs
index db24be1278..f110c54d11 100644
--- a/codex-rs/app-server/tests/suite/v2/mcp_tool.rs
+++ b/codex-rs/app-server/tests/suite/v2/mcp_tool.rs
@@ -25,6 +25,10 @@ use codex_app_server_protocol::RequestId;
 use codex_app_server_protocol::SelectedCapabilityRoot;
 use codex_app_server_protocol::ServerRequest;
 use codex_app_server_protocol::ThreadItem;
+use codex_app_server_protocol::ThreadReadParams;
+use codex_app_server_protocol::ThreadReadResponse;
+use codex_app_server_protocol::ThreadResumeParams;
+use codex_app_server_protocol::ThreadResumeResponse;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
 use codex_app_server_protocol::TurnEnvironmentParams;
@@ -561,6 +565,7 @@ async fn mcp_tool_call_completion_notification_contains_truncated_large_result()
         app_context: None,
         mcp_app_resource_uri: None,
         plugin_id: None,
+        read_only_hint: None,
         result: Some(result),
         error: None,
         duration_ms: None,
@@ -579,6 +584,164 @@ async fn mcp_tool_call_completion_notification_contains_truncated_large_result()
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn mcp_tool_call_hint_survives_mid_call_thread_read_and_resume() -> Result<()> {
+    let call_id = "call-mid-flight-mcp";
+    let namespace = format!("mcp__{TEST_SERVER_NAME}");
+    let responses = vec![
+        responses::sse(vec![
+            responses::ev_response_created("resp-mid-flight"),
+            responses::ev_function_call_with_namespace(
+                call_id,
+                &namespace,
+                TEST_TOOL_NAME,
+                &serde_json::to_string(&json!({
+                    "message": ELICITATION_TRIGGER_MESSAGE,
+                }))?,
+            ),
+            responses::ev_completed("resp-mid-flight"),
+        ]),
+        create_final_assistant_message_sse_response("done")?,
+    ];
+    let responses_server = create_mock_responses_server_sequence(responses).await;
+    let (mcp_server_url, mcp_server_handle) = start_mcp_server().await?;
+    let codex_home = TempDir::new()?;
+    mcp_tool_config(&responses_server.uri(), &mcp_server_url, AUTO_COMPACT_LIMIT)
+        .write(codex_home.path())?;
+
+    let mut mcp = TestAppServer::builder()
+        .with_codex_home(codex_home.path())
+        .build_initialized()
+        .await?;
+    let ThreadStartResponse { thread, .. } = mcp
+        .start_thread(ThreadStartParams {
+            model: Some("mock-model".to_string()),
+            approval_policy: Some(codex_app_server_protocol::AskForApproval::UnlessTrusted),
+            ..Default::default()
+        })
+        .await?;
+    let TurnStartResponse { turn, .. } = mcp
+        .request(|request_id| ClientRequest::TurnStart {
+            request_id,
+            params: TurnStartParams {
+                thread_id: thread.id.clone(),
+                client_user_message_id: None,
+                input: vec![V2UserInput::Text {
+                    text: "Call the MCP tool".to_string(),
+                    text_elements: Vec::new(),
+                }],
+                ..Default::default()
+            },
+        })
+        .await?;
+
+    let server_request = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_request_message(),
+    )
+    .await??;
+    let ServerRequest::McpServerElicitationRequest { request_id, .. } = server_request else {
+        panic!("expected MCP elicitation while the tool call is in progress");
+    };
+
+    let read_id = mcp
+        .send_thread_read_request(ThreadReadParams {
+            thread_id: thread.id.clone(),
+            include_turns: true,
+        })
+        .await?;
+    let ThreadReadResponse {
+        thread: read_thread,
+        ..
