Add support for policy engine in extensions (#20049)

Co-authored-by: Jerop Kipruto <jerop@google.com>

packages/core/src/config/config.ts

@@ -107,7 +107,12 @@ import { FileExclusions } from '../utils/ignorePatterns.js';
 import { MessageBus } from '../confirmation-bus/message-bus.js';
 import type { EventEmitter } from 'node:events';
 import { PolicyEngine } from '../policy/policy-engine.js';
-import { ApprovalMode, type PolicyEngineConfig } from '../policy/types.js';
+import {
+  ApprovalMode,
+  type PolicyEngineConfig,
+  type PolicyRule,
+  type SafetyCheckerRule,
+} from '../policy/types.js';
 import { HookSystem } from '../hooks/index.js';
 import type {
   UserTierId,
@@ -324,6 +329,14 @@ export interface GeminiCLIExtension {
    * These themes will be registered when the extension is activated.
    */
   themes?: CustomTheme[];
+  /**
+   * Policy rules contributed by this extension.
+   */
+  rules?: PolicyRule[];
+  /**
+   * Safety checkers contributed by this extension.
+   */
+  checkers?: SafetyCheckerRule[];
 }
 
 export interface ExtensionInstallMetadata {

packages/core/src/policy/config.test.ts

@@ -169,7 +169,7 @@ describe('createPolicyEngineConfig', () => {
         r.decision === PolicyDecision.ALLOW,
     );
     expect(rule).toBeDefined();
-    expect(rule?.priority).toBeCloseTo(3.3, 5); // Command line allow
+    expect(rule?.priority).toBeCloseTo(4.3, 5); // Command line allow
   });
 
   it('should deny tools in tools.exclude', async () => {
@@ -188,7 +188,7 @@ describe('createPolicyEngineConfig', () => {
         r.decision === PolicyDecision.DENY,
     );
     expect(rule).toBeDefined();
-    expect(rule?.priority).toBeCloseTo(3.4, 5); // Command line exclude
+    expect(rule?.priority).toBeCloseTo(4.4, 5); // Command line exclude
   });
 
   it('should allow tools from allowed MCP servers', async () => {
@@ -206,7 +206,7 @@ describe('createPolicyEngineConfig', () => {
         r.toolName === 'my-server__*' && r.decision === PolicyDecision.ALLOW,
     );
     expect(rule).toBeDefined();
-    expect(rule?.priority).toBe(3.1); // MCP allowed server
+    expect(rule?.priority).toBe(4.1); // MCP allowed server
   });
 
   it('should deny tools from excluded MCP servers', async () => {
@@ -224,7 +224,7 @@ describe('createPolicyEngineConfig', () => {
         r.toolName === 'my-server__*' && r.decision === PolicyDecision.DENY,
     );
     expect(rule).toBeDefined();
-    expect(rule?.priority).toBe(3.9); // MCP excluded server
+    expect(rule?.priority).toBe(4.9); // MCP excluded server
   });
 
   it('should allow tools from trusted MCP servers', async () => {
@@ -251,7 +251,7 @@ describe('createPolicyEngineConfig', () => {
         r.decision === PolicyDecision.ALLOW,
     );
     expect(trustedRule).toBeDefined();
-    expect(trustedRule?.priority).toBe(3.2); // MCP trusted server
+    expect(trustedRule?.priority).toBe(4.2); // MCP trusted server
 
     // Untrusted server should not have an allow rule
     const untrustedRule = config.rules?.find(
@@ -288,7 +288,7 @@ describe('createPolicyEngineConfig', () => {
         r.decision === PolicyDecision.ALLOW,
     );
     expect(allowedRule).toBeDefined();
-    expect(allowedRule?.priority).toBe(3.1); // MCP allowed server
+    expect(allowedRule?.priority).toBe(4.1); // MCP allowed server
 
     // Check trusted server
     const trustedRule = config.rules?.find(
@@ -297,7 +297,7 @@ describe('createPolicyEngineConfig', () => {
         r.decision === PolicyDecision.ALLOW,
     );
     expect(trustedRule).toBeDefined();
-    expect(trustedRule?.priority).toBe(3.2); // MCP trusted server
+    expect(trustedRule?.priority).toBe(4.2); // MCP trusted server
 
