diff --git a/docs/session-aware-migration-todo.md b/docs/session-aware-migration-todo.md
index 7f5be6c5..56fc6526 100644
--- a/docs/session-aware-migration-todo.md
+++ b/docs/session-aware-migration-todo.md
@@ -5,11 +5,11 @@ _Audit date: October 6, 2025_
 Reference: `docs/session_management_plan.md`
 
 ## Utilities
-- [ ] `src/mcp/tools/utilities/clean.ts` — session defaults: `projectPath`, `workspacePath`, `scheme`, `configuration`.
+- [x] `src/mcp/tools/utilities/clean.ts` — session defaults: `projectPath`, `workspacePath`, `scheme`, `configuration`.
 
 ## Project Discovery
-- [ ] `src/mcp/tools/project-discovery/list_schemes.ts` — session defaults: `projectPath`, `workspacePath`.
-- [ ] `src/mcp/tools/project-discovery/show_build_settings.ts` — session defaults: `projectPath`, `workspacePath`, `scheme`.
+- [x] `src/mcp/tools/project-discovery/list_schemes.ts` — session defaults: `projectPath`, `workspacePath`.
+- [x] `src/mcp/tools/project-discovery/show_build_settings.ts` — session defaults: `projectPath`, `workspacePath`, `scheme`.
 
 ## Device Workflows
 - [ ] `src/mcp/tools/device/build_device.ts` — session defaults: `projectPath`, `workspacePath`, `scheme`, `configuration`.
diff --git a/src/mcp/tools/project-discovery/__tests__/list_schemes.test.ts b/src/mcp/tools/project-discovery/__tests__/list_schemes.test.ts
index de2f2425..c38e6abd 100644
--- a/src/mcp/tools/project-discovery/__tests__/list_schemes.test.ts
+++ b/src/mcp/tools/project-discovery/__tests__/list_schemes.test.ts
@@ -4,40 +4,35 @@
  * Using dependency injection for deterministic testing
  */
 
-import { describe, it, expect } from 'vitest';
+import { describe, it, expect, beforeEach } from 'vitest';
 import { z } from 'zod';
 import { createMockExecutor } from '../../../../test-utils/mock-executors.ts';
 import plugin, { listSchemesLogic } from '../list_schemes.ts';
+import { sessionStore } from '../../../../utils/session-store.ts';
 
 describe('list_schemes plugin', () => {
+  beforeEach(() => {
+    sessionStore.clear();
+  });
+
   describe('Export Field Validation (Literal)', () => {
     it('should have correct name', () => {
       expect(plugin.name).toBe('list_schemes');
     });
 
     it('should have correct description', () => {
-      expect(plugin.description).toBe(
-        "Lists available schemes for either a project or a workspace. Provide exactly one of projectPath or workspacePath. Example: list_schemes({ projectPath: '/path/to/MyProject.xcodeproj' })",
-      );
+      expect(plugin.description).toBe('Lists schemes for a project or workspace.');
     });
 
     it('should have handler function', () => {
       expect(typeof plugin.handler).toBe('function');
     });
 
-    it('should validate schema with valid inputs', () => {
-      const schema = z.object(plugin.schema);
-      expect(schema.safeParse({ projectPath: '/path/to/MyProject.xcodeproj' }).success).toBe(true);
-      expect(schema.safeParse({ projectPath: '/Users/dev/App.xcodeproj' }).success).toBe(true);
-    });
-
-    it('should validate schema with invalid inputs', () => {
-      const schema = z.object(plugin.schema);
-      // Base schema allows empty object - XOR validation is in refinements
+    it('should expose an empty public schema', () => {
+      const schema = z.object(plugin.schema).strict();
       expect(schema.safeParse({}).success).toBe(true);
-      expect(schema.safeParse({ projectPath: 123 }).success).toBe(false);
-      expect(schema.safeParse({ projectPath: null }).success).toBe(false);
-      expect(schema.safeParse({ workspacePath: 123 }).success).toBe(false);
+      expect(schema.safeParse({ projectPath: '/path/to/MyProject.xcodeproj' }).success).toBe(false);
+      expect(Object.keys(plugin.schema)).toEqual([]);
     });
   });
 