+    } = timeout(DEFAULT_READ_TIMEOUT, mcp.read_response(read_id)).await??;
+    assert_eq!(read_thread.id, thread.id);
+
+    let resume_id = mcp
+        .send_thread_resume_request(ThreadResumeParams {
+            thread_id: thread.id.clone(),
+            ..Default::default()
+        })
+        .await?;
+    let ThreadResumeResponse {
+        thread: resumed_thread,
+        ..
+    } = timeout(DEFAULT_READ_TIMEOUT, mcp.read_response(resume_id)).await??;
+
+    let expected_item = ThreadItem::McpToolCall {
+        id: call_id.to_string(),
+        server: TEST_SERVER_NAME.to_string(),
+        tool: TEST_TOOL_NAME.to_string(),
+        status: McpToolCallStatus::InProgress,
+        arguments: json!({ "message": ELICITATION_TRIGGER_MESSAGE }),
+        app_context: None,
+        mcp_app_resource_uri: None,
+        plugin_id: None,
+        read_only_hint: Some(true),
+        result: None,
+        error: None,
+        duration_ms: None,
+    };
+    let resumed_item = resumed_thread
+        .turns
+        .iter()
+        .flat_map(|turn| &turn.items)
+        .find(|item| matches!(item, ThreadItem::McpToolCall { id, .. } if id == call_id))
+        .expect("resumed thread should include the in-progress MCP tool call");
+    assert_eq!(resumed_item, &expected_item);
+
+    mcp.send_response(
+        request_id,
+        serde_json::to_value(McpServerElicitationRequestResponse {
+            action: McpServerElicitationAction::Accept,
+            content: Some(json!({ "confirmed": true })),
+            meta: None,
+        })?,
+    )
+    .await?;
+
+    let completed = wait_for_mcp_tool_call_completed(&mut mcp, call_id).await?;
+    assert_eq!(completed.turn_id, turn.id);
+    let ThreadItem::McpToolCall {
+        status,
+        read_only_hint,
+        ..
+    } = &completed.item
+    else {
+        panic!("expected the completed MCP tool call item");
+    };
+    assert_eq!(status, &McpToolCallStatus::Completed);
+    assert_eq!(read_only_hint, &Some(true));
+
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("turn/completed"),
+    )
+    .await??;
+
+    let completed_read_id = mcp
+        .send_thread_read_request(ThreadReadParams {
+            thread_id: thread.id,
+            include_turns: true,
+        })
+        .await?;
+    let ThreadReadResponse {
+        thread: completed_read,
+        ..
+    } = timeout(DEFAULT_READ_TIMEOUT, mcp.read_response(completed_read_id)).await??;
+    let persisted_item = completed_read
+        .turns
+        .iter()
+        .flat_map(|turn| &turn.items)
+        .find(|item| matches!(item, ThreadItem::McpToolCall { id, .. } if id == call_id))
+        .expect("completed thread history should include the persisted MCP tool call");
+    assert_eq!(persisted_item, &completed.item);
+
+    mcp_server_handle.abort();
+    let _ = mcp_server_handle.await;
+
+    Ok(())
+}
+
 #[derive(Clone, Default)]
 struct ToolAppsMcpServer;
 
diff --git a/codex-rs/app-server/tests/suite/v2/thread_resume.rs b/codex-rs/app-server/tests/suite/v2/thread_resume.rs
index eb3a68f2a1..304e0ed5de 100644
--- a/codex-rs/app-server/tests/suite/v2/thread_resume.rs
+++ b/codex-rs/app-server/tests/suite/v2/thread_resume.rs
@@ -1357,6 +1357,7 @@ async fn thread_resume_redacts_payloads_for_chatgpt_remote_clients() -> Result<(
             let ThreadItem::McpToolCall {
                 arguments,
                 app_context,
+                read_only_hint,
                 result,
                 error,
                 ..
