diff --git a/app/.eslint-baseline.json b/app/.eslint-baseline.json
index 2d2e5a8c..6705a123 100644
--- a/app/.eslint-baseline.json
+++ b/app/.eslint-baseline.json
@@ -99,12 +99,15 @@
   "src/features/assessment/components/__tests__/AssessmentResults.test.tsx": 1,
   "src/features/assessment/components/__tests__/EnhancedAssessmentQuestion.test.tsx": 1,
   "src/features/assessment/hooks/useAssessmentPerformance.ts": 13,
+  "src/features/assessment/stores/__tests__/answerQuestionValidation.unit.test.ts": 1,
   "src/features/assessment/stores/__tests__/assessmentStore.basic.test.ts": 1,
   "src/features/assessment/stores/__tests__/assessmentStore.notes.test.ts": 1,
   "src/features/assessment/stores/__tests__/assessmentStore.test.ts": 1,
+  "src/features/assessment/stores/__tests__/crisisDetectionParity.unit.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__/crisisDetectionValidation.unit.test.ts": 1,
   "src/features/assessment/types/__tests__/schemas.test.ts": 1,
   "src/features/assessment/types/scoring.ts": 2,
   "src/features/assessment/types/validation.ts": 1,
diff --git a/app/__tests__/clinical/assessment-accuracy/comprehensive-scoring-validation.test.ts b/app/__tests__/clinical/assessment-accuracy/comprehensive-scoring-validation.test.ts
index 2996e41b..fc2bbf41 100644
--- a/app/__tests__/clinical/assessment-accuracy/comprehensive-scoring-validation.test.ts
+++ b/app/__tests__/clinical/assessment-accuracy/comprehensive-scoring-validation.test.ts
@@ -167,9 +167,14 @@ describe('COMPREHENSIVE CLINICAL SCORING VALIDATION - ALL 48 COMBINATIONS', () =
 
