Fix duplicate filter issues across all search tools

Closes: #817

Problem

Multiple search tools were incorrectly adding duplicate filters to user queries, causing GitHub API validation errors when users provided queries that already contained these filters. This affected three main areas:

1. Search Issues & Pull Requests (search_issues, search_pull_requests)

• Added duplicate is: and repo: filters
• Caused "More than five AND/OR/NOT operators were used" errors
• Broke complex queries with existing filters

2. User & Organization Search (search_users, search_orgs)

• Added duplicate type: filters unconditionally
• Caused HTTP 422 validation errors for queries already containing type:user or type:org

Example bugs:

• Issues: "repo:github/repo is:issue" → "is:issue repo:github/repo is:issue" ❌
• Users: "type:user location:seattle" → "type:user type:user location:seattle" ❌

Solution

Implemented comprehensive duplicate filter prevention across all search tools with a unified approach:

Core Helper Functions

// Detect specific filter:value combinations
func hasSpecificFilter(query, filterType, filterValue string) bool

// Detect any filter of a given type  
func hasFilter(query, filterType string) bool

// Convenience functions for common cases
func hasRepoFilter(query string) bool
func hasTypeFilter(query string) bool

Fixed Search Handlers

Issues/Pull Requests (searchHandler):

// Only add is:searchType if exact filter doesn't exist
if !hasSpecificFilter(query, "is", searchType) {
    query = fmt.Sprintf("is:%s %s", searchType, query)
}

// Only add repo filter if none exists  
if owner != "" && repo != "" && !hasRepoFilter(query) {
    query = fmt.Sprintf("repo:%s/%s %s", owner, repo, query)
}

Users/Organizations (userOrOrgHandler):

// Only add type filter if none exists
if !hasTypeFilter(query) {
    searchQuery = "type:" + accountType + " " + query
}

Enhanced Debugging & Observability

Added comprehensive logging to track filter logic and API interactions:

• Server initialization: Token validation and API endpoint logging
• Query construction: Shows original vs final queries with filter addition logic
• API responses: Detailed HTTP status, headers, and error bodies
• Authentication tracking: Masked token logging for security

This helps diagnose issues and validates that our fixes are working correctly in production.

What This Fixes

✅ search_issues: No more duplicate is:issue or repo: filters
✅ search_pull_requests: No more duplicate is:pr or repo: filters
✅ search_users: No more duplicate type:user filters
✅ search_orgs: No more duplicate type:org filters
✅ Complex queries: OR operators and parentheses work without hitting API limits
✅ User experience: Existing filters in queries are always preserved
✅ Debugging: Clear logging shows exactly what's happening at each step

Testing

Added extensive test coverage across all affected areas:

Unit Tests:

• 25+ test cases for helper functions covering edge cases
• Integration tests for each search tool with duplicate filter scenarios
• Complex query tests with OR operators and parentheses
• Regression tests ensuring existing functionality is preserved

Manual Validation:

• Verified fix works with authentication in place
• Tested against live GitHub API with various query patterns
• Confirmed logging provides clear visibility into filter logic

Real-World Impact

This fix resolves the frustrating experience users had when their perfectly valid GitHub search queries would fail with cryptic API errors. Now users can:

• Use complex queries with confidence: "repo:owner/repo is:issue (label:bug OR label:enhancement OR label:feature)"
• Provide queries with existing filters without worrying about duplicates
• Get clear debug information when issues occur
• Have a consistent experience across all search tools

Alternatives Considered

1. API-level deduplication: Let GitHub handle duplicate filters

   • Discarded: GitHub returns validation errors, poor UX

2. Query rewriting: Parse and reconstruct queries to remove conflicts

   • Discarded: Too complex, fragile, could break edge cases

3. Per-tool fixes: Fix each search tool individually

   • Discarded: Code duplication, inconsistent behavior

4. User education: Document that users shouldn't include certain filters

   • Discarded: Bad UX, GitHub's own UI includes these filters

The chosen approach provides a clean, maintainable solution that works consistently across all search tools while preserving user intent and providing excellent debugging capabilities.

Migration Notes

This is a backward-compatible fix. Existing queries will continue to work exactly as before, but queries that previously failed due to duplicate filters will now succeed.

No configuration changes or user action required - the fix is transparent and automatic.