diff --git a/lib/services/mimecast-blast-radius.test.ts b/lib/services/mimecast-blast-radius.test.ts
index 120bb88..54ebbd6 100644
--- a/lib/services/mimecast-blast-radius.test.ts
+++ b/lib/services/mimecast-blast-radius.test.ts
@@ -50,6 +50,7 @@ const BASE_INPUT: BlastRadiusInput = {
 describe('getBlastRadius', () => {
   beforeEach(() => {
     isMimecastConfiguredMock.mockReset().mockReturnValue(true);
+    getMimecastClientMock.mockClear();
     getMessageInfoMock.mockReset().mockResolvedValue(null);
     searchDeliveredMessagesMock.mockReset().mockResolvedValue({ messages: [] });
     getHeldMessagesMock.mockReset().mockResolvedValue({ messages: [], totalCount: 0 });
diff --git a/lib/services/mimecast-blast-radius.ts b/lib/services/mimecast-blast-radius.ts
index 7be67e5..31ee6ef 100644
--- a/lib/services/mimecast-blast-radius.ts
+++ b/lib/services/mimecast-blast-radius.ts
@@ -22,21 +22,20 @@
  *     `clicked: 0` means "no click-type threat event found in the events
  *     this module can see," NOT "confirmed zero clicks."
  *
- * (c) KNOWN LIMITATION — MULTI-TENANT GAP (D-05): this module uses only the
- *     single global env-var-configured getMimecastClient(), NOT the
- *     per-company `mimecast_tenants` table / getMimecastClientForTenant().
- *     Reports belonging to companies with their own registered Mimecast
- *     tenant (not covered by the global MIMECAST_CLIENT_ID) will return
- *     `status: 'unavailable'` even though Mimecast is technically configured
- *     for that company. Per-tenant resolution is a deliberate, documented v1
- *     gap — not a silent oversight — and would be a small, mechanical
- *     follow-up later (swap getMimecastClient() for a tenant lookup +
- *     getMimecastClientForTenant(), same fan-out/merge logic below).
+ * (c) PER-TENANT RESOLUTION (D-05, formerly a known gap): this module now
+ *     accepts an optional `options.client` — a pre-built MimecastClient for a
+ *     specific company's `mimecast_tenants` row (via
+ *     getMimecastClientForTenant()). Resolution of WHICH tenant to use is the
+ *     caller's responsibility (the campaign detail route looks up
+ *     reports.company_id -> mimecast_tenants); this module simply uses
+ *     whatever client it is given, or falls back to the single global
+ *     env-var-configured getMimecastClient() when no client is injected.
  */
 
 import {
   isMimecastConfigured,
   getMimecastClient,
+  type MimecastClient,
   type MimecastDeliveredMessage,
   type MimecastHeldMessage,
 } from './mimecast-client';
@@ -89,21 +88,27 @@ function isClickEvent(analysis: string[] | undefined): boolean {
   return (analysis ?? []).some((a) => /click/i.test(a));
 }
 
-export async function getBlastRadius(input: BlastRadiusInput): Promise<BlastRadiusResult> {
-  if (!isMimecastConfigured()) {
+export async function getBlastRadius(
+  input: BlastRadiusInput,
+  options?: { client?: MimecastClient; cacheScope?: string }
+): Promise<BlastRadiusResult> {
+  // An injected tenant client is self-sufficient (it carries its own
+  // credentials) — only fall back to the global env-configured client (and
+  // its isMimecastConfigured() gate) when no client was injected.
+  const client = options?.client ?? (isMimecastConfigured() ? getMimecastClient() : null);
+  if (!client) {
     return { status: 'unavailable', reason: 'not_configured' };
   }
 
+  const scope = options?.cacheScope ?? 'global';
   const cacheKey = input.messageId
-    ? `mimecast:blast-radius:msgid:${input.messageId}`
-    : `mimecast:blast-radius:composite:${input.sender}:${input.subject}:${input.dateWindow.start.toISOString()}:${input.dateWindow.end.toISOString()}`;
+    ? `mimecast:blast-radius:${scope}:msgid:${input.messageId}`
+    : `mimecast:blast-radius:${scope}:composite:${input.sender}:${input.subject}:${input.dateWindow.start.toISOString()}:${input.dateWindow.end.toISOString()}`;
 
   const cached = await getCachedData<BlastRadiusResult>(cacheKey);
   if (cached) return cached;
 
   try {
-    const client = getMimecastClient();
-
     // Supplementary only — body/header evidence, never gates the fan-out
     // (17-RESEARCH.md Pitfall 1: getMessageInfo() has no status/counts).
     if (input.messageId) {
@@ -127,6 +132,16 @@ export async function getBlastRadius(input: BlastRadiusInput): Promise<BlastRadi
       client.getThreatEvents(),
     ]);
 
+    // Bug 1 defense-in-depth: searchDeliveredMessages() swallows its own
+    // errors internally (returns { messages: [], error } rather than
+    // throwing) — e.g. a future end-date rejected by Mimecast as
+    // err_track_and_trace_invalid_end_date. Without this check, that
+    // swallowed error would silently present as a confident zero-count 'ok'.
+    // Surface it via the existing outer catch instead.
+    if (deliveredResult.error) {
+      throw new Error(deliveredResult.error);
+    }
+
     const deliveredRows: MimecastDeliveredMessage[] = deliveredResult.messages ?? [];
     const heldRows: MimecastHeldMessage[] = heldResult.messages ?? [];