     // Check excluded server
     const excludedRule = config.rules?.find(
@@ -306,7 +306,7 @@ describe('createPolicyEngineConfig', () => {
         r.decision === PolicyDecision.DENY,
     );
     expect(excludedRule).toBeDefined();
-    expect(excludedRule?.priority).toBe(3.9); // MCP excluded server
+    expect(excludedRule?.priority).toBe(4.9); // MCP excluded server
   });
 
   it('should allow all tools in YOLO mode', async () => {
@@ -387,11 +387,11 @@ describe('createPolicyEngineConfig', () => {
     );
 
     expect(serverDenyRule).toBeDefined();
-    expect(serverDenyRule?.priority).toBe(3.9); // MCP excluded server
+    expect(serverDenyRule?.priority).toBe(4.9); // MCP excluded server
     expect(toolAllowRule).toBeDefined();
-    expect(toolAllowRule?.priority).toBeCloseTo(3.3, 5); // Command line allow
+    expect(toolAllowRule?.priority).toBeCloseTo(4.3, 5); // Command line allow
 
-    // Server deny (3.9) has higher priority than tool allow (3.3),
+    // Server deny (4.9) has higher priority than tool allow (4.3),
     // so server deny wins (this is expected behavior - server-level blocks are security critical)
   });
 
@@ -424,7 +424,7 @@ describe('createPolicyEngineConfig', () => {
 
     expect(serverAllowRule).toBeDefined();
     expect(toolDenyRule).toBeDefined();
-    // Command line exclude (3.4) has higher priority than MCP server trust (3.2)
+    // Command line exclude (4.4) has higher priority than MCP server trust (4.2)
     // This is the correct behavior - specific exclusions should beat general server trust
     expect(toolDenyRule!.priority).toBeGreaterThan(serverAllowRule!.priority!);
   });
@@ -432,16 +432,16 @@ describe('createPolicyEngineConfig', () => {
   it('should handle complex priority scenarios correctly', async () => {
     const settings: PolicySettings = {
       tools: {
-        allowed: ['my-server__tool1', 'other-tool'], // Priority 3.3
-        exclude: ['my-server__tool2', 'glob'], // Priority 3.4
+        allowed: ['my-server__tool1', 'other-tool'], // Priority 4.3
+        exclude: ['my-server__tool2', 'glob'], // Priority 4.4
       },
       mcp: {
-        allowed: ['allowed-server'], // Priority 3.1
-        excluded: ['excluded-server'], // Priority 3.9
+        allowed: ['allowed-server'], // Priority 4.1
+        excluded: ['excluded-server'], // Priority 4.9
       },
       mcpServers: {
         'trusted-server': {
-          trust: true, // Priority 90 -> 3.2
+          trust: true, // Priority 4.2
         },
       },
     };
@@ -517,7 +517,7 @@ describe('createPolicyEngineConfig', () => {
     expect(globDenyRule).toBeDefined();
     expect(globAllowRule).toBeDefined();
     // Deny from settings (user tier)
-    expect(globDenyRule!.priority).toBeCloseTo(3.4, 5); // Command line exclude
+    expect(globDenyRule!.priority).toBeCloseTo(4.4, 5); // Command line exclude
     // Allow from default TOML: 1 + 50/1000 = 1.05
     expect(globAllowRule!.priority).toBeCloseTo(1.05, 5);
 
@@ -530,11 +530,11 @@ describe('createPolicyEngineConfig', () => {
       }))
       .sort((a, b) => (b.priority ?? 0) - (a.priority ?? 0));
 
-    // Check that the highest priority items are the excludes (user tier: 3.4 and 3.9)
+    // Check that the highest priority items are the excludes (user tier: 4.4 and 4.9)
     const highestPriorityExcludes = priorities?.filter(
       (p) =>
-        Math.abs(p.priority! - 3.4) < 0.01 ||
-        Math.abs(p.priority! - 3.9) < 0.01,
+        Math.abs(p.priority! - 4.4) < 0.01 ||
+        Math.abs(p.priority! - 4.9) < 0.01,
     );
     expect(
       highestPriorityExcludes?.every((p) => p.decision === PolicyDecision.DENY),
@@ -626,7 +626,7 @@ describe('createPolicyEngineConfig', () => {
         r.toolName === 'dangerous-tool' && r.decision === PolicyDecision.DENY,
     );
     expect(excludeRule).toBeDefined();
-    expect(excludeRule?.priority).toBeCloseTo(3.4, 5); // Command line exclude
+    expect(excludeRule?.priority).toBeCloseTo(4.4, 5); // Command line exclude
   });
 
