fix(symfony): end sub-request spans in handle post-hook to prevent scope leak

[BTC-Tim]

Problem

When Symfony renders an error response, HttpKernel::handle() is called twice: once for the MAIN_REQUEST and once internally as a SUB_REQUEST to render the error page via ExceptionController. The handle post-hook returns early for both calls because $exception is null for a successfully-rendered error page, leaving two scopes on the OTEL context stack:

[top]    scope 1 → sub-request span  (KIND_INTERNAL, child of scope 2)
[bottom] scope 2 → main request span (KIND_SERVER, root, no parent)

When terminate() fires it pops only the topmost scope (scope 1, the sub-request span) and ends it. Scope 2 — the root KIND_SERVER span — is never popped, never ended, and never exported.

In practice: child spans (e.g. Doctrine queries) appear in the trace backend with rootServiceName: <root span not yet received> because the parent never arrives.

This is distinct from the exception case addressed in #317. The bug occurs on normal request handling whenever Symfony produces a non-2xx response (404, 403, 500, etc.).

Fixes open-telemetry/opentelemetry-php#1905

Solution

Detect SUB_REQUEST in the handle post-hook and end those spans immediately, since sub-requests never receive a terminate() call:

$type = $params[1] ?? HttpKernelInterface::MAIN_REQUEST;

// Main request with no exception: terminate() hook handles ending the span
if ($type === HttpKernelInterface::MAIN_REQUEST && null === $exception) {
    return;
}

$span = Span::fromContext($scope->context());
$scope->detach();

if (null !== $exception) { ... }

// Sub-requests don't get a terminate() call — end the span here
if ($type === HttpKernelInterface::SUB_REQUEST) {
    $span->end();
}

By the time terminate() fires, only scope 2 (the main request span) remains on the stack and is properly ended and exported.

Also wraps $prop->inject() in a try-catch in the terminate hook to ensure $span->end() is always reached if response propagation fails.

Tests

• Updated test_http_kernel_handle_subrequest to remove the erroneous terminate() call — standalone sub-requests don't receive terminate() in real Symfony, and the span is now correctly exported from the handle post-hook directly.
• Added test_main_request_span_is_exported_when_subrequest_occurs: verifies that after a MAIN_REQUEST + SUB_REQUEST sequence followed by terminate(), both spans are exported, the sub-request span is a child of the main span, and the main span is a root span.
• Added test_subrequest_scope_does_not_leak_into_next_request: verifies that a subsequent request after a MAIN_REQUEST + SUB_REQUEST cycle starts with a clean context and produces an independent root span.

All 12 tests pass.

[welcome]

Thanks for opening your first pull request! If you haven't yet signed our Contributor License Agreement (CLA), then please do so that we can accept your contribution. A link should appear shortly in this PR if you have not already signed one.

[linux-foundation-easycla]

• ❌ - login: @BTC-Tim / name: Tim Kuijk . The commit (7628881) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

[BTC-Tim]

Sorry, this CLA is new for me / our organization. Review of it is in progress, but might take a while. Feel free to close or otherwise change this PR.