@@ -235,8 +230,8 @@ describe('list_schemes plugin', () => {
       // to verify Zod validation works properly. The createTypedTool wrapper handles validation.
       const result = await plugin.handler({});
       expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Parameter validation failed');
-      expect(result.content[0].text).toContain('Either projectPath or workspacePath is required');
+      expect(result.content[0].text).toContain('Missing required session defaults');
+      expect(result.content[0].text).toContain('Provide a project or workspace');
     });
   });
 
@@ -244,7 +239,8 @@ describe('list_schemes plugin', () => {
     it('should error when neither projectPath nor workspacePath provided', async () => {
       const result = await plugin.handler({});
       expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Either projectPath or workspacePath is required');
+      expect(result.content[0].text).toContain('Missing required session defaults');
+      expect(result.content[0].text).toContain('Provide a project or workspace');
     });
 
     it('should error when both projectPath and workspacePath provided', async () => {
@@ -253,7 +249,7 @@ describe('list_schemes plugin', () => {
         workspacePath: '/path/to/workspace.xcworkspace',
       });
       expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('mutually exclusive');
+      expect(result.content[0].text).toContain('Mutually exclusive parameters provided');
     });
 
     it('should handle empty strings as undefined', async () => {
@@ -262,7 +258,8 @@ describe('list_schemes plugin', () => {
         workspacePath: '',
       });
       expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Either projectPath or workspacePath is required');
+      expect(result.content[0].text).toContain('Missing required session defaults');
+      expect(result.content[0].text).toContain('Provide a project or workspace');
     });
   });
 
diff --git a/src/mcp/tools/project-discovery/__tests__/show_build_settings.test.ts b/src/mcp/tools/project-discovery/__tests__/show_build_settings.test.ts
index 5fd7f186..6084c5a8 100644
--- a/src/mcp/tools/project-discovery/__tests__/show_build_settings.test.ts
+++ b/src/mcp/tools/project-discovery/__tests__/show_build_settings.test.ts
@@ -1,27 +1,32 @@
-import { describe, it, expect } from 'vitest';
+import { describe, it, expect, beforeEach } from 'vitest';
 import { z } from 'zod';
 import { createMockExecutor } from '../../../../test-utils/mock-executors.ts';
 import plugin, { showBuildSettingsLogic } from '../show_build_settings.ts';
+import { sessionStore } from '../../../../utils/session-store.ts';
 
 describe('show_build_settings plugin', () => {
+  beforeEach(() => {
+    sessionStore.clear();
+  });
   describe('Export Field Validation (Literal)', () => {
     it('should have correct name', () => {
       expect(plugin.name).toBe('show_build_settings');
     });
 
     it('should have correct description', () => {
-      expect(plugin.description).toBe(
-        "Shows build settings from either a project or workspace using xcodebuild. Provide exactly one of projectPath or workspacePath, plus scheme. Example: show_build_settings({ projectPath: '/path/to/MyProject.xcodeproj', scheme: 'MyScheme' })",
-      );
+      expect(plugin.description).toBe('Shows xcodebuild build settings.');
     });
 
     it('should have handler function', () => {
       expect(typeof plugin.handler).toBe('function');
     });
 
-    it('should have schema object', () => {
-      expect(plugin.schema).toBeDefined();
-      expect(typeof plugin.schema).toBe('object');
+    it('should expose an empty public schema', () => {
+      const schema = z.object(plugin.schema).strict();
+      expect(schema.safeParse({}).success).toBe(true);
+      expect(schema.safeParse({ projectPath: '/path.xcodeproj' }).success).toBe(false);
+      expect(schema.safeParse({ scheme: 'App' }).success).toBe(false);
+      expect(Object.keys(plugin.schema)).toEqual([]);
     });
   });
 
@@ -50,8 +55,8 @@ describe('show_build_settings plugin', () => {
       });
 
       expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Parameter validation failed');
-      expect(result.content[0].text).toContain('projectPath');
+      expect(result.content[0].text).toContain('Missing required session defaults');
+      expect(result.content[0].text).toContain('Provide a project or workspace');
     });
 
     it('should return success with build settings', async () => {
@@ -169,7 +174,8 @@ describe('show_build_settings plugin', () => {
       });
 
       expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('Either projectPath or workspacePath is required');
+      expect(result.content[0].text).toContain('Missing required session defaults');
+      expect(result.content[0].text).toContain('Provide a project or workspace');
     });
 
     it('should error when both projectPath and workspacePath provided', async () => {
@@ -180,7 +186,7 @@ describe('show_build_settings plugin', () => {
       });
 
       expect(result.isError).toBe(true);
-      expect(result.content[0].text).toContain('mutually exclusive');
+      expect(result.content[0].text).toContain('Mutually exclusive parameters provided');
     });
 
     it('should work with projectPath only', async () => {
@@ -214,6 +220,28 @@ describe('show_build_settings plugin', () => {
     });
   });
 