   it('should support argsPattern in policy rules', async () => {
@@ -733,8 +733,8 @@ priority = 150
         r.decision === PolicyDecision.ALLOW,
     );
     expect(rule).toBeDefined();
-    // Priority 150 in user tier → 3.150
-    expect(rule?.priority).toBeCloseTo(3.15, 5);
+    // Priority 150 in user tier → 4.150
+    expect(rule?.priority).toBeCloseTo(4.15, 5);
     expect(rule?.argsPattern).toBeInstanceOf(RegExp);
     expect(rule?.argsPattern?.test('{"command":"git status"}')).toBe(true);
     expect(rule?.argsPattern?.test('{"command":"git diff"}')).toBe(true);
@@ -1046,7 +1046,7 @@ name = "invalid-name"
         r.decision === PolicyDecision.ALLOW,
     );
     expect(rule).toBeDefined();
-    expect(rule?.priority).toBeCloseTo(3.3, 5); // Command line allow
+    expect(rule?.priority).toBeCloseTo(4.3, 5); // Command line allow
 
     vi.doUnmock('node:fs/promises');
   });
@@ -1188,7 +1188,7 @@ modes = ["plan"]
         r.modes?.includes(ApprovalMode.PLAN),
     );
     expect(subagentRule).toBeDefined();
-    expect(subagentRule?.priority).toBeCloseTo(3.1, 5);
+    expect(subagentRule?.priority).toBeCloseTo(4.1, 5);
 
     vi.doUnmock('node:fs/promises');
   });

packages/core/src/policy/config.ts

@@ -13,8 +13,9 @@ import {
   type PolicyEngineConfig,
   PolicyDecision,
   type PolicyRule,
-  type ApprovalMode,
+  ApprovalMode,
   type PolicySettings,
+  type SafetyCheckerRule,
 } from './types.js';
 import type { PolicyEngine } from './policy-engine.js';
 import { loadPoliciesFromToml, type PolicyFileError } from './toml-loader.js';
@@ -39,14 +40,15 @@ export const DEFAULT_CORE_POLICIES_DIR = path.join(__dirname, 'policies');
 
 // Policy tier constants for priority calculation
 export const DEFAULT_POLICY_TIER = 1;
-export const WORKSPACE_POLICY_TIER = 2;
-export const USER_POLICY_TIER = 3;
-export const ADMIN_POLICY_TIER = 4;
+export const EXTENSION_POLICY_TIER = 2;
+export const WORKSPACE_POLICY_TIER = 3;
+export const USER_POLICY_TIER = 4;
+export const ADMIN_POLICY_TIER = 5;
 
 // Specific priority offsets and derived priorities for dynamic/settings rules.
 // These are added to the tier base (e.g., USER_POLICY_TIER).
 
-// Workspace tier (2) + high priority (950/1000) = ALWAYS_ALLOW_PRIORITY
+// Workspace tier (3) + high priority (950/1000) = ALWAYS_ALLOW_PRIORITY
 // This ensures user "always allow" selections are high priority
 // within the workspace tier but still lose to user/admin policies.
 export const ALWAYS_ALLOW_PRIORITY = WORKSPACE_POLICY_TIER + 0.95;
@@ -59,7 +61,9 @@ export const ALLOWED_MCP_SERVER_PRIORITY = USER_POLICY_TIER + 0.1;
 
 /**
  * Gets the list of directories to search for policy files, in order of increasing priority
- * (Default -> User -> Project -> Admin).
+ * (Default -> Extension -> Workspace -> User -> Admin).
+ *
+ * Note: Extension policies are loaded separately by the extension manager.
  *
  * @param defaultPoliciesDir Optional path to a directory containing default policies.
  * @param policyPaths Optional user-provided policy paths (from --policy flag).
@@ -95,7 +99,7 @@ export function getPolicyDirectories(
 }
 
 /**
- * Determines the policy tier (1=default, 2=user, 3=workspace, 4=admin) for a given directory.
+ * Determines the policy tier (1=default, 2=extension, 3=workspace, 4=user, 5=admin) for a given directory.
  * This is used by the TOML loader to assign priority bands.
  */
 export function getPolicyTier(
@@ -178,6 +182,69 @@ async function filterSecurePolicyDirectories(
   return results.filter((dir): dir is string => dir !== null);
 }
 
