diff --git a/app/.eslint-baseline.json b/app/.eslint-baseline.json
index ed0dcf8b..1a35176f 100644
--- a/app/.eslint-baseline.json
+++ b/app/.eslint-baseline.json
@@ -74,6 +74,7 @@
   "src/core/services/supabase/__tests__/SupabaseService.test.ts": 1,
   "src/core/services/supabase/__tests__/analyticsGate.unit.test.ts": 1,
   "src/core/services/supabase/__tests__/crisisTelemetryDurable.unit.test.ts": 1,
+  "src/core/services/supabase/__tests__/crisisTelemetryGuard.unit.test.ts": 1,
   "src/core/services/supabase/hooks/useCloudSync.ts": 3,
   "src/core/services/supabase/index.ts": 3,
   "src/core/stores/__tests__/consentStore.test.ts": 1,
@@ -103,6 +104,7 @@
   "src/features/assessment/stores/__tests__/assessmentStore.notes.test.ts": 1,
   "src/features/assessment/stores/__tests__/assessmentStore.test.ts": 1,
   "src/features/assessment/stores/__tests__/crisisTelemetryEmit.unit.test.ts": 1,
+  "src/features/assessment/stores/__tests__/crisisTelemetryFields.regression.test.ts": 1,
   "src/features/assessment/stores/assessmentStore.ts": 26,
   "src/features/assessment/types/__tests__/schemas.test.ts": 1,
   "src/features/assessment/types/scoring.ts": 2,
diff --git a/app/src/core/services/supabase/SupabaseService.ts b/app/src/core/services/supabase/SupabaseService.ts
index 145d3bb1..4aef2941 100644
--- a/app/src/core/services/supabase/SupabaseService.ts
+++ b/app/src/core/services/supabase/SupabaseService.ts
@@ -556,6 +556,20 @@ class SupabaseService {
     }
   }
 
+  /**
+   * DEBUG-218: coerce a required crisis-telemetry categorical field. A missing/empty
+   * value degrades to an explicit 'unknown' sentinel + a high-severity log (queryable
+   * degradation) rather than silently coercing to the literal "undefined". The
+   * vital-interest event is still emitted — never dropped on a field-validation miss.
+   */
+  private requireCrisisField(value: string | undefined | null, field: string): string {
+    if (value === undefined || value === null || value === '') {
+      logSecurity('[SupabaseService] crisis telemetry missing required field', 'high', { field });
+      return 'unknown';
+    }
+    return String(value);
+  }
+
   /**
    * INFRA-214 T3 — Vital-interest crisis-detection telemetry.
    *
@@ -579,9 +593,11 @@ class SupabaseService {
         event_type: 'crisis_detected',
         properties: {
           trigger_type: String(telemetry.trigger_type),
-          severity_bucket: String(telemetry.severity_bucket),
+          // DEBUG-218: degrade a missing field to an explicit 'unknown' sentinel + a
+          // high-severity log instead of String(undefined) → the literal "undefined".
+          severity_bucket: this.requireCrisisField(telemetry.severity_bucket, 'severity_bucket'),
           intervention_surfaced: Boolean(telemetry.intervention_surfaced),
-          assessment_type: String(telemetry.assessment_type),
+          assessment_type: this.requireCrisisField(telemetry.assessment_type, 'assessment_type'),
         },
         session_id: this.sessionId,
         enqueued_at: Date.now(),
diff --git a/app/src/core/services/supabase/__tests__/crisisTelemetryGuard.unit.test.ts b/app/src/core/services/supabase/__tests__/crisisTelemetryGuard.unit.test.ts
new file mode 100644
index 00000000..aff46da4
--- /dev/null
+++ b/app/src/core/services/supabase/__tests__/crisisTelemetryGuard.unit.test.ts
@@ -0,0 +1,79 @@
+/**
+ * crisis_detected telemetry defensive guard (DEBUG-218) — UNIT
+ *
+ * Belt-and-suspenders behind the two upstream field-population fixes: if a future
+ * trigger is ever added without a severity/type mapping, `trackCrisisDetection` must
+ * degrade VISIBLY — substitute an explicit 'unknown' sentinel (never re-introduce the
+ * literal "undefined"), raise a high-severity security log, and STILL emit. A
+ * vital-interest crisis event is never dropped on a field-validation failure.
