In `@router-tests/header_propagation_test.go`:
- Around line 1534-1768: In TestHeaderPropagationOnErrorResponses, within the
"router response headers should be propagated on bad request errors" subtest,
check err returned from xEnv.MakeGraphQLRequest before accessing res (swap the
require.NoError(t, err) to immediately follow the call to
xEnv.MakeGraphQLRequest and move any uses of res or
res.Response.StatusCode/Headers after that check) so you don't dereference res
when the request failed; adjust assertions using res (require.Equal on
StatusCode and header checks) to occur after require.NoError.

In `@router/core/batch.go`:
- Around line 200-206: The batch-level error path omits header propagation:
update the call to writeRequestErrors to include headerPropagation in the
writeRequestErrorsParams (pass the handler's headerPropagation value into the
params, e.g., add headerPropagation: headerPropagation) so router-level response
header expressions are applied for batch parsing/validation failures; then
thread HeaderPropagation through the batch handler's constructor/HandlerOpts at
the call site that builds HandlerOpts (ensure the graph mux/wiring that
constructs HandlerOpts supplies the HeaderPropagation instance).

In `@router/core/errors.go`:
- Around line 215-220: The call to params.logger in the error branch of
params.headerPropagation.ApplyRouterResponseHeaderRules can panic if
params.logger is nil; modify the block that calls ApplyRouterResponseHeaderRules
to check that params.logger != nil before calling params.logger.Error (or use a
safe fallback/no-op logger) so that logging the failure is guarded; ensure the
same nil-check pattern used in other branches of the surrounding function is
applied here for consistency with params.logger usage.

In `@router-tests/error_handling_test.go`:
- Around line 1715-1723: The test is ignoring the error returned by io.ReadAll
which can hide failures; update the test around the io.ReadAll call so you
capture its error and assert it was nil (e.g., replace "body, _ :=
io.ReadAll(resp.Body)" with code that calls io.ReadAll(resp.Body), stores the
error in a variable, and calls require.NoError(t, err) before asserting
require.Empty(t, body)); reference the io.ReadAll call and the
require.NoError/require.Empty assertions to locate the change.

In `@router-tests/http_subscriptions_test.go`:
- Around line 295-307: The test creates an http.Client with no timeout (client
:= http.Client{}) which can hang; update the client instantiation used in this
test to include a timeout consistent with other tests (e.g.,
http.Client{Timeout: time.Second * 100}) so requests and io.ReadAll(resp.Body)
cannot block indefinitely; ensure you import time if not already and keep the
rest of the test flow (req, resp, defer resp.Body.Close()) unchanged.