diff --git a/apps/daemon/src/project-routes.ts b/apps/daemon/src/project-routes.ts
index dc7ba442f..d7e2561db 100644
--- a/apps/daemon/src/project-routes.ts
+++ b/apps/daemon/src/project-routes.ts
@@ -32,7 +32,7 @@ export function registerProjectRoutes(app: Express, ctx: RegisterProjectRoutesDe
   const { listLatestProjectRunStatuses, listProjectsAwaitingInput, normalizeProjectDisplayStatus, composeProjectDisplayStatus, listProjects } = ctx.status;
   const { subscribeFileEvents, activeProjectEventSinks } = ctx.events;
   const { randomId } = ctx.ids;
-  const { validateProjectDesignSystemId } = ctx.validation;
+  const { validateProjectDesignSystemId, validateProjectSkillId } = ctx.validation;
   async function loadPluginRegistryView() {
     const [skills, designSystems] = await Promise.all([
       listSkills(SKILLS_DIR),
@@ -181,6 +181,11 @@ export function registerProjectRoutes(app: Express, ctx: RegisterProjectRoutesDe
         );
       }
       const normalizedDesignSystemId = designSystemValidation.id;
+      const skillValidation = await validateProjectSkillId(skillId);
+      if (!skillValidation.ok) {
+        return sendApiError(res, 400, skillValidation.code, skillValidation.message);
+      }
+      const normalizedSkillId = skillValidation.id;
       const projectMetadata =
         metadata && typeof metadata === 'object'
           ? {
@@ -200,7 +205,7 @@ export function registerProjectRoutes(app: Express, ctx: RegisterProjectRoutesDe
       const project = insertProject(db, {
         id,
         name: name.trim(),
-        skillId: skillId ?? null,
+        skillId: normalizedSkillId,
         designSystemId: normalizedDesignSystemId,
         pendingPrompt: pendingPrompt || null,
         metadata: projectMetadata,
@@ -403,6 +408,13 @@ export function registerProjectRoutes(app: Express, ctx: RegisterProjectRoutesDe
         }
         patch.designSystemId = designSystemValidation.id;
       }
+      if (Object.prototype.hasOwnProperty.call(patch, 'skillId')) {
+        const skillValidation = await validateProjectSkillId(patch.skillId);
+        if (!skillValidation.ok) {
+          return sendApiError(res, 400, skillValidation.code, skillValidation.message);
+        }
+        patch.skillId = skillValidation.id;
+      }
       const project = updateProject(db, req.params.id, patch);
       if (!project)
         return sendApiError(res, 404, 'PROJECT_NOT_FOUND', 'not found');
diff --git a/apps/daemon/src/server.ts b/apps/daemon/src/server.ts
index 0b0b20501..61981ed81 100644
--- a/apps/daemon/src/server.ts
+++ b/apps/daemon/src/server.ts
@@ -3957,6 +3957,29 @@ export async function startServer({
     return { ok: true, id };
   }
 
+  async function validateProjectSkillId(id) {
+    if (id === undefined || id === null || id === '') {
+      return { ok: true, id: null };
+    }
+    if (typeof id !== 'string') {
+      return {
+        ok: false,
+        code: 'INVALID_SKILL_ID',
+        message: 'skillId must be a string or null',
+      };
+    }
+    const skills = await listAllSkillLikeEntries();
+    const resolved = findSkillById(skills, id);
+    if (!resolved) {
+      return {
+        ok: false,
+        code: 'SKILL_NOT_FOUND',
+        message: 'skill not found',
+      };
+    }
+    return { ok: true, id: resolved.id };
+  }
+
   function userDesignSystemWorkspaceProjectId(id) {
     if (typeof id !== 'string' || !id.startsWith('user:')) return null;
     const dirId = id.slice('user:'.length);
@@ -5595,7 +5618,7 @@ export async function startServer({
     EmptyTranscriptError,
     redactSecrets,
   };
-  const validationDeps = { isSafeId, validateExternalApiBaseUrl, validateBaseUrl, validateProjectDesignSystemId };
+  const validationDeps = { isSafeId, validateExternalApiBaseUrl, validateBaseUrl, validateProjectDesignSystemId, validateProjectSkillId };
   const agentDeps = {
     listProviderModels,
     testProviderConnection,
diff --git a/apps/daemon/tests/project-skill-id-validation.test.ts b/apps/daemon/tests/project-skill-id-validation.test.ts
new file mode 100644
index 000000000..6ab9353dd
--- /dev/null
+++ b/apps/daemon/tests/project-skill-id-validation.test.ts
@@ -0,0 +1,225 @@
+import type http from 'node:http';
+import { randomUUID } from 'node:crypto';
+import { afterAll, beforeAll, describe, expect, it } from 'vitest';
+
+import { startServer } from '../src/server.js';
+
+describe('project skillId validation', () => {