+  describe('Session requirement handling', () => {
+    it('should require scheme when not provided', async () => {
+      const result = await plugin.handler({
+        projectPath: '/path/to/MyProject.xcodeproj',
+      } as any);
+
+      expect(result.isError).toBe(true);
+      expect(result.content[0].text).toContain('Missing required session defaults');
+      expect(result.content[0].text).toContain('scheme is required');
+    });
+
+    it('should surface project/workspace requirement even with scheme default', async () => {
+      sessionStore.setDefaults({ scheme: 'MyScheme' });
+
+      const result = await plugin.handler({});
+
+      expect(result.isError).toBe(true);
+      expect(result.content[0].text).toContain('Missing required session defaults');
+      expect(result.content[0].text).toContain('Provide a project or workspace');
+    });
+  });
+
   describe('showBuildSettingsLogic function', () => {
     it('should return success with build settings', async () => {
       const calls: any[] = [];
diff --git a/src/mcp/tools/project-discovery/list_schemes.ts b/src/mcp/tools/project-discovery/list_schemes.ts
index 56102e66..82064ffc 100644
--- a/src/mcp/tools/project-discovery/list_schemes.ts
+++ b/src/mcp/tools/project-discovery/list_schemes.ts
@@ -11,7 +11,7 @@ import type { CommandExecutor } from '../../../utils/execution/index.ts';
 import { getDefaultCommandExecutor } from '../../../utils/execution/index.ts';
 import { createTextResponse } from '../../../utils/responses/index.ts';
 import { ToolResponse } from '../../../types/common.ts';
-import { createTypedTool } from '../../../utils/typed-tool-factory.ts';
+import { createSessionAwareTool } from '../../../utils/typed-tool-factory.ts';
 import { nullifyEmptyStrings } from '../../../utils/schema-helpers.ts';
 
 // Unified schema: XOR between projectPath and workspacePath
@@ -109,14 +109,22 @@ export async function listSchemesLogic(
   }
 }
 
+const publicSchemaObject = baseSchemaObject.omit({
+  projectPath: true,
+  workspacePath: true,
+} as const);
+
 export default {
   name: 'list_schemes',
-  description:
-    "Lists available schemes for either a project or a workspace. Provide exactly one of projectPath or workspacePath. Example: list_schemes({ projectPath: '/path/to/MyProject.xcodeproj' })",
-  schema: baseSchemaObject.shape,
-  handler: createTypedTool<ListSchemesParams>(
-    listSchemesSchema as z.ZodType<ListSchemesParams>,
-    listSchemesLogic,
-    getDefaultCommandExecutor,
-  ),
+  description: 'Lists schemes for a project or workspace.',
+  schema: publicSchemaObject.shape,
+  handler: createSessionAwareTool<ListSchemesParams>({
+    internalSchema: listSchemesSchema as unknown as z.ZodType<ListSchemesParams>,
+    logicFunction: listSchemesLogic,
+    getExecutor: getDefaultCommandExecutor,
+    requirements: [
+      { oneOf: ['projectPath', 'workspacePath'], message: 'Provide a project or workspace' },
+    ],
+    exclusivePairs: [['projectPath', 'workspacePath']],
+  }),
 };
diff --git a/src/mcp/tools/project-discovery/show_build_settings.ts b/src/mcp/tools/project-discovery/show_build_settings.ts
index 4a8f0fb4..e2a5b9db 100644
--- a/src/mcp/tools/project-discovery/show_build_settings.ts
+++ b/src/mcp/tools/project-discovery/show_build_settings.ts
@@ -11,7 +11,7 @@ import type { CommandExecutor } from '../../../utils/execution/index.ts';
 import { getDefaultCommandExecutor } from '../../../utils/execution/index.ts';
 import { createTextResponse } from '../../../utils/responses/index.ts';
 import { ToolResponse } from '../../../types/common.ts';
-import { createTypedTool } from '../../../utils/typed-tool-factory.ts';
+import { createSessionAwareTool } from '../../../utils/typed-tool-factory.ts';
 import { nullifyEmptyStrings } from '../../../utils/schema-helpers.ts';
 
