feat: add file change tracking to session metrics (#6094)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Jacob Richman <[email protected]>

10 files changed, 291 insertions, 35 deletions

diff --git a/packages/cli/src/ui/components/SessionSummaryDisplay.test.tsx b/packages/cli/src/ui/components/SessionSummaryDisplay.test.tsx
index 38400caf..816948f2 100644
--- a/packages/cli/src/ui/components/SessionSummaryDisplay.test.tsx
+++ b/packages/cli/src/ui/components/SessionSummaryDisplay.test.tsx
@@ -60,6 +60,10 @@ describe('<SessionSummaryDisplay />', () => {
         totalDecisions: { accept: 0, reject: 0, modify: 0 },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 42,
+        totalLinesRemoved: 15,
+      },
     };
 
     const { lastFrame } = renderWithMockedStats(metrics);
diff --git a/packages/cli/src/ui/components/StatsDisplay.test.tsx b/packages/cli/src/ui/components/StatsDisplay.test.tsx
index eed105e3..6d6fa809 100644
--- a/packages/cli/src/ui/components/StatsDisplay.test.tsx
+++ b/packages/cli/src/ui/components/StatsDisplay.test.tsx
@@ -50,6 +50,10 @@ describe('<StatsDisplay />', () => {
         totalDecisions: { accept: 0, reject: 0, modify: 0 },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     };
 
     const { lastFrame } = renderWithMockedStats(zeroMetrics);
@@ -96,6 +100,10 @@ describe('<StatsDisplay />', () => {
         totalDecisions: { accept: 0, reject: 0, modify: 0 },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     };
 
     const { lastFrame } = renderWithMockedStats(metrics);
@@ -139,6 +147,10 @@ describe('<StatsDisplay />', () => {
           },
         },
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     };
 
     const { lastFrame } = renderWithMockedStats(metrics);
@@ -172,6 +184,10 @@ describe('<StatsDisplay />', () => {
             },
           },
         },
+        files: {
+          totalLinesAdded: 0,
+          totalLinesRemoved: 0,
+        },
       };
 
       const { lastFrame } = renderWithMockedStats(metrics);
@@ -206,6 +222,10 @@ describe('<StatsDisplay />', () => {
           totalDecisions: { accept: 0, reject: 0, modify: 0 },
           byName: {},
         },
+        files: {
+          totalLinesAdded: 0,
+          totalLinesRemoved: 0,
+        },
       };
 
       const { lastFrame } = renderWithMockedStats(metrics);
@@ -228,6 +248,10 @@ describe('<StatsDisplay />', () => {
           totalDecisions: { accept: 0, reject: 0, modify: 0 },
           byName: {},
         },
+        files: {
+          totalLinesAdded: 0,
+          totalLinesRemoved: 0,
+        },
       };
       const { lastFrame } = renderWithMockedStats(metrics);
       expect(lastFrame()).toMatchSnapshot();
@@ -244,6 +268,10 @@ describe('<StatsDisplay />', () => {
           totalDecisions: { accept: 0, reject: 0, modify: 0 },
           byName: {},
         },
+        files: {
+          totalLinesAdded: 0,
+          totalLinesRemoved: 0,
+        },
       };
       const { lastFrame } = renderWithMockedStats(metrics);
       expect(lastFrame()).toMatchSnapshot();
@@ -260,12 +288,68 @@ describe('<StatsDisplay />', () => {
           totalDecisions: { accept: 0, reject: 0, modify: 0 },
           byName: {},
         },
+        files: {
+          totalLinesAdded: 0,
+          totalLinesRemoved: 0,
+        },
       };
       const { lastFrame } = renderWithMockedStats(metrics);
       expect(lastFrame()).toMatchSnapshot();
     });
   });
 
