diff --git a/src/renderer/lib/sessionActivity.ts b/src/renderer/lib/sessionActivity.ts
index 14bfc5d..73d2cc7 100644
--- a/src/renderer/lib/sessionActivity.ts
+++ b/src/renderer/lib/sessionActivity.ts
@@ -7,6 +7,7 @@ export interface AgentActivityState {
   agentName: string;
   activityType?: SessionEventRecord['activityType'];
   toolName?: string;
+  toolArguments?: Record<string, unknown>;
 }
 
 export interface SessionUsageState {
@@ -45,6 +46,7 @@ export function applySessionEventActivity(
           agentName: event.agentName?.trim() || event.agentId?.trim() || agentKey,
           activityType: event.activityType,
           toolName: event.toolName,
+          toolArguments: event.toolArguments,
         },
       },
     };
diff --git a/src/shared/domain/runTimeline.ts b/src/shared/domain/runTimeline.ts
index ffa6cf0..12262ce 100644
--- a/src/shared/domain/runTimeline.ts
+++ b/src/shared/domain/runTimeline.ts
@@ -494,6 +494,7 @@ function normalizeRunTimelineEvent(
     targetAgentName: normalizeOptionalString(event.targetAgentName),
     toolName: normalizeOptionalString(event.toolName),
     toolCallId: normalizeOptionalString(event.toolCallId),
+    toolArguments: event.toolArguments,
     fileChanges: normalizeToolCallFileChanges(event.fileChanges),
     approvalId: normalizeOptionalString(event.approvalId),
     approvalKind: event.approvalKind,
diff --git a/tests/renderer/sessionActivity.test.ts b/tests/renderer/sessionActivity.test.ts
index 40fb16b..13b126a 100644
--- a/tests/renderer/sessionActivity.test.ts
+++ b/tests/renderer/sessionActivity.test.ts
@@ -99,6 +99,32 @@ describe('session activity helpers', () => {
     });
   });
 
+  test('includes toolArguments in activity state', () => {
+    const event: SessionEventRecord = {
+      sessionId: 'session-1',
+      kind: 'agent-activity',
+      occurredAt: '2026-03-23T00:00:00.000Z',
+      activityType: 'tool-calling',
+      agentId: 'architect',
+      agentName: 'Architect',
+      toolName: 'view',
+      toolArguments: { path: 'src/main.ts', view_range: [1, 50] },
+    };
+
+    const result = applySessionEventActivity({}, event);
+    expect(result).toEqual({
+      'session-1': {
+        architect: {
+          agentId: 'architect',
+          agentName: 'Architect',
+          activityType: 'tool-calling',
+          toolName: 'view',
+          toolArguments: { path: 'src/main.ts', view_range: [1, 50] },
+        },
+      },
+    });
+  });
+
   test('warns when an agent-activity event is missing identifiers', () => {
     const originalWarn = console.warn;
     const warnings: unknown[][] = [];
diff --git a/tests/shared/runTimeline.test.ts b/tests/shared/runTimeline.test.ts
index 67131cb..8f5b77f 100644
--- a/tests/shared/runTimeline.test.ts
+++ b/tests/shared/runTimeline.test.ts
@@ -9,6 +9,7 @@ import {
   upsertRunApprovalEvent,
   upsertRunMessageEvent,
 } from '@shared/domain/runTimeline';
+import type { SessionRunRecord } from '@shared/domain/runTimeline';
 import type { ProjectRecord } from '@shared/domain/project';
 import type { PendingApprovalRecord } from '@shared/domain/approval';
 
@@ -265,6 +266,71 @@ describe('run timeline helpers', () => {
     expect(normalizeSessionRunRecords(undefined)).toEqual([]);
   });
 
+  test('preserves toolArguments through normalization round-trip', () => {
+    const baseRun = createSessionRunRecord({
+      requestId: 'turn-1',
+      project: createProject(),
+      workspaceKind: 'project',
+      workflow: createWorkflow(),
+      triggerMessageId: 'msg-user-1',
+      startedAt: '2026-03-23T00:00:01.000Z',
+    });
+
+    const run = appendRunActivityEvent(baseRun, {
+      activityType: 'tool-calling',
+      occurredAt: '2026-03-23T00:00:02.000Z',
+      agentId: 'agent-writer',
+      toolName: 'view',
+      toolCallId: 'tool-call-view-1',
+      toolArguments: { path: 'src/main.ts', view_range: [1, 50] },
+    });
+
+    // Simulate persisting and reloading via normalizeSessionRunRecords
+    const roundTripped = normalizeSessionRunRecords(
+      JSON.parse(JSON.stringify([run])) as SessionRunRecord[],
+    );
+
+    expect(roundTripped).toHaveLength(1);
+    const toolCallEvent = roundTripped[0].events.find(
+      (event) => event.kind === 'tool-call',
+    );
+    expect(toolCallEvent).toBeDefined();
+    expect(toolCallEvent!.toolArguments).toEqual({
+      path: 'src/main.ts',
+      view_range: [1, 50],
+    });
+  });
+
+  test('handles missing toolArguments gracefully during normalization', () => {
+    const baseRun = createSessionRunRecord({
+      requestId: 'turn-1',
+      project: createProject(),
+      workspaceKind: 'project',
+      workflow: createWorkflow(),
+      triggerMessageId: 'msg-user-1',
+      startedAt: '2026-03-23T00:00:01.000Z',
+    });
+
+    const run = appendRunActivityEvent(baseRun, {
+      activityType: 'tool-calling',
+      occurredAt: '2026-03-23T00:00:02.000Z',
+      agentId: 'agent-writer',
+      toolName: 'rg',
+      toolCallId: 'tool-call-rg-1',
+      // No toolArguments provided
+    });
+
+    const roundTripped = normalizeSessionRunRecords(
+      JSON.parse(JSON.stringify([run])) as SessionRunRecord[],
+    );
+
+    const toolCallEvent = roundTripped[0].events.find(
+      (event) => event.kind === 'tool-call',
+    );
+    expect(toolCallEvent).toBeDefined();
+    expect(toolCallEvent!.toolArguments).toBeUndefined();
+  });
+
   test('tracks approval checkpoints as a single timeline event that can be resolved later', () => {
     const baseRun = createSessionRunRecord({
       requestId: 'turn-1',