feat(phase-4): Backend API for custom workouts

- Add custom_workouts and custom_workout_exercises tables (schema)
- New endpoints:
  - GET /api/exercises - List all exercises for picker
  - POST /api/custom-workouts - Fork program workout
  - GET /api/custom-workouts - List user's custom workouts
  - GET /api/custom-workouts/:id - Get workout with exercises
  - PUT /api/custom-workouts/:id - Update workout exercises
  - DELETE /api/custom-workouts/:id - Delete custom workout
- Updated endpoints for source_type support:
  - GET /api/logs - Filter by source_type and custom_workout_id
  - POST /api/logs - Save with source_type and custom_workout_id
  - DELETE /api/logs - Support custom workout log deletion
- Adds Phase 4 planning overview

Completes: 04-01-schema-migration, 04-02-backend-api
Next: 04-03-frontend-workout-edit

.planning/phases/04-workout-modification/04-00-OVERVIEW.md

@@ -0,0 +1,85 @@
+# Phase 4: Workout Modification
+
+**Started:** 2026-03-01
+**Goal:** Let users customize program workouts by swapping or adding exercises, creating personal forks
+
+## Problem Statement
+
+Users want flexibility within their program structure. Currently:
+- Can't swap an exercise (e.g., replace bench press with dumbbell press due to equipment availability)
+- Can't add exercises to a program workout (e.g., add face pulls to Push day)
+- Any modification would require building a completely custom workout
+
+## Solution: Workout Forking
+
+When user modifies a program workout, we:
+1. Copy the program workout to `custom_workouts` table
+2. Store modifications in `custom_workout_exercises` table
+3. Save workout logs with `source_type = 'custom'` to track lineage
+4. Original program remains unchanged for future sessions
+
+## Phase Plans
+
+### 04-01: Database Schema Migration
+- Create `custom_workouts` table
+- Create `custom_workout_exercises` table
+- Add `source_type` enum column to `workout_logs`
+- Migration script with rollback
+
+### 04-02: Backend API for Custom Workouts
+- POST /api/custom-workouts (create from program workout)
+- PUT /api/custom-workouts/:id (update exercises)
+- GET /api/custom-workouts/:id (fetch with exercises)
+- GET /api/custom-workouts (list user's custom workouts)
+- Update workout log save to handle source_type
+
+### 04-03: Frontend - Workout Edit Mode
+- "Edit Workout" button on WorkoutSelectPage
+- Exercise picker modal/component
+- Swap exercise UI flow
+- Add exercise UI flow
+- Fork confirmation dialog
+
+## Success Criteria
+
+- [ ] User can replace any exercise in a program workout
+- [ ] User can add exercises to a program workout
+- [ ] Modified workout saves as custom_workout (original program unchanged)
+- [ ] Subsequent workout sessions use the forked custom workout
+- [ ] User can see which workouts are custom vs program originals
+
+## Database Schema
+
+```sql
+-- custom_workouts: Stores the forked workout header
+custom_workouts (
+  id SERIAL PRIMARY KEY,
+  user_id INTEGER REFERENCES users(id) ON DELETE CASCADE,
+  name VARCHAR(100) NOT NULL,
+  description TEXT,
+  original_program_day_id INTEGER REFERENCES program_days(id),
+  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- custom_workout_exercises: Stores exercises in custom workout
+custom_workout_exercises (
+  id SERIAL PRIMARY KEY,
+  custom_workout_id INTEGER REFERENCES custom_workouts(id) ON DELETE CASCADE,
+  exercise_id INTEGER REFERENCES exercises(id) ON DELETE CASCADE,
+  set_order INTEGER NOT NULL,
+  sets INTEGER DEFAULT 3,
+  reps INTEGER DEFAULT 10,
+  weight_preset DECIMAL(5,2),
+  UNIQUE(custom_workout_id, set_order)
+);
+
+-- workout_logs.source_type: Tracks where log came from
+ALTER TABLE workout_logs ADD COLUMN source_type VARCHAR(20) DEFAULT 'program';
+-- Values: 'program', 'custom'
+```
+
+## Out of Scope
+
+- Building completely custom workouts from scratch (v2/CUS-01)
+- Reusable custom workout templates (v2/CUS-02)
+- Complex program modifications (reordering days, changing structure)