+  describe('Code Changes Display', () => {
+    it('displays Code Changes when line counts are present', () => {
+      const metrics: SessionMetrics = {
+        models: {},
+        tools: {
+          totalCalls: 1,
+          totalSuccess: 1,
+          totalFail: 0,
+          totalDurationMs: 100,
+          totalDecisions: { accept: 0, reject: 0, modify: 0 },
+          byName: {},
+        },
+        files: {
+          totalLinesAdded: 42,
+          totalLinesRemoved: 18,
+        },
+      };
+
+      const { lastFrame } = renderWithMockedStats(metrics);
+      const output = lastFrame();
+
+      expect(output).toContain('Code Changes:');
+      expect(output).toContain('+42');
+      expect(output).toContain('-18');
+      expect(output).toMatchSnapshot();
+    });
+
+    it('hides Code Changes when no lines are added or removed', () => {
+      const metrics: SessionMetrics = {
+        models: {},
+        tools: {
+          totalCalls: 1,
+          totalSuccess: 1,
+          totalFail: 0,
+          totalDurationMs: 100,
+          totalDecisions: { accept: 0, reject: 0, modify: 0 },
+          byName: {},
+        },
+        files: {
+          totalLinesAdded: 0,
+          totalLinesRemoved: 0,
+        },
+      };
+
+      const { lastFrame } = renderWithMockedStats(metrics);
+      const output = lastFrame();
+
+      expect(output).not.toContain('Code Changes:');
+      expect(output).toMatchSnapshot();
+    });
+  });
+
   describe('Title Rendering', () => {
     const zeroMetrics: SessionMetrics = {
       models: {},
@@ -277,6 +361,10 @@ describe('<StatsDisplay />', () => {
         totalDecisions: { accept: 0, reject: 0, modify: 0 },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     };
 
     it('renders the default title when no title prop is provided', () => {
diff --git a/packages/cli/src/ui/components/StatsDisplay.tsx b/packages/cli/src/ui/components/StatsDisplay.tsx
index 71c88aef..8dd00efd 100644
--- a/packages/cli/src/ui/components/StatsDisplay.tsx
+++ b/packages/cli/src/ui/components/StatsDisplay.tsx
@@ -7,7 +7,7 @@
 import React from 'react';
 import { Box, Text } from 'ink';
 import Gradient from 'ink-gradient';
-import { Colors } from '../colors.js';
+import { theme } from '../semantic-colors.js';
 import { formatDuration } from '../utils/formatters.js';
 import { useSessionStats, ModelMetrics } from '../contexts/SessionContext.js';
 import {
@@ -29,7 +29,7 @@ const StatRow: React.FC<StatRowProps> = ({ title, children }) => (
   <Box>
     {/* Fixed width for the label creates a clean "gutter" for alignment */}
     <Box width={28}>
-      <Text color={Colors.LightBlue}>{title}</Text>
+      <Text color={theme.text.link}>{title}</Text>
     </Box>
     {children}
   </Box>
@@ -111,12 +111,12 @@ const ModelUsageTable: React.FC<{
             <Text>{modelMetrics.api.totalRequests}</Text>
           </Box>
           <Box width={inputTokensWidth} justifyContent="flex-end">
-            <Text color={Colors.AccentYellow}>
+            <Text color={theme.status.warning}>
               {modelMetrics.tokens.prompt.toLocaleString()}
             </Text>
           </Box>
           <Box width={outputTokensWidth} justifyContent="flex-end">
-            <Text color={Colors.AccentYellow}>
+            <Text color={theme.status.warning}>
               {modelMetrics.tokens.candidates.toLocaleString()}
             </Text>
           </Box>
@@ -125,12 +125,12 @@ const ModelUsageTable: React.FC<{
       {cacheEfficiency > 0 && (
         <Box flexDirection="column" marginTop={1}>
           <Text>
-            <Text color={Colors.AccentGreen}>Savings Highlight:</Text>{' '}
+            <Text color={theme.status.success}>Savings Highlight:</Text>{' '}
             {totalCachedTokens.toLocaleString()} ({cacheEfficiency.toFixed(1)}
             %) of input tokens were served from the cache, reducing costs.
           </Text>
           <Box height={1} />
-          <Text color={Colors.Gray}>
+          <Text color={theme.text.secondary}>
             » Tip: For a full token breakdown, run `/stats model`.
           </Text>
         </Box>
@@ -150,7 +150,7 @@ export const StatsDisplay: React.FC<StatsDisplayProps> = ({
 }) => {
   const { stats } = useSessionStats();
   const { metrics } = stats;
-  const { models, tools } = metrics;
+  const { models, tools, files } = metrics;
   const computed = computeSessionStats(metrics);
 
