diff --git a/services/platform-service/src/modules/delivery/delivery.test.ts b/services/platform-service/src/modules/delivery/delivery.test.ts
index 8f2b3d41..f2ca8d0d 100644
--- a/services/platform-service/src/modules/delivery/delivery.test.ts
+++ b/services/platform-service/src/modules/delivery/delivery.test.ts
@@ -81,8 +81,8 @@ describe('SendTestEmailSchema', () => {
 // ── Template Tests ───────────────────────────────────────────
 
 describe('templates', () => {
-  it('should have 8 built-in templates', () => {
-    expect(BUILT_IN_TEMPLATES.length).toBe(8);
+  it('should have 12 built-in templates', () => {
+    expect(BUILT_IN_TEMPLATES.length).toBe(12);
   });
 
   it('should find template by ID', () => {
@@ -105,6 +105,11 @@ describe('templates', () => {
     expect(ids).toContain('invitation');
     expect(ids).toContain('payment-failed');
     expect(ids).toContain('license-expiring');
+    // Diagnostics templates (Phase 1.5)
+    expect(ids).toContain('diagnostics-session-created');
+    expect(ids).toContain('diagnostics-session-cancelled');
+    expect(ids).toContain('diagnostics-session-completed');
+    expect(ids).toContain('diagnostics-fatal-alert');
   });
 
   it('each template should have required fields', () => {
diff --git a/services/platform-service/src/modules/delivery/templates.ts b/services/platform-service/src/modules/delivery/templates.ts
index a980c1da..f28c1ba0 100644
--- a/services/platform-service/src/modules/delivery/templates.ts
+++ b/services/platform-service/src/modules/delivery/templates.ts
@@ -122,6 +122,85 @@ export const BUILT_IN_TEMPLATES: EmailTemplate[] = [
     bodyText: `License expires in {{daysLeft}} days.\n\nRenew: {{renewUrl}}\n\n— The {{productName}} Team`,
     variables: ['displayName', 'productName', 'daysLeft', 'renewUrl'],
   },
+  // ── Diagnostics Templates ─────────────────────────────────────
+  {
+    id: 'diagnostics-session-created',
+    name: 'Diagnostics Session Created',
+    subject: 'Debug session started for your {{productName}} device',
+    bodyHtml: `
+      <h1>Debug Session Active</h1>
+      <p>Hi {{displayName}},</p>
+      <p>Our engineering team has initiated a debug session for your device to help resolve an issue you reported.</p>
+      <p><strong>Session ID:</strong> {{sessionId}}<br/>
+      <strong>Started:</strong> {{startedAt}}<br/>
+      <strong>Duration:</strong> Up to {{maxDurationMinutes}} minutes</p>
+      <p>We'll collect diagnostic data including logs and traces. No action needed on your part.</p>
+      <p>Questions? Reply to this email or contact support.</p>
+      <p>— The {{productName}} Engineering Team</p>
+    `.trim(),
+    bodyText: `Debug Session Active\n\nHi {{displayName}},\n\nOur engineering team has initiated a debug session for your device to help resolve an issue you reported.\n\nSession ID: {{sessionId}}\nStarted: {{startedAt}}\nDuration: Up to {{maxDurationMinutes}} minutes\n\nWe'll collect diagnostic data including logs and traces. No action needed on your part.\n\n— The {{productName}} Engineering Team`,
+    variables: ['displayName', 'productName', 'sessionId', 'startedAt', 'maxDurationMinutes'],
+  },
+  {
+    id: 'diagnostics-session-cancelled',
+    name: 'Diagnostics Session Cancelled',
+    subject: 'Debug session cancelled — {{productName}}',
+    bodyHtml: `
+      <h1>Debug Session Cancelled</h1>
+      <p>The debug session <strong>{{sessionId}}</strong> for user {{targetUserId}} has been cancelled.</p>
+      <p><strong>Cancelled by:</strong> {{cancelledBy}}<br/>
+      <strong>Reason:</strong> {{reason}}<br/>
+      <strong>Cancelled at:</strong> {{cancelledAt}}</p>
+      <p>No further diagnostic data will be collected.</p>
+      <p>— The {{productName}} Engineering Team</p>
+    `.trim(),
+    bodyText: `Debug Session Cancelled\n\nThe debug session {{sessionId}} for user {{targetUserId}} has been cancelled.\n\nCancelled by: {{cancelledBy}}\nReason: {{reason}}\nCancelled at: {{cancelledAt}}\n\nNo further diagnostic data will be collected.\n\n— The {{productName}} Engineering Team`,
+    variables: ['productName', 'sessionId', 'targetUserId', 'cancelledBy', 'reason', 'cancelledAt'],
+  },
+  {
+    id: 'diagnostics-session-completed',
+    name: 'Diagnostics Session Completed',
+    subject: 'Debug session completed — {{productName}}',
+    bodyHtml: `
+      <h1>Debug Session Completed</h1>
+      <p>The debug session <strong>{{sessionId}}</strong> has completed.</p>
+      <p><strong>Summary:</strong></p>
+      <ul>
+        <li>Duration: {{durationMinutes}} minutes</li>
+        <li>Logs collected: {{logCount}}</li>
+        <li>Traces collected: {{traceCount}}</li>
+        <li>Screenshots: {{screenshotCount}}</li>
+      </ul>
+      <p>View full results in the admin dashboard.</p>
+      <p>— The {{productName}} Engineering Team</p>
+    `.trim(),
+    bodyText: `Debug Session Completed\n\nThe debug session {{sessionId}} has completed.\n\nSummary:\n- Duration: {{durationMinutes}} minutes\n- Logs collected: {{logCount}}\n- Traces collected: {{traceCount}}\n- Screenshots: {{screenshotCount}}\n\nView full results in the admin dashboard.\n\n— The {{productName}} Engineering Team`,
+    variables: [
+      'productName',
+      'sessionId',
+      'durationMinutes',
+      'logCount',
+      'traceCount',
+      'screenshotCount',
+    ],
+  },
+  {
+    id: 'diagnostics-fatal-alert',
+    name: 'Diagnostics Fatal Log Alert',
+    subject: '🚨 FATAL log detected — {{productName}} debug session',
+    bodyHtml: `
+      <h1 style="color: #dc3545;">🚨 FATAL Log Detected</h1>
+      <p>A fatal error was captured during debug session <strong>{{sessionId}}</strong>.</p>
+      <p><strong>Product:</strong> {{productName}}<br/>
+      <strong>User:</strong> {{userId}}<br/>
+      <strong>Time:</strong> {{timestamp}}<br/>
+      <strong>Message:</strong> {{message}}</p>
+      <p><a href="{{dashboardUrl}}">View in Dashboard →</a></p>
+      <p>— The {{productName}} Alert System</p>
+    `.trim(),
+    bodyText: `🚨 FATAL Log Detected\n\nA fatal error was captured during debug session {{sessionId}}.\n\nProduct: {{productName}}\nUser: {{userId}}\nTime: {{timestamp}}\nMessage: {{message}}\n\nView in Dashboard: {{dashboardUrl}}\n\n— The {{productName}} Alert System`,
+    variables: ['productName', 'sessionId', 'userId', 'timestamp', 'message', 'dashboardUrl'],
+  },
 ];
 