@@ -1375,6 +1376,7 @@ async fn thread_resume_redacts_payloads_for_chatgpt_remote_clients() -> Result<(
                     action_name: Some("lookup".to_string()),
                 })
             );
+            assert_eq!(read_only_hint, &Some(false));
             let result = result.as_ref().expect("redacted MCP result");
             assert_eq!(
                 result.content,
@@ -1410,6 +1412,7 @@ async fn thread_resume_redacts_payloads_for_chatgpt_remote_clients() -> Result<(
     let ThreadItem::McpToolCall {
         arguments,
         app_context,
+        read_only_hint,
         result,
         ..
     } = normal_mcp_item
@@ -1427,6 +1430,7 @@ async fn thread_resume_redacts_payloads_for_chatgpt_remote_clients() -> Result<(
             action_name: Some("lookup".to_string()),
         })
     );
+    assert_eq!(read_only_hint, &Some(false));
     let result = result.as_ref().expect("normal MCP result");
     assert_eq!(
         result.content,
@@ -1534,6 +1538,7 @@ fn append_resume_redaction_history(
             app_name: Some("Calendar".to_string()),
             action_name: Some("lookup".to_string()),
             plugin_id: None,
+            read_only_hint: Some(false),
             duration: Duration::from_millis(8),
             result: Ok(CallToolResult {
                 content: vec![json!({
diff --git a/codex-rs/core/src/mcp_tool_call.rs b/codex-rs/core/src/mcp_tool_call.rs
index 669edf35a1..6b95e49e49 100644
--- a/codex-rs/core/src/mcp_tool_call.rs
+++ b/codex-rs/core/src/mcp_tool_call.rs
@@ -340,6 +340,7 @@ struct McpToolCallItemMetadata {
     app_name: Option<String>,
     action_name: Option<String>,
     plugin_id: Option<String>,
+    read_only_hint: Option<bool>,
 }
 
 impl McpToolCallItemMetadata {
@@ -364,6 +365,9 @@ impl McpToolCallItemMetadata {
                 .filter(|action_name| !action_name.is_empty())
                 .map(str::to_string),
             plugin_id: metadata.and_then(|metadata| metadata.plugin_id.clone()),
+            read_only_hint: metadata
+                .and_then(|metadata| metadata.annotations.as_ref())
+                .and_then(|annotations| annotations.read_only_hint),
         }
     }
 }
@@ -918,6 +922,7 @@ async fn notify_mcp_tool_call_started(
         app_name: item_metadata.app_name,
         action_name: item_metadata.action_name,
         plugin_id: item_metadata.plugin_id,
+        read_only_hint: item_metadata.read_only_hint,
         status: McpToolCallStatus::InProgress,
         result: None,
         error: None,
@@ -962,6 +967,7 @@ async fn notify_mcp_tool_call_completed(
         app_name: item_metadata.app_name,
         action_name: item_metadata.action_name,
         plugin_id: item_metadata.plugin_id,
+        read_only_hint: item_metadata.read_only_hint,
         status,
         result,
         error,
diff --git a/codex-rs/core/src/mcp_tool_call_tests.rs b/codex-rs/core/src/mcp_tool_call_tests.rs
index f5355fc18d..4db1cdbd5c 100644
--- a/codex-rs/core/src/mcp_tool_call_tests.rs
+++ b/codex-rs/core/src/mcp_tool_call_tests.rs
@@ -1155,6 +1155,11 @@ fn mcp_tool_call_item_metadata_only_trusts_codex_apps_identity() {
         /*tool_description*/ None,
     );
     metadata.link_id = Some("link_fedcba9876543210fedcba9876543210".to_string());