   const successThresholds = {
@@ -169,18 +169,18 @@ export const StatsDisplay: React.FC<StatsDisplayProps> = ({
 
   const renderTitle = () => {
     if (title) {
-      return Colors.GradientColors && Colors.GradientColors.length > 0 ? (
-        <Gradient colors={Colors.GradientColors}>
+      return theme.ui.gradient && theme.ui.gradient.length > 0 ? (
+        <Gradient colors={theme.ui.gradient}>
           <Text bold>{title}</Text>
         </Gradient>
       ) : (
-        <Text bold color={Colors.AccentPurple}>
+        <Text bold color={theme.text.accent}>
           {title}
         </Text>
       );
     }
     return (
-      <Text bold color={Colors.AccentPurple}>
+      <Text bold color={theme.text.accent}>
         Session Stats
       </Text>
     );
@@ -189,7 +189,7 @@ export const StatsDisplay: React.FC<StatsDisplayProps> = ({
   return (
     <Box
       borderStyle="round"
-      borderColor={Colors.Gray}
+      borderColor={theme.border.default}
       flexDirection="column"
       paddingY={1}
       paddingX={2}
@@ -204,8 +204,8 @@ export const StatsDisplay: React.FC<StatsDisplayProps> = ({
         <StatRow title="Tool Calls:">
           <Text>
             {tools.totalCalls} ({' '}
-            <Text color={Colors.AccentGreen}>✔ {tools.totalSuccess}</Text>{' '}
-            <Text color={Colors.AccentRed}>✖ {tools.totalFail}</Text> )
+            <Text color={theme.status.success}>✔ {tools.totalSuccess}</Text>{' '}
+            <Text color={theme.status.error}>✖ {tools.totalFail}</Text> )
           </Text>
         </StatRow>
         <StatRow title="Success Rate:">
@@ -215,12 +215,25 @@ export const StatsDisplay: React.FC<StatsDisplayProps> = ({
           <StatRow title="User Agreement:">
             <Text color={agreementColor}>
               {computed.agreementRate.toFixed(1)}%{' '}
-              <Text color={Colors.Gray}>
+              <Text color={theme.text.secondary}>
                 ({computed.totalDecisions} reviewed)
               </Text>
             </Text>
           </StatRow>
         )}
+        {files &&
+          (files.totalLinesAdded > 0 || files.totalLinesRemoved > 0) && (
+            <StatRow title="Code Changes:">
+              <Text>
+                <Text color={theme.status.success}>
+                  +{files.totalLinesAdded}
+                </Text>{' '}
+                <Text color={theme.status.error}>
+                  -{files.totalLinesRemoved}
+                </Text>
+              </Text>
+            </StatRow>
+          )}
       </Section>
 
