fix(claude-agents): put the input content write inside the guard too

The prompt write ran before the try that fails the root, so a raise while
serialising it left the root open: never ended, never exported, so the run
disappeared from AI Config Monitoring along with the feature_flag event it
carries. Both paths had it.

Two tests, one per path.

Found by Bugbot on #34, which is this shape in langchain-messages.

Author: apucacao

packages/claude-agents/src/launchdarkly_ai_claude_agents/handler.py

@@ -422,13 +422,6 @@ async def _call_impl(
             config.get("tools"), th
         )
         catalog = ToolCatalog(config.get("tools"), _native_tool_aliases(th))
-        set_input_content_attributes(
-            span,
-            capture_content,
-            system_instructions=opening.system_instructions,
-            messages=opening.messages,
-            tool_definitions=catalog.current,
-        )
 
         # Declared out here so the except clause can end a chat span the throw left open.
         inference = InferenceSpans(config, parent, capture_content, catalog, opening)
@@ -438,6 +431,16 @@ async def _call_impl(
         root_usage_written = False
         gen: AsyncIterator[Any] | None = None
         try:
+            # Inside the guard, because serialising the prompt raises on anything that is not
+            # JSON-serialisable and a raise out here would leave the root open: never ended, never
+            # exported, and the run gone from AI Config Monitoring with the feature_flag event on it.
+            set_input_content_attributes(
+                span,
+                capture_content,
+                system_instructions=opening.system_instructions,
+                messages=opening.messages,
+                tool_definitions=catalog.current,
+            )
             tool_mcp = (
                 await build_tool_mcp(user_config_tools, th)
                 if user_config_tools
@@ -582,13 +585,6 @@ async def _stream_gen(
         config.get("tools"), tool_handlers
     )
     catalog = ToolCatalog(config.get("tools"), _native_tool_aliases(tool_handlers))
-    set_input_content_attributes(
-        span,
-        capture_content,
-        system_instructions=opening.system_instructions,
-        messages=opening.messages,
-        tool_definitions=catalog.current,
-    )
 
     inference = InferenceSpans(config, parent, capture_content, catalog, opening)
     tool_telemetry: ToolTelemetry | None = None
@@ -598,6 +594,16 @@ async def _stream_gen(
     gen: AsyncIterator[Any] | None = None
 
     try:
+        # Inside the guard, because serialising the prompt raises on anything that is not
+        # JSON-serialisable. A raise out here would leave the root open with the `finally` never
+        # entered, so the run would vanish from AI Config Monitoring with its feature_flag event.
+        set_input_content_attributes(
+            span,
+            capture_content,
+            system_instructions=opening.system_instructions,
+            messages=opening.messages,
+            tool_definitions=catalog.current,
+        )
         tool_mcp = (
             await build_tool_mcp(user_config_tools, tool_handlers)
             if user_config_tools

packages/claude-agents/tests/test_handler.py

@@ -1840,3 +1840,53 @@ async def _no_result(**_kwargs: Any) -> AsyncIterator[Any]:
         attrs = root().attributes or {}
         assert "gen_ai.usage.input_tokens" not in attrs
         assert "gen_ai.usage.total_tokens" not in attrs
+
+
+class TestInputWritesNeverLeakASpan:
+    """Serialising the prompt must not be able to strand the root span.
+
+    The input content write ran before the guard that fails the root, so a raise there left it open:
+    never ended, never exported, so the run disappeared from AI Config Monitoring along with the
+    feature_flag event it carries.
+    """
+
+    async def test_the_blocking_root_still_ends(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        async def _q(**_kwargs: Any) -> AsyncIterator[Any]:
+            yield result_message("done")
+
+        monkeypatch.setattr(handler_mod, "query", _q)
+        monkeypatch.setattr(
+            handler_mod,
+            "set_input_content_attributes",
+            MagicMock(side_effect=TypeError("cannot serialise this prompt")),
+        )
+        with pytest.raises(TypeError):
+            await create_claude_agents_handler(capture_content=True)(
+                BASE_CONFIG, "q", {}, {}
+            )
+
+        assert root().end_time is not None, "the root span leaked"
+        assert root().status.status_code == StatusCode.ERROR
+
+    async def test_the_streaming_root_still_ends(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        async def _q(**_kwargs: Any) -> AsyncIterator[Any]:
+            yield stream_event("chunk")
+            yield result_message("done")
+
+        monkeypatch.setattr(handler_mod, "query", _q)
+        monkeypatch.setattr(
+            handler_mod,
+            "set_input_content_attributes",
+            MagicMock(side_effect=TypeError("cannot serialise this prompt")),
+        )
+        with pytest.raises(TypeError):
+            async for _ in await create_claude_agents_handler(
+                capture_content=True
+            ).stream(BASE_CONFIG, "q", {}, {}):
+                pass
+
+        assert root().end_time is not None, "the root span leaked"