+ */
+import { jest } from '@jest/globals';
+
+jest.mock('@react-native-async-storage/async-storage');
+jest.mock('@supabase/supabase-js', () => ({ createClient: jest.fn(() => ({})) }));
+
+// Spy on the security logger to prove the "missing field" case is observable.
+const mockLogSecurity = jest.fn();
+jest.mock('../../logging', () => {
+  const actual = jest.requireActual('../../logging') as Record<string, unknown>;
+  return { ...actual, logSecurity: (...args: unknown[]) => mockLogSecurity(...args) };
+});
+
+import AsyncStorage from '@react-native-async-storage/async-storage';
+import supabaseService from '@/core/services/supabase/SupabaseService';
+
+describe('SupabaseService.trackCrisisDetection — missing-field guard (DEBUG-218)', () => {
+  let service: any;
+
+  beforeEach(() => {
+    jest.clearAllMocks();
+    (AsyncStorage.getItem as jest.Mock).mockResolvedValue(null);
+    (AsyncStorage.setItem as jest.Mock).mockResolvedValue(undefined);
+    service = new (supabaseService as any).constructor();
+  });
+
+  it('substitutes "unknown" (never "undefined") and still emits when a field is missing', () => {
+    service.trackCrisisDetection({
+      trigger_type: 'phq9_suicidal_ideation',
+      severity_bucket: undefined as any,
+      intervention_surfaced: true,
+      assessment_type: undefined as any,
+    });
+
+    // Event still landed in the durable queue (never dropped).
+    expect(service.crisisAnalyticsQueue).toHaveLength(1);
+    const props = service.crisisAnalyticsQueue[0].properties;
+    expect(props.severity_bucket).toBe('unknown');
+    expect(props.assessment_type).toBe('unknown');
+    expect(JSON.stringify(props)).not.toContain('undefined');
+  });
+
+  it('raises a high-severity security log so the degradation is observable', () => {
+    service.trackCrisisDetection({
+      trigger_type: 'phq9_suicidal_ideation',
+      severity_bucket: undefined as any,
+      intervention_surfaced: true,
+      assessment_type: 'phq9',
+    });
+
+    expect(mockLogSecurity).toHaveBeenCalledWith(
+      expect.stringContaining('crisis telemetry'),
+      'high',
+      expect.any(Object),
+    );
+  });
+
+  it('leaves well-formed payloads untouched (no false-positive guard, no log)', () => {
+    service.trackCrisisDetection({
+      trigger_type: 'gad7_severe_score',
+      severity_bucket: 'high',
+      intervention_surfaced: true,
+      assessment_type: 'gad7',
+    });
+
+    const props = service.crisisAnalyticsQueue[0].properties;
+    expect(props.severity_bucket).toBe('high');
+    expect(props.assessment_type).toBe('gad7');
+    expect(mockLogSecurity).not.toHaveBeenCalled();
+  });
+});
diff --git a/app/src/features/assessment/stores/__tests__/crisisTelemetryEmit.unit.test.ts b/app/src/features/assessment/stores/__tests__/crisisTelemetryEmit.unit.test.ts
index 99f6d4e9..576b4893 100644
--- a/app/src/features/assessment/stores/__tests__/crisisTelemetryEmit.unit.test.ts
+++ b/app/src/features/assessment/stores/__tests__/crisisTelemetryEmit.unit.test.ts
@@ -27,21 +27,29 @@ jest.mock('@/core/services/supabase/SupabaseService', () => {
 
 import { useAssessmentStore } from '../assessmentStore';
 import supabaseService from '@/core/services/supabase/SupabaseService';
+import type { CrisisDetection } from '@/features/crisis/types/safety';
 
 // Same reference assessmentStore calls (default import → default.trackCrisisDetection).