       <Section title="Performance">
@@ -233,7 +246,7 @@ export const StatsDisplay: React.FC<StatsDisplayProps> = ({
         <SubStatRow title="API Time:">
           <Text>
             {formatDuration(computed.totalApiTime)}{' '}
-            <Text color={Colors.Gray}>
+            <Text color={theme.text.secondary}>
               ({computed.apiTimePercent.toFixed(1)}%)
             </Text>
           </Text>
@@ -241,7 +254,7 @@ export const StatsDisplay: React.FC<StatsDisplayProps> = ({
         <SubStatRow title="Tool Time:">
           <Text>
             {formatDuration(computed.totalToolTime)}{' '}
-            <Text color={Colors.Gray}>
+            <Text color={theme.text.secondary}>
               ({computed.toolTimePercent.toFixed(1)}%)
             </Text>
           </Text>
diff --git a/packages/cli/src/ui/components/__snapshots__/SessionSummaryDisplay.test.tsx.snap b/packages/cli/src/ui/components/__snapshots__/SessionSummaryDisplay.test.tsx.snap
index 98e7722e..97a0b525 100644
--- a/packages/cli/src/ui/components/__snapshots__/SessionSummaryDisplay.test.tsx.snap
+++ b/packages/cli/src/ui/components/__snapshots__/SessionSummaryDisplay.test.tsx.snap
@@ -9,6 +9,7 @@ exports[`<SessionSummaryDisplay /> > renders the summary display with a title 1`
 │  Session ID:                                                                                     │
 │  Tool Calls:                 0 ( ✔ 0 ✖ 0 )                                                       │
 │  Success Rate:               0.0%                                                                │
+│  Code Changes:               +42 -15                                                             │
 │                                                                                                  │
 │  Performance                                                                                     │
 │  Wall Time:                  1h 23m 45s                                                          │
diff --git a/packages/cli/src/ui/components/__snapshots__/StatsDisplay.test.tsx.snap b/packages/cli/src/ui/components/__snapshots__/StatsDisplay.test.tsx.snap
index 09202599..d6842188 100644
--- a/packages/cli/src/ui/components/__snapshots__/StatsDisplay.test.tsx.snap
+++ b/packages/cli/src/ui/components/__snapshots__/StatsDisplay.test.tsx.snap
@@ -1,5 +1,46 @@
 // Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
 
+exports[`<StatsDisplay /> > Code Changes Display > displays Code Changes when line counts are present 1`] = `
+"╭──────────────────────────────────────────────────────────────────────────────────────────────────╮
+│                                                                                                  │
+│  Session Stats                                                                                   │
+│                                                                                                  │
+│  Interaction Summary                                                                             │
+│  Session ID:                 test-session-id                                                     │
+│  Tool Calls:                 1 ( ✔ 1 ✖ 0 )                                                       │
+│  Success Rate:               100.0%                                                              │
+│  Code Changes:               +42 -18                                                             │
+│                                                                                                  │
+│  Performance                                                                                     │
+│  Wall Time:                  1s                                                                  │
+│  Agent Active:               100ms                                                               │
+│    » API Time:               0s (0.0%)                                                           │
+│    » Tool Time:              100ms (100.0%)                                                      │
+│                                                                                                  │
+│                                                                                                  │
+╰──────────────────────────────────────────────────────────────────────────────────────────────────╯"
+`;
+
+exports[`<StatsDisplay /> > Code Changes Display > hides Code Changes when no lines are added or removed 1`] = `
+"╭──────────────────────────────────────────────────────────────────────────────────────────────────╮
+│                                                                                                  │
+│  Session Stats                                                                                   │
+│                                                                                                  │
+│  Interaction Summary                                                                             │
+│  Session ID:                 test-session-id                                                     │
+│  Tool Calls:                 1 ( ✔ 1 ✖ 0 )                                                       │
+│  Success Rate:               100.0%                                                              │
+│                                                                                                  │
+│  Performance                                                                                     │
+│  Wall Time:                  1s                                                                  │
+│  Agent Active:               100ms                                                               │
+│    » API Time:               0s (0.0%)                                                           │
+│    » Tool Time:              100ms (100.0%)                                                      │
+│                                                                                                  │
+│                                                                                                  │
+╰──────────────────────────────────────────────────────────────────────────────────────────────────╯"
+`;
+
 exports[`<StatsDisplay /> > Conditional Color Tests > renders success rate in green for high values 1`] = `
 "╭──────────────────────────────────────────────────────────────────────────────────────────────────╮
 │                                                                                                  │
diff --git a/packages/cli/src/ui/contexts/SessionContext.tsx b/packages/cli/src/ui/contexts/SessionContext.tsx
index 80c2454c..6c48c60b 100644
--- a/packages/cli/src/ui/contexts/SessionContext.tsx
+++ b/packages/cli/src/ui/contexts/SessionContext.tsx
@@ -44,6 +44,8 @@ export interface ComputedSessionStats {
   agreementRate: number;
   totalCachedTokens: number;
   totalPromptTokens: number;
+  totalLinesAdded: number;
+  totalLinesRemoved: number;
 }
 