+/**
+ * Loads and sanitizes policies from an extension's policies directory.
+ * Security: Filters out 'ALLOW' rules and YOLO mode configurations.
+ */
+export async function loadExtensionPolicies(
+  extensionName: string,
+  policyDir: string,
+): Promise<{
+  rules: PolicyRule[];
+  checkers: SafetyCheckerRule[];
+  errors: PolicyFileError[];
+}> {
+  const result = await loadPoliciesFromToml(
+    [policyDir],
+    () => EXTENSION_POLICY_TIER,
+  );
+
+  const rules = result.rules.filter((rule) => {
+    // Security: Extensions are not allowed to automatically approve tool calls.
+    if (rule.decision === PolicyDecision.ALLOW) {
+      debugLogger.warn(
+        `[PolicyConfig] Extension "${extensionName}" attempted to contribute an ALLOW rule for tool "${rule.toolName}". Ignoring this rule for security.`,
+      );
+      return false;
+    }
+
+    // Security: Extensions are not allowed to contribute YOLO mode rules.
+    if (rule.modes?.includes(ApprovalMode.YOLO)) {
+      debugLogger.warn(
+        `[PolicyConfig] Extension "${extensionName}" attempted to contribute a rule for YOLO mode. Ignoring this rule for security.`,
+      );
+      return false;
+    }
+
+    // Prefix source with extension name to avoid collisions and double prefixing.
+    // toml-loader.ts adds "Extension: file.toml", we transform it to "Extension (name): file.toml".
+    rule.source = rule.source?.replace(
+      /^Extension: /,
+      `Extension (${extensionName}): `,
+    );
+    return true;
+  });
+
+  const checkers = result.checkers.filter((checker) => {
+    // Security: Extensions are not allowed to contribute YOLO mode checkers.
+    if (checker.modes?.includes(ApprovalMode.YOLO)) {
+      debugLogger.warn(
+        `[PolicyConfig] Extension "${extensionName}" attempted to contribute a safety checker for YOLO mode. Ignoring this checker for security.`,
+      );
+      return false;
+    }
+
+    // Prefix source with extension name.
+    checker.source = checker.source?.replace(
+      /^Extension: /,
+      `Extension (${extensionName}): `,
+    );
+    return true;
+  });
+
+  return { rules, checkers, errors: result.errors };
+}
+
 export async function createPolicyEngineConfig(
   settings: PolicySettings,
   approvalMode: ApprovalMode,
@@ -234,17 +301,19 @@ export async function createPolicyEngineConfig(
   const checkers = [...tomlCheckers];
 
   // Priority system for policy rules:
+
   // - Higher priority numbers win over lower priority numbers
   // - When multiple rules match, the highest priority rule is applied
   // - Rules are evaluated in order of priority (highest first)
   //
   // Priority bands (tiers):
   // - Default policies (TOML): 1 + priority/1000 (e.g., priority 100 → 1.100)
-  // - Workspace policies (TOML): 2 + priority/1000 (e.g., priority 100 → 2.100)
-  // - User policies (TOML): 3 + priority/1000 (e.g., priority 100 → 3.100)
-  // - Admin policies (TOML): 4 + priority/1000 (e.g., priority 100 → 4.100)
+  // - Extension policies (TOML): 2 + priority/1000 (e.g., priority 100 → 2.100)
+  // - Workspace policies (TOML): 3 + priority/1000 (e.g., priority 100 → 3.100)
+  // - User policies (TOML): 4 + priority/1000 (e.g., priority 100 → 4.100)
+  // - Admin policies (TOML): 5 + priority/1000 (e.g., priority 100 → 5.100)
   //
-  // This ensures Admin > User > Workspace > Default hierarchy is always preserved,
+  // This ensures Admin > User > Workspace > Extension > Default hierarchy is always preserved,
   // while allowing user-specified priorities to work within each tier.
   //
   // Settings-based and dynamic rules (mixed tiers):
@@ -254,7 +323,7 @@ export async function createPolicyEngineConfig(
   //   TRUSTED_MCP_SERVER_PRIORITY:  MCP servers with trust=true (persistent trusted servers)
   //   ALLOWED_MCP_SERVER_PRIORITY:  MCP servers allowed list (persistent general server allows)
   //   ALWAYS_ALLOW_PRIORITY:        Tools that the user has selected as "Always Allow" in the interactive UI
-  //                                 (Workspace tier 2.x - scoped to the project)
+  //                                 (Workspace tier 3.x - scoped to the project)
   //
   // TOML policy priorities (before transformation):
   //   10: Write tools default to ASK_USER (becomes 1.010 in default tier)

packages/core/src/policy/policy-engine.test.ts

@@ -406,6 +406,40 @@ describe('PolicyEngine', () => {
       expect(remainingRules.some((r) => r.toolName === 'tool2')).toBe(true);
     });
 
