diff --git a/apps/web/src/components/radar/types.ts b/apps/web/src/components/radar/types.ts
index 67ea1ac..e7dd307 100644
--- a/apps/web/src/components/radar/types.ts
+++ b/apps/web/src/components/radar/types.ts
@@ -3,4 +3,5 @@ export interface DrilldownDialogProps {
   onOpenChange: (open: boolean) => void
   agentId: string
   agentName: string
+  isAgentRunning?: boolean
 }
diff --git a/apps/web/src/routes/__tests__/radar.test.tsx b/apps/web/src/routes/__tests__/radar.test.tsx
index 5472ff7..01f110e 100644
--- a/apps/web/src/routes/__tests__/radar.test.tsx
+++ b/apps/web/src/routes/__tests__/radar.test.tsx
@@ -3,6 +3,39 @@ import '@testing-library/jest-dom/vitest'
 import { render, screen, fireEvent, within } from '@testing-library/react'
 import { vi, describe, it, expect, beforeEach } from 'vitest'
 
+vi.mock('@/components/radar/CompactionEventsDialog', () => ({
+  CompactionEventsDialog: ({ open, agentId, agentName, isAgentRunning, onOpenChange }: any) =>
+    open ? (
+      <div data-testid="compaction-dialog" data-agent-id={agentId} data-agent-name={agentName} data-is-running={String(isAgentRunning)}>
+        <button onClick={() => onOpenChange(false)}>close</button>
+      </div>
+    ) : null,
+}))
+vi.mock('@/components/radar/SubagentSpawnsDialog', () => ({
+  SubagentSpawnsDialog: ({ open, agentId, agentName, isAgentRunning, onOpenChange }: any) =>
+    open ? (
+      <div data-testid="subagents-dialog" data-agent-id={agentId} data-agent-name={agentName} data-is-running={String(isAgentRunning)}>
+        <button onClick={() => onOpenChange(false)}>close</button>
+      </div>
+    ) : null,
+}))
+vi.mock('@/components/radar/QuestionsAskedDialog', () => ({
+  QuestionsAskedDialog: ({ open, agentId, agentName, isAgentRunning, onOpenChange }: any) =>
+    open ? (
+      <div data-testid="questions-dialog" data-agent-id={agentId} data-agent-name={agentName} data-is-running={String(isAgentRunning)}>
+        <button onClick={() => onOpenChange(false)}>close</button>
+      </div>
+    ) : null,
+}))
+vi.mock('@/components/radar/InterAgentMessagesDialog', () => ({
+  InterAgentMessagesDialog: ({ open, agentId, agentName, isAgentRunning, onOpenChange }: any) =>
+    open ? (
+      <div data-testid="messages-dialog" data-agent-id={agentId} data-agent-name={agentName} data-is-running={String(isAgentRunning)}>
+        <button onClick={() => onOpenChange(false)}>close</button>
+      </div>
+    ) : null,
+}))
+
 type AgentRadarRow = {
   id: string
   name: string
@@ -277,6 +310,125 @@ describe('RadarPage', () => {
     const skeletons = document.querySelectorAll('.animate-pulse')
     expect(skeletons.length).toBeGreaterThanOrEqual(5)
   })
+
+  describe('dialog integration', () => {
+    const alphaAgent = {
+      id: 'agent-alpha-id',
+      name: 'agent-alpha',
+      mode: 'execute',
+      status: 'running',
+      initiativeId: null,
+      initiativeName: null,
+      taskId: null,
+      taskName: null,
+      createdAt: new Date(Date.now() - 3600_000).toISOString(),
+      questionsCount: 3,
+      messagesCount: 2,
+      subagentsCount: 1,
+      compactionsCount: 4,
+    }
+    const betaAgent = {
+      id: 'agent-beta-id',
+      name: 'agent-beta',
+      mode: 'execute',
+      status: 'stopped',
+      initiativeId: null,
+      initiativeName: null,
+      taskId: null,
+      taskName: null,
+      createdAt: new Date(Date.now() - 7200_000).toISOString(),
+      questionsCount: 0,
+      messagesCount: 0,
+      subagentsCount: 0,
+      compactionsCount: 0,
+    }
+
+    beforeEach(() => {
+      mockListForRadarUseQuery.mockReturnValue({ data: [alphaAgent, betaAgent], isLoading: false })
+    })
+
+    it('clicking a non-zero Compactions cell opens CompactionEventsDialog with correct agentId and agentName', async () => {
+      render(<RadarPage />)
+      const cell = screen.getByTestId(`cell-compactions-agent-alpha-id`)
+      fireEvent.click(cell)