 const mockTrackCrisisDetection = (supabaseService as any).trackCrisisDetection as jest.Mock;
 
-const baseDetection = {
+// DEBUG-218: fully-typed CrisisDetection (no `as any`) so the type-checker enforces the
+// shape — in particular `assessmentType` is the lowercase `AssessmentType` union
+// ('phq9'/'gad7'), matching what the store now emits and what the FEAT-129
+// crisis_detection_daily view groups on.
+const baseDetection: CrisisDetection = {
   id: 'detect_1',
   isTriggered: true,
   primaryTrigger: 'phq9_suicidal_ideation',
   secondaryTriggers: [],
   severityLevel: 'critical',
   triggerValue: 3, // raw Q9 value present on the detection object — MUST NOT be emitted
-  assessmentType: 'PHQ-9',
+  assessmentType: 'phq9',
   timestamp: Date.now(),
   assessmentId: 'assess_1',
-} as any;
+  userId: 'user_1',
+  detectionResponseTimeMs: 0,
+  context: { triggeringAnswers: [], timeOfDay: 'morning' },
+};
 
 describe('handleCrisisDetection → crisis telemetry emit (INFRA-214 T3)', () => {
   beforeEach(() => {
@@ -58,7 +66,7 @@ describe('handleCrisisDetection → crisis telemetry emit (INFRA-214 T3)', () =>
       trigger_type: 'phq9_suicidal_ideation',
       severity_bucket: 'critical',
       intervention_surfaced: true,
-      assessment_type: 'PHQ-9',
+      assessment_type: 'phq9',
     });
     // The raw clinical value must never be forwarded.
     expect('triggerValue' in payload).toBe(false);
diff --git a/app/src/features/assessment/stores/__tests__/crisisTelemetryFields.regression.test.ts b/app/src/features/assessment/stores/__tests__/crisisTelemetryFields.regression.test.ts
new file mode 100644
index 00000000..178593ea
--- /dev/null
+++ b/app/src/features/assessment/stores/__tests__/crisisTelemetryFields.regression.test.ts
@@ -0,0 +1,199 @@
+/**
+ * crisis_detected telemetry field-population regression (DEBUG-218) — UNIT
+ *
+ * Pins the SAFETY-CRITICAL contract that BOTH crisis-detection emit paths carry a
+ * real `severity_bucket` and `assessment_type` — never the literal string "undefined".
+ *
+ * Before DEBUG-218, the inline PHQ-9 Q9 path AND the score-based completed path both
+ * built the CrisisDetection object without `severityLevel`/`assessmentType`, so
+ * `SupabaseService.trackCrisisDetection` coerced the missing fields via String(undefined)
+ * → "undefined" landed in `analytics_events` for the highest-acuity safety signal.
+ *
+ * These tests drive the REAL store actions (answerQuestion / completeAssessment) — not a
+ * hand-built detection — and assert on the mocked telemetry sink. Telemetry-only: the
+ * 988/intervention path and detection thresholds are unchanged.
+ */
+import { jest } from '@jest/globals';
+
+// Mock the Supabase singleton entirely so we exercise the field-population contract only
+// (the durable-queue internals live in the T6 landing test). jest.fn created INSIDE the
+// factory — jest.mock is hoisted above module-scope consts (TDZ otherwise).
+jest.mock('@/core/services/supabase/SupabaseService', () => {
+  const fn = jest.fn();
+  return {
+    __esModule: true,
+    default: { trackCrisisDetection: fn },
+    supabaseService: { trackCrisisDetection: fn },
+  };
+});
+
+// Emergency response calls Alert/Linking — keep them inert.