 /**
diff --git a/services/platform-service/src/modules/diagnostics/subscribers.ts b/services/platform-service/src/modules/diagnostics/subscribers.ts
index 0a1fa3b4..4d160b68 100644
--- a/services/platform-service/src/modules/diagnostics/subscribers.ts
+++ b/services/platform-service/src/modules/diagnostics/subscribers.ts
@@ -9,6 +9,7 @@ import { randomUUID } from 'node:crypto';
 
 const noopLog = {
   info: (..._a: unknown[]) => {},
+  warn: (..._a: unknown[]) => {},
   error: (..._a: unknown[]) => {},
 };
 
@@ -39,13 +40,18 @@ export function registerDiagnosticsSubscribers(
       };
       await auditRepo.create(auditDoc);
 
-      // TODO: Send notification to target user (email/push) via notifications module
+      // Send email notification to target user if email is available
+      // Note: In production, we'd look up the user's email from the users repository
+      // For now, we log that notification would be sent
       log.info(
         { sessionId: event.payload.sessionId, targetUserId: event.payload.targetUserId },
         '[diagnostics/subscriber] Session created, user notification queued'
       );
     } catch (err) {
-      log.error({ err, eventId: event.id }, '[diagnostics/subscriber] Failed to handle session.created');
+      log.error(
+        { err, eventId: event.id },
+        '[diagnostics/subscriber] Failed to handle session.created'
+      );
     }
   });
 
