UnboundLocalError: 'os' in serve() when both port and callback_url are explicit

[code-tmpl]

Summary

AgentServerHandler.serve() raises UnboundLocalError: cannot access local variable 'os' when port is passed explicitly and agent.base_url is already set (e.g. via callback_url= on the Agent constructor).

Repro

from agentfield import Agent

app = Agent(
    node_id="demo",
    agentfield_server="https://example.invalid",
    callback_url="http://demo.local:8001",
)

if __name__ == "__main__":
    app.serve(host="0.0.0.0", port=8001)

Traceback (most recent call last):
  File ".../main.py", line 49, in <module>
    app.serve(host="0.0.0.0", port=8001)
  File ".../agentfield/agent_server.py", line 1140, in serve
    env_log_level = os.getenv("UVICORN_LOG_LEVEL", log_level).lower()
                    ^^
UnboundLocalError: cannot access local variable 'os' where it is not associated with a value

Root cause

agent_server.py imports os at module level (line 3), but serve() also contains two import os statements inside conditional branches:

• Line 838 — only runs when port is None
• Line 902 — only runs when not self.agent.base_url

Because Python's compiler treats any name assigned anywhere in a function (including via import) as local for the entire function scope, those nested imports shadow the module-level os throughout serve(). When neither branch executes (explicit port + explicit callback_url), the local os is declared but never bound, and line 1140's os.getenv(...) raises UnboundLocalError.

Fix

Drop the two redundant import os lines inside serve() — the module-level import already covers them.

@@ line ~838 @@
         if port is None:
             # Check for AgentField CLI integration via environment variable
-            import os
-
             env_port = os.getenv("PORT")

@@ line ~902 @@
         if not self.agent.base_url:
             # Check AGENT_CALLBACK_URL environment variable before defaulting to localhost
-            import os
             import urllib.parse

             env_callback_url = os.getenv("AGENT_CALLBACK_URL")

Environment

• agentfield 0.1.9
• Python 3.14
• macOS (Darwin 25.3.0, arm64)

[abhinavmathur-atlan]

I checked current main before opening a PR. This appears to already be fixed there: sdk/python/agentfield/agent_server.py has a module-level import os and the serve() branches no longer contain the nested import os statements described in the issue, so the explicit port + explicit callback_url path should not hit the local-shadowing UnboundLocalError anymore. The fix also appears to be mentioned in the changelog. If this still reproduces from main, please share the commit/version and I can take another look.