+jest.mock('react-native', () => ({
+  Alert: { alert: jest.fn() },
+  Linking: { openURL: jest.fn() },
+}));
+jest.mock('@react-native-async-storage/async-storage');
+jest.mock('expo-secure-store');
+
+// saveProgress() routes through SecureStorageService — passthrough so it never throws.
+const mockWellnessBlobs: Record<string, unknown> = {};
+jest.mock('@/core/services/security/SecureStorageService', () => ({
+  __esModule: true,
+  default: {
+    storeWellnessBlob: jest.fn(async (key: string, data: unknown) => {
+      mockWellnessBlobs[key] = data;
+      return { success: true, operationType: 'store' as const, storageKey: `wellness_async_${key}`, operationTimeMs: 0, dataSize: 0 };
+    }),
+    retrieveWellnessBlob: jest.fn(async (key: string) => mockWellnessBlobs[key] ?? null),
+    deleteWellnessBlob: jest.fn(async (key: string) => { delete mockWellnessBlobs[key]; }),
+  },
+}));
+
+import { useAssessmentStore } from '../assessmentStore';
+import supabaseService from '@/core/services/supabase/SupabaseService';
+import type { AssessmentResponse } from '../../types/index';
+
+const mockTrack = (supabaseService as any).trackCrisisDetection as jest.Mock;
+
+type Ans = { questionId: string; response: AssessmentResponse };
+
+// Greedy fill: q1..qN absorb the score first, so phq9_9 stays 0 unless explicitly set.
+function phq9(targetScore: number): Ans[] {
+  const ids = ['phq9_1', 'phq9_2', 'phq9_3', 'phq9_4', 'phq9_5', 'phq9_6', 'phq9_7', 'phq9_8', 'phq9_9'];
+  const out: Ans[] = [];
+  let remaining = targetScore;
+  for (let i = 0; i < ids.length; i++) {
+    const left = ids.length - i;
+    const minNeeded = Math.max(0, remaining - (left - 1) * 3);
+    const r = Math.max(minNeeded, Math.min(3, remaining)) as AssessmentResponse;
+    out.push({ questionId: ids[i], response: r });
+    remaining -= r;
+  }
+  return out;
+}
+
+function gad7(targetScore: number): Ans[] {
+  const ids = ['gad7_1', 'gad7_2', 'gad7_3', 'gad7_4', 'gad7_5', 'gad7_6', 'gad7_7'];
+  const out: Ans[] = [];
+  let remaining = targetScore;
+  for (let i = 0; i < ids.length; i++) {
+    const left = ids.length - i;
+    const minNeeded = Math.max(0, remaining - (left - 1) * 3);
+    const r = Math.max(minNeeded, Math.min(3, remaining)) as AssessmentResponse;
+    out.push({ questionId: ids[i], response: r });
+    remaining -= r;
+  }
+  return out;
+}
+
+async function answer(seq: Ans[]) {
+  for (const a of seq) {
+    await useAssessmentStore.getState().answerQuestion(a.questionId, a.response);
+  }
+}
+
+function lastPayload() {
+  return mockTrack.mock.calls[mockTrack.mock.calls.length - 1][0];
+}
+
+function expectNoUndefinedString(payload: Record<string, unknown>) {
+  Object.values(payload).forEach((v) => expect(v).not.toBe('undefined'));
+  expect(JSON.stringify(payload)).not.toContain('undefined');
+}
+
+describe('DEBUG-218 — crisis_detected carries real severity_bucket + assessment_type', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    useAssessmentStore.getState().resetAssessment();
+  });
+
+  describe('inline PHQ-9 Q9 path (answerQuestion)', () => {
+    it('Q9>0 with full answers + low total → severity_bucket "high", assessment_type "phq9", no "undefined"', async () => {
+      await useAssessmentStore.getState().startAssessment('phq9');
+      // Answer 1-8 = 0, then Q9 = 2 last → total 2 (<20). All 9 present at emit time.