+    metadata.annotations = Some(annotations(
+        Some(false),
+        /*destructive*/ None,
+        /*open_world*/ None,
+    ));
     metadata.codex_apps_meta = Some(
         serde_json::json!({
             "resource_uri": "/asdk_app_0123456789abcdef0123456789abcdef/link_fedcba9876543210fedcba9876543210/create_event",
@@ -1173,6 +1178,7 @@ fn mcp_tool_call_item_metadata_only_trusts_codex_apps_identity() {
             app_name: Some("Calendar".to_string()),
             action_name: Some("create_event".to_string()),
             plugin_id: None,
+            read_only_hint: Some(false),
         }
     );
     assert_eq!(
@@ -1184,6 +1190,7 @@ fn mcp_tool_call_item_metadata_only_trusts_codex_apps_identity() {
             app_name: None,
             action_name: None,
             plugin_id: None,
+            read_only_hint: Some(false),
         }
     );
 }
@@ -1208,6 +1215,7 @@ async fn mcp_tool_call_item_includes_app_identity() {
             app_name: Some("Calendar".to_string()),
             action_name: Some("create_event".to_string()),
             plugin_id: Some("sample@test".to_string()),
+            read_only_hint: Some(false),
         },
     )
     .await;
@@ -1234,6 +1242,7 @@ async fn mcp_tool_call_item_includes_app_identity() {
     assert_eq!(item.plugin_id.as_deref(), Some("sample@test"));
     assert_eq!(item.app_name.as_deref(), Some("Calendar"));
     assert_eq!(item.action_name.as_deref(), Some("create_event"));
+    assert_eq!(item.read_only_hint, Some(false));
 }
 
 #[tokio::test]
diff --git a/codex-rs/core/src/tools/handlers/mcp_resource.rs b/codex-rs/core/src/tools/handlers/mcp_resource.rs
index 0ae1d178fa..9196566a14 100644
--- a/codex-rs/core/src/tools/handlers/mcp_resource.rs
+++ b/codex-rs/core/src/tools/handlers/mcp_resource.rs
@@ -227,6 +227,7 @@ async fn emit_tool_call_begin(
         app_name: None,
         action_name: None,
         plugin_id: None,
+        read_only_hint: None,
         status: McpToolCallStatus::InProgress,
         result: None,
         error: None,
@@ -270,6 +271,7 @@ async fn emit_tool_call_end(
         app_name: None,
         action_name: None,
         plugin_id: None,
+        read_only_hint: None,
         status,
         result,
         error,
diff --git a/codex-rs/core/tests/suite/mcp_turn_metadata.rs b/codex-rs/core/tests/suite/mcp_turn_metadata.rs
index 7e29df07d3..8d00d2e8f0 100644
--- a/codex-rs/core/tests/suite/mcp_turn_metadata.rs
+++ b/codex-rs/core/tests/suite/mcp_turn_metadata.rs
@@ -9,11 +9,15 @@ use codex_protocol::config_types::ApprovalsReviewer;
 use codex_protocol::config_types::CollaborationMode;
 use codex_protocol::config_types::ModeKind;
 use codex_protocol::config_types::Settings;
+use codex_protocol::items::McpToolCallStatus;
+use codex_protocol::items::TurnItem;
 use codex_protocol::models::PermissionProfile;
 use codex_protocol::protocol::AskForApproval;
 use codex_protocol::protocol::ElicitationAction;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::Op;
+use codex_protocol::protocol::RolloutItem;
+use codex_protocol::protocol::RolloutLine;
 use codex_protocol::request_user_input::RequestUserInputAnswer;
 use codex_protocol::request_user_input::RequestUserInputResponse;
 use codex_protocol::user_input::UserInput;