+    it('should remove rules for specific tool and source', () => {
+      engine.addRule({
+        toolName: 'tool1',
+        decision: PolicyDecision.ALLOW,
+        source: 'source1',
+      });
+      engine.addRule({
+        toolName: 'tool1',
+        decision: PolicyDecision.DENY,
+        source: 'source2',
+      });
+      engine.addRule({
+        toolName: 'tool2',
+        decision: PolicyDecision.ALLOW,
+        source: 'source1',
+      });
+
+      expect(engine.getRules()).toHaveLength(3);
+
+      engine.removeRulesForTool('tool1', 'source1');
+
+      const rules = engine.getRules();
+      expect(rules).toHaveLength(2);
+      expect(
+        rules.some((r) => r.toolName === 'tool1' && r.source === 'source2'),
+      ).toBe(true);
+      expect(
+        rules.some((r) => r.toolName === 'tool2' && r.source === 'source1'),
+      ).toBe(true);
+      expect(
+        rules.some((r) => r.toolName === 'tool1' && r.source === 'source1'),
+      ).toBe(false);
+    });
+
     it('should handle removing non-existent tool', () => {
       engine.addRule({ toolName: 'existing', decision: PolicyDecision.ALLOW });
 
@@ -2836,6 +2870,34 @@ describe('PolicyEngine', () => {
     });
   });
 
+  describe('removeRulesBySource', () => {
+    it('should remove rules matching a specific source', () => {
+      engine.addRule({
+        toolName: 'rule1',
+        decision: PolicyDecision.ALLOW,
+        source: 'source1',
+      });
+      engine.addRule({
+        toolName: 'rule2',
+        decision: PolicyDecision.ALLOW,
+        source: 'source2',
+      });
+      engine.addRule({
+        toolName: 'rule3',
+        decision: PolicyDecision.ALLOW,
+        source: 'source1',
+      });
+
+      expect(engine.getRules()).toHaveLength(3);
+
+      engine.removeRulesBySource('source1');
+
+      const rules = engine.getRules();
+      expect(rules).toHaveLength(1);
+      expect(rules[0].toolName).toBe('rule2');
+    });
+  });
+
   describe('removeCheckersByTier', () => {
     it('should remove checkers matching a specific tier', () => {
       engine.addChecker({
@@ -2861,6 +2923,31 @@ describe('PolicyEngine', () => {
     });
   });
 
+  describe('removeCheckersBySource', () => {
+    it('should remove checkers matching a specific source', () => {
+      engine.addChecker({
+        checker: { type: 'external', name: 'c1' },
+        source: 'sourceA',
+      });
+      engine.addChecker({
+        checker: { type: 'external', name: 'c2' },
+        source: 'sourceB',
+      });
+      engine.addChecker({
+        checker: { type: 'external', name: 'c3' },
+        source: 'sourceA',
+      });
+
+      expect(engine.getCheckers()).toHaveLength(3);
+
+      engine.removeCheckersBySource('sourceA');
+
+      const checkers = engine.getCheckers();
+      expect(checkers).toHaveLength(1);
+      expect(checkers[0].checker.name).toBe('c2');
+    });
+  });
+
   describe('Tool Annotations', () => {
     it('should match tools by semantic annotations', async () => {
       engine = new PolicyEngine({
@@ -2924,4 +3011,22 @@ describe('PolicyEngine', () => {
       ).toBe(PolicyDecision.ALLOW);
     });
   });
+
+  describe('hook checkers', () => {
+    it('should add and retrieve hook checkers in priority order', () => {
+      engine.addHookChecker({
+        checker: { type: 'external', name: 'h1' },
+        priority: 5,
+      });
+      engine.addHookChecker({
+        checker: { type: 'external', name: 'h2' },
+        priority: 10,
+      });
+
+      const hookCheckers = engine.getHookCheckers();
+      expect(hookCheckers).toHaveLength(2);
+      expect(hookCheckers[0].priority).toBe(10);
+      expect(hookCheckers[1].priority).toBe(5);
+    });
+  });
 });