 // Defines the final "value" of our context, including the state
diff --git a/packages/cli/src/ui/utils/computeStats.test.ts b/packages/cli/src/ui/utils/computeStats.test.ts
index 0e32ffe2..e9085fb3 100644
--- a/packages/cli/src/ui/utils/computeStats.test.ts
+++ b/packages/cli/src/ui/utils/computeStats.test.ts
@@ -121,6 +121,10 @@ describe('computeSessionStats', () => {
         totalDecisions: { accept: 0, reject: 0, modify: 0 },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     };
 
     const result = computeSessionStats(metrics);
@@ -137,6 +141,8 @@ describe('computeSessionStats', () => {
       agreementRate: 0,
       totalPromptTokens: 0,
       totalCachedTokens: 0,
+      totalLinesAdded: 0,
+      totalLinesRemoved: 0,
     });
   });
 
@@ -163,6 +169,10 @@ describe('computeSessionStats', () => {
         totalDecisions: { accept: 0, reject: 0, modify: 0 },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     };
 
     const result = computeSessionStats(metrics);
@@ -197,6 +207,10 @@ describe('computeSessionStats', () => {
         totalDecisions: { accept: 0, reject: 0, modify: 0 },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     };
 
     const result = computeSessionStats(metrics);
@@ -215,6 +229,10 @@ describe('computeSessionStats', () => {
         totalDecisions: { accept: 6, reject: 2, modify: 2 },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     };
 
     const result = computeSessionStats(metrics);
@@ -234,6 +252,10 @@ describe('computeSessionStats', () => {
         totalDecisions: { accept: 0, reject: 0, modify: 0 },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     };
 
     const result = computeSessionStats(metrics);
@@ -244,4 +266,27 @@ describe('computeSessionStats', () => {
     expect(result.successRate).toBe(0);
     expect(result.agreementRate).toBe(0);
   });
+
+  it('should correctly include line counts', () => {
+    const metrics: SessionMetrics = {
+      models: {},
+      tools: {
+        totalCalls: 0,
+        totalSuccess: 0,
+        totalFail: 0,
+        totalDurationMs: 0,
+        totalDecisions: { accept: 0, reject: 0, modify: 0 },
+        byName: {},
+      },
+      files: {
+        totalLinesAdded: 42,
+        totalLinesRemoved: 18,
+      },
+    };
+
+    const result = computeSessionStats(metrics);
+
+    expect(result.totalLinesAdded).toBe(42);
+    expect(result.totalLinesRemoved).toBe(18);
+  });
 });
diff --git a/packages/cli/src/ui/utils/computeStats.ts b/packages/cli/src/ui/utils/computeStats.ts
index e0483c3b..ec7c49fa 100644
--- a/packages/cli/src/ui/utils/computeStats.ts
+++ b/packages/cli/src/ui/utils/computeStats.ts
@@ -34,7 +34,7 @@ export function calculateCacheHitRate(metrics: ModelMetrics): number {
 export const computeSessionStats = (
   metrics: SessionMetrics,
 ): ComputedSessionStats => {
-  const { models, tools } = metrics;
+  const { models, tools, files } = metrics;
   const totalApiTime = Object.values(models).reduce(
     (acc, model) => acc + model.api.totalLatencyMs,
     0,
@@ -80,5 +80,7 @@ export const computeSessionStats = (
     agreementRate,
     totalCachedTokens,
     totalPromptTokens,
+    totalLinesAdded: files.totalLinesAdded,
+    totalLinesRemoved: files.totalLinesRemoved,
   };
 };
diff --git a/packages/core/src/telemetry/uiTelemetry.test.ts b/packages/core/src/telemetry/uiTelemetry.test.ts
index cd509a8e..a64f839e 100644
--- a/packages/core/src/telemetry/uiTelemetry.test.ts
+++ b/packages/core/src/telemetry/uiTelemetry.test.ts
@@ -108,6 +108,10 @@ describe('UiTelemetryService', () => {
         },
         byName: {},
       },
+      files: {
+        totalLinesAdded: 0,
+        totalLinesRemoved: 0,
+      },
     });
     expect(service.getLastPromptTokenCount()).toBe(0);
   });
@@ -342,9 +346,9 @@ describe('UiTelemetryService', () => {
         ToolConfirmationOutcome.ProceedOnce,
       );
       service.addEvent({
-        ...JSON.parse(JSON.stringify(new ToolCallEvent(toolCall))),
+        ...structuredClone(new ToolCallEvent(toolCall)),
         'event.name': EVENT_TOOL_CALL,
-      });
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL });
 