+  let server: http.Server;
+  let baseUrl: string;
+  const projectsToClean: string[] = [];
+
+  beforeAll(async () => {
+    const started = (await startServer({ port: 0, returnServer: true })) as {
+      url: string;
+      server: http.Server;
+    };
+    baseUrl = started.url;
+    server = started.server;
+  });
+
+  afterAll(async () => {
+    for (const id of projectsToClean.splice(0)) {
+      await fetch(`${baseUrl}/api/projects/${encodeURIComponent(id)}`, {
+        method: 'DELETE',
+      }).catch(() => {});
+    }
+    await new Promise<void>((resolve) => server.close(() => resolve()));
+  });
+
+  function uniqueId(prefix: string): string {
+    return `${prefix}-${randomUUID()}`;
+  }
+
+  async function createProject(body: Record<string, unknown>) {
+    return fetch(`${baseUrl}/api/projects`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(body),
+    });
+  }
+
+  describe('POST /api/projects', () => {
+    it('rejects unknown skillId with 400 SKILL_NOT_FOUND', async () => {
+      const id = uniqueId('p');
+      const resp = await createProject({
+        id,
+        name: 'Skill id check',
+        skillId: 'definitely-not-a-real-skill',
+      });
+      expect(resp.status).toBe(400);
+      const body = (await resp.json()) as { error: { code: string } };
+      expect(body.error.code).toBe('SKILL_NOT_FOUND');
+      // Project must not have been persisted.
+      const getResp = await fetch(`${baseUrl}/api/projects/${encodeURIComponent(id)}`);
+      expect(getResp.status).toBe(404);
+    });
+
+    it('accepts a valid bundled skill id and stores it as-is', async () => {
+      const id = uniqueId('p');
+      const resp = await createProject({
+        id,
+        name: 'Bundled skill',
+        skillId: 'open-design-landing',
+      });
+      expect(resp.status).toBe(200);
+      projectsToClean.push(id);
+      const body = (await resp.json()) as { project: { skillId: string } };
+      expect(body.project.skillId).toBe('open-design-landing');
+    });
+
+    it('accepts a design-template id (source-of-truth = listAllSkillLikeEntries)', async () => {
+      const id = uniqueId('p');
+      const resp = await createProject({
+        id,
+        name: 'Template skill',
+        skillId: 'dashboard',
+      });
+      expect(resp.status).toBe(200);
+      projectsToClean.push(id);
+      const body = (await resp.json()) as { project: { skillId: string } };
+      expect(body.project.skillId).toBe('dashboard');
+    });
+
+    it('canonicalizes an aliased skill id (editorial-collage → open-design-landing)', async () => {
+      const id = uniqueId('p');
+      const resp = await createProject({
+        id,
+        name: 'Aliased skill',
+        skillId: 'editorial-collage',
+      });
+      expect(resp.status).toBe(200);
+      projectsToClean.push(id);
+      const body = (await resp.json()) as { project: { skillId: string } };
+      expect(body.project.skillId).toBe('open-design-landing');
+    });
+
+    it('normalizes empty string skillId to null', async () => {
+      const id = uniqueId('p');
+      const resp = await createProject({ id, name: 'Empty skill', skillId: '' });
+      expect(resp.status).toBe(200);
+      projectsToClean.push(id);
+      const body = (await resp.json()) as { project: { skillId: string | null } };
+      expect(body.project.skillId).toBeNull();
+    });
+
+    it('treats null skillId as no skill pinned', async () => {
+      const id = uniqueId('p');
+      const resp = await createProject({ id, name: 'Null skill', skillId: null });
+      expect(resp.status).toBe(200);
+      projectsToClean.push(id);
+      const body = (await resp.json()) as { project: { skillId: string | null } };
+      expect(body.project.skillId).toBeNull();
+    });
+
+    it('treats omitted skillId as no skill pinned', async () => {
+      const id = uniqueId('p');
+      const resp = await createProject({ id, name: 'Omitted skill' });
+      expect(resp.status).toBe(200);
+      projectsToClean.push(id);
+      const body = (await resp.json()) as { project: { skillId: string | null } };
+      expect(body.project.skillId).toBeNull();
+    });
+
+    it('rejects numeric skillId with 400 INVALID_SKILL_ID', async () => {
+      const id = uniqueId('p');
+      const resp = await createProject({ id, name: 'Bad type', skillId: 42 });
+      expect(resp.status).toBe(400);
+      const body = (await resp.json()) as { error: { code: string } };