         if (expectCrisis) {
           expect(finalStore.crisisDetection).toBeTruthy();
+          // DEBUG-229 / MAINT-226 Decision E — dual-threshold tiers: ≥20 (no Q9)
+          // is the intervention tier `phq9_severe_score`; 15–19 is the support tier
+          // `phq9_moderate_severe_score`. Q9>0 always wins as suicidal-ideation.
           const expectedTrigger = suicidalResponse > 0
             ? 'phq9_suicidal_ideation'
-            : 'phq9_moderate_severe_score';
+            : score >= CRISIS_THRESHOLDS.PHQ9_SEVERE_THRESHOLD
+              ? 'phq9_severe_score'
+              : 'phq9_moderate_severe_score';
           expect(finalStore.crisisDetection?.primaryTrigger).toBe(expectedTrigger);
           // triggerValue: when answerQuestion fires inline crisis for phq9_9 > 0,
           // the detection carries the *actual response value* (1, 2, or 3) — that
diff --git a/app/src/features/assessment/stores/__tests__/answerQuestionValidation.unit.test.ts b/app/src/features/assessment/stores/__tests__/answerQuestionValidation.unit.test.ts
new file mode 100644
index 00000000..a6911bac
--- /dev/null
+++ b/app/src/features/assessment/stores/__tests__/answerQuestionValidation.unit.test.ts
@@ -0,0 +1,76 @@
+/**
+ * answerQuestionValidation.unit.test.ts — DEBUG-229 (TEST-08 / SEC-06)
+ *
+ * `answerQuestion` MUST validate per-question responses against the 0–3 clinical
+ * scale (`AssessmentResponseSchema`) BEFORE storing/scoring. Out-of-range values
+ * are rejected fail-loud: the answer is not stored, `error` is set, and the
+ * inline Q9 crisis check never runs on a corrupt value.
+ */
+import { jest } from '@jest/globals';
+
+jest.mock('@/core/services/supabase/SupabaseService', () => {
+  const fn = jest.fn();
+  return { __esModule: true, default: { trackCrisisDetection: fn }, supabaseService: { trackCrisisDetection: fn } };
+});
+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');
+
+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;
+// Force out-of-range / wrong-type values past the TS signature for the runtime guard test.
+const bad = (v: unknown) => v as AssessmentResponse;
+
+describe('DEBUG-229 — answerQuestion 0–3 validation (fail-loud reject)', () => {
+  beforeEach(async () => {
+    jest.clearAllMocks();
+    useAssessmentStore.getState().resetAssessment();
+    await useAssessmentStore.getState().startAssessment('phq9');
+  });
+
+  it('stores a valid in-range response (0–3) and scores it', async () => {
+    await useAssessmentStore.getState().answerQuestion('phq9_1', 3 as AssessmentResponse);
+    const s = useAssessmentStore.getState();
+    expect(s.answers.find((a) => a.questionId === 'phq9_1')?.response).toBe(3);
+    expect(s.error).toBeNull();
+  });
+
+  it.each([5, 4, -1, 1.5, NaN, null, undefined, '2'])(
+    'rejects out-of-range/invalid response %p — not stored, error set',
+    async (value) => {
+      await useAssessmentStore.getState().answerQuestion('phq9_1', bad(value));
+      const s = useAssessmentStore.getState();
+      expect(s.answers.find((a) => a.questionId === 'phq9_1')).toBeUndefined();
+      expect(s.error).toBeTruthy();
+    },
+  );
+
+  it('does NOT fire the inline Q9 crisis check for an out-of-range Q9 value', async () => {
+    await useAssessmentStore.getState().answerQuestion('phq9_9', bad(5));
+    const s = useAssessmentStore.getState();
+    expect(s.answers.find((a) => a.questionId === 'phq9_9')).toBeUndefined();
+    expect(s.crisisDetection).toBeNull();
+    expect(mockTrack).not.toHaveBeenCalled();
+  });
+
+  it('a valid Q9>0 still triggers the inline crisis path (guard does not over-reject)', async () => {
+    await useAssessmentStore.getState().answerQuestion('phq9_9', 1 as AssessmentResponse);
+    expect(useAssessmentStore.getState().crisisDetection?.primaryTrigger).toBe('phq9_suicidal_ideation');
+  });
+});
diff --git a/app/src/features/assessment/stores/__tests__/crisisDetectionParity.unit.test.ts b/app/src/features/assessment/stores/__tests__/crisisDetectionParity.unit.test.ts
new file mode 100644
index 00000000..330cc038
--- /dev/null
+++ b/app/src/features/assessment/stores/__tests__/crisisDetectionParity.unit.test.ts
@@ -0,0 +1,108 @@
+/**
+ * crisisDetectionParity.unit.test.ts — DEBUG-229 / MAINT-226 Decision E
+ *
+ * Pins the "ONE source of truth" invariant: the store's production crisis path
+ * (startAssessment → answerQuestion → completeAssessment, read back via
+ * `store.crisisDetection`) MUST return the same `primaryTrigger` + `severityLevel`
+ * as the pure `detectCrisis()` in `@/features/crisis/types/safety` for the
+ * dual-threshold boundary set {14, 15, 19, 20, Q9>0}.
+ *
+ * The store's CrisisDetectionService now delegates to the pure function, so a
+ * future threshold/trigger-vocabulary divergence (the exact defect TEST-07 found)
+ * cannot silently reappear. Asserts through the production store API — never a
+ * test-local reimplementation (AC #3).
+ */
+import { jest } from '@jest/globals';
+
+jest.mock('@/core/services/supabase/SupabaseService', () => {
+  const fn = jest.fn();
+  return { __esModule: true, default: { trackCrisisDetection: fn }, supabaseService: { trackCrisisDetection: fn } };
+});
+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');
+
+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 { detectCrisis } from '@/features/crisis/types/safety';
+import type { PHQ9Result } from '@/features/assessment/types';
+import type { AssessmentResponse } from '../../types/index';
+
+type Ans = { questionId: string; response: AssessmentResponse };
+
+/** Greedy fill q1..q8 to the target, leaving phq9_9 = `q9` (default 0). */
+function phq9Answers(targetScore: number, q9 = 0): Ans[] {
+  const ids = ['phq9_1', 'phq9_2', 'phq9_3', 'phq9_4', 'phq9_5', 'phq9_6', 'phq9_7', 'phq9_8'];
+  const out: Ans[] = [];
+  let remaining = targetScore - q9;
+  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;
+  }
+  out.push({ questionId: 'phq9_9', response: q9 as AssessmentResponse });
+  return out;
+}
+
+const pureResult = (totalScore: number, suicidalIdeation = false): PHQ9Result => ({
+  totalScore,
+  severity: 'minimal',
+  isCrisis: false,
+  suicidalIdeation,
+  completedAt: Date.now(),
+  answers: [],
+});
+
+async function runStore(answers: Ans[]) {
+  const store = useAssessmentStore.getState();
+  store.resetAssessment();
+  await store.startAssessment('phq9');
+  for (const a of answers) {
+    await useAssessmentStore.getState().answerQuestion(a.questionId, a.response);
+  }
+  await useAssessmentStore.getState().completeAssessment();
+  return useAssessmentStore.getState().crisisDetection;
+}
+
+describe('DEBUG-229 — pure detectCrisis ⇄ store CrisisDetectionService parity', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    useAssessmentStore.getState().resetAssessment();
+  });
+
+  it('PHQ-9 14, Q9=0 → both produce no crisis', async () => {
+    expect(detectCrisis(pureResult(14), 'u1')).toBeNull();
+    expect(await runStore(phq9Answers(14))).toBeNull();
+  });
+
+  it.each([15, 19, 20, 24])('PHQ-9 %i, Q9=0 → store matches pure (primaryTrigger + severityLevel)', async (score) => {
+    const pure = detectCrisis(pureResult(score), 'u1');
+    expect(pure).not.toBeNull();
+    const fromStore = await runStore(phq9Answers(score));
+    expect(fromStore).toBeTruthy();
+    expect(fromStore!.primaryTrigger).toBe(pure!.primaryTrigger);
+    expect(fromStore!.severityLevel).toBe(pure!.severityLevel);
+  });
+
+  it('PHQ-9 17 with Q9>0 → both report suicidal-ideation primary at "high"', async () => {
+    const pure = detectCrisis(pureResult(17, true), 'u1');
+    expect(pure!.primaryTrigger).toBe('phq9_suicidal_ideation');
+    const fromStore = await runStore(phq9Answers(17, 2));
+    expect(fromStore!.primaryTrigger).toBe(pure!.primaryTrigger);
+    expect(fromStore!.severityLevel).toBe(pure!.severityLevel);
+  });
+});
diff --git a/app/src/features/assessment/stores/__tests__/crisisTelemetryFields.regression.test.ts b/app/src/features/assessment/stores/__tests__/crisisTelemetryFields.regression.test.ts
index 178593ea..cd302fd6 100644
--- a/app/src/features/assessment/stores/__tests__/crisisTelemetryFields.regression.test.ts
+++ b/app/src/features/assessment/stores/__tests__/crisisTelemetryFields.regression.test.ts
@@ -159,14 +159,17 @@ describe('DEBUG-218 — crisis_detected carries real severity_bucket + assessmen
   });
 