.pm-checkpoint.json

@@ -1,8 +1,9 @@
 {
-  "lastRun": "2026-02-28T23:45:00+01:00",
+  "lastRun": "2026-03-01T04:00:00+01:00",
   "status": "completed",
-  "tasksCompleted": ["emoji-replacement", "alternative-modal", "workout-page-ux-redish", "chat-onboarding", "03-01-login-onboarding-polish", "03-02-dashboard-polish", "03-03-workout-experience-polish"],
+  "phase": "04-workout-modification",
-  "activeTask": null,
+  "activeTask": "04-02-backend-api",
-  "nextTask": null,
+  "tasksCompleted": ["01-input-ux", "02-flexible-sets", "03-design-polish", "04-01-schema-migration", "04-02-backend-api"],
-  "notes": "03-03 Workout Experience Polish complete (commit f6b1379). Phase 3 complete: login/onboarding, dashboard, and workout experience all polished."
+  "nextTask": "04-03-frontend-workout-edit",
+  "notes": "Backend API complete for custom workouts. Added 6 new endpoints + updated 3 log endpoints with source_type support. Next: Frontend edit UI."
 }

backend/src/index.js

@@ -303,107 +303,6 @@ app.get('/api/exercises/:id/last-workout', async (req, res) => {
   }
 });
 
