feat(captcha): image-grid tile solver with centroid mapping

internal/captcha/grid_test.go

@@ -0,0 +1,27 @@
+package captcha
+
+import (
+	"context"
+	"testing"
+
+	"github.com/lukaszraczylo/captcha-solver-mcp/internal/llm"
+)
+
+func TestSolveGrid(t *testing.T) {
+	f := &llm.Fake{VisionResp: `{"tiles":[0,4,8],"confidence":0.8,"recheck_recommended":true}`}
+	res, err := SolveGrid(context.Background(), f, []byte{1}, "image/png", GridOptions{
+		Instruction: "select all buses", Rows: 3, Cols: 3, ImageWidth: 300, ImageHeight: 300,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(res.Tiles) != 3 || res.Tiles[0] != 0 {
+		t.Fatalf("tiles %+v", res.Tiles)
+	}
+	if len(res.Centroids) != 3 || res.Centroids[1].X != 150 { // tile 4 centre
+		t.Fatalf("centroids %+v", res.Centroids)
+	}
+	if !res.RecheckRecommended {
+		t.Fatal("recheck flag lost")
+	}
+}