scaleapi
diff --git a/src/agentex/lib/core/clients/temporal/utils.py b/src/agentex/lib/core/clients/temporal/utils.py
@@ -9,6 +9,8 @@
 from temporalio.converter import PayloadCodec, DataConverter
 from temporalio.contrib.pydantic import pydantic_data_converter
 
+from agentex.lib.core.tracing.temporal import temporal_tracing_interceptors
+
 # class DateTimeJSONEncoder(AdvancedJSONEncoder):
 #     def default(self, o: Any) -> Any:
 #         if isinstance(o, datetime.datetime):
@@ -136,6 +138,9 @@ async def get_temporal_client(
     connect_kwargs: dict[str, Any] = {
         "target_host": temporal_address,
         "plugins": plugins,
+        # Propagate OTel trace context on outbound start_workflow / execute_activity
+        # (enabled by default; AGENTEX_TEMPORAL_TRACE_INTERCEPTOR_ENABLED=false to disable).
+        "interceptors": temporal_tracing_interceptors(),
     }
 
     if data_converter is not None:

diff --git a/src/agentex/lib/core/temporal/workers/worker.py b/src/agentex/lib/core/temporal/workers/worker.py
@@ -29,6 +29,7 @@
 
 from agentex.lib.utils.logging import make_logger
 from agentex.lib.utils.registration import register_agent
+from agentex.lib.core.tracing.temporal import temporal_tracing_interceptors
 from agentex.lib.environment_variables import EnvironmentVariables
 from agentex.lib.core.compat.version_guard import assert_backend_compatible
 
@@ -126,6 +127,9 @@ async def get_temporal_client(
     connect_kwargs: dict[str, Any] = {
         "target_host": temporal_address,
         "plugins": plugins,
+        # Propagate OTel trace context on outbound start_workflow / execute_activity
+        # (enabled by default; AGENTEX_TEMPORAL_TRACE_INTERCEPTOR_ENABLED=false to disable).
+        "interceptors": temporal_tracing_interceptors(),
     }
 
     if data_converter is not None:
@@ -229,7 +233,9 @@ async def run(
             max_concurrent_activities=self.max_concurrent_activities,
             build_id=str(uuid.uuid4()),
             debug_mode=debug_enabled,  # Disable deadlock detection in debug mode
-            interceptors=self.interceptors,  # Pass interceptors to Worker
+            # Tracing interceptor OUTERMOST so business interceptors (and the spans
+            # they create) nest under the propagated workflow/activity span.
+            interceptors=[*temporal_tracing_interceptors(), *self.interceptors],
         )
 
         logger.info(f"Starting workers for task queue: {self.task_queue}")