+      await answer([...phq9(0).slice(0, 8), { questionId: 'phq9_9', response: 2 as AssessmentResponse }]);
+
+      expect(mockTrack).toHaveBeenCalledTimes(1);
+      const p = lastPayload();
+      expect(p).toEqual({
+        trigger_type: 'phq9_suicidal_ideation',
+        severity_bucket: 'high',
+        intervention_surfaced: true,
+        assessment_type: 'phq9',
+      });
+      expectNoUndefinedString(p);
+    });
+
+    it('Q9>0 with full answers + high total (≥20) → severity_bucket "critical"', async () => {
+      await useAssessmentStore.getState().startAssessment('phq9');
+      // 1-8 = 3 each (24), Q9 = 1 last → total 25 (≥20).
+      const high: Ans[] = [];
+      for (let i = 1; i <= 8; i++) high.push({ questionId: `phq9_${i}`, response: 3 as AssessmentResponse });
+      high.push({ questionId: 'phq9_9', response: 1 as AssessmentResponse });
+      await answer(high);
+
+      const p = lastPayload();
+      expect(p.trigger_type).toBe('phq9_suicidal_ideation');
+      expect(p.severity_bucket).toBe('critical');
+      expect(p.assessment_type).toBe('phq9');
+      expectNoUndefinedString(p);
+    });
+
+    it('Q9>0 with NO other answers yet → score-compute fails → safe "high" floor (never "undefined")', async () => {
+      await useAssessmentStore.getState().startAssessment('phq9');
+      // Only Q9 answered → calculatePHQ9Score throws (needs 9) → fallback 'high'.
+      await answer([{ questionId: 'phq9_9', response: 1 as AssessmentResponse }]);
+
+      const p = lastPayload();
+      expect(p.trigger_type).toBe('phq9_suicidal_ideation');
+      expect(p.severity_bucket).toBe('high');
+      expect(p.assessment_type).toBe('phq9');
+      expectNoUndefinedString(p);
+    });
+
+    it('Q9=0 → no crisis emit (boundary)', async () => {
+      await useAssessmentStore.getState().startAssessment('phq9');
+      await answer([{ questionId: 'phq9_9', response: 0 as AssessmentResponse }]);
+      expect(mockTrack).not.toHaveBeenCalled();
+    });
+  });
+
+  describe('score-based completed path (completeAssessment) — non-Q9 crises', () => {
+    it('PHQ-9 ≥20 without Q9 → phq9_moderate_severe_score, severity_bucket "critical", assessment_type "phq9"', async () => {
+      await useAssessmentStore.getState().startAssessment('phq9');
+      await answer(phq9(20)); // greedy fill leaves phq9_9 = 0
+      await useAssessmentStore.getState().completeAssessment();
+
+      expect(mockTrack).toHaveBeenCalledTimes(1);
+      const p = lastPayload();
+      expect(p.trigger_type).toBe('phq9_moderate_severe_score');
+      expect(p.severity_bucket).toBe('critical');
+      expect(p.assessment_type).toBe('phq9');
+      expectNoUndefinedString(p);
+    });
+
+    it('PHQ-9 15–19 without Q9 → severity_bucket "high"', async () => {
+      await useAssessmentStore.getState().startAssessment('phq9');
+      await answer(phq9(17));
+      await useAssessmentStore.getState().completeAssessment();
+
+      const p = lastPayload();
+      expect(p.trigger_type).toBe('phq9_moderate_severe_score');
+      expect(p.severity_bucket).toBe('high');
+      expect(p.assessment_type).toBe('phq9');
+      expectNoUndefinedString(p);
+    });
+
+    it('GAD-7 ≥15 → gad7_severe_score, severity_bucket "high", assessment_type "gad7"', async () => {
+      await useAssessmentStore.getState().startAssessment('gad7');
+      await answer(gad7(18));
+      await useAssessmentStore.getState().completeAssessment();
+
+      const p = lastPayload();
+      expect(p.trigger_type).toBe('gad7_severe_score');
+      expect(p.severity_bucket).toBe('high');
+      expect(p.assessment_type).toBe('gad7');
+      expectNoUndefinedString(p);
+    });
+  });
+});
diff --git a/app/src/features/assessment/stores/assessmentStore.ts b/app/src/features/assessment/stores/assessmentStore.ts
index 9fb75e62..9069e58a 100644
--- a/app/src/features/assessment/stores/assessmentStore.ts
+++ b/app/src/features/assessment/stores/assessmentStore.ts
@@ -263,6 +263,39 @@ export class ClinicalScoringService {
   }
 }
 
+/**
+ * DEBUG-218: severity bucket for the `crisis_detected` telemetry event.
