fix: use correct Gamma API parameter for filtering open markets

[pennycott]

📋 Description

The Gamma API requires closed: "false" to filter for open/active markets, not active: "true" which was being used. This caused all market discovery tools (trending, categories, featured, etc.) to return only closed markets from 2020 instead of current active markets.

🎯 Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📖 Documentation update
• 🧪 Test improvements
• 🔧 Refactoring (no functional changes)
• ⚡ Performance improvement

🔗 Related Issues

Markets discovery tools return closed markets from 2020 instead of current open markets when using demo mode (or any mode).

🧪 Testing

Test Configuration

• Python Version: 3.14
• OS: macOS
• Branch: fix/gamma-api-market-filter-parameter

Tests Performed

• All existing tests pass (pytest)
• Added new tests for new functionality
• Tested manually with real Polymarket API
• Verified safety limits still work
• Tested with Claude Desktop integration

Test Results

tests/test_market_tools.py::TestMarketDiscovery::test_search_markets PASSED
tests/test_market_tools.py::TestMarketDiscovery::test_get_trending_markets PASSED
tests/test_market_tools.py::TestMarketDiscovery::test_filter_markets_by_category PASSED
tests/test_market_tools.py::TestMarketDiscovery::test_get_featured_markets PASSED
tests/test_market_tools.py::TestMarketDiscovery::test_get_closing_soon_markets PASSED
tests/test_market_tools.py::TestMarketDiscovery::test_get_sports_markets PASSED
tests/test_market_tools.py::TestMarketDiscovery::test_get_crypto_markets PASSED
tests/test_market_tools.py::TestMarketDiscovery::test_get_event_markets PASSED
======================== 8 passed, 1 warning in 12.01s =========================

📸 Screenshots / Examples

Before fix - returns 2020 closed markets:

Markets from 2020...

After fix - returns current open markets:

# Trending markets now correctly return current 2025 markets:
- "Russia x Ukraine ceasefire in 2025?" (ends: 2025-12-31)
- "Will Bitcoin reach $1,000,000 by December 31, 2025?" (ends: 2025-12-31)
- "Will Bitcoin reach $200,000 by December 31, 2025?" (ends: 2025-12-31)

✅ Checklist

• My code follows the project's code style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published
• I have checked my code and corrected any misspellings
• I have updated the CHANGELOG.md file

🔒 Security

• This PR does not introduce security vulnerabilities
• I have verified no credentials are exposed
• Safety limits are still enforced
• Input validation is adequate

⚠️ Breaking Changes

Does this PR introduce breaking changes?

• Yes (describe below)
• No

💬 Additional Notes

Changed all 6 affected functions in src/polymarket_mcp/tools/market_discovery.py:

• get_trending_markets() - line 137
• filter_markets_by_category() - line 185
• get_featured_markets() - line 249
• get_closing_soon_markets() - line 285
• get_sports_markets() - line 335
• get_crypto_markets() - line 374

The fix simply changes the API parameter from {"active": "true"} to {"closed": "false"} which is what the Gamma API actually expects. This can be verified in test_real_data.py which already uses the correct parameter.

🤖 Generated with Claude Code

[baalimago]

This works! I ran into the same issue and re-did the changes on a local version. Now it shows recent markets.