diff --git a/python/packages/foundry_hosting/agent_framework_foundry_hosting/_toolbox.py b/python/packages/foundry_hosting/agent_framework_foundry_hosting/_toolbox.py
index 0696e70d8c1..46ae6d89ea6 100644
--- a/python/packages/foundry_hosting/agent_framework_foundry_hosting/_toolbox.py
+++ b/python/packages/foundry_hosting/agent_framework_foundry_hosting/_toolbox.py
@@ -22,6 +22,7 @@
 )
 from agent_framework._telemetry import mark_feature_used
 from azure.ai.agentserver.core import get_request_context
+from azure.ai.agentserver.core.platform_headers import FOUNDRY_CALL_ID
 from typing_extensions import override
 
 from ._feature_usage import FeatureIndex
@@ -103,6 +104,8 @@ def __init__(self, credential: AzureCredentialTypes, scope: str) -> None:
 
     def _apply_headers(self, request: httpx.Request, token: AccessToken) -> None:
         request.headers["Authorization"] = f"Bearer {token.token}"
+        # A Request may be retried or reused after an earlier auth flow, so absence must clear prior caller context.
+        request.headers.pop(FOUNDRY_CALL_ID, None)
         for key, value in get_request_context().platform_headers().items():
             request.headers[key] = value
 
diff --git a/python/packages/foundry_hosting/tests/test_toolbox.py b/python/packages/foundry_hosting/tests/test_toolbox.py
index 444b3007260..9ff23376c0e 100644
--- a/python/packages/foundry_hosting/tests/test_toolbox.py
+++ b/python/packages/foundry_hosting/tests/test_toolbox.py
@@ -217,6 +217,38 @@ async def test_auth_flow_omits_call_id_when_absent() -> None:
     assert "x-agent-foundry-call-id" not in prepared.headers
 
 
+async def test_async_auth_flow_removes_call_id_from_reused_request_when_context_absent() -> None:
+    auth = _ToolboxAuth(_FakeCredential(), "scope")  # type: ignore
+    request = httpx.Request("POST", "https://h/toolboxes/tb/mcp")
+
+    token = set_request_context(FoundryAgentRequestContext(call_id="canary-call-id"))
+    try:
+        prepared = await anext(auth.async_auth_flow(request))
+        assert prepared.headers["x-agent-foundry-call-id"] == "canary-call-id"
+    finally:
+        reset_request_context(token)
+
+    prepared = await anext(auth.async_auth_flow(request))
+
+    assert "x-agent-foundry-call-id" not in prepared.headers
+
+
+def test_sync_auth_flow_removes_call_id_from_reused_request_when_context_absent() -> None:
+    auth = _ToolboxAuth(_FakeCredential(), "scope")  # type: ignore
+    request = httpx.Request("POST", "https://h/toolboxes/tb/mcp")
+
+    token = set_request_context(FoundryAgentRequestContext(call_id="canary-call-id"))
+    try:
+        prepared = next(auth.sync_auth_flow(request))
+        assert prepared.headers["x-agent-foundry-call-id"] == "canary-call-id"
+    finally:
+        reset_request_context(token)
+
+    prepared = next(auth.sync_auth_flow(request))
+
+    assert "x-agent-foundry-call-id" not in prepared.headers
+
+
 async def test_close_closes_owned_http_client() -> None:
     toolbox = FoundryToolbox(
         _FakeCredential(),  # type: ignore