packages/core/src/policy/policy-engine.ts

@@ -562,6 +562,13 @@ export class PolicyEngine {
     );
   }
 
+  /**
+   * Remove rules matching a specific source.
+   */
+  removeRulesBySource(source: string): void {
+    this.rules = this.rules.filter((rule) => rule.source !== source);
+  }
+
   /**
    * Remove checkers matching a specific tier (priority band).
    */
@@ -571,6 +578,15 @@ export class PolicyEngine {
     );
   }
 
+  /**
+   * Remove checkers matching a specific source.
+   */
+  removeCheckersBySource(source: string): void {
+    this.checkers = this.checkers.filter(
+      (checker) => checker.source !== source,
+    );
+  }
+
   /**
    * Remove rules for a specific tool.
    * If source is provided, only rules matching that source are removed.

packages/core/src/policy/toml-loader.test.ts

@@ -262,30 +262,34 @@ deny_message = "Deletion is permanent"
       expect(result.errors).toHaveLength(0);
     });
 
-    it('should support modes property for Tier 2 and Tier 3 policies', async () => {
+    it('should support modes property for Tier 4 and Tier 5 policies', async () => {
       await fs.writeFile(
-        path.join(tempDir, 'tier2.toml'),
+        path.join(tempDir, 'tier4.toml'),
         `
 [[rule]]
-toolName = "tier2-tool"
+toolName = "tier4-tool"
 decision = "allow"
 priority = 100
 modes = ["autoEdit"]
 `,
       );
 
-      const getPolicyTier2 = (_dir: string) => 2; // Tier 2
+      const getPolicyTier4 = (_dir: string) => 4; // Tier 4 (User)
+      const result4 = await loadPoliciesFromToml([tempDir], getPolicyTier4);
+
+      expect(result4.rules).toHaveLength(1);
+      expect(result4.rules[0].toolName).toBe('tier4-tool');
+      expect(result4.rules[0].modes).toEqual(['autoEdit']);
+      expect(result4.rules[0].source).toBe('User: tier4.toml');
+
+      const getPolicyTier2 = (_dir: string) => 2; // Tier 2 (Extension)
       const result2 = await loadPoliciesFromToml([tempDir], getPolicyTier2);
+      expect(result2.rules[0].source).toBe('Extension: tier4.toml');
 
-      expect(result2.rules).toHaveLength(1);
-      expect(result2.rules[0].toolName).toBe('tier2-tool');
-      expect(result2.rules[0].modes).toEqual(['autoEdit']);
-      expect(result2.rules[0].source).toBe('Workspace: tier2.toml');
-
-      const getPolicyTier3 = (_dir: string) => 3; // Tier 3
-      const result3 = await loadPoliciesFromToml([tempDir], getPolicyTier3);
-      expect(result3.rules[0].source).toBe('User: tier2.toml');
-      expect(result3.errors).toHaveLength(0);
+      const getPolicyTier5 = (_dir: string) => 5; // Tier 5 (Admin)
+      const result5 = await loadPoliciesFromToml([tempDir], getPolicyTier5);
+      expect(result5.rules[0].source).toBe('Admin: tier4.toml');
+      expect(result5.errors).toHaveLength(0);
     });
 
     it('should handle TOML parse errors', async () => {

packages/core/src/policy/toml-loader.ts

@@ -108,7 +108,7 @@ export type PolicyFileErrorType =
 export interface PolicyFileError {
   filePath: string;
   fileName: string;
-  tier: 'default' | 'user' | 'workspace' | 'admin';
+  tier: 'default' | 'extension' | 'user' | 'workspace' | 'admin';
   ruleIndex?: number;
   errorType: PolicyFileErrorType;
   message: string;
@@ -173,11 +173,14 @@ export async function readPolicyFiles(
 /**
  * Converts a tier number to a human-readable tier name.
  */
-function getTierName(tier: number): 'default' | 'user' | 'workspace' | 'admin' {
+function getTierName(
+  tier: number,
+): 'default' | 'extension' | 'user' | 'workspace' | 'admin' {
   if (tier === 1) return 'default';
-  if (tier === 2) return 'workspace';
-  if (tier === 3) return 'user';
-  if (tier === 4) return 'admin';
+  if (tier === 2) return 'extension';
+  if (tier === 3) return 'workspace';
+  if (tier === 4) return 'user';
+  if (tier === 5) return 'admin';
   return 'default';
 }
 

packages/core/src/policy/workspace-policy.test.ts

@@ -34,7 +34,7 @@ describe('Workspace-Level Policies', () => {
     vi.doUnmock('node:fs/promises');
   });
 
