chore(py): use timezone-aware UTC timestamps [skip changelog]

Author: liuyuran02

examples/quickstart/agent_summarizer.py

@@ -21,7 +21,7 @@
 
 
 def now() -> str:
-    return datetime.datetime.utcnow().isoformat() + "Z"
+    return datetime.datetime.now(datetime.timezone.utc).isoformat().replace("+00:00", "Z")
 
 
 def make_id() -> str:

examples/quickstart/orchestrator.py

@@ -21,7 +21,7 @@
 # ── ACP message helpers (inline, no SDK dependency) ──────────────────────────
 
 def now() -> str:
-    return datetime.datetime.utcnow().isoformat() + "Z"
+    return datetime.datetime.now(datetime.timezone.utc).isoformat().replace("+00:00", "Z")
 
 def make_id() -> str:
     return "msg_" + uuid.uuid4().hex[:12]

relay/acp_relay.py

@@ -3453,7 +3453,9 @@ def _init_security_posture():
     """v2.71: Populate _SECURITY_POSTURE with real installed package versions at startup."""
     import importlib.metadata as _ilm
     import datetime as _dt
-    _SECURITY_POSTURE["scanned_at"] = _dt.datetime.utcnow().isoformat() + "Z"
+    _SECURITY_POSTURE["scanned_at"] = (
+        _dt.datetime.now(_dt.timezone.utc).isoformat().replace("+00:00", "Z")
+    )
     for comp in _SECURITY_POSTURE["components"]:
         try:
             comp["version"] = _ilm.version(comp["name"])
@@ -13661,7 +13663,9 @@ def _do_cancel(tid):
             # Build and store evidence entry
             entries = _task_evidence.setdefault(task_id, [])
             seq = len(entries)
-            recorded_at = datetime.datetime.utcnow().isoformat() + "Z"
+            recorded_at = (
+                datetime.datetime.now(datetime.timezone.utc).isoformat().replace("+00:00", "Z")
+            )
             entry = {
                 "seq":         seq,
                 "event_type":  event_type,

sdk/python/acp_sdk/message.py

@@ -68,7 +68,11 @@ class ACPMessage:
     # Auto-generated fields
     acp: str = "0.1"
     id: str = field(default_factory=lambda: "msg_" + str(uuid.uuid4()).replace("-", "")[:16])
-    ts: str = field(default_factory=lambda: datetime.datetime.utcnow().isoformat() + "Z")
+    ts: str = field(
+        default_factory=lambda: datetime.datetime.now(datetime.timezone.utc)
+        .isoformat()
+        .replace("+00:00", "Z")
+    )
 
     # Optional fields
     correlation_id: Optional[str] = None