diff --git a/lib/services/pax8-company-match-resolver.ts b/lib/services/pax8-company-match-resolver.ts
new file mode 100644
index 0000000..67f9379
--- /dev/null
+++ b/lib/services/pax8-company-match-resolver.ts
@@ -0,0 +1,87 @@
+/**
+ * resolvePax8CompanyMatch — the two-table transactional write behind
+ * POST /api/pax8/company-matches/[id]/resolve.
+ *
+ * Both `pax8_companies.match_method='manual'` and
+ * `pax8_company_match_review.resolved_at` must be set in the same
+ * transaction, or pax8-company-matcher.ts's re-scoring eligibility guard
+ * (lines ~216-231: `c.match_method IS DISTINCT FROM 'manual' AND NOT EXISTS
+ * (... resolved_at IS NOT NULL)`) will re-flag the company on the next sync.
+ *
+ * Deliberately does NOT check `candidate_company_ids` membership — D-05
+ * (manual-search fallback) and D-09 (zero-candidate case) require accepting
+ * a companyId that was never one of the stored candidates, as long as it
+ * exists and is active.
+ */
+
+export type ResolveResult =
+  | { ok: true; resolvedToCompanyId: number }
+  | { ok: false; code: 'not_found' | 'already_resolved' | 'company_not_found'; message: string };
+
+interface TxLike {
+  query: <T = unknown>(sql: string, params?: unknown[]) => Promise<{ rows: T[]; rowCount: number }>;
+}
+
+interface ResolveParams {
+  reviewId: string;
+  companyId: number;
+  note: string | null;
+  userId: string | null;
+}
+
+interface ReviewRow {
+  pax8_company_id: string;
+  resolved_at: string | null;
+}
+
+export async function resolvePax8CompanyMatch(
+  tx: TxLike,
+  params: ResolveParams
+): Promise<ResolveResult> {
+  const { reviewId, companyId, note, userId } = params;
+
+  const reviewRes = await tx.query<ReviewRow>(
+    `SELECT pax8_company_id, resolved_at
+       FROM pax8_company_match_review
+      WHERE id = $1
+      FOR UPDATE`,
+    [reviewId]
+  );
+  if (reviewRes.rowCount === 0) {
+    return { ok: false, code: 'not_found', message: 'Review not found' };
+  }
+  const review = reviewRes.rows[0];
+  if (review.resolved_at) {
+    return { ok: false, code: 'already_resolved', message: 'Already resolved' };
+  }
+
+  const companyRes = await tx.query(
+    `SELECT 1 FROM companies WHERE id = $1 AND is_active = true AND is_deleted = false`,
+    [companyId]
+  );
+  if (companyRes.rowCount === 0) {
+    return { ok: false, code: 'company_not_found', message: 'Target company not found or inactive' };
+  }
+
+  await tx.query(
+    `UPDATE pax8_companies
+        SET autotask_company_id = $2,
+            match_confidence     = NULL,
+            match_method         = 'manual',
+            matched_at           = NOW()
+      WHERE id = $1`,
+    [review.pax8_company_id, companyId]
+  );
+
+  await tx.query(
+    `UPDATE pax8_company_match_review
+        SET resolved_at          = NOW(),
+            resolved_by_user_id  = $2,
+            resolved_to_company_id = $3,
+            resolution_note      = $4
+      WHERE id = $1`,
+    [reviewId, userId, companyId, note]
+  );
+
+  return { ok: true, resolvedToCompanyId: companyId };
+}