-  it('should load workspace policies with correct priority (Tier 2)', async () => {
+  it('should load workspace policies with correct priority (Tier 3)', async () => {
     const workspacePoliciesDir = '/mock/workspace/policies';
     const defaultPoliciesDir = '/mock/default/policies';
 
@@ -98,21 +98,21 @@ priority = 10
 toolName = "test_tool"
 decision = "deny"
 priority = 10
-`; // Tier 3 -> 3.010
+`; // Tier 4 -> 4.010
       }
       if (path.includes('workspace.toml')) {
         return `[[rule]]
 toolName = "test_tool"
 decision = "allow"
 priority = 10
-`; // Tier 2 -> 2.010
+`; // Tier 3 -> 3.010
       }
       if (path.includes('admin.toml')) {
         return `[[rule]]
 toolName = "test_tool"
 decision = "deny"
 priority = 10
-`; // Tier 4 -> 4.010
+`; // Tier 5 -> 5.010
       }
       return '';
     });
@@ -144,9 +144,9 @@ priority = 10
 
     // Check for all 4 rules
     const defaultRule = rules?.find((r) => r.priority === 1.01);
-    const workspaceRule = rules?.find((r) => r.priority === 2.01);
-    const userRule = rules?.find((r) => r.priority === 3.01);
-    const adminRule = rules?.find((r) => r.priority === 4.01);
+    const workspaceRule = rules?.find((r) => r.priority === 3.01);
+    const userRule = rules?.find((r) => r.priority === 4.01);
+    const adminRule = rules?.find((r) => r.priority === 5.01);
 
     expect(defaultRule).toBeDefined();
     expect(userRule).toBeDefined();
@@ -224,7 +224,7 @@ priority=10`,
     expect(rules![0].priority).toBe(1.01);
   });
 
-  it('should load workspace policies and correctly transform to Tier 2', async () => {
+  it('should load workspace policies and correctly transform to Tier 3', async () => {
     const workspacePoliciesDir = '/mock/workspace/policies';
 
     // Mock FS
@@ -284,7 +284,7 @@ priority=500`,
 
     const rule = config.rules?.find((r) => r.toolName === 'p_tool');
     expect(rule).toBeDefined();
-    // Workspace Tier (2) + 500/1000 = 2.5
-    expect(rule?.priority).toBe(2.5);
+    // Workspace Tier (3) + 500/1000 = 3.5
+    expect(rule?.priority).toBe(3.5);
   });
 });

packages/core/src/utils/extensionLoader.test.ts

@@ -14,6 +14,7 @@ import {
   type MockInstance,
 } from 'vitest';
 import { SimpleExtensionLoader } from './extensionLoader.js';
+import { PolicyDecision } from '../policy/types.js';
 import type { Config, GeminiCLIExtension } from '../config/config.js';
 import { type McpClientManager } from '../tools/mcp-client-manager.js';
 import type { GeminiClient } from '../core/client.js';
@@ -38,6 +39,12 @@ describe('SimpleExtensionLoader', () => {
   let mockHookSystemInit: MockInstance;
   let mockAgentRegistryReload: MockInstance;
   let mockSkillsReload: MockInstance;
+  let mockPolicyEngine: {
+    addRule: MockInstance;
+    addChecker: MockInstance;
+    removeRulesBySource: MockInstance;
+    removeCheckersBySource: MockInstance;
+  };
 