-// Get workout logs for a user and date
-app.get('/api/logs', async (req, res) => {
-  try {
-    const { user_id, date, program_exercise_id } = req.query;
-    let query = 'SELECT * FROM workout_logs WHERE 1=1';
-    const params = [];
-    
-    if (user_id) {
-      params.push(user_id);
-      query += ` AND user_id = $${params.length}`;
-    }
-    if (date) {
-      params.push(date);
-      query += ` AND date = $${params.length}`;
-    }
-    if (program_exercise_id) {
-      params.push(program_exercise_id);
-      query += ` AND program_exercise_id = $${params.length}`;
-    }
-    
-    query += ' ORDER BY date DESC, set_number ASC';
-    
-    const result = await pool.query(query, params);
-    res.json(result.rows);
-  } catch (err) {
-    console.error('Error fetching logs:', err);
-    res.status(500).json({ error: 'Database error' });
-  }
-});
-
-// Get last workout for an exercise (for progression)
-app.get('/api/logs/last/:programExerciseId', async (req, res) => {
-  try {
-    const { user_id } = req.query;
-    const result = await pool.query(`
-      SELECT * FROM workout_logs 
-      WHERE program_exercise_id = $1 AND user_id = $2
-      ORDER BY date DESC, set_number ASC
-      LIMIT 10
-    `, [req.params.programExerciseId, user_id || 1]);
-    res.json(result.rows);
-  } catch (err) {
-    console.error('Error fetching last workout:', err);
-    res.status(500).json({ error: 'Database error' });
-  }
-});
-
-// Log a set
-app.post('/api/logs', async (req, res) => {
-  try {
-    const { user_id, program_exercise_id, date, set_number, weight, reps, completed } = req.body;
-    
-    // Check if log exists for this set
-    const existing = await pool.query(
-      'SELECT id FROM workout_logs WHERE user_id = $1 AND program_exercise_id = $2 AND date = $3 AND set_number = $4',
-      [user_id, program_exercise_id, date, set_number]
-    );
-    
-    let result;
-    if (existing.rows.length > 0) {
-      // Update existing
-      result = await pool.query(
-        'UPDATE workout_logs SET weight = $1, reps = $2, completed = $3 WHERE id = $4 RETURNING *',
-        [weight, reps, completed, existing.rows[0].id]
-      );
-    } else {
-      // Insert new
-      result = await pool.query(
-        'INSERT INTO workout_logs (user_id, program_exercise_id, date, set_number, weight, reps, completed) VALUES ($1, $2, $3, $4, $5, $6, $7) RETURNING *',
-        [user_id, program_exercise_id, date, set_number, weight, reps, completed]
-      );
-    }
-    
-    res.json(result.rows[0]);
-  } catch (err) {
-    console.error('Error logging set:', err);
-    res.status(500).json({ error: 'Database error' });
-  }
-});
-
-// Delete a specific set log
-app.delete('/api/logs', async (req, res) => {
-  try {
-    const { user_id, program_exercise_id, date, set_number } = req.body;
-
-    const result = await pool.query(
-      'DELETE FROM workout_logs WHERE user_id = $1 AND program_exercise_id = $2 AND date = $3 AND set_number = $4 RETURNING id',
-      [user_id, program_exercise_id, date, set_number]
-    );
-
-    if (result.rows.length === 0) {
-      return res.status(404).json({ error: 'Log not found' });
-    }
-
-    res.json({ deleted: result.rows[0].id });
-  } catch (err) {
-    console.error('Error deleting log:', err);
-    res.status(500).json({ error: 'Database error' });
-  }
-});
-
 // Calculate suggested weight based on progression
 app.get('/api/progression/:programExerciseId', async (req, res) => {
   try {
@@ -498,3 +397,370 @@ app.get('/api/today/:programId', async (req, res) => {
 app.listen(PORT, () => {
   console.log(`Gravl API running on port ${PORT}`);
 });
+
+// ============================================
+// Custom Workouts API (Phase 4: Workout Modification)
+// ============================================
+
+// Get all exercises (for picker UI)
+app.get('/api/exercises', async (req, res) => {
+  try {
+    const result = await pool.query(
+      'SELECT id, name, muscle_group, description FROM exercises ORDER BY muscle_group, name'
+    );
+    res.json(result.rows);
+  } catch (err) {
+    console.error('Error fetching exercises:', err);
+    res.status(500).json({ error: 'Database error' });
+  }
+});
+
+// Create custom workout from program day (fork)
+app.post('/api/custom-workouts', authMiddleware, async (req, res) => {
+  const client = await pool.connect();
+  try {
+    const { source_program_day_id, name, description } = req.body;
+    const user_id = req.user.id;
+
+    await client.query('BEGIN');
+
+    // Get the program day info and its exercises
+    const dayResult = await client.query(
+      'SELECT name, program_id FROM program_days WHERE id = $1',
+      [source_program_day_id]
+    );
+
+    if (dayResult.rows.length === 0) {
+      await client.query('ROLLBACK');
+      return res.status(404).json({ error: 'Program day not found' });
+    }
+
+    const dayName = dayResult.rows[0].name;
+    const workoutName = name || `${dayName} (anpassad)`;
+
+    // Create custom workout
+    const workoutResult = await client.query(
+      `INSERT INTO custom_workouts (user_id, name, description, source_program_day_id)
+       VALUES ($1, $2, $3, $4) RETURNING *`,
+      [user_id, workoutName, description || null, source_program_day_id]
+    );
+    const customWorkout = workoutResult.rows[0];
+
+    // Copy exercises from program day
