diff --git a/src/mcp/tools/session-management/__tests__/session_clear_defaults.test.ts b/src/mcp/tools/session-management/__tests__/session_clear_defaults.test.ts
index a5fa8a147..e28f5d676 100644
--- a/src/mcp/tools/session-management/__tests__/session_clear_defaults.test.ts
+++ b/src/mcp/tools/session-management/__tests__/session_clear_defaults.test.ts
@@ -44,7 +44,8 @@ describe('session-clear-defaults tool', () => {
       const current = sessionStore.getAll();
       expect(current.scheme).toBeUndefined();
       expect(current.deviceId).toBeUndefined();
-      expect(current.derivedDataPath).toBeUndefined();
+      // derivedDataPath is computed from projectPath when not explicitly set
+      expect(current.derivedDataPath).toContain('proj-');
       expect(current.projectPath).toBe('/path/to/proj.xcodeproj');
       expect(current.simulatorName).toBe('iPhone 17');
       expect(current.useLatestOS).toBe(true);
diff --git a/src/utils/__tests__/session-store.test.ts b/src/utils/__tests__/session-store.test.ts
index 7d45c6a2f..4488394c4 100644
--- a/src/utils/__tests__/session-store.test.ts
+++ b/src/utils/__tests__/session-store.test.ts
@@ -121,4 +121,49 @@ describe('SessionStore', () => {
     const stored = sessionStore.getAll();
     expect(stored.env).toEqual({ API_KEY: 'secret' });
   });
+
+  it('computes a workspace-scoped derivedDataPath when workspacePath is set', () => {
+    sessionStore.setDefaults({ workspacePath: '/Users/dev/clone-1/MyApp.xcworkspace' });
+
+    const defaults = sessionStore.getAll();
+    expect(defaults.derivedDataPath).toMatch(/MyApp-[a-f0-9]{12}$/);
+  });
+
+  it('computes a project-scoped derivedDataPath when projectPath is set', () => {
+    sessionStore.setDefaults({ projectPath: '/Users/dev/clone-2/MyApp.xcodeproj' });
+
+    const defaults = sessionStore.getAll();
+    expect(defaults.derivedDataPath).toMatch(/MyApp-[a-f0-9]{12}$/);
+  });
+
+  it('does not override an explicitly set derivedDataPath', () => {
+    sessionStore.setDefaults({
+      workspacePath: '/Users/dev/clone-1/MyApp.xcworkspace',
+      derivedDataPath: '/custom/path',
+    });
+
+    expect(sessionStore.getAll().derivedDataPath).toBe('/custom/path');
+  });
+
+  it('produces different hashes for different workspace paths', () => {
+    sessionStore.setDefaults({ workspacePath: '/clone-1/MyApp.xcworkspace' });
+    const path1 = sessionStore.getAll().derivedDataPath;
+
+    sessionStore.clearAll();
+    sessionStore.setDefaults({ workspacePath: '/clone-2/MyApp.xcworkspace' });
+    const path2 = sessionStore.getAll().derivedDataPath;
+
+    expect(path1).not.toBe(path2);
+  });
+
+  it('recomputes derivedDataPath when workspacePath changes', () => {
+    sessionStore.setDefaults({ workspacePath: '/clone-1/MyApp.xcworkspace' });
+    const path1 = sessionStore.getAll().derivedDataPath;
+
+    sessionStore.setDefaults({ workspacePath: '/clone-2/MyApp.xcworkspace' });
+    const path2 = sessionStore.getAll().derivedDataPath;
+
+    expect(path1).not.toBe(path2);
+    expect(path2).toMatch(/MyApp-[a-f0-9]{12}$/);
+  });
 });
diff --git a/src/utils/build-preflight.ts b/src/utils/build-preflight.ts
index 2f3c2d4f0..9c393ed57 100644
--- a/src/utils/build-preflight.ts
+++ b/src/utils/build-preflight.ts
@@ -1,6 +1,7 @@
 import path from 'node:path';
 import os from 'node:os';
 import { resolveEffectiveDerivedDataPath } from './derived-data-path.ts';
+import { sessionStore } from './session-store.ts';
 
