diff --git a/src/routes/api/v1/api-contract.integration.test.ts b/src/routes/api/v1/api-contract.integration.test.ts
index 82ae634..342bed2 100644
--- a/src/routes/api/v1/api-contract.integration.test.ts
+++ b/src/routes/api/v1/api-contract.integration.test.ts
@@ -446,7 +446,11 @@ describe('API contract integration', () => {
 		const repositoryId = seedRepo(db);
 		const versionId = seedVersion(db, repositoryId, 'v18.3.0');
 		const documentId = seedDocument(db, repositoryId, versionId);
-		seedRules(db, repositoryId, ['Prefer hooks over classes']);
+		// Insert version-specific rules (versioned queries no longer inherit the NULL row).
+		db.prepare(
+			`INSERT INTO repository_configs (repository_id, version_id, rules, updated_at)
+			 VALUES (?, ?, ?, ?)`
+		).run(repositoryId, versionId, JSON.stringify(['Prefer hooks over classes']), NOW_S);
 		seedSnippet(db, {
 			documentId,
 			repositoryId,
@@ -497,12 +501,12 @@ describe('API contract integration', () => {
 		});
 	});
 
-	it('GET /api/v1/context returns merged repo-wide and version-specific rules', async () => {
+	it('GET /api/v1/context returns only version-specific rules for versioned queries (no NULL row contamination)', async () => {
 		const repositoryId = seedRepo(db);
 		const versionId = seedVersion(db, repositoryId, 'v2.0.0');
 		const documentId = seedDocument(db, repositoryId, versionId);
 
-		// Insert repo-wide rules (version_id IS NULL).
+		// Insert repo-wide rules (version_id IS NULL) — these must NOT appear in versioned queries.
 		db.prepare(
 			`INSERT INTO repository_configs (repository_id, version_id, rules, updated_at)
 			 VALUES (?, NULL, ?, ?)`
@@ -529,8 +533,8 @@ describe('API contract integration', () => {
 
 		expect(response.status).toBe(200);
 		const body = await response.json();
-		// Both repo-wide and version-specific rules should appear (deduped).
-		expect(body.rules).toEqual(['Repo-wide rule', 'Version-specific rule']);
+		// Only the version-specific rule should appear — NULL row must not contaminate.
+		expect(body.rules).toEqual(['Version-specific rule']);
 	});
 
 	it('GET /api/v1/context returns only repo-wide rules when no version is requested', async () => {
@@ -556,12 +560,13 @@ describe('API contract integration', () => {
 		expect(body.rules).toEqual(['Repo-wide rule only']);
 	});
 
-	it('GET /api/v1/context deduplicates rules that appear in both repo-wide and version config', async () => {
+	it('GET /api/v1/context versioned query returns only the version-specific rules row', async () => {
 		const repositoryId = seedRepo(db);
 		const versionId = seedVersion(db, repositoryId, 'v3.0.0');
 		const documentId = seedDocument(db, repositoryId, versionId);
 
 		const sharedRule = 'Use TypeScript strict mode';
+		// Insert repo-wide NULL row — must NOT bleed into versioned query results.
 		db.prepare(
 			`INSERT INTO repository_configs (repository_id, version_id, rules, updated_at)
 			 VALUES (?, NULL, ?, ?)`
@@ -582,10 +587,35 @@ describe('API contract integration', () => {
 
 		expect(response.status).toBe(200);
 		const body = await response.json();
-		// sharedRule appears once, version-only rule appended.
+		// Returns only the version-specific row as stored — no NULL row merge.
 		expect(body.rules).toEqual([sharedRule, 'Version-only rule']);
 	});
 
+	it('GET /api/v1/context versioned query returns empty rules when only NULL row exists (no NULL contamination)', async () => {
+		const repositoryId = seedRepo(db);
+		const versionId = seedVersion(db, repositoryId, 'v1.0.0');
+		const documentId = seedDocument(db, repositoryId, versionId);
+
+		// Only a repo-wide NULL row exists — no version-specific config.
+		db.prepare(
+			`INSERT INTO repository_configs (repository_id, version_id, rules, updated_at)
+			 VALUES (?, NULL, ?, ?)`
+		).run(repositoryId, JSON.stringify(['HEAD rules that must not contaminate v1']), NOW_S);
+
+		seedSnippet(db, { documentId, repositoryId, versionId, content: 'v1 content' });
+
+		const response = await getContext({
+			url: new URL(
+				`http://test/api/v1/context?libraryId=${encodeURIComponent(`${repositoryId}/v1.0.0`)}&query=${encodeURIComponent('v1 content')}`
+			)
+		} as never);
+
+		expect(response.status).toBe(200);
+		const body = await response.json();
+		// No version-specific config row → empty rules. NULL row must not bleed in.
+		expect(body.rules).toEqual([]);
+	});
+
 	it('GET /api/v1/context returns 404 with VERSION_NOT_FOUND when version does not exist', async () => {
 		const repositoryId = seedRepo(db);
 
diff --git a/src/routes/api/v1/context/+server.ts b/src/routes/api/v1/context/+server.ts
index ed711dc..214713c 100644
--- a/src/routes/api/v1/context/+server.ts
+++ b/src/routes/api/v1/context/+server.ts
@@ -69,35 +69,25 @@ function getRules(
 	repositoryId: string,
 	versionId?: string
 ): string[] {
-	// Repo-wide rules (version_id IS NULL).
-	const repoRow = db
-		.prepare<
-			[string],
-			RawRepoConfig
-		>(`SELECT rules FROM repository_configs WHERE repository_id = ? AND version_id IS NULL`)
-		.get(repositoryId);
+	if (!versionId) {
+		// Unversioned query: return repo-wide (HEAD) rules only.
+		const row = db
+			.prepare<
+				[string],
+				RawRepoConfig
+			>(`SELECT rules FROM repository_configs WHERE repository_id = ? AND version_id IS NULL`)
+			.get(repositoryId);
+		return parseRulesJson(row?.rules);
+	}
 
-	const repoRules = parseRulesJson(repoRow?.rules);
-
-	if (!versionId) return repoRules;
-
-	// Version-specific rules.
-	const versionRow = db
+	// Versioned query: return only version-specific rules (no NULL row merge).
+	const row = db
 		.prepare<
 			[string, string],
 			RawRepoConfig
 		>(`SELECT rules FROM repository_configs WHERE repository_id = ? AND version_id = ?`)
 		.get(repositoryId, versionId);
-
-	const versionRules = parseRulesJson(versionRow?.rules);
-
-	// Merge: repo-wide first, then version-specific (deduped by content).
-	const seen = new Set(repoRules);
-	const merged = [...repoRules];
-	for (const r of versionRules) {
-		if (!seen.has(r)) merged.push(r);
-	}
-	return merged;
+	return parseRulesJson(row?.rules);
 }
 
 interface RawRepoState {