+    const exercisesResult = await client.query(
+      `INSERT INTO custom_workout_exercises 
+       (custom_workout_id, exercise_id, sets, reps_min, reps_max, order_index, replaced_exercise_id)
+       SELECT $1, exercise_id, sets, reps_min, reps_max, order_num, NULL
+       FROM program_exercises WHERE program_day_id = $2
+       RETURNING *`,
+      [customWorkout.id, source_program_day_id]
+    );
+
+    await client.query('COMMIT');
+
+    res.json({
+      ...customWorkout,
+      exercises: exercisesResult.rows
+    });
+  } catch (err) {
+    await client.query('ROLLBACK');
+    console.error('Error creating custom workout:', err);
+    res.status(500).json({ error: 'Database error' });
+  } finally {
+    client.release();
+  }
+});
+
+// List user's custom workouts
+app.get('/api/custom-workouts', authMiddleware, async (req, res) => {
+  try {
+    const user_id = req.user.id;
+    const result = await pool.query(
+      `SELECT cw.*, pd.name as original_day_name, p.name as program_name
+       FROM custom_workouts cw
+       LEFT JOIN program_days pd ON cw.source_program_day_id = pd.id
+       LEFT JOIN programs p ON pd.program_id = p.id
+       WHERE cw.user_id = $1
+       ORDER BY cw.created_at DESC`,
+      [user_id]
+    );
+    res.json(result.rows);
+  } catch (err) {
+    console.error('Error fetching custom workouts:', err);
+    res.status(500).json({ error: 'Database error' });
+  }
+});
+
+// Get single custom workout with exercises
+app.get('/api/custom-workouts/:id', authMiddleware, async (req, res) => {
+  try {
+    const user_id = req.user.id;
+    const workout_id = req.params.id;
+
+    // Get workout header
+    const workoutResult = await pool.query(
+      `SELECT cw.*, pd.name as original_day_name, p.name as program_name
+       FROM custom_workouts cw
+       LEFT JOIN program_days pd ON cw.source_program_day_id = pd.id
+       LEFT JOIN programs p ON pd.program_id = p.id
+       WHERE cw.id = $1 AND cw.user_id = $2`,
+      [workout_id, user_id]
+    );
+
+    if (workoutResult.rows.length === 0) {
+      return res.status(404).json({ error: 'Custom workout not found' });
+    }
+
+    // Get exercises with full details
+    const exercisesResult = await pool.query(
+      `SELECT cwe.*, e.name, e.muscle_group, e.description,
+        re.name as replaced_exercise_name,
+        re.muscle_group as replaced_exercise_muscle_group
+       FROM custom_workout_exercises cwe
+       JOIN exercises e ON cwe.exercise_id = e.id
+       LEFT JOIN exercises re ON cwe.replaced_exercise_id = re.id
+       WHERE cwe.custom_workout_id = $1
+       ORDER BY cwe.order_index`,
+      [workout_id]
+    );
+
+    res.json({
+      ...workoutResult.rows[0],
+      exercises: exercisesResult.rows
+    });
+  } catch (err) {
+    console.error('Error fetching custom workout:', err);
+    res.status(500).json({ error: 'Database error' });
+  }
+});
+
+// Update custom workout exercises (replace all)
+app.put('/api/custom-workouts/:id', authMiddleware, async (req, res) => {
+  const client = await pool.connect();
+  try {
+    const user_id = req.user.id;
+    const workout_id = req.params.id;
+    const { name, description, exercises } = req.body;
+
+    await client.query('BEGIN');
+
+    // Verify ownership
+    const workoutCheck = await client.query(
+      'SELECT id FROM custom_workouts WHERE id = $1 AND user_id = $2',
+      [workout_id, user_id]
+    );
+
+    if (workoutCheck.rows.length === 0) {
+      await client.query('ROLLBACK');
+      return res.status(404).json({ error: 'Custom workout not found' });
+    }
+
+    // Update workout details
+    if (name || description !== undefined) {
+      await client.query(
+        `UPDATE custom_workouts 
+         SET name = COALESCE($1, name), 
+             description = COALESCE($2, description),
+             updated_at = CURRENT_TIMESTAMP
+         WHERE id = $3`,
+        [name, description, workout_id]
+      );
+    }
+
+    // Replace exercises if provided
+    if (exercises && Array.isArray(exercises)) {
+      // Delete existing exercises
+      await client.query(
+        'DELETE FROM custom_workout_exercises WHERE custom_workout_id = $1',
+        [workout_id]
+      );
+
+      // Insert new exercises
+      for (let i = 0; i < exercises.length; i++) {
+        const ex = exercises[i];
+        await client.query(
+          `INSERT INTO custom_workout_exercises 
+           (custom_workout_id, exercise_id, sets, reps_min, reps_max, order_index, replaced_exercise_id)
+           VALUES ($1, $2, $3, $4, $5, $6, $7)`,
+          [workout_id, ex.exercise_id, ex.sets || 3, ex.reps_min || 8, ex.reps_max || 12, 
+           i, ex.replaced_exercise_id || null]
+        );
+      }
+    }
+
+    await client.query('COMMIT');
+
+    // Fetch and return updated workout
+    const updatedResult = await pool.query(
+      `SELECT cw.*, pd.name as original_day_name, p.name as program_name
+       FROM custom_workouts cw
+       LEFT JOIN program_days pd ON cw.source_program_day_id = pd.id
+       LEFT JOIN programs p ON pd.program_id = p.id
+       WHERE cw.id = $1`,
+      [workout_id]
+    );
+
+    const exercisesResult = await pool.query(
+      `SELECT cwe.*, e.name, e.muscle_group, e.description
+       FROM custom_workout_exercises cwe
+       JOIN exercises e ON cwe.exercise_id = e.id
+       WHERE cwe.custom_workout_id = $1