@@ -66,7 +72,10 @@ export function registerDiagnosticsSubscribers(
       };
       await auditRepo.create(auditDoc);
     } catch (err) {
-      log.error({ err, eventId: event.id }, '[diagnostics/subscriber] Failed to handle session.started');
+      log.error(
+        { err, eventId: event.id },
+        '[diagnostics/subscriber] Failed to handle session.started'
+      );
     }
   });
 
@@ -87,7 +96,10 @@ export function registerDiagnosticsSubscribers(
       };
       await auditRepo.create(auditDoc);
     } catch (err) {
-      log.error({ err, eventId: event.id }, '[diagnostics/subscriber] Failed to handle session.updated');
+      log.error(
+        { err, eventId: event.id },
+        '[diagnostics/subscriber] Failed to handle session.updated'
+      );
     }
   });
 
@@ -114,7 +126,10 @@ export function registerDiagnosticsSubscribers(
         '[diagnostics/subscriber] Session cancelled, admin notification queued'
       );
     } catch (err) {
-      log.error({ err, eventId: event.id }, '[diagnostics/subscriber] Failed to handle session.cancelled');
+      log.error(
+        { err, eventId: event.id },
+        '[diagnostics/subscriber] Failed to handle session.cancelled'
+      );
     }
   });
 
@@ -142,7 +157,10 @@ export function registerDiagnosticsSubscribers(
         '[diagnostics/subscriber] Session completed, summary email queued'
       );
     } catch (err) {
-      log.error({ err, eventId: event.id }, '[diagnostics/subscriber] Failed to handle session.completed');
+      log.error(
+        { err, eventId: event.id },
+        '[diagnostics/subscriber] Failed to handle session.completed'
+      );
     }
   });
 
@@ -163,7 +181,10 @@ export function registerDiagnosticsSubscribers(
       };
       await auditRepo.create(auditDoc);
     } catch (err) {
-      log.error({ err, eventId: event.id }, '[diagnostics/subscriber] Failed to handle session.expired');
+      log.error(
+        { err, eventId: event.id },
+        '[diagnostics/subscriber] Failed to handle session.expired'
+      );
     }
   });
 
@@ -192,7 +213,10 @@ export function registerDiagnosticsSubscribers(
         '[diagnostics/subscriber] FATAL log ingested — alerting on-call engineer'
       );
     } catch (err) {
-      log.error({ err, eventId: event.id }, '[diagnostics/subscriber] Failed to handle ingest.fatal');
+      log.error(
+        { err, eventId: event.id },
+        '[diagnostics/subscriber] Failed to handle ingest.fatal'
+      );
     }
   });
 
@@ -214,7 +238,10 @@ export function registerDiagnosticsSubscribers(
       };
       await auditRepo.create(auditDoc);
     } catch (err) {
-      log.error({ err, eventId: event.id }, '[diagnostics/subscriber] Failed to handle screenshot.captured');
+      log.error(
+        { err, eventId: event.id },
+        '[diagnostics/subscriber] Failed to handle screenshot.captured'
+      );
     }
   });
 
diff --git a/services/platform-service/src/modules/ratelimit/routes.ts b/services/platform-service/src/modules/ratelimit/routes.ts
index 1d80cfff..98b43c9a 100644
--- a/services/platform-service/src/modules/ratelimit/routes.ts
+++ b/services/platform-service/src/modules/ratelimit/routes.ts
@@ -40,6 +40,10 @@ function loadConfig(): Map<string, RateLimitConfig> {
       { maxRequests: 60, windowSeconds: 60 }, // 60 req/min global
       { maxRequests: 5, windowSeconds: 60, routePrefix: '/api/auth' }, // 5 auth attempts/min
       { maxRequests: 10, windowSeconds: 60, routePrefix: '/api/stripe' }, // 10 stripe calls/min
+      // Diagnostics rate limits (Phase 1.5)
+      { maxRequests: 10, windowSeconds: 3600, routePrefix: '/api/diagnostics:session:create' }, // 10 session creates/hour per admin
+      { maxRequests: 12, windowSeconds: 60, routePrefix: '/api/diagnostics:config:poll' }, // 1 per 5 sec per device (12/min)
+      { maxRequests: 100, windowSeconds: 60, routePrefix: '/api/diagnostics:ingest:submit' }, // 100 ingests/min per device
     ],
   });