fix TSamFailedOnly and the output formatting for the go-runner

tests/test_samurai_failed_only_spec.lua

@@ -178,6 +178,49 @@ describe("TSamFailedOnly", function()
     assert.are.same({ "go", "test", "-json", "./...", "-run", "^(TestFoo/first|TestBar)$" }, calls[2].cmd)
   end)
 
+  it("uses go parser for failed-only output (no raw JSON)", function()
+    local json_line = vim.json.encode({
+      Action = "fail",
+      Test = "TestHandleGet/returns_200",
+    })
+
+    local calls, orig_jobstart = stub_jobstart({
+      exit_codes = { 1, 1 },
+      stdout = { { json_line }, { json_line } },
+    })
+
+    local bufnr = mkbuf("/tmp/project/foo_failed_only_output_test.go", "go", {
+      "package main",
+      "import \"testing\"",
+      "",
+      "func TestHandleGet(t *testing.T) {",
+      "  t.Run(\"returns_200\", func(t *testing.T) {",
+      "    -- inside test",
+      "  })",
+      "}",
+    })
+
+    vim.api.nvim_set_current_buf(bufnr)
+
+    core.run_all()
+    core.run_failed_only()
+
+    local out_buf = vim.api.nvim_get_current_buf()
+    local lines = vim.api.nvim_buf_get_lines(out_buf, 0, -1, false)
+
+    vim.fn.jobstart = orig_jobstart
+
+    assert.equals(2, #calls)
+    local has_raw = false
+    for _, line in ipairs(lines) do
+      if line == json_line then
+        has_raw = true
+        break
+      end
+    end
+    assert.is_false(has_raw)
+  end)
+
   it("does not affect TSamLast history", function()
     local json = vim.json.encode({
       testResults = {