diff --git a/scripts/check-test-isolation.sh b/scripts/check-test-isolation.sh
index 1ad904a71..c9bbaa91e 100755
--- a/scripts/check-test-isolation.sh
+++ b/scripts/check-test-isolation.sh
@@ -18,6 +18,12 @@
 #  R4: any file that creates `new PGLiteEngine(` must call `.disconnect(`
 #      inside an `afterAll(` block. Without disconnect, engines leak across
 #      file boundaries within a shard process.
+#  R5: any file that calls `configureGateway(` or
+#      `__setEmbedTransportForTests(` must also call `resetGateway()` and
+#      have an `afterAll(`/`afterEach(` hook. The gateway is module-global;
+#      a configured remote provider + fake key left past the file boundary
+#      makes the next embed-triggering file in the shard fire a live HTTP
+#      call (issue #3066; master shard 6 broke twice this way).
 #
 # Scope:
 #  - Recursively scans `test/**/*.test.ts`.
@@ -132,6 +138,22 @@ while IFS= read -r f; do
       emit_violation "$f" "R4" "creates PGLiteEngine but missing afterAll(() => engine.disconnect()); engine leaks across files in the shard process" ""
     fi
   fi
+
+  # R5: gateway configuration requires resetGateway + an afterAll/afterEach
+  # hook. Same loose two-grep shape as R4 — `resetGateway(` present plus at
+  # least one afterAll(/afterEach( — but on comment-stripped lines: a prose
+  # mention like "a test that calls resetGateway()" must not satisfy the
+  # rule (that exact false pass hid the cycle-consolidate leaker).
+  # No [[:space:]]* before the paren on the trigger side: prose in a test
+  # name ("works WITHOUT configureGateway (reads registry...)") must not
+  # trigger the rule; real call sites are always `configureGateway(`.
+  r5_code=$(grep -vE '^[[:space:]]*(//|\*)' "$f" 2>/dev/null || true)
+  if printf '%s\n' "$r5_code" | grep -qE 'configureGateway\(|__setEmbedTransportForTests\('; then
+    if ! printf '%s\n' "$r5_code" | grep -qE 'resetGateway\(' \
+       || ! printf '%s\n' "$r5_code" | grep -qE 'afterAll[[:space:]]*\(|afterEach[[:space:]]*\('; then
+      emit_violation "$f" "R5" "configures the AI gateway but never calls resetGateway() in afterAll/afterEach; gateway state (provider, fake keys, transports) leaks across files in the shard process" ""
+    fi
+  fi
 done <<EOF
 $FILE_LIST
 EOF
diff --git a/test/ai/gateway-cache-breakpoint.test.ts b/test/ai/gateway-cache-breakpoint.test.ts
index 8a9b65ca9..a25266d0d 100644
--- a/test/ai/gateway-cache-breakpoint.test.ts
+++ b/test/ai/gateway-cache-breakpoint.test.ts
@@ -29,7 +29,7 @@
  * the bug made you believe was sufficient.
  */
 
-import { describe, test, expect, beforeEach } from 'bun:test';
+import { describe, test, expect, beforeEach, afterAll } from 'bun:test';
 import {
   chat,
   configureGateway,
@@ -37,6 +37,12 @@ import {
   __setGenerateTextTransportForTests,
 } from '../../src/core/ai/gateway.ts';
 
+// R5 shard hygiene: leave no configured gateway past the file boundary.
+afterAll(() => {
+  resetGateway();
+  __setGenerateTextTransportForTests(null);
+});
+
 describe('gbrain#2490 — Anthropic cache breakpoint placement', () => {
   beforeEach(() => {
     resetGateway();
diff --git a/test/ai/gateway-chat.test.ts b/test/ai/gateway-chat.test.ts
index 4aee06a26..a105c4d9c 100644
--- a/test/ai/gateway-chat.test.ts
+++ b/test/ai/gateway-chat.test.ts
@@ -16,7 +16,7 @@
  * `generateText` import via Bun's module-replace pattern.
  */
 
-import { describe, test, expect, beforeEach, mock } from 'bun:test';
+import { describe, test, expect, beforeEach, mock, afterAll } from 'bun:test';
 import {
   configureGateway,
   resetGateway,
@@ -30,6 +30,12 @@ import { parseModelId, resolveRecipe, assertTouchpoint } from '../../src/core/ai
 import { AIConfigError } from '../../src/core/ai/errors.ts';
 import { listRecipes, getRecipe } from '../../src/core/ai/recipes/index.ts';
 