   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 () => {
+    // DEBUG-229 / MAINT-226 Decision E: ≥20 now emits the intervention-tier
+    // trigger `phq9_severe_score` (was `phq9_moderate_severe_score` — the store's
+    // missing-severe-tier bug this work item fixes). severity_bucket stays "critical".
+    it('PHQ-9 ≥20 without Q9 → phq9_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.trigger_type).toBe('phq9_severe_score');
       expect(p.severity_bucket).toBe('critical');
       expect(p.assessment_type).toBe('phq9');
       expectNoUndefinedString(p);
diff --git a/app/src/features/assessment/stores/assessmentStore.ts b/app/src/features/assessment/stores/assessmentStore.ts
index 9069e58a..3d41f635 100644
--- a/app/src/features/assessment/stores/assessmentStore.ts
+++ b/app/src/features/assessment/stores/assessmentStore.ts
@@ -47,6 +47,10 @@ import {
   CRISIS_THRESHOLDS,
   ASSESSMENT_RESPONSE_LABELS,
 } from '../types/index';
+// DEBUG-229 / MAINT-226 Decision E: pure detectCrisis is the single source of
+// truth for crisis thresholds + trigger taxonomy; the store delegates to it.
+import { detectCrisis as detectCrisisPure } from '@/features/crisis/types/safety';
+import { validateSingleResponse } from '../types/schemas';
 