+      expect(body.error.code).toBe('INVALID_SKILL_ID');
+      const getResp = await fetch(`${baseUrl}/api/projects/${encodeURIComponent(id)}`);
+      expect(getResp.status).toBe(404);
+    });
+
+    it('rejects object skillId with 400 INVALID_SKILL_ID', async () => {
+      const id = uniqueId('p');
+      const resp = await createProject({ id, name: 'Bad type', skillId: {} });
+      expect(resp.status).toBe(400);
+      const body = (await resp.json()) as { error: { code: string } };
+      expect(body.error.code).toBe('INVALID_SKILL_ID');
+      const getResp = await fetch(`${baseUrl}/api/projects/${encodeURIComponent(id)}`);
+      expect(getResp.status).toBe(404);
+    });
+  });
+
+  async function patchProject(id: string, patch: Record<string, unknown>) {
+    return fetch(`${baseUrl}/api/projects/${encodeURIComponent(id)}`, {
+      method: 'PATCH',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(patch),
+    });
+  }
+
+  describe('PATCH /api/projects/:id', () => {
+    it('rejects unknown skillId with 400 SKILL_NOT_FOUND', async () => {
+      const id = uniqueId('p');
+      const created = await createProject({ id, name: 'Patch target' });
+      expect(created.status).toBe(200);
+      projectsToClean.push(id);
+
+      const resp = await patchProject(id, { skillId: 'still-not-a-real-skill' });
+      expect(resp.status).toBe(400);
+      const body = (await resp.json()) as { error: { code: string } };
+      expect(body.error.code).toBe('SKILL_NOT_FOUND');
+
+      // skillId on the row stays unchanged (null since create).
+      const get = await fetch(`${baseUrl}/api/projects/${encodeURIComponent(id)}`);
+      const getBody = (await get.json()) as { project: { skillId: string | null } };
+      expect(getBody.project.skillId).toBeNull();
+    });
+
+    it('canonicalizes an aliased skillId on patch', async () => {
+      const id = uniqueId('p');
+      await createProject({ id, name: 'Patch alias' });
+      projectsToClean.push(id);
+      const resp = await patchProject(id, { skillId: 'editorial-collage' });
+      expect(resp.status).toBe(200);
+      const body = (await resp.json()) as { project: { skillId: string } };
+      expect(body.project.skillId).toBe('open-design-landing');
+    });
+
+    it('normalizes empty-string skillId on patch to null', async () => {
+      const id = uniqueId('p');
+      await createProject({ id, name: 'Patch empty', skillId: 'open-design-landing' });
+      projectsToClean.push(id);
+      const resp = await patchProject(id, { skillId: '' });
+      expect(resp.status).toBe(200);
+      const body = (await resp.json()) as { project: { skillId: string | null } };
+      expect(body.project.skillId).toBeNull();
+    });
+
+    it('treats null skillId on patch as unset', async () => {
+      const id = uniqueId('p');
+      await createProject({ id, name: 'Patch null', skillId: 'open-design-landing' });
+      projectsToClean.push(id);
+      const resp = await patchProject(id, { skillId: null });
+      expect(resp.status).toBe(200);
+      const body = (await resp.json()) as { project: { skillId: string | null } };
+      expect(body.project.skillId).toBeNull();
+    });
+
+    it('leaves skillId untouched when the field is omitted from patch', async () => {
+      const id = uniqueId('p');
+      await createProject({ id, name: 'Patch omit', skillId: 'open-design-landing' });
+      projectsToClean.push(id);
+      const resp = await patchProject(id, { name: 'Renamed' });
+      expect(resp.status).toBe(200);
+      const body = (await resp.json()) as { project: { skillId: string; name: string } };
+      expect(body.project.skillId).toBe('open-design-landing');
+      expect(body.project.name).toBe('Renamed');
+    });
+
+    it('rejects numeric skillId on patch with 400 INVALID_SKILL_ID', async () => {
+      const id = uniqueId('p');
+      await createProject({ id, name: 'Patch bad type' });
+      projectsToClean.push(id);
+      const resp = await patchProject(id, { skillId: 42 });
+      expect(resp.status).toBe(400);
+      const body = (await resp.json()) as { error: { code: string } };
+      expect(body.error.code).toBe('INVALID_SKILL_ID');
+      const get = await fetch(`${baseUrl}/api/projects/${encodeURIComponent(id)}`);
+      const getBody = (await get.json()) as { project: { skillId: string | null } };
+      expect(getBody.project.skillId).toBeNull();
+    });
+  });
+});