+// R5 shard hygiene: leave no configured gateway past the file boundary.
+afterAll(() => {
+  resetGateway();
+  __setGenerateTextTransportForTests(null);
+});
+
 describe('chat touchpoint — recipe registry', () => {
   test('all six chat-capable providers ship a chat touchpoint with supports_subagent_loop', () => {
     const expected = ['anthropic', 'openai', 'google', 'deepseek', 'groq', 'together'];
diff --git a/test/ai/gateway-openai-prompt-cache-key.test.ts b/test/ai/gateway-openai-prompt-cache-key.test.ts
index 8d49e56b2..44964e409 100644
--- a/test/ai/gateway-openai-prompt-cache-key.test.ts
+++ b/test/ai/gateway-openai-prompt-cache-key.test.ts
@@ -16,7 +16,7 @@
  *     nothing), and config `provider_chat_options` overrides the derived key
  */
 
-import { describe, test, expect, beforeEach } from 'bun:test';
+import { describe, test, expect, beforeEach, afterAll } from 'bun:test';
 import {
   chat,
   configureGateway,
@@ -25,6 +25,12 @@ import {
   __setGenerateTextTransportForTests,
 } from '../../src/core/ai/gateway.ts';
 
+// R5 shard hygiene: leave no configured gateway past the file boundary.
+afterAll(() => {
+  resetGateway();
+  __setGenerateTextTransportForTests(null);
+});
+
 describe('openAIPromptCacheKey — derivation', () => {
   test('same system + same tools → identical stable key (sticky routing)', () => {
     const a = openAIPromptCacheKey({ system: 'SYS', toolNames: ['search', 'put_page'] });
diff --git a/test/cycle-consolidate.test.ts b/test/cycle-consolidate.test.ts
index fe3462bc5..b0e7b374d 100644
--- a/test/cycle-consolidate.test.ts
+++ b/test/cycle-consolidate.test.ts
@@ -10,7 +10,7 @@
 
 import { describe, test, expect, beforeAll, afterAll, beforeEach } from 'bun:test';
 import { PGLiteEngine } from '../src/core/pglite-engine.ts';
-import { configureGateway } from '../src/core/ai/gateway.ts';
+import { configureGateway, resetGateway } from '../src/core/ai/gateway.ts';
 import { runPhaseConsolidate } from '../src/core/cycle/phases/consolidate.ts';
 
 let engine: PGLiteEngine;
@@ -37,6 +37,7 @@ beforeAll(async () => {
 
 afterAll(async () => {
   await engine.disconnect();
+  resetGateway();
 });
 
 beforeEach(async () => {
diff --git a/test/doctor-federation-health.test.ts b/test/doctor-federation-health.test.ts
index 71a808fd8..bfbb557a5 100644
--- a/test/doctor-federation-health.test.ts
+++ b/test/doctor-federation-health.test.ts
@@ -8,7 +8,7 @@
  */
 import { describe, test, expect, beforeAll, afterAll, beforeEach } from 'bun:test';
 import { PGLiteEngine } from '../src/core/pglite-engine.ts';
-import { configureGateway } from '../src/core/ai/gateway.ts';
+import { configureGateway, resetGateway } from '../src/core/ai/gateway.ts';
 import { checkFederationHealth } from '../src/commands/doctor.ts';
 
 let engine: PGLiteEngine;
@@ -33,6 +33,7 @@ beforeAll(async () => {
 
 afterAll(async () => {
   await engine.disconnect();
+  resetGateway();
 });
 
 beforeEach(async () => {
diff --git a/test/engine-find-trajectory.test.ts b/test/engine-find-trajectory.test.ts
index 4415c4a4b..2f6fd08a8 100644
--- a/test/engine-find-trajectory.test.ts
+++ b/test/engine-find-trajectory.test.ts
@@ -15,7 +15,7 @@
 
 import { describe, test, expect, beforeAll, afterAll, beforeEach } from 'bun:test';
 import { PGLiteEngine } from '../src/core/pglite-engine.ts';
-import { configureGateway } from '../src/core/ai/gateway.ts';
+import { configureGateway, resetGateway } from '../src/core/ai/gateway.ts';
 import {
   detectRegressions,
   computeDriftScore,
@@ -45,6 +45,7 @@ beforeAll(async () => {
 
 afterAll(async () => {
   await engine.disconnect();
+  resetGateway();
 });
 