@@ -129,6 +133,25 @@ async fn submit_user_turn(
     Ok(())
 }
 
+async fn wait_for_mcp_tool_call_item(
+    test: &TestCodex,
+    call_id: &str,
+    status: McpToolCallStatus,
+) -> Option<bool> {
+    wait_for_event_match(&test.codex, |event| {
+        let item = match event {
+            EventMsg::ItemStarted(event) => &event.item,
+            EventMsg::ItemCompleted(event) => &event.item,
+            _ => return None,
+        };
+        let TurnItem::McpToolCall(item) = item else {
+            return None;
+        };
+        (item.id == call_id && item.status == status).then_some(item.read_only_hint)
+    })
+    .await
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn approved_mcp_tool_call_metadata_records_prior_user_input_request() -> Result<()> {
     skip_if_no_network!(Ok(()));
@@ -405,6 +428,10 @@ async fn apps_default_writes_prompts_for_writes_but_not_reads() -> Result<()> {
     )
     .await?;
 
+    assert_eq!(
+        wait_for_mcp_tool_call_item(&test, read_call_id, McpToolCallStatus::InProgress).await,
+        Some(true)
+    );
     let EventMsg::McpToolCallBegin(read_begin) = wait_for_event(&test.codex, |event| {
         matches!(event, EventMsg::McpToolCallBegin(_))
     })
@@ -413,7 +440,16 @@ async fn apps_default_writes_prompts_for_writes_but_not_reads() -> Result<()> {
         unreachable!("event guard guarantees McpToolCallBegin");
     };
     assert_eq!(read_begin.call_id, read_call_id);
+    assert_eq!(read_begin.read_only_hint, Some(true));
 
+    assert_eq!(
+        wait_for_mcp_tool_call_item(&test, read_call_id, McpToolCallStatus::Completed).await,
+        Some(true)
+    );
+    assert_eq!(
+        wait_for_mcp_tool_call_item(&test, write_call_id, McpToolCallStatus::InProgress).await,
+        Some(false)
+    );
     let next_route = wait_for_event(&test.codex, |event| {
         matches!(
             event,
@@ -425,6 +461,7 @@ async fn apps_default_writes_prompts_for_writes_but_not_reads() -> Result<()> {
         panic!("read-only app action should not prompt in writes mode");
     };
     assert_eq!(write_begin.call_id, write_call_id);
+    assert_eq!(write_begin.read_only_hint, Some(false));
 
     let EventMsg::ElicitationRequest(request) = wait_for_event(&test.codex, |event| {
         matches!(
@@ -447,6 +484,10 @@ async fn apps_default_writes_prompts_for_writes_but_not_reads() -> Result<()> {
         })
         .await?;
 
+    assert_eq!(
+        wait_for_mcp_tool_call_item(&test, write_call_id, McpToolCallStatus::Completed).await,
+        Some(false)
+    );
     wait_for_event(&test.codex, |event| {
         matches!(event, EventMsg::TurnComplete(_))
     })
@@ -456,6 +497,32 @@ async fn apps_default_writes_prompts_for_writes_but_not_reads() -> Result<()> {
     recorded_apps_tool_call_by_call_id(&server, read_call_id).await;
     recorded_apps_tool_call_by_call_id(&server, write_call_id).await;
 
+    test.codex.ensure_rollout_materialized().await;
+    test.codex.flush_rollout().await?;
+    let rollout_path = test.codex.rollout_path().expect("rollout path");
+    let persisted_hints = tokio::fs::read_to_string(rollout_path)
+        .await?
+        .lines()
+        .map(serde_json::from_str::<RolloutLine>)
+        .collect::<serde_json::Result<Vec<_>>>()?
