diff --git a/server.js b/server.js
index 7ee363f1..6a87bc51 100644
--- a/server.js
+++ b/server.js
@@ -431,8 +431,49 @@ app.get('/claude/api/claude/sessions', requireAuth, (req, res) => {
 
 app.post('/claude/api/claude/sessions', requireAuth, (req, res) => {
   try {
-    const { workingDir, metadata } = req.body;
-    const session = claudeService.createSession({ workingDir, metadata });
+    const { workingDir, metadata, projectId } = req.body;
+
+    // Validate projectId if provided
+    let validatedProjectId = null;
+    if (projectId !== null && projectId !== undefined) {
+      validatedProjectId = validateProjectId(projectId);
+      if (!validatedProjectId) {
+        return res.status(400).json({ error: 'Invalid project ID' });
+      }
+
+      // Verify project exists and is not deleted
+      const project = db.prepare(`
+        SELECT id FROM projects
+        WHERE id = ? AND deletedAt IS NULL
+      `).get(validatedProjectId);
+
+      if (!project) {
+        return res.status(404).json({ error: 'Project not found' });
+      }
+    }
+
+    // Create session with projectId in metadata
+    const sessionMetadata = {
+      ...metadata,
+      ...(validatedProjectId ? { projectId: validatedProjectId } : {})
+    };
+    const session = claudeService.createSession({ workingDir, metadata: sessionMetadata });
+
+    // Store session in database with projectId
+    db.prepare(`
+      INSERT INTO sessions (id, projectId, deletedAt)
+      VALUES (?, ?, NULL)
+    `).run(session.id, validatedProjectId);
+
+    // Update project's lastActivity if session was assigned to a project
+    if (validatedProjectId) {
+      const now = new Date().toISOString();
+      db.prepare(`
+        UPDATE projects
+        SET lastActivity = ?
+        WHERE id = ?
+      `).run(now, validatedProjectId);
+    }
 
     res.json({
       success: true,
@@ -441,7 +482,8 @@ app.post('/claude/api/claude/sessions', requireAuth, (req, res) => {
         pid: session.pid,
         workingDir: session.workingDir,
         status: session.status,
-        createdAt: session.createdAt
+        createdAt: session.createdAt,
+        projectId: validatedProjectId
       }
     });
   } catch (error) {
@@ -578,6 +620,9 @@ app.post('/claude/api/claude/sessions/:id/duplicate', requireAuth, (req, res) =>
       return res.status(400).json({ error: 'Invalid working directory' });
     }
 
+    // Get projectId from source session (if exists)
+    const sourceProjectId = sourceSession.metadata.projectId || null;
+
     // Create new session with same settings
     const newSession = claudeService.createSession({
       workingDir: sourceSession.workingDir,
@@ -588,6 +633,22 @@ app.post('/claude/api/claude/sessions/:id/duplicate', requireAuth, (req, res) =>
       }
     });
 
+    // Store duplicated session in database with same projectId as source
+    db.prepare(`
+      INSERT INTO sessions (id, projectId, deletedAt)
+      VALUES (?, ?, NULL)
+    `).run(newSession.id, sourceProjectId);
+
+    // Update project's lastActivity if session was assigned to a project
+    if (sourceProjectId) {
+      const now = new Date().toISOString();
+      db.prepare(`
+        UPDATE projects
+        SET lastActivity = ?
+        WHERE id = ?
+      `).run(now, sourceProjectId);
+    }
+
     res.json({
       success: true,
       session: {
@@ -596,7 +657,8 @@ app.post('/claude/api/claude/sessions/:id/duplicate', requireAuth, (req, res) =>
         workingDir: newSession.workingDir,
         status: newSession.status,
         createdAt: newSession.createdAt,
-        metadata: newSession.metadata
+        metadata: newSession.metadata,
+        projectId: sourceProjectId
       }
     });
   } catch (error) {