       const metrics = service.getMetrics();
       const { tools } = metrics;
@@ -376,9 +380,9 @@ describe('UiTelemetryService', () => {
         ToolConfirmationOutcome.Cancel,
       );
       service.addEvent({
-        ...JSON.parse(JSON.stringify(new ToolCallEvent(toolCall))),
+        ...structuredClone(new ToolCallEvent(toolCall)),
         'event.name': EVENT_TOOL_CALL,
-      });
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL });
 
       const metrics = service.getMetrics();
       const { tools } = metrics;
@@ -410,9 +414,9 @@ describe('UiTelemetryService', () => {
         ToolConfirmationOutcome.ModifyWithEditor,
       );
       service.addEvent({
-        ...JSON.parse(JSON.stringify(new ToolCallEvent(toolCall))),
+        ...structuredClone(new ToolCallEvent(toolCall)),
         'event.name': EVENT_TOOL_CALL,
-      });
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL });
 
       const metrics = service.getMetrics();
       const { tools } = metrics;
@@ -426,9 +430,9 @@ describe('UiTelemetryService', () => {
     it('should process a ToolCallEvent without a decision', () => {
       const toolCall = createFakeCompletedToolCall('test_tool', true, 100);
       service.addEvent({
-        ...JSON.parse(JSON.stringify(new ToolCallEvent(toolCall))),
+        ...structuredClone(new ToolCallEvent(toolCall)),
         'event.name': EVENT_TOOL_CALL,
-      });
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL });
 
       const metrics = service.getMetrics();
       const { tools } = metrics;
@@ -462,13 +466,13 @@ describe('UiTelemetryService', () => {
       );
 
       service.addEvent({
-        ...JSON.parse(JSON.stringify(new ToolCallEvent(toolCall1))),
+        ...structuredClone(new ToolCallEvent(toolCall1)),
         'event.name': EVENT_TOOL_CALL,
-      });
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL });
       service.addEvent({
-        ...JSON.parse(JSON.stringify(new ToolCallEvent(toolCall2))),
+        ...structuredClone(new ToolCallEvent(toolCall2)),
         'event.name': EVENT_TOOL_CALL,
-      });
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL });
 
       const metrics = service.getMetrics();
       const { tools } = metrics;
@@ -497,13 +501,13 @@ describe('UiTelemetryService', () => {
       const toolCall1 = createFakeCompletedToolCall('tool_A', true, 100);
       const toolCall2 = createFakeCompletedToolCall('tool_B', false, 200);
       service.addEvent({
-        ...JSON.parse(JSON.stringify(new ToolCallEvent(toolCall1))),
+        ...structuredClone(new ToolCallEvent(toolCall1)),
         'event.name': EVENT_TOOL_CALL,
-      });
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL });
       service.addEvent({
-        ...JSON.parse(JSON.stringify(new ToolCallEvent(toolCall2))),
+        ...structuredClone(new ToolCallEvent(toolCall2)),
         'event.name': EVENT_TOOL_CALL,
-      });
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL });
 