diff --git a/src/agentex/lib/core/tracing/temporal.py b/src/agentex/lib/core/tracing/temporal.py
@@ -0,0 +1,73 @@
+"""OpenTelemetry trace-context propagation across Temporal boundaries.
+
+Temporal serializes ``start_workflow`` / ``execute_activity`` across (potentially
+cross-process) boundaries, and does NOT carry the active W3C ``traceparent`` by
+default. So any span created inside a workflow or activity becomes a **new
+detached root** -- the trace shatters at every Temporal hop.
+
+This bites agentex directly: ``adk.tracing.span`` runs span creation as a
+Temporal activity when ``in_temporal_workflow()`` is true, so without propagation
+those business spans detach from the turn's obs trace.
+
+Wiring temporalio's first-party ``TracingInterceptor`` onto the Temporal client
+and worker injects the active span context into Temporal headers on the caller
+side and extracts + continues it on the workflow/activity side, using the global
+OpenTelemetry propagator -- so ``client -> workflow -> activity`` is one trace.
+
+Enabled by DEFAULT. Set ``AGENTEX_TEMPORAL_TRACE_INTERCEPTOR_ENABLED=false``
+(also accepts ``0`` / ``no`` / ``off``) to turn it off. It also degrades to a
+no-op -- and never raises -- if temporalio's OpenTelemetry contrib isn't
+importable, so enabling it by default can't break a worker.
+"""
+
+from __future__ import annotations
+
+import os
+from typing import Any
+
+from agentex.lib.utils.logging import make_logger
+
+logger = make_logger(__name__)
+
+_ENABLE_ENV = "AGENTEX_TEMPORAL_TRACE_INTERCEPTOR_ENABLED"
+_FALSEY = {"0", "false", "no", "off"}
+
+
+def temporal_trace_interceptor_enabled() -> bool:
+    """Whether the Temporal OTel trace interceptor should be installed.
+
+    Defaults to True; disabled only when ``AGENTEX_TEMPORAL_TRACE_INTERCEPTOR_ENABLED``
+    is set to a falsy value (``0`` / ``false`` / ``no`` / ``off``)."""
+    return os.environ.get(_ENABLE_ENV, "true").strip().lower() not in _FALSEY
+
+
+def temporal_tracing_interceptors() -> list[Any]:
+    """Interceptors that propagate OpenTelemetry trace context across Temporal.
+
+    Returns ``[TracingInterceptor()]`` (enabled by default) so callers can splat
+    it into a client's / worker's ``interceptors=`` list. Returns ``[]`` when
+    disabled via env, or when temporalio's OpenTelemetry contrib is not
+    importable. Never raises -- observability wiring must not break a worker.
+
+    ``TracingInterceptor`` implements both the client and worker interceptor
+    interfaces, so the same call is used on both sides:
+      - on the **client**, it injects context on outbound ``start_workflow`` /
+        ``execute_activity`` calls;
+      - on the **worker**, it extracts context and roots the workflow / activity
+        execution spans under it.
+    """
+    if not temporal_trace_interceptor_enabled():
+        logger.info("Temporal OTel trace interceptor disabled via %s", _ENABLE_ENV)
+        return []
+    try:
+        from temporalio.contrib.opentelemetry import TracingInterceptor
+
+        # Construct inside the try so a constructor failure (not just a missing
+        # contrib) also falls back to a no-op instead of aborting worker startup.
+        return [TracingInterceptor()]
+    except Exception as exc:  # contrib unavailable OR constructor failure -> no-op, never raise
+        logger.warning(
+            "Temporal OTel trace interceptor unavailable (%s); traces will not propagate across Temporal boundaries.",
+            exc,
+        )
+        return []
diff --git a/tests/lib/core/tracing/test_temporal_interceptor.py b/tests/lib/core/tracing/test_temporal_interceptor.py
@@ -0,0 +1,40 @@
+"""Unit tests for the Temporal OTel trace-interceptor wiring.
+
+Verifies the interceptor is on by default, the opt-out env flag, and the safe
+no-op fallback when temporalio's OpenTelemetry contrib isn't importable.
+"""
+
+import sys
+
+import pytest
+
+from agentex.lib.core.tracing import temporal as temporal_tracing
+
+
+class TestTemporalTraceInterceptor:
+    def test_enabled_by_default(self, monkeypatch):
+        monkeypatch.delenv("AGENTEX_TEMPORAL_TRACE_INTERCEPTOR_ENABLED", raising=False)
+        assert temporal_tracing.temporal_trace_interceptor_enabled() is True
+
+        interceptors = temporal_tracing.temporal_tracing_interceptors()
+        assert len(interceptors) == 1
+        # temporalio's first-party OTel interceptor
+        assert type(interceptors[0]).__name__ == "TracingInterceptor"
+
+    @pytest.mark.parametrize("value", ["false", "0", "no", "off", "FALSE", "Off"])
+    def test_disabled_via_env(self, monkeypatch, value):
+        monkeypatch.setenv("AGENTEX_TEMPORAL_TRACE_INTERCEPTOR_ENABLED", value)
+        assert temporal_tracing.temporal_trace_interceptor_enabled() is False
+        assert temporal_tracing.temporal_tracing_interceptors() == []
+
+    @pytest.mark.parametrize("value", ["true", "1", "yes", "TRUE", "anything"])
+    def test_enabled_for_non_falsy_values(self, monkeypatch, value):
+        monkeypatch.setenv("AGENTEX_TEMPORAL_TRACE_INTERCEPTOR_ENABLED", value)
+        assert temporal_tracing.temporal_trace_interceptor_enabled() is True
+
+    def test_no_op_when_contrib_unimportable(self, monkeypatch):
+        # Enabled, but temporalio's OTel contrib not importable -> [] (never raises),
+        # so default-on can't break a worker that lacks the contrib.
+        monkeypatch.delenv("AGENTEX_TEMPORAL_TRACE_INTERCEPTOR_ENABLED", raising=False)
+        monkeypatch.setitem(sys.modules, "temporalio.contrib.opentelemetry", None)
+        assert temporal_tracing.temporal_tracing_interceptors() == []