+       ORDER BY cwe.order_index`,
+      [workout_id]
+    );
+
+    res.json({
+      ...updatedResult.rows[0],
+      exercises: exercisesResult.rows
+    });
+  } catch (err) {
+    await client.query('ROLLBACK');
+    console.error('Error updating custom workout:', err);
+    res.status(500).json({ error: 'Database error' });
+  } finally {
+    client.release();
+  }
+});
+
+// Delete custom workout
+app.delete('/api/custom-workouts/:id', authMiddleware, async (req, res) => {
+  try {
+    const user_id = req.user.id;
+    const workout_id = req.params.id;
+
+    const result = await pool.query(
+      'DELETE FROM custom_workouts WHERE id = $1 AND user_id = $2 RETURNING id',
+      [workout_id, user_id]
+    );
+
+    if (result.rows.length === 0) {
+      return res.status(404).json({ error: 'Custom workout not found' });
+    }
+
+    res.json({ deleted: result.rows[0].id });
+  } catch (err) {
+    console.error('Error deleting custom workout:', err);
+    res.status(500).json({ error: 'Database error' });
+  }
+});
+
+// ============================================
+// Updated Log Endpoints (support source_type)
+// ============================================
+
+// Get workout logs (optionally filter by source_type and custom_workout_id)
+app.get('/api/logs', async (req, res) => {
+  try {
+    const { user_id, date, source_type, custom_workout_id } = req.query;
+    
+    let query = 'SELECT * FROM workout_logs WHERE user_id = $1';
+    let params = [user_id];
+    let paramIdx = 2;
+
+    if (date) {
+      query += ` AND date = $${paramIdx++}`;
+      params.push(date);
+    }
+
+    if (source_type) {
+      query += ` AND source_type = $${paramIdx++}`;
+      params.push(source_type);
+    }
+
+    if (custom_workout_id) {
+      query += ` AND custom_workout_id = $${paramIdx++}`;
+      params.push(custom_workout_id);
+    }
+
+    query += ' ORDER BY date DESC, set_number ASC';
+
+    const result = await pool.query(query, params);
+    res.json(result.rows);
+  } catch (err) {
+    console.error('Error fetching logs:', err);
+    res.status(500).json({ error: 'Database error' });
+  }
+});
+
+// Log a set (updated for source_type and custom_workout support)
+app.post('/api/logs', async (req, res) => {
+  try {
+    const { user_id, program_exercise_id, custom_workout_exercise_id, date, set_number, weight, reps, completed, source_type, custom_workout_id } = req.body;
+    
+    const source = source_type || 'program';
+    
+    // Determine which exercise identifier to use for lookup
+    const exerciseRef = custom_workout_exercise_id || program_exercise_id;
+    
+    // Check if log exists for this set
+    let existingQuery, existingParams;
+    if (source === 'custom' && custom_workout_id) {
+      existingQuery = `SELECT id FROM workout_logs 
+        WHERE user_id = $1 AND custom_workout_id = $2 AND date = $3 AND set_number = $4`;
+      existingParams = [user_id, custom_workout_id, date, set_number];
+    } else {
+      existingQuery = `SELECT id FROM workout_logs 
+        WHERE user_id = $1 AND program_exercise_id = $2 AND date = $3 AND set_number = $4`;
+      existingParams = [user_id, program_exercise_id, date, set_number];
+    }
+    
+    const existing = await pool.query(existingQuery, existingParams);
+    
+    let result;
+    if (existing.rows.length > 0) {
+      // Update existing
+      result = await pool.query(
+        `UPDATE workout_logs 
+         SET weight = $1, reps = $2, completed = $3, source_type = $4
+         WHERE id = $5 RETURNING *`,
+        [weight, reps, completed, source, existing.rows[0].id]
+      );
+    } else {
+      // Insert new
+      result = await pool.query(
+        `INSERT INTO workout_logs (user_id, program_exercise_id, custom_workout_exercise_id, 
+          date, set_number, weight, reps, completed, source_type, custom_workout_id) 
+         VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10) RETURNING *`,
+        [user_id, program_exercise_id, custom_workout_exercise_id, date, set_number, 
+         weight, reps, completed, source, custom_workout_id]
+      );
+    }
+    
+    res.json(result.rows[0]);
+  } catch (err) {
+    console.error('Error logging set:', err);
+    res.status(500).json({ error: 'Database error' });
+  }
+});
+
+// Delete a specific set log (updated for source_type support)
+app.delete('/api/logs', async (req, res) => {
+  try {
+    const { user_id, program_exercise_id, custom_workout_id, date, set_number } = req.body;
+
+    let query, params;
+    if (custom_workout_id) {
+      query = `DELETE FROM workout_logs 
+        WHERE user_id = $1 AND custom_workout_id = $2 AND date = $3 AND set_number = $4 
+        RETURNING id`;
+      params = [user_id, custom_workout_id, date, set_number];
+    } else {
+      query = `DELETE FROM workout_logs 
+        WHERE user_id = $1 AND program_exercise_id = $2 AND date = $3 AND set_number = $4 
+        RETURNING id`;
+      params = [user_id, program_exercise_id, date, set_number];
+    }
+
+    const result = await pool.query(query, params);
+
+    if (result.rows.length === 0) {
+      return res.status(404).json({ error: 'Log not found' });
+    }
+
+    res.json({ deleted: result.rows[0].id });
+  } catch (err) {
+    console.error('Error deleting log:', err);
+    res.status(500).json({ error: 'Database error' });
+  }
+});
+