+      const dialog = await screen.findByTestId('compaction-dialog')
+      expect(dialog).toBeInTheDocument()
+      expect(dialog).toHaveAttribute('data-agent-name', 'agent-alpha')
+      expect(dialog).toHaveAttribute('data-agent-id', 'agent-alpha-id')
+    })
+
+    it('clicking a non-zero Subagents cell opens SubagentSpawnsDialog', async () => {
+      render(<RadarPage />)
+      const cell = screen.getByTestId(`cell-subagents-agent-alpha-id`)
+      fireEvent.click(cell)
+      const dialog = await screen.findByTestId('subagents-dialog')
+      expect(dialog).toBeInTheDocument()
+      expect(dialog).toHaveAttribute('data-agent-name', 'agent-alpha')
+      expect(dialog).toHaveAttribute('data-agent-id', 'agent-alpha-id')
+    })
+
+    it('clicking a non-zero Questions cell opens QuestionsAskedDialog', async () => {
+      render(<RadarPage />)
+      const cell = screen.getByTestId(`cell-questions-agent-alpha-id`)
+      fireEvent.click(cell)
+      const dialog = await screen.findByTestId('questions-dialog')
+      expect(dialog).toBeInTheDocument()
+      expect(dialog).toHaveAttribute('data-agent-name', 'agent-alpha')
+      expect(dialog).toHaveAttribute('data-agent-id', 'agent-alpha-id')
+    })
+
+    it('clicking a non-zero Messages cell opens InterAgentMessagesDialog', async () => {
+      render(<RadarPage />)
+      const cell = screen.getByTestId(`cell-messages-agent-alpha-id`)
+      fireEvent.click(cell)
+      const dialog = await screen.findByTestId('messages-dialog')
+      expect(dialog).toBeInTheDocument()
+      expect(dialog).toHaveAttribute('data-agent-name', 'agent-alpha')
+      expect(dialog).toHaveAttribute('data-agent-id', 'agent-alpha-id')
+    })
+
+    it('dialog closes when onOpenChange(false) fires', async () => {
+      render(<RadarPage />)
+      const cell = screen.getByTestId(`cell-compactions-agent-alpha-id`)
+      fireEvent.click(cell)
+      const dialog = await screen.findByTestId('compaction-dialog')
+      expect(dialog).toBeInTheDocument()
+      fireEvent.click(screen.getByRole('button', { name: 'close' }))
+      expect(screen.queryByTestId('compaction-dialog')).not.toBeInTheDocument()
+    })
+
+    it('zero metric cells do not open any dialog when clicked', () => {
+      render(<RadarPage />)
+      // agent-beta has all zeros — click each zero metric cell
+      fireEvent.click(screen.getByTestId('cell-compactions-agent-beta-id'))
+      fireEvent.click(screen.getByTestId('cell-subagents-agent-beta-id'))
+      fireEvent.click(screen.getByTestId('cell-questions-agent-beta-id'))
+      fireEvent.click(screen.getByTestId('cell-messages-agent-beta-id'))
+      expect(screen.queryByTestId('compaction-dialog')).not.toBeInTheDocument()
+      expect(screen.queryByTestId('subagents-dialog')).not.toBeInTheDocument()
+      expect(screen.queryByTestId('questions-dialog')).not.toBeInTheDocument()
+      expect(screen.queryByTestId('messages-dialog')).not.toBeInTheDocument()
+    })
+
+    it('passes isAgentRunning=true when the agent status is "running"', async () => {
+      render(<RadarPage />)
+      const cell = screen.getByTestId(`cell-compactions-agent-alpha-id`)
+      fireEvent.click(cell)
+      const dialog = await screen.findByTestId('compaction-dialog')
+      expect(dialog).toHaveAttribute('data-is-running', 'true')
+    })
+
+    it('passes isAgentRunning=false when the agent status is "stopped"', async () => {
+      // Use a stopped agent with non-zero compactions
+      const stoppedAgent = { ...betaAgent, id: 'stopped-agent-id', name: 'stopped-agent', compactionsCount: 2, status: 'stopped' }
+      mockListForRadarUseQuery.mockReturnValue({ data: [stoppedAgent], isLoading: false })
+      render(<RadarPage />)
+      const cell = screen.getByTestId('cell-compactions-stopped-agent-id')
+      fireEvent.click(cell)
+      const dialog = await screen.findByTestId('compaction-dialog')
+      expect(dialog).toHaveAttribute('data-is-running', 'false')
+    })
+  })
 })
 