+        .into_iter()
+        .filter_map(|line| match line.item {
+            RolloutItem::EventMsg(EventMsg::McpToolCallEnd(event))
+                if event.call_id == read_call_id || event.call_id == write_call_id =>
+            {
+                Some((event.call_id, event.read_only_hint))
+            }
+            _ => None,
+        })
+        .collect::<Vec<_>>();
+    assert_eq!(
+        persisted_hints,
+        vec![
+            (read_call_id.to_string(), Some(true)),
+            (write_call_id.to_string(), Some(false)),
+        ]
+    );
+
     Ok(())
 }
 
diff --git a/codex-rs/core/tests/suite/rmcp_client.rs b/codex-rs/core/tests/suite/rmcp_client.rs
index 1eb63cf408..808da39c48 100644
--- a/codex-rs/core/tests/suite/rmcp_client.rs
+++ b/codex-rs/core/tests/suite/rmcp_client.rs
@@ -1970,6 +1970,7 @@ async fn stdio_image_responses_round_trip() -> anyhow::Result<()> {
             app_name: None,
             action_name: None,
             plugin_id: None,
+            read_only_hint: Some(true),
         },
     );
 
diff --git a/codex-rs/exec/src/event_processor_with_jsonl_output_tests.rs b/codex-rs/exec/src/event_processor_with_jsonl_output_tests.rs
index 83cd6d3c6b..9aa5b63268 100644
--- a/codex-rs/exec/src/event_processor_with_jsonl_output_tests.rs
+++ b/codex-rs/exec/src/event_processor_with_jsonl_output_tests.rs
@@ -101,6 +101,7 @@ fn mcp_tool_call_result_preserves_meta_in_jsonl_event() {
                 app_context: None,
                 mcp_app_resource_uri: None,
                 plugin_id: None,
+                read_only_hint: None,
                 result: Some(Box::new(codex_app_server_protocol::McpToolCallResult {
                     content: vec![json!({"type": "text", "text": "search result"})],
                     structured_content: None,
diff --git a/codex-rs/exec/tests/event_processor_with_json_output.rs b/codex-rs/exec/tests/event_processor_with_json_output.rs
index 85a3872f77..891442ecbd 100644
--- a/codex-rs/exec/tests/event_processor_with_json_output.rs
+++ b/codex-rs/exec/tests/event_processor_with_json_output.rs
@@ -489,6 +489,7 @@ fn mcp_tool_call_begin_and_end_emit_item_events() {
                 app_context: None,
                 mcp_app_resource_uri: None,
                 plugin_id: None,
+                read_only_hint: None,
                 result: None,
                 error: None,
                 duration_ms: None,
@@ -508,6 +509,7 @@ fn mcp_tool_call_begin_and_end_emit_item_events() {
                 app_context: None,
                 mcp_app_resource_uri: None,
                 plugin_id: None,
+                read_only_hint: None,
                 result: Some(Box::new(McpToolCallResult {
                     content: Vec::new(),
                     structured_content: None,
@@ -581,6 +583,7 @@ fn mcp_tool_call_failure_sets_failed_status() {
                 app_context: None,
                 mcp_app_resource_uri: None,
                 plugin_id: None,
+                read_only_hint: None,
                 result: None,
                 error: Some(McpToolCallError {
                     message: "tool exploded".to_string(),
@@ -631,6 +634,7 @@ fn mcp_tool_call_defaults_arguments_and_preserves_structured_content() {
                 app_context: None,
                 mcp_app_resource_uri: None,
                 plugin_id: None,
+                read_only_hint: None,
                 result: None,
                 error: None,
                 duration_ms: None,
@@ -650,6 +654,7 @@ fn mcp_tool_call_defaults_arguments_and_preserves_structured_content() {
                 app_context: None,
                 mcp_app_resource_uri: None,
                 plugin_id: None,
+                read_only_hint: None,
                 result: Some(Box::new(McpToolCallResult {
                     content: vec![json!({
                         "type": "text",
diff --git a/codex-rs/protocol/src/items.rs b/codex-rs/protocol/src/items.rs
index e76bd16895..7c25d79a20 100644
--- a/codex-rs/protocol/src/items.rs
+++ b/codex-rs/protocol/src/items.rs
@@ -400,6 +400,9 @@ pub struct McpToolCallItem {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     #[ts(optional)]
     pub plugin_id: Option<String>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub read_only_hint: Option<bool>,