 beforeEach(async () => {
diff --git a/test/eval-retrieval-quality.test.ts b/test/eval-retrieval-quality.test.ts
index 9312a2892..5922fe903 100644
--- a/test/eval-retrieval-quality.test.ts
+++ b/test/eval-retrieval-quality.test.ts
@@ -14,7 +14,7 @@ import { readFileSync } from 'fs';
 import { join } from 'path';
 import { PGLiteEngine } from '../src/core/pglite-engine.ts';
 import { hybridSearch } from '../src/core/search/hybrid.ts';
-import { __setEmbedTransportForTests } from '../src/core/ai/gateway.ts';
+import { __setEmbedTransportForTests, resetGateway } from '../src/core/ai/gateway.ts';
 import { parseQuestionsJsonl, runRetrievalQuality, evaluateGate, type SearchFn } from '../src/eval/retrieval-quality/harness.ts';
 import type { ChunkInput } from '../src/core/types.ts';
 
@@ -60,7 +60,7 @@ beforeAll(async () => {
 });
 
 afterAll(async () => {
-  __setEmbedTransportForTests(null);
+  resetGateway();
   await engine.disconnect();
 });
 
diff --git a/test/propose-takes.test.ts b/test/propose-takes.test.ts
index 8430f2ed4..2d74429d7 100644
--- a/test/propose-takes.test.ts
+++ b/test/propose-takes.test.ts
@@ -14,7 +14,7 @@
  *  - parseExtractorOutput unit tests for the raw JSON parser
  */
 
-import { describe, test, expect } from 'bun:test';
+import { describe, test, expect, afterAll } from 'bun:test';
 import {
   runPhaseProposeTakes,
   parseExtractorOutput,
@@ -28,6 +28,11 @@ import {
   type ProposedTake,
 } from '../src/core/cycle/propose-takes.ts';
 import { configureGateway, resetGateway } from '../src/core/ai/gateway.ts';
+
+// R5 shard hygiene: leave no configured gateway past the file boundary.
+afterAll(() => {
+  resetGateway();
+});
 import { BudgetMeter } from '../src/core/cycle/budget-meter.ts';
 import type { OperationContext } from '../src/core/operations.ts';
 import type { BrainEngine } from '../src/core/engine.ts';
diff --git a/test/scripts/check-test-isolation.test.ts b/test/scripts/check-test-isolation.test.ts
index b4fa8ba0d..dcf292867 100644
--- a/test/scripts/check-test-isolation.test.ts
+++ b/test/scripts/check-test-isolation.test.ts
@@ -199,6 +199,84 @@ describe('check-test-isolation.sh', () => {
     });
   });
 
+  describe('R5 — gateway configuration requires resetGateway teardown (#3066)', () => {
+    it('flags configureGateway without resetGateway in a teardown hook', () => {
+      const r = runLintIn([
+        {
+          path: 'gateway-leak.test.ts',
+          contents:
+            `import { beforeAll, test, expect } from 'bun:test';\n` +
+            `import { configureGateway } from '../src/core/ai/gateway.ts';\n` +
+            `beforeAll(() => { configureGateway({ env: {} }); });\n` +
+            `test('x', () => expect(1).toBe(1));\n`,
+        },
+      ]);
+      expect(r.status).toBe(1);
+      expect(r.stdout).toContain('R5');
+      expect(r.stdout).toContain('gateway-leak.test.ts');
+    });
+
+    it('flags __setEmbedTransportForTests without resetGateway', () => {
+      const r = runLintIn([
+        {
+          path: 'transport-leak.test.ts',
+          contents:
+            `import { afterAll, test, expect } from 'bun:test';\n` +
+            `import { __setEmbedTransportForTests } from '../src/core/ai/gateway.ts';\n` +
+            `__setEmbedTransportForTests(async () => ({ embeddings: [] }));\n` +
+            `afterAll(() => { /* disconnect only */ });\n` +
+            `test('x', () => expect(1).toBe(1));\n`,
+        },
+      ]);
+      expect(r.status).toBe(1);
+      expect(r.stdout).toContain('R5');
+    });
+
+    it('passes when resetGateway is called and an afterAll hook exists', () => {
+      const r = runLintIn([
+        {
+          path: 'gateway-clean.test.ts',
+          contents:
+            `import { beforeAll, afterAll, test, expect } from 'bun:test';\n` +
+            `import { configureGateway, resetGateway } from '../src/core/ai/gateway.ts';\n` +
+            `beforeAll(() => { configureGateway({ env: {} }); });\n` +
+            `afterAll(() => { resetGateway(); });\n` +
+            `test('x', () => expect(1).toBe(1));\n`,
+        },
+      ]);
+      expect(r.status).toBe(0);
+    });
+
+    it('a comment mentioning resetGateway() does not satisfy the rule', () => {
+      const r = runLintIn([
+        {
+          path: 'gateway-comment-leak.test.ts',
+          contents:
+            `import { beforeAll, afterAll, test, expect } from 'bun:test';\n` +
+            `import { configureGateway } from '../src/core/ai/gateway.ts';\n` +
+            `// a co-sharded test that calls resetGateway() would clear this\n` +
+            `beforeAll(() => { configureGateway({ env: {} }); });\n` +
+            `afterAll(() => { /* disconnect only */ });\n` +
+            `test('x', () => expect(1).toBe(1));\n`,
+        },
+      ]);
+      expect(r.status).toBe(1);
+      expect(r.stdout).toContain('R5');
+    });
+
+    it('a test name mentioning "configureGateway (" does not trigger the rule', () => {
+      const r = runLintIn([
+        {
+          path: 'gateway-prose.test.ts',
+          contents:
+            `import { test, expect } from 'bun:test';\n` +
+            `test('works WITHOUT configureGateway (reads registry)', () => expect(1).toBe(1));\n`,
+        },
+      ]);
+      expect(r.status).toBe(0);
+    });
+  });
+
   describe('scope', () => {
     it('skips *.serial.test.ts files entirely', () => {
       const r = runLintIn([
diff --git a/test/search/search-diagnose.test.ts b/test/search/search-diagnose.test.ts
index e16c0dddd..9cee1b822 100644
--- a/test/search/search-diagnose.test.ts
+++ b/test/search/search-diagnose.test.ts
@@ -6,7 +6,7 @@
 