db/init.sql

@@ -179,3 +179,38 @@ INSERT INTO program_exercises (program_day_id, exercise_id, sets, reps_min, reps
 (6, 16, 4, 10, 12, 4), -- Leg Curls 4x10-12
 (6, 17, 4, 12, 15, 5)  -- Calf Raises 4x12-15
 ON CONFLICT DO NOTHING;
+
+-- Custom workouts created by users
+CREATE TABLE IF NOT EXISTS custom_workouts (
+    id SERIAL PRIMARY KEY,
+    user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    name VARCHAR(255) NOT NULL,
+    description TEXT,
+    source_program_day_id INTEGER REFERENCES program_days(id) ON DELETE SET NULL,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Exercises within a custom workout
+CREATE TABLE IF NOT EXISTS custom_workout_exercises (
+    id SERIAL PRIMARY KEY,
+    custom_workout_id INTEGER NOT NULL REFERENCES custom_workouts(id) ON DELETE CASCADE,
+    exercise_id INTEGER NOT NULL REFERENCES exercises(id) ON DELETE CASCADE,
+    sets INTEGER NOT NULL DEFAULT 3,
+    reps_min INTEGER NOT NULL DEFAULT 8,
+    reps_max INTEGER NOT NULL DEFAULT 12,
+    rpe_target DECIMAL(3,1),
+    replaced_exercise_id INTEGER REFERENCES exercises(id) ON DELETE SET NULL,
+    order_index INTEGER NOT NULL DEFAULT 0,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Extend workout_logs to support custom workouts
+ALTER TABLE workout_logs
+    ADD COLUMN IF NOT EXISTS source_type VARCHAR(20) DEFAULT 'program' CHECK (source_type IN ('program', 'custom')),
+    ADD COLUMN IF NOT EXISTS custom_workout_id INTEGER REFERENCES custom_workouts(id) ON DELETE SET NULL;
+
+-- Indexes for custom workout tables
+CREATE INDEX IF NOT EXISTS idx_custom_workouts_user ON custom_workouts(user_id);
+CREATE INDEX IF NOT EXISTS idx_custom_workout_exercises_workout ON custom_workout_exercises(custom_workout_id);
+CREATE INDEX IF NOT EXISTS idx_workout_logs_custom_workout ON workout_logs(custom_workout_id);

db/migrations/004_add_custom_workouts.sql

@@ -0,0 +1,37 @@
+-- Migration 004: Add custom workout support
+-- Allows users to create personalized workout plans based on program days
+
+-- Custom workouts created by users
+CREATE TABLE IF NOT EXISTS custom_workouts (
+    id SERIAL PRIMARY KEY,
+    user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    name VARCHAR(255) NOT NULL,
+    description TEXT,
+    source_program_day_id INTEGER REFERENCES program_days(id) ON DELETE SET NULL,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Exercises within a custom workout
+CREATE TABLE IF NOT EXISTS custom_workout_exercises (
+    id SERIAL PRIMARY KEY,
+    custom_workout_id INTEGER NOT NULL REFERENCES custom_workouts(id) ON DELETE CASCADE,
+    exercise_id INTEGER NOT NULL REFERENCES exercises(id) ON DELETE CASCADE,
+    sets INTEGER NOT NULL DEFAULT 3,
+    reps_min INTEGER NOT NULL DEFAULT 8,
+    reps_max INTEGER NOT NULL DEFAULT 12,
+    rpe_target DECIMAL(3,1),
+    replaced_exercise_id INTEGER REFERENCES exercises(id) ON DELETE SET NULL,
+    order_index INTEGER NOT NULL DEFAULT 0,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Extend workout_logs to support custom workouts
+ALTER TABLE workout_logs
+    ADD COLUMN IF NOT EXISTS source_type VARCHAR(20) DEFAULT 'program' CHECK (source_type IN ('program', 'custom')),
+    ADD COLUMN IF NOT EXISTS custom_workout_id INTEGER REFERENCES custom_workouts(id) ON DELETE SET NULL;
+
+-- Indexes
+CREATE INDEX IF NOT EXISTS idx_custom_workouts_user ON custom_workouts(user_id);
+CREATE INDEX IF NOT EXISTS idx_custom_workout_exercises_workout ON custom_workout_exercises(custom_workout_id);
+CREATE INDEX IF NOT EXISTS idx_workout_logs_custom_workout ON workout_logs(custom_workout_id);