We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Capture Celery Time-in-queue


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `src/scout_apm/celery.py`
Content:
```
1 # coding=utf-8
2 from __future__ import absolute_import, division, print_function, unicode_literals
3 
4 from celery.signals import task_postrun, task_prerun
5 
6 import scout_apm.core
7 from scout_apm.core.tracked_request import TrackedRequest
8 
9 
10 def prerun_callback(task=None, **kwargs):
11     tracked_request = TrackedRequest.instance()
12     tracked_request.mark_real_request()
13 
14     delivery_info = task.request.delivery_info
15     tracked_request.tag("is_eager", delivery_info.get("is_eager", False))
16     tracked_request.tag("exchange", delivery_info.get("exchange", "unknown"))
17     tracked_request.tag("routing_key", delivery_info.get("routing_key", "unknown"))
18     tracked_request.tag("queue", delivery_info.get("queue", "unknown"))
19 
20     tracked_request.start_span(operation=("Job/" + task.name))
21 
22 
23 def postrun_callback(task=None, **kwargs):
24     tracked_request = TrackedRequest.instance()
25     tracked_request.stop_span()
26 
27 
28 def install():
29     installed = scout_apm.core.install()
30     if not installed:
31         return
32 
33     task_prerun.connect(prerun_callback)
34     task_postrun.connect(postrun_callback)
35 
36 
37 def uninstall():
38     task_prerun.disconnect(prerun_callback)
39     task_postrun.disconnect(postrun_callback)
40
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/src/scout_apm/celery.py b/src/scout_apm/celery.py
--- a/src/scout_apm/celery.py
+++ b/src/scout_apm/celery.py
@@ -1,16 +1,34 @@
 # coding=utf-8
 from __future__ import absolute_import, division, print_function, unicode_literals
 
-from celery.signals import task_postrun, task_prerun
+import datetime as dt
+
+from celery.signals import before_task_publish, task_postrun, task_prerun
 
 import scout_apm.core
+from scout_apm.compat import datetime_to_timestamp
 from scout_apm.core.tracked_request import TrackedRequest
 
 
+def before_publish_callback(headers=None, properties=None, **kwargs):
+    if "scout_task_start" not in headers:
+        headers["scout_task_start"] = datetime_to_timestamp(dt.datetime.utcnow())
+
+
 def prerun_callback(task=None, **kwargs):
     tracked_request = TrackedRequest.instance()
     tracked_request.mark_real_request()
 
+    start = getattr(task.request, "scout_task_start", None)
+    if start is not None:
+        now = datetime_to_timestamp(dt.datetime.utcnow())
+        try:
+            queue_time = now - start
+        except TypeError:
+            pass
+        else:
+            tracked_request.tag("queue_time", queue_time)
+
     delivery_info = task.request.delivery_info
     tracked_request.tag("is_eager", delivery_info.get("is_eager", False))
     tracked_request.tag("exchange", delivery_info.get("exchange", "unknown"))
@@ -30,10 +48,12 @@
     if not installed:
         return
 
+    before_task_publish.connect(before_publish_callback)
     task_prerun.connect(prerun_callback)
     task_postrun.connect(postrun_callback)
 
 
 def uninstall():
+    before_task_publish.disconnect(before_publish_callback)
     task_prerun.disconnect(prerun_callback)
     task_postrun.disconnect(postrun_callback)

{"golden_diff": "diff --git a/src/scout_apm/celery.py b/src/scout_apm/celery.py\n--- a/src/scout_apm/celery.py\n+++ b/src/scout_apm/celery.py\n@@ -1,16 +1,34 @@\n # coding=utf-8\n from __future__ import absolute_import, division, print_function, unicode_literals\n \n-from celery.signals import task_postrun, task_prerun\n+import datetime as dt\n+\n+from celery.signals import before_task_publish, task_postrun, task_prerun\n \n import scout_apm.core\n+from scout_apm.compat import datetime_to_timestamp\n from scout_apm.core.tracked_request import TrackedRequest\n \n \n+def before_publish_callback(headers=None, properties=None, **kwargs):\n+    if \"scout_task_start\" not in headers:\n+        headers[\"scout_task_start\"] = datetime_to_timestamp(dt.datetime.utcnow())\n+\n+\n def prerun_callback(task=None, **kwargs):\n     tracked_request = TrackedRequest.instance()\n     tracked_request.mark_real_request()\n \n+    start = getattr(task.request, \"scout_task_start\", None)\n+    if start is not