fix(api): clamp negative offset instead of erroring + clarify duration_sec=0

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/api/convert_test.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"net/url"
 	"testing"
 
 	"github.com/jackc/pgx/v5/pgtype"
@@ -149,3 +150,78 @@ func TestTrackRefFromNilPositions(t *testing.T) {
 		t.Errorf("nil positions should be 0, got %+v", got)
 	}
 }
+
+func TestParsePaging(t *testing.T) {
+	tests := []struct {
+		name      string
+		query     url.Values
+		wantLimit int
+		wantOffset int
+		wantErr   bool
+	}{
+		{
+			name:       "default (empty values)",
+			query:      url.Values{},
+			wantLimit:  50,
+			wantOffset: 0,
+			wantErr:    false,
+		},
+		{
+			name:       "limit=0 clamps to 1",
+			query:      url.Values{"limit": {"0"}},
+			wantLimit:  1,
+			wantOffset: 0,
+			wantErr:    false,
+		},
+		{
+			name:       "limit=500 clamps to 200",
+			query:      url.Values{"limit": {"500"}},
+			wantLimit:  200,
+			wantOffset: 0,
+			wantErr:    false,
+		},
+		{
+			name:       "offset=-5 clamps to 0",
+			query:      url.Values{"offset": {"-5"}},
+			wantLimit:  50,
+			wantOffset: 0,
+			wantErr:    false,
+		},
+		{
+			name:       "limit=abc errors",
+			query:      url.Values{"limit": {"abc"}},
+			wantLimit:  0,
+			wantOffset: 0,
+			wantErr:    true,
+		},
+		{
+			name:       "offset=xyz errors",
+			query:      url.Values{"offset": {"xyz"}},
+			wantLimit:  0,
+			wantOffset: 0,
+			wantErr:    true,
+		},
+		{
+			name:       "normal values",
+			query:      url.Values{"limit": {"25"}, "offset": {"100"}},
+			wantLimit:  25,
+			wantOffset: 100,
+			wantErr:    false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotLimit, gotOffset, err := parsePaging(tt.query)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("parsePaging() err = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if gotLimit != tt.wantLimit {
+				t.Errorf("parsePaging() limit = %d, want %d", gotLimit, tt.wantLimit)
+			}
+			if gotOffset != tt.wantOffset {
+				t.Errorf("parsePaging() offset = %d, want %d", gotOffset, tt.wantOffset)
+			}
+		})
+	}
+}