Adding Features to Existing Code

# WRONG - no context (AI invents an incompatible solution):
> Add a password reset feature

# CORRECT - context first:
> I need to add a password reset feature. Here is the relevant context:

  Current UserModel (relevant methods):
  [paste findByEmail(), create(), updatePassword()]

  Current AuthController (relevant methods):
  [paste showLogin(), processLogin()]

  Database: users table has columns: id, email, password_hash, name

  Now add password reset:
  - "Forgot Password" link on login page
  - Form to enter email address
  - Generate a secure token, save to password_resets table (email, token, expires_at)
  - Send email with reset link (use PHP mail())
  - Reset form where user enters new password
  - Invalidate token after use

> Add email notifications to the existing TaskFlow app.
  Read UserModel and TaskModel first.

  When a task is assigned to a user:
  - Send email to the assigned user
  - Subject: "New task assigned: [task title]"
  - Body: task title, description, due date, project name, link to task

  Create: app/services/EmailService.php using PHP mail()
  Update: TaskModel::create() and update() to call EmailService
  Create: config/email.php with FROM_EMAIL, FROM_NAME constants

  Do NOT change any existing method signatures.

> Add file attachments to tasks.
  Read tasks table schema and views/tasks/form.php first.

  - Users can upload up to 5 files per task (PDF, images, docs)
  - Max 10MB per file
  - Store in /storage/attachments/{task_id}/
  - Table: task_attachments (id, task_id, filename, original_name, size, mime_type, uploaded_by, created_at)
  - Show attachment list in task edit form with delete button
  - Download link for each attachment

  Add to views/tasks/form.php (existing form).
  Create app/models/AttachmentModel.php for DB operations.

> Add a global search feature to the app.
  Read the header.php template and UserModel/TaskModel/ProjectModel first.

  - Search box in the navbar (all pages)
  - Searches: projects (name, description), tasks (title, description), users (name, email - admin only)
  - Results page at /search.php?q=query
  - Group results by type with count: "3 Projects, 12 Tasks"
  - Highlight the search term in results (bold)
  - Min 2 characters to search

> Add CSV export for tasks.
  Read TaskModel::getByProject() first.

  Add "Export CSV" button to views/projects/show.php.
  Clicking it calls GET /api/tasks/export?project_id=X
  which returns a CSV file download with columns:
  Task ID, Title, Status, Priority, Assigned To, Due Date, Created At, Completed At

  Implement in api/tasks.php alongside existing endpoints.
  No separate library needed - use fputcsv().

> Add an activity log to track all changes.
  Read TaskModel and ProjectModel first.

  Table: activity_log (id, user_id, action_type, entity_type, entity_id, old_value, new_value, created_at)

  Log these events:
  - task.created, task.updated, task.status_changed, task.deleted
  - project.created, project.archived, project.member_added

  Create: app/services/ActivityLogger.php
  Update: TaskModel and ProjectModel to call ActivityLogger after each operation.

  Show activity log at bottom of views/projects/show.php
  (last 20 events, most recent first).

# Feature 6: Dark mode
"Add a dark mode toggle to the navbar. Store preference in localStorage.
 Toggle a .dark-mode class on body. Write CSS for dark mode in assets/css/app.css
 (dark backgrounds, light text for all components)."

# Feature 7: Two-factor authentication
"Add TOTP-based 2FA to the login flow. Use a QR code library.
 Read AuthController::processLogin() first.
 Users can enable 2FA in their profile settings."

# Feature 8: Recurring tasks
"Add recurring tasks. Read TaskModel::create() first.
 Add recurrence fields to tasks: recurrence_type(daily/weekly/monthly/none), recurrence_end.
 Create a cron-style PHP script that generates the next occurrence when a task is completed."

# Feature 9: Notifications bell
"Add an in-app notification center. Badge on navbar bell icon showing unread count.
 Table: notifications (id, user_id, type, message, entity_type, entity_id, read_at, created_at).
 Dropdown shows last 10 notifications. Mark as read on click."

# Feature 10: Subtasks
"Add subtasks (checklist items) to tasks. Read tasks table schema.
 Table: subtasks (id, task_id, title, completed, sort_order).
 Show as checklist inside task detail. Progress bar showing completion %.
 Task progress bar updates as subtasks are checked."

# Rule 1: New files are safer than modified files
"Create a new EmailService class instead of adding email logic to UserModel"
- New files cannot break existing functionality
- Modified files can introduce bugs in untouched methods

# Rule 2: State what must NOT change
"Add the new method WITHOUT modifying create() or update()"
"Only add to the views, do not touch any PHP files"

# Rule 3: Add feature flags during development
"Wrap the new notification code in: if (FEATURE_NOTIFICATIONS)"
"Add FEATURE_NOTIFICATIONS = false to config/app.php"
- Test the feature flag disabled (everything still works)
- Then enable and test the feature

# Rule 4: Add to a branch, not main
"Before starting: remind me to create a git branch: git checkout -b feature/email-notifications"

# Verify nothing broke:
> Run all existing tests. Did any fail after the changes?
> Review what files were changed. Is anything modified that I did not intend?

# Check the new feature:
> Walk me through the email notification feature you just added.
  What happens step by step when a task is assigned?

# Check for edge cases:
> What happens if the email server is unreachable when a task is assigned?
  Does it fail silently or throw an error that breaks the task save?

# Security check:
> Review the file attachment upload code for security issues.
  Can a user upload PHP files? Can they access other users' files?