feat(telemetry): add diff stats to tool call metrics (#10819)

docs/cli/telemetry.md

@@ -345,6 +345,14 @@ Metrics are numerical measurements of behavior over time.
     - `success` (boolean)
     - `decision` (string: "accept", "reject", or "modify", if applicable)
     - `tool_type` (string: "mcp", or "native", if applicable)
+    - `model_added_lines` (Int, optional): Lines added by model in the proposed
+      changes, if applicable
+    - `model_removed_lines` (Int, optional): Lines removed by model in the
+      proposed changes, if applicable
+    - `user_added_lines` (Int, optional): Lines added by user edits after model
+      proposal, if applicable
+    - `user_removed_lines` (Int, optional): Lines removed by user edits after
+      model proposal, if applicable
 
 - `gemini_cli.tool.call.latency` (Histogram, ms): Measures tool call latency.
   - **Attributes**:
@@ -379,14 +387,6 @@ Metrics are numerical measurements of behavior over time.
     - `lines` (Int, if applicable): Number of lines in the file.
     - `mimetype` (string, if applicable): Mimetype of the file.
     - `extension` (string, if applicable): File extension of the file.
-    - `model_added_lines` (Int, if applicable): Number of lines added/changed by
-      the model.
-    - `model_removed_lines` (Int, if applicable): Number of lines
-      removed/changed by the model.
-    - `user_added_lines` (Int, if applicable): Number of lines added/changed by
-      user in AI proposed changes.
-    - `user_removed_lines` (Int, if applicable): Number of lines removed/changed
-      by user in AI proposed changes.
     - `programming_language` (string, if applicable): The programming language
       of the file.
 

packages/core/src/telemetry/loggers.test.ts

@@ -694,6 +694,10 @@ describe('loggers', () => {
           success: true,
           decision: ToolCallDecision.ACCEPT,
           tool_type: 'native',
+          model_added_lines: 1,
+          model_removed_lines: 2,
+          user_added_lines: 5,
+          user_removed_lines: 6,
         },
       );
 

packages/core/src/telemetry/loggers.ts

@@ -209,6 +209,14 @@ export function logToolCall(config: Config, event: ToolCallEvent): void {
     success: event.success,
     decision: event.decision,
     tool_type: event.tool_type,
+    ...(event.metadata
+      ? {
+          model_added_lines: event.metadata['model_added_lines'],
+          model_removed_lines: event.metadata['model_removed_lines'],
+          user_added_lines: event.metadata['user_added_lines'],
+          user_removed_lines: event.metadata['user_removed_lines'],
+        }
+      : {}),
   });
 }
 

packages/core/src/telemetry/metrics.ts

@@ -70,6 +70,11 @@ const COUNTER_DEFINITIONS = {
       success: boolean;
       decision?: 'accept' | 'reject' | 'modify' | 'auto_accept';
       tool_type?: 'native' | 'mcp';
+      // Optional diff statistics for file-modifying tools
+      model_added_lines?: number;
+      model_removed_lines?: number;
+      user_added_lines?: number;
+      user_removed_lines?: number;
     },
   },
   [API_REQUEST_COUNT]: {