 // Clinical scoring algorithms (validated for 100% accuracy)
 const PHQ9_QUESTIONS = [
@@ -309,35 +313,25 @@ class CrisisDetectionService {
     const startTime = Date.now();
 
     try {
-      let triggerType: CrisisDetection['primaryTrigger'] | null = null;
-      let triggerValue = result.totalScore;
-
-      if (type === 'phq9') {
-        const phqResult = result as PHQ9Result;
-        if (phqResult.suicidalIdeation) {
-          triggerType = 'phq9_suicidal_ideation';
-          triggerValue = 1; // Indicates suicidal ideation present
-        } else if (phqResult.totalScore >= CRISIS_THRESHOLDS.PHQ9_CRISIS_SCORE) {
-          triggerType = 'phq9_moderate_severe_score';
-        }
-      } else if (type === 'gad7') {
-        if (result.totalScore >= CRISIS_THRESHOLDS.GAD7_CRISIS_SCORE) {
-          triggerType = 'gad7_severe_score';
-        }
-      }
-
-      if (!triggerType) {
+      // DEBUG-229 / MAINT-226 Decision E: delegate threshold + trigger logic to the
+      // pure detectCrisis (single source of truth). This fixes the store's previous
+      // divergence — it emitted `phq9_moderate_severe_score` even at ≥20 and never
+      // the intervention-tier `phq9_severe_score`. userId is not part of the
+      // store-side detection (pass ''); assessmentId is overridden below with the
+      // live session id so handleCrisisDetection's per-session dedup works.
+      const pure = detectCrisisPure(result, '');
+      if (!pure) {
         return null;
       }
 
       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,
+        primaryTrigger: pure.primaryTrigger,
+        secondaryTriggers: pure.secondaryTriggers,
+        // severityLevel + assessmentType populate the score-based crisis_detected
+        // telemetry buckets (DEBUG-218) — now sourced from the pure function.
+        severityLevel: pure.severityLevel,
+        triggerValue: pure.triggerValue,
         assessmentType: type,
         timestamp: Date.now(),
         assessmentId
@@ -558,6 +552,15 @@ export const useAssessmentStore = create<AssessmentStore>()(
             throw new Error('No active assessment session');
           }
 
+          // DEBUG-229 (TEST-08 / SEC-06): validate the per-question response against
+          // the 0–3 clinical scale BEFORE storing/scoring. Reject fail-loud — a
+          // corrupt value must never reach scoring or the inline Q9 crisis check.
+          const responseCheck = validateSingleResponse(response);
+          if (!responseCheck.success) {
+            set({ error: `Invalid response (must be 0–3): ${responseCheck.error}` });
+            return;
+          }
+
           try {
             const answer: AssessmentAnswer = {
               questionId,
diff --git a/app/src/features/assessment/types/__tests__/crisisDetectionValidation.unit.test.ts b/app/src/features/assessment/types/__tests__/crisisDetectionValidation.unit.test.ts
new file mode 100644
index 00000000..17429916
--- /dev/null
+++ b/app/src/features/assessment/types/__tests__/crisisDetectionValidation.unit.test.ts
@@ -0,0 +1,49 @@
+/**
+ * crisisDetectionValidation.unit.test.ts — DEBUG-229 / MAINT-226 Decision E
+ *
+ * `validateCrisisDetection` must recognize the support tier introduced by the
+ * dual-threshold fix: a `phq9_moderate_severe_score` detection is valid only in
+ * the 15–19 band (≥ PHQ9_MODERATE_SEVERE_THRESHOLD, < PHQ9_SEVERE_THRESHOLD).
+ * The pre-existing `phq9_severe_score` ≥20 guard is unchanged.
+ */
+import { validateCrisisDetection } from '@/features/assessment/types/validation';
+import type { CrisisDetection, CrisisTriggerType } from '@/features/crisis/types/safety';
+
+function detection(
+  primaryTrigger: CrisisTriggerType,
+  triggerValue: number,
+): CrisisDetection {
+  return {
+    id: 'd1',
+    isTriggered: true,
+    primaryTrigger,
+    secondaryTriggers: [],
+    severityLevel: primaryTrigger === 'phq9_severe_score' ? 'critical' : 'high',
+    triggerValue,
+    assessmentType: 'phq9',
+    timestamp: Date.now(),
+    assessmentId: 'a1',
+    userId: 'u1',
+    detectionResponseTimeMs: 0,
+    context: { triggeringAnswers: [], timeOfDay: 'morning' },
+  };
+}
+
+describe('DEBUG-229 — validateCrisisDetection support tier', () => {
+  it('phq9_moderate_severe_score at 17 is valid (within 15–19 support band)', () => {
+    expect(validateCrisisDetection(detection('phq9_moderate_severe_score', 17)).isValid).toBe(true);
+  });
+
+  it('phq9_moderate_severe_score at 15 (floor) is valid', () => {
+    expect(validateCrisisDetection(detection('phq9_moderate_severe_score', 15)).isValid).toBe(true);
+  });
+
+  it('phq9_moderate_severe_score at 12 is invalid (below support floor)', () => {
+    expect(validateCrisisDetection(detection('phq9_moderate_severe_score', 12)).isValid).toBe(false);
+  });
+
+  it('phq9_severe_score at 22 is valid; at 18 is invalid (intervention floor unchanged)', () => {
+    expect(validateCrisisDetection(detection('phq9_severe_score', 22)).isValid).toBe(true);
+    expect(validateCrisisDetection(detection('phq9_severe_score', 18)).isValid).toBe(false);
+  });
+});
diff --git a/app/src/features/assessment/types/validation.ts b/app/src/features/assessment/types/validation.ts
index ef3577ed..75dc87a6 100644
--- a/app/src/features/assessment/types/validation.ts
+++ b/app/src/features/assessment/types/validation.ts
@@ -359,11 +359,23 @@ export function validateCrisisDetection(detection: unknown): ValidationResult {
   
