Expose MCP read-only hints in tool call items (#36055)

## What changed

- Propagate MCP tool `readOnlyHint` annotations through tool-call start and
  completion events.
- Include the optional hint in persisted thread history and app-server
  `mcpToolCall` items, preserving compatibility when the annotation is absent.
- Document that the hint describes tool capability, not the outcome of a
  particular invocation.

## Testing

- Cover read-only and write-capable tools in live events and persisted rollout
  data.
- Verify the hint survives thread reads and resumes for both in-progress and
  completed MCP calls.

GitOrigin-RevId: dddfe905146075e5137a1094da485b86b99807f0

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,