 describe('AppLayout - Radar nav item', () => {
diff --git a/apps/web/src/routes/radar.tsx b/apps/web/src/routes/radar.tsx
index 8547b6c..7e68b3b 100644
--- a/apps/web/src/routes/radar.tsx
+++ b/apps/web/src/routes/radar.tsx
@@ -4,6 +4,10 @@ import { trpc } from '@/lib/trpc'
 import { useLiveUpdates } from '@/hooks'
 import type { LiveUpdateRule } from '@/hooks'
 import { Card, CardContent } from '@/components/ui/card'
+import { CompactionEventsDialog } from '@/components/radar/CompactionEventsDialog'
+import { SubagentSpawnsDialog } from '@/components/radar/SubagentSpawnsDialog'
+import { QuestionsAskedDialog } from '@/components/radar/QuestionsAskedDialog'
+import { InterAgentMessagesDialog } from '@/components/radar/InterAgentMessagesDialog'
 
 type TimeRange = '1h' | '6h' | '24h' | '7d' | 'all'
 type StatusFilter = 'all' | 'running' | 'completed' | 'crashed'
@@ -74,6 +78,14 @@ export function RadarPage() {
 
   const { data: initiatives = [] } = trpc.listInitiatives.useQuery()
 
+  type DrilldownType = 'questions' | 'messages' | 'subagents' | 'compactions'
+
+  const [drilldown, setDrilldown] = useState<{
+    type: DrilldownType
+    agentId: string
+    agentName: string
+  } | null>(null)
+
   const [sortState, setSortState] = useState<{ column: SortColumn; direction: 'asc' | 'desc' }>({
     column: 'started',
     direction: 'desc',
@@ -156,21 +168,9 @@ export function RadarPage() {
     )
   }
 
-  function MetricCell({ value }: { value: number }) {
-    if (value > 0) {
-      return (
-        <td
-          className="cursor-pointer hover:bg-muted/50 text-right px-3 py-2"
-          onClick={() => {
-            // TODO: open drilldown dialog — wired in Phase 4 (Dialog Integration)
-          }}
-        >
-          {value}
-        </td>
-      )
-    }
-    return <td className="text-muted-foreground text-right px-3 py-2">0</td>
-  }
+  const isAgentRunning = drilldown
+    ? agents.find((a) => a.id === drilldown.agentId)?.status === 'running'
+    : false
 
   return (
     <div className="space-y-6">
@@ -313,15 +313,76 @@ export function RadarPage() {
                     <td className="px-3 py-2">
                       {new Date(agent.createdAt).toLocaleString()}
                     </td>
-                    <MetricCell value={agent.questionsCount} />
-                    <MetricCell value={agent.messagesCount} />
-                    <MetricCell value={agent.subagentsCount} />
-                    <MetricCell value={agent.compactionsCount} />
+                    <td
+                      data-testid={`cell-questions-${agent.id}`}
+                      className={agent.questionsCount > 0 ? 'cursor-pointer hover:bg-muted/50 text-right px-3 py-2' : 'text-muted-foreground text-right px-3 py-2'}
+                      onClick={agent.questionsCount > 0
+                        ? () => setDrilldown({ type: 'questions', agentId: agent.id, agentName: agent.name })
+                        : undefined}
+                    >
+                      {agent.questionsCount}
+                    </td>
+                    <td
+                      data-testid={`cell-messages-${agent.id}`}
+                      className={agent.messagesCount > 0 ? 'cursor-pointer hover:bg-muted/50 text-right px-3 py-2' : 'text-muted-foreground text-right px-3 py-2'}
+                      onClick={agent.messagesCount > 0
+                        ? () => setDrilldown({ type: 'messages', agentId: agent.id, agentName: agent.name })
+                        : undefined}
+                    >
+                      {agent.messagesCount}
+                    </td>
+                    <td
+                      data-testid={`cell-subagents-${agent.id}`}
+                      className={agent.subagentsCount > 0 ? 'cursor-pointer hover:bg-muted/50 text-right px-3 py-2' : 'text-muted-foreground text-right px-3 py-2'}
+                      onClick={agent.subagentsCount > 0
+                        ? () => setDrilldown({ type: 'subagents', agentId: agent.id, agentName: agent.name })
+                        : undefined}
+                    >
+                      {agent.subagentsCount}
+                    </td>
+                    <td
+                      data-testid={`cell-compactions-${agent.id}`}
+                      className={agent.compactionsCount > 0 ? 'cursor-pointer hover:bg-muted/50 text-right px-3 py-2' : 'text-muted-foreground text-right px-3 py-2'}
+                      onClick={agent.compactionsCount > 0
+                        ? () => setDrilldown({ type: 'compactions', agentId: agent.id, agentName: agent.name })
+                        : undefined}
+                    >
+                      {agent.compactionsCount}
+                    </td>
                   </tr>
                 ))}
           </tbody>
         </table>
       )}
+
+      <CompactionEventsDialog
+        open={drilldown?.type === 'compactions'}
+        onOpenChange={(open) => { if (!open) setDrilldown(null) }}
+        agentId={drilldown?.agentId ?? ''}
+        agentName={drilldown?.agentName ?? ''}
+        isAgentRunning={isAgentRunning}
+      />
+      <SubagentSpawnsDialog
+        open={drilldown?.type === 'subagents'}
+        onOpenChange={(open) => { if (!open) setDrilldown(null) }}
+        agentId={drilldown?.agentId ?? ''}
+        agentName={drilldown?.agentName ?? ''}
+        isAgentRunning={isAgentRunning}
+      />
+      <QuestionsAskedDialog
+        open={drilldown?.type === 'questions'}
+        onOpenChange={(open) => { if (!open) setDrilldown(null) }}
+        agentId={drilldown?.agentId ?? ''}
+        agentName={drilldown?.agentName ?? ''}
+        isAgentRunning={isAgentRunning}
+      />
+      <InterAgentMessagesDialog
+        open={drilldown?.type === 'messages'}
+        onOpenChange={(open) => { if (!open) setDrilldown(null) }}
+        agentId={drilldown?.agentId ?? ''}
+        agentName={drilldown?.agentName ?? ''}
+        isAgentRunning={isAgentRunning}
+      />
     </div>
   )
 }