None:\n+        now = datetime_to_timestamp(dt.datetime.utcnow())\n+        try:\n+            queue_time = now - start\n+        except TypeError:\n+            pass\n+        else:\n+            tracked_request.tag(\"queue_time\", queue_time)\n+\n     delivery_info = task.request.delivery_info\n     tracked_request.tag(\"is_eager\", delivery_info.get(\"is_eager\", False))\n     tracked_request.tag(\"exchange\", delivery_info.get(\"exchange\", \"unknown\"))\n@@ -30,10 +48,12 @@\n     if not installed:\n         return\n \n+    before_task_publish.connect(before_publish_callback)\n     task_prerun.connect(prerun_callback)\n     task_postrun.connect(postrun_callback)\n \n \n def uninstall():\n+    before_task_publish.disconnect(before_publish_callback)\n     task_prerun.disconnect(prerun_callback)\n     task_postrun.disconnect(postrun_callback)\n", "issue": "Capture Celery Time-in-queue\n\n", "before_files": [{"content": "# coding=utf-8\nfrom __future__ import absolute_import, division, print_function, unicode_literals\n\nfrom celery.signals import task_postrun, task_prerun\n\nimport scout_apm.core\nfrom scout_apm.core.tracked_request import TrackedRequest\n\n\ndef prerun_callback(task=None, **kwargs):\n    tracked_request = TrackedRequest.instance()\n    tracked_request.mark_real_request()\n\n    delivery_info = task.request.delivery_info\n    tracked_request.tag(\"is_eager\", delivery_info.get(\"is_eager\", False))\n    tracked_request.tag(\"exchange\", delivery_info.get(\"exchange\", \"unknown\"))\n    tracked_request.tag(\"routing_key\", delivery_info.get(\"routing_key\", \"unknown\"))\n    tracked_request.tag(\"queue\", delivery_info.get(\"queue\", \"unknown\"))\n\n    tracked_request.start_span(operation=(\"Job/\" + task.name))\n\n\ndef postrun_callback(task=None, **kwargs):\n    tracked_request = TrackedRequest.instance()\n    tracked_request.stop_span()\n\n\ndef install():\n    installed = scout_apm.core.install()\n    if not installed:\n        return\n\n    task_prerun.connect(prerun_callback)\n    task_postrun.connect(postrun_callback)\n\n\ndef uninstall():\n    task_prerun.disconnect(prerun_callback)\n    task_postrun.disconnect(postrun_callback)\n", "path": "src/scout_apm/celery.py"}], "after_files": [{"content": "# coding=utf-8\nfrom __future__ import absolute_import, division, print_function, unicode_literals\n\nimport datetime as dt\n\nfrom celery.signals import before_task_publish, task_postrun, task_prerun\n\nimport scout_apm.core\nfrom scout_apm.compat import datetime_to_timestamp\nfrom scout_apm.core.tracked_request import TrackedRequest\n\n\ndef before_publish_callback(headers=None, properties=None, **kwargs):\n    if \"scout_task_start\" not in headers:\n        headers[\"scout_task_start\"] = datetime_to_timestamp(dt.datetime.utcnow())\n\n\ndef prerun_callback(task=None, **kwargs):\n    tracked_request = TrackedRequest.instance()\n    tracked_request.mark_real_request()\n\n    start = getattr(task.request, \"scout_task_start\", None)\n    if start is not None:\n        now = datetime_to_timestamp(dt.datetime.utcnow())\n        try:\n            queue_time = now - start\n        except TypeError:\n            pass\n        else:\n            tracked_request.tag(\"queue_time\", queue_time)\n\n    delivery_info = task.request.delivery_info\n    tracked_request.tag(\"is_eager\", delivery_info.get(\"is_eager\", False))\n    tracked_request.tag(\"exchange\", delivery_info.get(\"exchange\", \"unknown\"))\n    tracked_request.tag(\"routing_key\", delivery_info.get(\"routing_key\", \"unknown\"))\n    tracked_request.tag(\"queue\", delivery_info.get(\"queue\", \"unknown\"))\n\n    tracked_request.start_span(operation=(\"Job/\" + task.name))\n\n\ndef postrun_callback(task=None, **kwargs):\n    tracked_request = TrackedRequest.instance()\n    tracked_request.stop_span()\n\n\ndef install():\n    installed = scout_apm.core.install()\n    if not installed:\n        return\n\n    before_task_publish.connect(before_publish_callback)\n    task_prerun.connect(prerun_callback)\n    task_postrun.connect(postrun_callback)\n\n\ndef uninstall():\n    before_task_publish.disconnect(before_publish_callback)\n    task_prerun.disconnect(prerun_callback)\n    task_postrun.disconnect(postrun_callback)\n", "path": "src/scout_apm/celery.py"}]}