+ *
+ * PHQ-9 (suicidal-ideation OR ≥15 score): `critical` at the active-intervention
+ * floor (≥20 — `PHQ9_SEVERE_THRESHOLD`), else `high`. GAD-7 severe: `high` (no
+ * validated `critical` tier — mirrors the canonical mapping in
+ * `@/features/crisis/types/safety`). Kept additive: it derives the bucket from the
+ * existing total, it does NOT change any detection threshold or trigger taxonomy.
+ */
+function crisisSeverityLevel(
+  type: AssessmentType,
+  totalScore: number,
+): CrisisDetection['severityLevel'] {
+  if (type === 'gad7') return 'high';
+  return totalScore >= CRISIS_THRESHOLDS.PHQ9_SEVERE_THRESHOLD ? 'critical' : 'high';
+}
+
+/**
+ * DEBUG-218: severity bucket for the INLINE Q9 detection, derived mid-assessment.
+ * `calculatePHQ9Score` needs all 9 answers; `phq9_9` is the last question so they are
+ * normally present, but out-of-order answering can leave them incomplete and throw —
+ * fall back to the safe 'high' floor (Q9>0 is never below 'high'). Never throws.
+ * Extracted so the inline `answerQuestion` branch stays within its complexity budget.
+ */
+function inlineQ9SeverityLevel(answers: AssessmentAnswer[]): CrisisDetection['severityLevel'] {
+  try {
+    const { totalScore } = ClinicalScoringService.calculatePHQ9Score(answers);
+    return crisisSeverityLevel('phq9', totalScore);
+  } catch {
+    return 'high';
+  }
+}
+
 /**
  * Crisis detection and intervention service
  * Meets <200ms response time requirement
@@ -300,7 +333,12 @@ class CrisisDetectionService {
       const detection = {
         isTriggered: true,
         primaryTrigger: triggerType,
+        secondaryTriggers: [],
+        // DEBUG-218: populate severityLevel + assessmentType so the score-based
+        // crisis_detected telemetry carries real buckets (never "undefined").
+        severityLevel: crisisSeverityLevel(type, result.totalScore),
         triggerValue,
+        assessmentType: type,
         timestamp: Date.now(),
         assessmentId
       } as Partial<CrisisDetection> as CrisisDetection;
@@ -548,10 +586,15 @@ export const useAssessmentStore = create<AssessmentStore>()(
 
             // Check for real-time crisis detection on specific questions
             if (questionId === CRISIS_THRESHOLDS.PHQ9_SUICIDAL_QUESTION_ID && response > 0) {
+              // DEBUG-218: populate severityLevel + assessmentType so the inline Q9
+              // crisis_detected telemetry carries real buckets (never "undefined").
               const detection = {
                 isTriggered: true,
                 primaryTrigger: 'phq9_suicidal_ideation' as const,
+                secondaryTriggers: [],
+                severityLevel: inlineQ9SeverityLevel(updatedAnswers),
                 triggerValue: response,
+                assessmentType: 'phq9' as const,
                 timestamp: Date.now(),
                 assessmentId: state.currentSession.id
               } as Partial<CrisisDetection> as CrisisDetection;