 // Unified schema: XOR between projectPath and workspacePath
@@ -102,14 +102,24 @@ export async function showBuildSettingsLogic(
   }
 }
 
+const publicSchemaObject = baseSchemaObject.omit({
+  projectPath: true,
+  workspacePath: true,
+  scheme: true,
+} as const);
+
 export default {
   name: 'show_build_settings',
-  description:
-    "Shows build settings from either a project or workspace using xcodebuild. Provide exactly one of projectPath or workspacePath, plus scheme. Example: show_build_settings({ projectPath: '/path/to/MyProject.xcodeproj', scheme: 'MyScheme' })",
-  schema: baseSchemaObject.shape,
-  handler: createTypedTool<ShowBuildSettingsParams>(
-    showBuildSettingsSchema as z.ZodType<ShowBuildSettingsParams>,
-    showBuildSettingsLogic,
-    getDefaultCommandExecutor,
-  ),
+  description: 'Shows xcodebuild build settings.',
+  schema: publicSchemaObject.shape,
+  handler: createSessionAwareTool<ShowBuildSettingsParams>({
+    internalSchema: showBuildSettingsSchema as unknown as z.ZodType<ShowBuildSettingsParams>,
+    logicFunction: showBuildSettingsLogic,
+    getExecutor: getDefaultCommandExecutor,
+    requirements: [
+      { allOf: ['scheme'], message: 'scheme is required' },
+      { oneOf: ['projectPath', 'workspacePath'], message: 'Provide a project or workspace' },
+    ],
+    exclusivePairs: [['projectPath', 'workspacePath']],
+  }),
 };
diff --git a/src/mcp/tools/utilities/__tests__/clean.test.ts b/src/mcp/tools/utilities/__tests__/clean.test.ts
index 59191cd1..2e4b0269 100644
--- a/src/mcp/tools/utilities/__tests__/clean.test.ts
+++ b/src/mcp/tools/utilities/__tests__/clean.test.ts
@@ -1,20 +1,43 @@
-import { describe, it, expect } from 'vitest';
+import { describe, it, expect, beforeEach } from 'vitest';
+import { z } from 'zod';
 import tool, { cleanLogic } from '../clean.ts';
 import { createMockExecutor } from '../../../../test-utils/mock-executors.ts';
+import { sessionStore } from '../../../../utils/session-store.ts';
 
 describe('clean (unified) tool', () => {
+  beforeEach(() => {
+    sessionStore.clear();
+  });
+
   it('exports correct name/description/schema/handler', () => {
     expect(tool.name).toBe('clean');
-    expect(typeof tool.description).toBe('string');
-    expect(tool.schema).toBeDefined();
+    expect(tool.description).toBe('Cleans build products with xcodebuild.');
     expect(typeof tool.handler).toBe('function');
+
+    const schema = z.object(tool.schema).strict();
+    expect(schema.safeParse({}).success).toBe(true);
+    expect(
+      schema.safeParse({
+        derivedDataPath: '/tmp/Derived',
+        extraArgs: ['--quiet'],
+        preferXcodebuild: true,
+        platform: 'iOS Simulator',
+      }).success,
+    ).toBe(true);
+    expect(schema.safeParse({ configuration: 'Debug' }).success).toBe(false);
+
+    const schemaKeys = Object.keys(tool.schema).sort();
+    expect(schemaKeys).toEqual(
+      ['derivedDataPath', 'extraArgs', 'platform', 'preferXcodebuild'].sort(),
+    );
   });
 
   it('handler validation: error when neither projectPath nor workspacePath provided', async () => {
     const result = await (tool as any).handler({});
     expect(result.isError).toBe(true);
-    const text = String(result.content?.[1]?.text ?? result.content?.[0]?.text ?? '');
-    expect(text).toContain('Invalid parameters');
+    const text = String(result.content?.[0]?.text ?? '');
+    expect(text).toContain('Missing required session defaults');
+    expect(text).toContain('Provide a project or workspace');
   });
 
   it('handler validation: error when both projectPath and workspacePath provided', async () => {
@@ -23,8 +46,8 @@ describe('clean (unified) tool', () => {
       workspacePath: '/w.xcworkspace',
     });
     expect(result.isError).toBe(true);
-    const text = String(result.content?.[1]?.text ?? result.content?.[0]?.text ?? '');
-    expect(text).toContain('Invalid parameters');
+    const text = String(result.content?.[0]?.text ?? '');
+    expect(text).toContain('Mutually exclusive parameters provided');
   });
 