   const activeExtension: GeminiCLIExtension = {
     name: 'test-extension',
@@ -47,7 +54,22 @@ describe('SimpleExtensionLoader', () => {
     contextFiles: [],
     excludeTools: ['some-tool'],
     id: '123',
+    rules: [
+      {
+        toolName: 'test-tool',
+        decision: PolicyDecision.ALLOW,
+        source: 'Extension (test-extension): policies.toml',
+      },
+    ],
+    checkers: [
+      {
+        toolName: 'test-tool',
+        checker: { type: 'external', name: 'test-checker' },
+        source: 'Extension (test-extension): policies.toml',
+      },
+    ],
   };
+
   const inactiveExtension: GeminiCLIExtension = {
     name: 'test-extension',
     isActive: false,
@@ -67,6 +89,12 @@ describe('SimpleExtensionLoader', () => {
     mockHookSystemInit = vi.fn();
     mockAgentRegistryReload = vi.fn();
     mockSkillsReload = vi.fn();
+    mockPolicyEngine = {
+      addRule: vi.fn(),
+      addChecker: vi.fn(),
+      removeRulesBySource: vi.fn(),
+      removeCheckersBySource: vi.fn(),
+    };
     mockConfig = {
       getMcpClientManager: () => mockMcpClientManager,
       getEnableExtensionReloading: () => extensionReloadingEnabled,
@@ -81,6 +109,7 @@ describe('SimpleExtensionLoader', () => {
         reload: mockAgentRegistryReload,
       }),
       reloadSkills: mockSkillsReload,
+      getPolicyEngine: () => mockPolicyEngine,
     } as unknown as Config;
   });
 
@@ -88,6 +117,29 @@ describe('SimpleExtensionLoader', () => {
     vi.restoreAllMocks();
   });
 
+  it('should register policies when an extension starts', async () => {
+    const loader = new SimpleExtensionLoader([activeExtension]);
+    await loader.start(mockConfig);
+    expect(mockPolicyEngine.addRule).toHaveBeenCalledWith(
+      activeExtension.rules![0],
+    );
+    expect(mockPolicyEngine.addChecker).toHaveBeenCalledWith(
+      activeExtension.checkers![0],
+    );
+  });
+
+  it('should unregister policies when an extension stops', async () => {
+    const loader = new TestingSimpleExtensionLoader([activeExtension]);
+    await loader.start(mockConfig);
+    await loader.stopExtension(activeExtension);
+    expect(mockPolicyEngine.removeRulesBySource).toHaveBeenCalledWith(
+      'Extension (test-extension): policies.toml',
+    );
+    expect(mockPolicyEngine.removeCheckersBySource).toHaveBeenCalledWith(
+      'Extension (test-extension): policies.toml',
+    );
+  });
+
   it('should start active extensions', async () => {
     const loader = new SimpleExtensionLoader([activeExtension]);
     await loader.start(mockConfig);

packages/core/src/utils/extensionLoader.ts

@@ -75,6 +75,21 @@ export abstract class ExtensionLoader {
       await this.config.getMcpClientManager()!.startExtension(extension);
       await this.maybeRefreshGeminiTools(extension);
 
+      // Register policy rules and checkers
+      if (extension.rules || extension.checkers) {
+        const policyEngine = this.config.getPolicyEngine();
+        if (extension.rules) {
+          for (const rule of extension.rules) {
+            policyEngine.addRule(rule);
+          }
+        }
+        if (extension.checkers) {
+          for (const checker of extension.checkers) {
+            policyEngine.addChecker(checker);
+          }
+        }
+      }
+
       // Note: Context files are loaded only once all extensions are done
       // loading/unloading to reduce churn, see the `maybeRefreshMemories` call
       // below.
@@ -168,6 +183,27 @@ export abstract class ExtensionLoader {
       await this.config.getMcpClientManager()!.stopExtension(extension);
       await this.maybeRefreshGeminiTools(extension);
 
+      // Unregister policy rules and checkers
+      if (extension.rules || extension.checkers) {
+        const policyEngine = this.config.getPolicyEngine();
+        const sources = new Set<string>();
+        if (extension.rules) {
+          for (const rule of extension.rules) {
+            if (rule.source) sources.add(rule.source);
+          }
+        }
+        if (extension.checkers) {
+          for (const checker of extension.checkers) {
+            if (checker.source) sources.add(checker.source);
+          }
+        }
+
+        for (const source of sources) {
+          policyEngine.removeRulesBySource(source);
+          policyEngine.removeCheckersBySource(source);
+        }
+      }
+
       // Note: Context files are loaded only once all extensions are done
       // loading/unloading to reduce churn, see the `maybeRefreshMemories` call
       // below.