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docs/lessons-learned/001-dependency-version-conflicts.md

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+# Lesson Learned #001: Dependency Version Conflicts
+
+## Issue Name
+Dependency Version Conflicts in Requirements Files
+
+## Date
+2025-08-02
+
+## Description
+During project setup, encountered version conflicts with Python package dependencies:
+- `pytest-dash==2.5.0` - Version did not exist in PyPI (max available: 2.1.2)
+- `python-bcrypt==4.1.2` - Incorrect package name (should be `bcrypt==4.1.2`)
+
+## Error Messages
+```
+ERROR: Could not find a version that satisfies the requirement pytest-dash==2.5.0 
+(from versions: 0.1.0, 0.1.1, 0.1.2, 0.1.3, 0.2.0rc1, 0.2.0rc2, 0.2.0rc3, 1.0.0, 1.0.1, 1.1.0, 2.0.0rc1, 2.0.0rc2, 2.0.0rc3, 2.0.0rc4, 2.0.0rc5, 2.0.0, 2.1.0, 2.1.1, 2.1.2)
+
+ERROR: Could not find a version that satisfies the requirement python-bcrypt==4.1.2 
+(from versions: 0.3.1, 0.3.2)
+```
+
+## Root Cause
+1. Incorrect package versions specified without checking PyPI availability
+2. Wrong package name used for bcrypt library
+
+## Solution Applied
+1. **Updated pytest-dash version**:
+   - Changed from `pytest-dash==2.5.0` to `pytest-dash==2.1.2`
+   - Verified latest available version on PyPI
+
+2. **Fixed bcrypt package name**:
+   - Changed from `python-bcrypt==4.1.2` to `bcrypt==4.1.2`
+   - Used correct package name
+
+## Files Modified
+- `requirements-backend.txt` - Fixed bcrypt package name
+- `requirements-frontend.txt` - Updated pytest-dash version
+
+## Prevention Strategy
+1. Always verify package versions exist on PyPI before adding to requirements
+2. Use `pip search` or check PyPI website for correct package names
+3. Consider using version ranges instead of exact pins for non-critical dependencies
+4. Implement CI/CD checks to validate requirements files
+
+## Impact
+- ✅ All dependencies now install successfully
+- ✅ Project setup process is streamlined
+- ✅ Development environment can be started without version conflicts