   // Validate trigger conditions
   if (detection.assessmentType === 'phq9') {
-    if (detection.primaryTrigger === 'phq9_severe_score' && 
-        detection.triggerValue < CRISIS_SAFETY_THRESHOLDS.PHQ9_CRISIS_SCORE) {
+    if (detection.primaryTrigger === 'phq9_severe_score' &&
+        detection.triggerValue < CRISIS_SAFETY_THRESHOLDS.PHQ9_SEVERE_THRESHOLD) {
       errors.push({
         code: 'INVALID_PHQ9_CRISIS_TRIGGER',
-        message: `PHQ-9 score ${detection.triggerValue} below crisis threshold ${CRISIS_SAFETY_THRESHOLDS.PHQ9_CRISIS_SCORE}`,
+        message: `PHQ-9 score ${detection.triggerValue} below crisis threshold ${CRISIS_SAFETY_THRESHOLDS.PHQ9_SEVERE_THRESHOLD}`,
+        field: 'triggerValue',
+        value: detection.triggerValue,
+        severity: 'critical'
+      });
+    }
+    // DEBUG-229 / MAINT-226 Decision E: the support tier is valid only in the
+    // 15–19 band (≥ moderate-severe floor, < active-intervention floor).
+    if (detection.primaryTrigger === 'phq9_moderate_severe_score' &&
+        detection.triggerValue < CRISIS_SAFETY_THRESHOLDS.PHQ9_MODERATE_SEVERE_THRESHOLD) {
+      errors.push({
+        code: 'INVALID_PHQ9_SUPPORT_TRIGGER',
+        message: `PHQ-9 score ${detection.triggerValue} below support threshold ${CRISIS_SAFETY_THRESHOLDS.PHQ9_MODERATE_SEVERE_THRESHOLD}`,
         field: 'triggerValue',
         value: detection.triggerValue,
         severity: 'critical'
diff --git a/app/src/features/crisis/__tests__/detection.quick.test.ts b/app/src/features/crisis/__tests__/detection.quick.test.ts
index a88c1af3..db2073b1 100644
--- a/app/src/features/crisis/__tests__/detection.quick.test.ts
+++ b/app/src/features/crisis/__tests__/detection.quick.test.ts
@@ -30,15 +30,33 @@ const gad = (totalScore: number): GAD7Result => ({
 });
 
 describe('detectCrisis — quick branch coverage', () => {
-  it('PHQ-9 score below 20 with no Q9 → no crisis', () => {
-    expect(detectCrisis(phq(19), 'u1')).toBeNull();
+  // DEBUG-229 / MAINT-226 Decision E — dual-threshold support-vs-intervention tiers.
+  // The "≥15 = support resources offered" contract requires 15–19 to FIRE a distinct
+  // support tier; the old assertion `detectCrisis(phq(19)) === null` actively pinned
+  // the zero-false-negative bug and has been inverted.
+  it('PHQ-9 14 with no Q9 → no crisis (below support floor)', () => {
+    expect(detectCrisis(phq(14), 'u1')).toBeNull();
   });
 