 export interface ToolPreflightParams {
   operation:
@@ -94,7 +95,7 @@ export function formatToolPreflight(params: ToolPreflightParams): string {
   }
 
   lines.push(
-    `   Derived Data: ${displayPath(resolveEffectiveDerivedDataPath(params.derivedDataPath))}`,
+    `   Derived Data: ${displayPath(resolveEffectiveDerivedDataPath(params.derivedDataPath ?? sessionStore.get('derivedDataPath')))}`,
   );
 
   if (params.arch) {
diff --git a/src/utils/session-store.ts b/src/utils/session-store.ts
index 2d1cdf1be..4082167be 100644
--- a/src/utils/session-store.ts
+++ b/src/utils/session-store.ts
@@ -1,3 +1,6 @@
+import * as crypto from 'node:crypto';
+import * as path from 'node:path';
+import { DERIVED_DATA_DIR } from './log-paths.ts';
 import { log } from './logger.ts';
 
 export type SessionDefaults = {
@@ -76,7 +79,7 @@ class SessionStore {
   }
 
   setDefaultsForProfile(profile: string | null, partial: Partial<SessionDefaults>): void {
-    const previous = this.getAllForProfile(profile);
+    const previous = this.getRawForProfile(profile);
     const next = { ...previous, ...partial };
     this.setDefaultsForResolvedProfile(profile, next);
     this.revision += 1;
@@ -114,7 +117,7 @@ class SessionStore {
       return;
     }
 
-    const next = this.getAllForProfile(profile);
+    const next = this.getRawForProfile(profile);
     for (const k of keys) delete next[k];
 
     this.setDefaultsForResolvedProfile(profile, next);
@@ -132,6 +135,22 @@ class SessionStore {
   }
 
   getAllForProfile(profile: string | null): SessionDefaults {
+    const result = this.getRawForProfile(profile);
+
+    if (!result.derivedDataPath) {
+      const anchor = result.workspacePath ?? result.projectPath;
+      if (anchor) {
+        const resolved = path.resolve(anchor);
+        const hash = crypto.createHash('sha256').update(resolved).digest('hex').slice(0, 12);
+        const name = path.basename(resolved, path.extname(resolved));
+        result.derivedDataPath = path.join(DERIVED_DATA_DIR, `${name}-${hash}`);
+      }
+    }
+
+    return result;
+  }
+
+  private getRawForProfile(profile: string | null): SessionDefaults {
     const defaults = profile === null ? this.globalDefaults : (this.profiles[profile] ?? {});
     return this.cloneDefaults(defaults);
   }
diff --git a/src/utils/xcodebuild-pipeline.ts b/src/utils/xcodebuild-pipeline.ts
index f2c0d3671..5f9752fad 100644
--- a/src/utils/xcodebuild-pipeline.ts
+++ b/src/utils/xcodebuild-pipeline.ts
@@ -8,6 +8,7 @@ import { createXcodebuildRunState } from './xcodebuild-run-state.ts';
 import type { XcodebuildRunState } from './xcodebuild-run-state.ts';
 import { displayPath } from './build-preflight.ts';
 import { resolveEffectiveDerivedDataPath } from './derived-data-path.ts';
+import { sessionStore } from './session-store.ts';
 import { formatDeviceId } from './device-name-resolver.ts';
 import { createLogCapture, createParserDebugCapture } from './xcodebuild-log-capture.ts';
 import { log as appLog } from './logging/index.ts';
@@ -158,7 +159,8 @@ function buildHeaderParams(
 
   // Always show Derived Data even if not explicitly provided
   if (!result.some((r) => r.label === 'Derived Data')) {
-    result.push({ label: 'Derived Data', value: displayPath(resolveEffectiveDerivedDataPath()) });
+    const effectivePath = resolveEffectiveDerivedDataPath(sessionStore.get('derivedDataPath'));
+    result.push({ label: 'Derived Data', value: displayPath(effectivePath) });
   }
 
   return result;