   it('runs project-path flow via logic', async () => {
@@ -45,8 +68,9 @@ describe('clean (unified) tool', () => {
   it('handler validation: requires scheme when workspacePath is provided', async () => {
     const result = await (tool as any).handler({ workspacePath: '/w.xcworkspace' });
     expect(result.isError).toBe(true);
-    const text = String(result.content?.[1]?.text ?? result.content?.[0]?.text ?? '');
-    expect(text).toContain('Invalid parameters');
+    const text = String(result.content?.[0]?.text ?? '');
+    expect(text).toContain('Parameter validation failed');
+    expect(text).toContain('scheme is required when workspacePath is provided');
   });
 
   it('uses iOS platform by default', async () => {
@@ -121,7 +145,8 @@ describe('clean (unified) tool', () => {
       platform: 'InvalidPlatform',
     });
     expect(result.isError).toBe(true);
-    const text = String(result.content?.[1]?.text ?? result.content?.[0]?.text ?? '');
-    expect(text).toContain('Invalid parameters');
+    const text = String(result.content?.[0]?.text ?? '');
+    expect(text).toContain('Parameter validation failed');
+    expect(text).toContain('platform');
   });
 });
diff --git a/src/mcp/tools/utilities/clean.ts b/src/mcp/tools/utilities/clean.ts
index f18db019..062319a4 100644
--- a/src/mcp/tools/utilities/clean.ts
+++ b/src/mcp/tools/utilities/clean.ts
@@ -6,7 +6,7 @@
  */
 
 import { z } from 'zod';
-import { createTypedTool } from '../../../utils/typed-tool-factory.ts';
+import { createSessionAwareTool } from '../../../utils/typed-tool-factory.ts';
 import type { CommandExecutor } from '../../../utils/execution/index.ts';
 import { getDefaultCommandExecutor } from '../../../utils/execution/index.ts';
 import { executeXcodeBuildCommand } from '../../../utils/build/index.ts';
@@ -146,14 +146,24 @@ export async function cleanLogic(
   );
 }
 
+const publicSchemaObject = baseSchemaObject.omit({
+  projectPath: true,
+  workspacePath: true,
+  scheme: true,
+  configuration: true,
+} as const);
+
 export default {
   name: 'clean',
-  description:
-    "Cleans build products for either a project or a workspace using xcodebuild. Provide exactly one of projectPath or workspacePath. Platform defaults to iOS if not specified. Example: clean({ projectPath: '/path/to/MyProject.xcodeproj', scheme: 'MyScheme', platform: 'iOS' })",
-  schema: baseSchemaObject.shape,
-  handler: createTypedTool<CleanParams>(
-    cleanSchema as z.ZodType<CleanParams>,
-    cleanLogic,
-    getDefaultCommandExecutor,
-  ),
+  description: 'Cleans build products with xcodebuild.',
+  schema: publicSchemaObject.shape,
+  handler: createSessionAwareTool<CleanParams>({
+    internalSchema: cleanSchema as unknown as z.ZodType<CleanParams>,
+    logicFunction: cleanLogic,
+    getExecutor: getDefaultCommandExecutor,
+    requirements: [
+      { oneOf: ['projectPath', 'workspacePath'], message: 'Provide a project or workspace' },
+    ],
+    exclusivePairs: [['projectPath', 'workspacePath']],
+  }),
 };
diff --git a/src/utils/typed-tool-factory.ts b/src/utils/typed-tool-factory.ts
index 86a68008..153757da 100644
--- a/src/utils/typed-tool-factory.ts
+++ b/src/utils/typed-tool-factory.ts
@@ -92,7 +92,9 @@ export function createSessionAwareTool<TParams>(opts: {
       // Sanitize args: treat null/undefined as "not provided" so they don't override session defaults
       const sanitizedArgs: Record<string, unknown> = {};
       for (const [k, v] of Object.entries(rawArgs)) {
-        if (v !== null && v !== undefined) sanitizedArgs[k] = v;
+        if (v === null || v === undefined) continue;
+        if (typeof v === 'string' && v.trim() === '') continue;
+        sanitizedArgs[k] = v;
       }
 
       // Factory-level mutual exclusivity check: if user provides multiple explicit values