-  it('PHQ-9 score at 20 with no Q9 → crisis with phq9_severe_score primaryTrigger', () => {
+  it('PHQ-9 15 with no Q9 → support tier (phq9_moderate_severe_score, high)', () => {
+    const d = detectCrisis(phq(15), 'u1');
+    expect(d).not.toBeNull();
+    expect(d!.primaryTrigger).toBe('phq9_moderate_severe_score');
+    expect(d!.severityLevel).toBe('high');
+  });
+
+  it('PHQ-9 19 with no Q9 → support tier (phq9_moderate_severe_score, high)', () => {
+    const d = detectCrisis(phq(19), 'u1');
+    expect(d).not.toBeNull();
+    expect(d!.primaryTrigger).toBe('phq9_moderate_severe_score');
+    expect(d!.severityLevel).toBe('high');
+  });
+
+  it('PHQ-9 score at 20 with no Q9 → intervention tier (phq9_severe_score, critical)', () => {
     const d = detectCrisis(phq(20), 'u1');
     expect(d).not.toBeNull();
     expect(d!.primaryTrigger).toBe('phq9_severe_score');
-    expect(d!.severityLevel).toBe('high');
+    expect(d!.severityLevel).toBe('critical');
   });
 
   it('PHQ-9 with Q9>0 (suicidal) and low total → crisis with phq9_suicidal_ideation primaryTrigger', () => {
@@ -56,6 +74,14 @@ describe('detectCrisis — quick branch coverage', () => {
     expect(d!.secondaryTriggers).toContain('phq9_severe_score');
   });
 
+  it('PHQ-9 with Q9>0 (suicidal) in the 15–19 band → suicidal primary, support tier retained as secondary', () => {
+    const d = detectCrisis(phq(17, true), 'u1');
+    expect(d).not.toBeNull();
+    expect(d!.primaryTrigger).toBe('phq9_suicidal_ideation');
+    expect(d!.severityLevel).toBe('high'); // 17 < 20
+    expect(d!.secondaryTriggers).toContain('phq9_moderate_severe_score');
+  });
+
   it('GAD-7 score below 15 → no crisis', () => {
     expect(detectCrisis(gad(14), 'u1')).toBeNull();
   });
diff --git a/app/src/features/crisis/types/safety.ts b/app/src/features/crisis/types/safety.ts
index f55840d3..5687afc3 100644
--- a/app/src/features/crisis/types/safety.ts
+++ b/app/src/features/crisis/types/safety.ts
@@ -347,15 +347,26 @@ export function detectCrisis(
       primaryTrigger = 'phq9_suicidal_ideation';
     }
     
-    // Check for severe depression score
-    if (result.totalScore >= CRISIS_SAFETY_THRESHOLDS.PHQ9_CRISIS_SCORE) {
+    // Score tier (DEBUG-229 / MAINT-226 Decision E — dual-threshold contract):
+    //   ≥20 → active-intervention tier (phq9_severe_score, critical)
+    //   15–19 → support tier (phq9_moderate_severe_score, high) — "≥15 = support
+    //     resources offered". Omitting this band was the zero-false-negative bug.
+    // Q9>0 keeps precedence as primaryTrigger; the score tier is recorded as a
+    // secondary trigger so both signals are preserved end-to-end.
+    if (result.totalScore >= CRISIS_SAFETY_THRESHOLDS.PHQ9_SEVERE_THRESHOLD) {
       triggers.push('phq9_severe_score');
       if (!primaryTrigger!) {
         primaryTrigger = 'phq9_severe_score';
+        severityLevel = 'critical';
+      }
+    } else if (result.totalScore >= CRISIS_SAFETY_THRESHOLDS.PHQ9_MODERATE_SEVERE_THRESHOLD) {
+      triggers.push('phq9_moderate_severe_score');
+      if (!primaryTrigger!) {
+        primaryTrigger = 'phq9_moderate_severe_score';
         severityLevel = 'high';
       }
     }
-  } 
+  }
   // GAD-7 Crisis Detection
   else {
     if (result.totalScore >= CRISIS_SAFETY_THRESHOLDS.GAD7_CRISIS_SCORE) {