     pub status: McpToolCallStatus,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     #[ts(optional)]
diff --git a/codex-rs/protocol/src/legacy_events.rs b/codex-rs/protocol/src/legacy_events.rs
index d5799982a0..847bc3441a 100644
--- a/codex-rs/protocol/src/legacy_events.rs
+++ b/codex-rs/protocol/src/legacy_events.rs
@@ -473,6 +473,7 @@ impl McpToolCallItem {
             app_name: self.app_name.clone(),
             action_name: self.action_name.clone(),
             plugin_id: self.plugin_id.clone(),
+            read_only_hint: self.read_only_hint,
         })
     }
 
@@ -496,6 +497,7 @@ impl McpToolCallItem {
             app_name: self.app_name.clone(),
             action_name: self.action_name.clone(),
             plugin_id: self.plugin_id.clone(),
+            read_only_hint: self.read_only_hint,
             duration: self.duration?,
             result,
         }))
diff --git a/codex-rs/protocol/src/protocol.rs b/codex-rs/protocol/src/protocol.rs
index f9c6642c8b..c17ada9342 100644
--- a/codex-rs/protocol/src/protocol.rs
+++ b/codex-rs/protocol/src/protocol.rs
@@ -2430,6 +2430,10 @@ pub struct McpToolCallBeginEvent {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     #[ts(optional)]
     pub plugin_id: Option<String>,
+    /// Whether the selected tool is annotated as read-only, not its execution outcome.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub read_only_hint: Option<bool>,
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS, PartialEq)]
@@ -2455,6 +2459,9 @@ pub struct McpToolCallEndEvent {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     #[ts(optional)]
     pub plugin_id: Option<String>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub read_only_hint: Option<bool>,
     #[ts(type = "string")]
     pub duration: Duration,
     /// Result of the tool call. Note this could be an error.
@@ -5308,6 +5315,7 @@ mod tests {
                 app_name: Some("Calendar".into()),
                 action_name: Some("create_event".into()),
                 plugin_id: Some("sample@test".into()),
+                read_only_hint: Some(false),
                 status: McpToolCallStatus::InProgress,
                 result: None,
                 error: None,
@@ -5331,6 +5339,7 @@ mod tests {
                 assert_eq!(event.app_name.as_deref(), Some("Calendar"));
                 assert_eq!(event.action_name.as_deref(), Some("create_event"));
                 assert_eq!(event.plugin_id.as_deref(), Some("sample@test"));
+                assert_eq!(event.read_only_hint, Some(false));
             }
             _ => panic!("expected McpToolCallBegin event"),
         }
@@ -5426,6 +5435,7 @@ mod tests {
                 app_name: Some("Calendar".into()),
                 action_name: Some("create_event".into()),
                 plugin_id: Some("sample@test".into()),
+                read_only_hint: None,
                 status: McpToolCallStatus::Completed,
                 result: Some(CallToolResult {
                     content: vec![json!({"type": "text", "text": "ok"})],
diff --git a/codex-rs/tui/src/chatwidget/tests/history_replay.rs b/codex-rs/tui/src/chatwidget/tests/history_replay.rs
index 0f421dc63d..8c93b7c6f9 100644
--- a/codex-rs/tui/src/chatwidget/tests/history_replay.rs
+++ b/codex-rs/tui/src/chatwidget/tests/history_replay.rs
@@ -1171,6 +1171,7 @@ async fn replayed_in_progress_mcp_tool_call_stays_active() {
             app_context: None,
             mcp_app_resource_uri: None,
             plugin_id: None,
+            read_only_hint: None,
             result: None,
             error: None,
             duration_ms: None,
@@ -1204,6 +1205,7 @@ async fn deferred_mcp_lifecycle_events_keep_fifo_after_stream_finishes() {
         app_context: None,
         mcp_app_resource_uri: None,
         plugin_id: None,
+        read_only_hint: None,
         result: None,
         error: None,
         duration_ms: None,
@@ -1220,6 +1222,7 @@ async fn deferred_mcp_lifecycle_events_keep_fifo_after_stream_finishes() {
         app_context: None,
         mcp_app_resource_uri: None,
         plugin_id: None,
+        read_only_hint: None,
         result: Some(Box::new(codex_app_server_protocol::McpToolCallResult {
             content: vec![json!({"type": "text", "text": "deferred result"})],
             structured_content: None,