feat: accept string or number for index parameters (#121)

This change makes index parameters more flexible by accepting both
numeric and string values. LLM agents often pass issue/PR indices
as strings (e.g., "123") since they appear as string identifiers in
URLs and CLI contexts. The implementation:

- Created pkg/params package with GetIndex() helper function
- Updated 25+ tool functions across issue, pull, label, and timetracking operations
- Improved error messages to say "must be a valid integer" instead of misleading "is required"
- Added comprehensive tests for both numeric and string inputs

This improves UX for MCP clients and LLMs while maintaining backward
compatibility with existing numeric callers.

Fixes: #121

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

pkg/params/params.go

@@ -0,0 +1,33 @@
+package params
+
+import (
+	"fmt"
+	"strconv"
+)
+
+// GetIndex extracts an index parameter from MCP tool arguments.
+// It accepts both numeric (float64 from JSON) and string representations.
+// This provides better UX for LLM callers that may naturally use strings
+// for identifiers like issue/PR numbers.
+func GetIndex(args map[string]interface{}, key string) (int64, error) {
+	val, exists := args[key]
+	if !exists {
+		return 0, fmt.Errorf("%s is required", key)
+	}
+
+	// Try float64 (JSON number type)
+	if f, ok := val.(float64); ok {
+		return int64(f), nil
+	}
+
+	// Try string and parse to integer
+	if s, ok := val.(string); ok {
+		i, err := strconv.ParseInt(s, 10, 64)
+		if err != nil {
+			return 0, fmt.Errorf("%s must be a valid integer (got %q)", key, s)
+		}
+		return i, nil
+	}
+
+	return 0, fmt.Errorf("%s must be a number or numeric string", key)
+}

pkg/params/params_test.go

@@ -0,0 +1,116 @@
+package params
+
+import (
+	"testing"
+)
+
+func TestGetIndex(t *testing.T) {
+	tests := []struct {
+		name      string
+		args      map[string]interface{}
+		key       string
+		wantIndex int64
+		wantErr   bool
+		errMsg    string
+	}{
+		{
+			name:      "valid float64",
+			args:      map[string]interface{}{"index": float64(123)},
+			key:       "index",
+			wantIndex: 123,
+			wantErr:   false,
+		},
+		{
+			name:      "valid string",
+			args:      map[string]interface{}{"index": "456"},
+			key:       "index",
+			wantIndex: 456,
+			wantErr:   false,
+		},
+		{
+			name:      "valid string with large number",
+			args:      map[string]interface{}{"index": "999999"},
+			key:       "index",
+			wantIndex: 999999,
+			wantErr:   false,
+		},
+		{
+			name:    "missing parameter",
+			args:    map[string]interface{}{},
+			key:     "index",
+			wantErr: true,
+			errMsg:  "index is required",
+		},
+		{
+			name:    "invalid string (not a number)",
+			args:    map[string]interface{}{"index": "abc"},
+			key:     "index",
+			wantErr: true,
+			errMsg:  "must be a valid integer",
+		},
+		{
+			name:    "invalid string (decimal)",
+			args:    map[string]interface{}{"index": "12.34"},
+			key:     "index",
+			wantErr: true,
+			errMsg:  "must be a valid integer",
+		},
+		{
+			name:    "invalid type (bool)",
+			args:    map[string]interface{}{"index": true},
+			key:     "index",
+			wantErr: true,
+			errMsg:  "must be a number or numeric string",
+		},
+		{
+			name:    "invalid type (map)",
+			args:    map[string]interface{}{"index": map[string]string{"foo": "bar"}},
+			key:     "index",
+			wantErr: true,
+			errMsg:  "must be a number or numeric string",
+		},
+		{
+			name:      "custom key name",
+			args:      map[string]interface{}{"pr_index": "789"},
+			key:       "pr_index",
+			wantIndex: 789,
+			wantErr:   false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotIndex, err := GetIndex(tt.args, tt.key)
+			if tt.wantErr {
+				if err == nil {
+					t.Errorf("GetIndex() expected error but got nil")
+					return
+				}
+				if tt.errMsg != "" && !contains(err.Error(), tt.errMsg) {
+					t.Errorf("GetIndex() error = %v, want error containing %q", err, tt.errMsg)
+				}
+				return
+			}
+			if err != nil {
+				t.Errorf("GetIndex() unexpected error = %v", err)
+				return
+			}
+			if gotIndex != tt.wantIndex {
+				t.Errorf("GetIndex() = %v, want %v", gotIndex, tt.wantIndex)
+			}
+		})
+	}
+}
+
+func contains(s, substr string) bool {
+	return len(s) >= len(substr) && (s == substr || len(s) > len(substr) && (s[:len(substr)] == substr || s[len(s)-len(substr):] == substr || containsMiddle(s, substr)))
+}
+
+func containsMiddle(s, substr string) bool {
+	for i := 0; i <= len(s)-len(substr); i++ {
+		if s[i:i+len(substr)] == substr {
+			return true
+		}
+	}
+	return false
+}