       const metrics = service.getMetrics();
       const { tools } = metrics;
@@ -629,4 +633,42 @@ describe('UiTelemetryService', () => {
       expect(spy).toHaveBeenCalledOnce();
     });
   });
+
+  describe('Tool Call Event with Line Count Metadata', () => {
+    it('should aggregate valid line count metadata', () => {
+      const toolCall = createFakeCompletedToolCall('test_tool', true, 100);
+      const event = {
+        ...structuredClone(new ToolCallEvent(toolCall)),
+        'event.name': EVENT_TOOL_CALL,
+        metadata: {
+          ai_added_lines: 10,
+          ai_removed_lines: 5,
+        },
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL };
+
+      service.addEvent(event);
+
+      const metrics = service.getMetrics();
+      expect(metrics.files.totalLinesAdded).toBe(10);
+      expect(metrics.files.totalLinesRemoved).toBe(5);
+    });
+
+    it('should ignore null/undefined values in line count metadata', () => {
+      const toolCall = createFakeCompletedToolCall('test_tool', true, 100);
+      const event = {
+        ...structuredClone(new ToolCallEvent(toolCall)),
+        'event.name': EVENT_TOOL_CALL,
+        metadata: {
+          ai_added_lines: null,
+          ai_removed_lines: undefined,
+        },
+      } as ToolCallEvent & { 'event.name': typeof EVENT_TOOL_CALL };
+
+      service.addEvent(event);
+
+      const metrics = service.getMetrics();
+      expect(metrics.files.totalLinesAdded).toBe(0);
+      expect(metrics.files.totalLinesRemoved).toBe(0);
+    });
+  });
 });
diff --git a/packages/core/src/telemetry/uiTelemetry.ts b/packages/core/src/telemetry/uiTelemetry.ts
index 8d1b044f..318478aa 100644
--- a/packages/core/src/telemetry/uiTelemetry.ts
+++ b/packages/core/src/telemetry/uiTelemetry.ts
@@ -63,6 +63,10 @@ export interface SessionMetrics {
     };
     byName: Record<string, ToolCallStats>;
   };
+  files: {
+    totalLinesAdded: number;
+    totalLinesRemoved: number;
+  };
 }
 
 const createInitialModelMetrics = (): ModelMetrics => ({
@@ -96,6 +100,10 @@ const createInitialMetrics = (): SessionMetrics => ({
     },
     byName: {},
   },
+  files: {
+    totalLinesAdded: 0,
+    totalLinesRemoved: 0,
+  },
 });
 
 export class UiTelemetryService extends EventEmitter {
@@ -171,7 +179,7 @@ export class UiTelemetryService extends EventEmitter {
   }
 
   private processToolCall(event: ToolCallEvent) {
-    const { tools } = this.#metrics;
+    const { tools, files } = this.#metrics;
     tools.totalCalls++;
     tools.totalDurationMs += event.duration_ms;
 
@@ -209,6 +217,16 @@ export class UiTelemetryService extends EventEmitter {
       tools.totalDecisions[event.decision]++;
       toolStats.decisions[event.decision]++;
     }
+
+    // Aggregate line count data from metadata
+    if (event.metadata) {
+      if (event.metadata['ai_added_lines'] !== undefined) {
+        files.totalLinesAdded += event.metadata['ai_added_lines'];
+      }
+      if (event.metadata['ai_removed_lines'] !== undefined) {
+        files.totalLinesRemoved += event.metadata['ai_removed_lines'];
+      }
+    }
   }
 }