diff --git a/apps/api/src/tenders/geo/nuts-bundesland.spec.ts b/apps/api/src/tenders/geo/nuts-bundesland.spec.ts
new file mode 100644
index 0000000..2fae885
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+++ b/apps/api/src/tenders/geo/nuts-bundesland.spec.ts
@@ -0,0 +1,74 @@
+import { describe, expect, it } from 'vitest';
+import { bundeslandFromRegion, nutsPrefixFor } from './nuts-bundesland';
+
+/**
+ * nuts-bundesland.spec — RED-first (TDD) proof for FILTER-02 (Pitfall 1,
+ * Assumption A1). `bundesland` is 100% NULL in the live Tender data
+ * (verified: 0/1671 rows) because the Phase-10 normalizer deferred
+ * NUTS->Bundesland mapping to this phase. This spec locks the derivation
+ * that makes the Bundesland filter return real hits instead of a
+ * constant-zero result.
+ *
+ * Real region samples cross-checked against the live DB (verified via
+ * `docker exec tessera-ctl-db-1 psql`):
+ *   DE212 (60 rows) -> Oberbayern -> Bayern
+ *   DE300 (56 rows) -> Berlin
+ *   DE600 (38 rows) -> Hamburg
+ *   DE712 (34 rows) -> Darmstadt -> Hessen
+ *   DEA22 (24 rows) -> Köln -> Nordrhein-Westfalen
+ */
+describe('bundeslandFromRegion', () => {
+  it('maps all 16 NUTS-1 prefixes (DE1..DEG) to their Bundesland name', () => {
+    expect(bundeslandFromRegion('DE1')).toBe('Baden-Württemberg');
+    expect(bundeslandFromRegion('DE2')).toBe('Bayern');
+    expect(bundeslandFromRegion('DE3')).toBe('Berlin');
+    expect(bundeslandFromRegion('DE4')).toBe('Brandenburg');
+    expect(bundeslandFromRegion('DE5')).toBe('Bremen');
+    expect(bundeslandFromRegion('DE6')).toBe('Hamburg');
+    expect(bundeslandFromRegion('DE7')).toBe('Hessen');
+    expect(bundeslandFromRegion('DE8')).toBe('Mecklenburg-Vorpommern');
+    expect(bundeslandFromRegion('DE9')).toBe('Niedersachsen');
+    expect(bundeslandFromRegion('DEA')).toBe('Nordrhein-Westfalen');
+    expect(bundeslandFromRegion('DEB')).toBe('Rheinland-Pfalz');
+    expect(bundeslandFromRegion('DEC')).toBe('Saarland');
+    expect(bundeslandFromRegion('DED')).toBe('Sachsen');
+    expect(bundeslandFromRegion('DEE')).toBe('Sachsen-Anhalt');
+    expect(bundeslandFromRegion('DEF')).toBe('Schleswig-Holstein');
+    expect(bundeslandFromRegion('DEG')).toBe('Thüringen');
+  });
+
+  it('maps real NUTS-3-level region samples from the live DB (Assumption A1 validation)', () => {
+    expect(bundeslandFromRegion('DE212')).toBe('Bayern');
+    expect(bundeslandFromRegion('DE300')).toBe('Berlin');
+    expect(bundeslandFromRegion('DE600')).toBe('Hamburg');
+    expect(bundeslandFromRegion('DE712')).toBe('Hessen');
+    expect(bundeslandFromRegion('DEA22')).toBe('Nordrhein-Westfalen');
+  });
+
+  it('is case-insensitive on the NUTS prefix', () => {
+    expect(bundeslandFromRegion('de212')).toBe('Bayern');
+  });
+
+  it('returns null for null/undefined/empty region — 17%+ of live rows have region=null, must never crash', () => {
+    expect(bundeslandFromRegion(null)).toBeNull();
+    expect(bundeslandFromRegion(undefined)).toBeNull();
+    expect(bundeslandFromRegion('')).toBeNull();
+  });
+
+  it('returns null for an unrecognized/malformed prefix instead of throwing', () => {
+    expect(bundeslandFromRegion('XX123')).toBeNull();
+    expect(bundeslandFromRegion('FR')).toBeNull();
+  });
+});
+
+describe('nutsPrefixFor', () => {
+  it('reverses a Bundesland name to its NUTS-1 prefix (for region startsWith filtering)', () => {
+    expect(nutsPrefixFor('Bayern')).toBe('DE2');
+    expect(nutsPrefixFor('Nordrhein-Westfalen')).toBe('DEA');
+    expect(nutsPrefixFor('Thüringen')).toBe('DEG');
+  });
+
+  it('returns null for an unrecognized Bundesland name', () => {
+    expect(nutsPrefixFor('Nicht-Existent')).toBeNull();
+  });
+});