fix: drop None attributes from OTel span events

docs/observability.md

@@ -35,6 +35,8 @@ pip install httpware[otel]
 
 httpware then adds each event to the current span with `trace.get_current_span().add_event(...)`. It never creates spans itself, so the events only show up when something else has started one. The next section shows the minimal setup that does.
 
+A span event leaves out any attribute whose value is `None`, such as `last_status` when the last attempt raised instead of returning a response, because OpenTelemetry SDKs before 1.45 reject `None` values. The log record still has them.
+
 ## Wiring OpenTelemetry
 
 `httpware[otel]` only installs `opentelemetry-api`. To see the events you also need `opentelemetry-sdk` to collect spans, and `opentelemetry-instrumentation-httpx` to create a span for each HTTP call. httpware's events attach to that span.

src/httpware/_internal/observability.py

@@ -33,7 +33,9 @@ def _emit_event(
     1. Always emits a structured log record at ``level`` with ``extra=attributes``
        (so log aggregators that index ``extra`` see structured fields).
     2. If ``opentelemetry-api`` is installed, calls
-       ``trace.get_current_span().add_event(event_name, attributes=attributes)``.
+       ``trace.get_current_span().add_event(event_name, attributes=attributes)``,
+       leaving out attributes whose value is ``None``: OTel SDKs before 1.45 reject
+       them with a warning. The log record keeps them.
        When no tracer is active, ``get_current_span()`` returns a ``NonRecordingSpan``
        whose ``add_event`` is a documented no-op — so the call is unconditional
        behind the install gate. If the install gate is wrong (the namespace exists
@@ -58,5 +60,6 @@ def _emit_event(
         # add_event (e.g. a recording span with a broken exporter or attribute validation).
         # The structured log record above has already fired; CancelledError/KeyboardInterrupt
         # are not Exception subclasses and will still propagate.
+        span_attributes = {key: value for key, value in safe_attributes.items() if value is not None}
         with contextlib.suppress(Exception):
-            trace.get_current_span().add_event(event_name, attributes=safe_attributes)
+            trace.get_current_span().add_event(event_name, attributes=span_attributes)

tests/test_observability.py

@@ -158,3 +158,26 @@ def test_emit_event_swallows_add_event_failure() -> None:
             attributes={"k": "v"},
         )
     mock_span.add_event.assert_called_once()
+
+
+def test_emit_event_drops_none_attributes_from_otel_event_only(caplog: pytest.LogCaptureFixture) -> None:
+    """OTel SDKs before 1.45 reject None attribute values, so the span event omits them; the log record keeps them."""
+    mock_span = MagicMock(name="MockSpan")
+    with (
+        caplog.at_level(logging.WARNING, logger="httpware.test.observability"),
+        patch("httpware._internal.import_checker.is_otel_installed", True),
+        patch("opentelemetry.trace.get_current_span", return_value=mock_span),
+    ):
+        _emit_event(
+            _TEST_LOGGER,
+            "test.event",
+            level=logging.WARNING,
+            message="partial",
+            attributes={"last_status": None, "url": "https://example.test/x?token=s", "attempts": 3},
+        )
+
+    mock_span.add_event.assert_called_once_with(
+        "test.event",
+        attributes={"url": "https://example.test/x?token=REDACTED", "attempts": 3},
+    )
+    assert caplog.records[0].last_status is None  # ty: ignore[unresolved-attribute]