 import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
 import { PGLiteEngine } from '../../src/core/pglite-engine.ts';
-import { __setEmbedTransportForTests } from '../../src/core/ai/gateway.ts';
+import { __setEmbedTransportForTests, resetGateway } from '../../src/core/ai/gateway.ts';
 import { runSearchDiagnose } from '../../src/commands/search-diagnose.ts';
 import type { ChunkInput } from '../../src/core/types.ts';
 
@@ -35,7 +35,7 @@ beforeAll(async () => {
   await engine.setPageAliases('projects/mingtang', 'default', ['hall of light']);
 });
 
-afterAll(async () => { __setEmbedTransportForTests(null); await engine.disconnect(); });
+afterAll(async () => { resetGateway(); await engine.disconnect(); });
 
 describe('search diagnose', () => {
   test('alias query: trace shows alias match + hybrid rank 1', async () => {
diff --git a/test/search/searchvector-maxpool.test.ts b/test/search/searchvector-maxpool.test.ts
index 29359270c..64ea9f0b1 100644
--- a/test/search/searchvector-maxpool.test.ts
+++ b/test/search/searchvector-maxpool.test.ts
@@ -23,7 +23,7 @@
 
 import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
 import { PGLiteEngine } from '../../src/core/pglite-engine.ts';
-import { configureGateway } from '../../src/core/ai/gateway.ts';
+import { configureGateway, resetGateway } from '../../src/core/ai/gateway.ts';
 import type { ChunkInput } from '../../src/core/types.ts';
 
 let engine: PGLiteEngine;
@@ -95,6 +95,7 @@ beforeAll(async () => {
 
 afterAll(async () => {
   await engine.disconnect();
+  resetGateway();
 });
 
 describe('searchVector per-page max-pool (T1)', () => {
diff --git a/test/search/title-retrieval-arm.test.ts b/test/search/title-retrieval-arm.test.ts
index 45d0af622..3015db2e2 100644
--- a/test/search/title-retrieval-arm.test.ts
+++ b/test/search/title-retrieval-arm.test.ts
@@ -27,7 +27,7 @@ import { PGLiteEngine } from '../../src/core/pglite-engine.ts';
 import { resetPgliteState } from '../helpers/reset-pglite.ts';
 import { hybridSearch } from '../../src/core/search/hybrid.ts';
 import { buildOrFallbackWebsearchQuery } from '../../src/core/search/sql-ranking.ts';
-import { configureGateway } from '../../src/core/ai/gateway.ts';
+import { configureGateway, resetGateway } from '../../src/core/ai/gateway.ts';
 
 let engine: PGLiteEngine;
 
@@ -48,6 +48,7 @@ beforeAll(async () => {
 
 afterAll(async () => {
   await engine.disconnect();
+  resetGateway();
   // Restore the preload-equivalent gateway for sibling files in this shard.
   configureGateway({
     embedding_model: 'openai:text-embedding-3-large',