fix(agents): a startedAt too large for a float counts as live (Issue #31, review)

json.load reads a huge integer as an int, and math.isfinite raised
OverflowError on it outside any try: conversation_in_use and purge_artifacts
(which must never raise) threw, where 6f4f40a had taken it as live. The
conversion to float now comes first, and an overflow means live.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/lib_py/agents/adapters/claude.py

@@ -78,12 +78,17 @@ def _session_file_live(data: dict, pid) -> bool:
     except OSError:
         pass
     # startedAt is epoch ms: a finite positive number. A bool, a string, NaN
-    # (every comparison with it is false) or an infinity is no time at all.
+    # (every comparison with it is false), an infinity or an int too large
+    # for a float is no time at all.
     started = data.get("startedAt")
-    if isinstance(started, bool) or not isinstance(started, (int, float)) \
-            or not math.isfinite(started) or started <= 0:
+    if isinstance(started, bool) or not isinstance(started, (int, float)):
+        return True
+    try:
+        started = float(started) / 1000.0
+    except OverflowError:
+        return True
+    if not math.isfinite(started) or started <= 0:
         return True
-    started = started / 1000.0
     # lstart in UTC: a local time is ambiguous in the hour a DST change repeats.
     try:
         out = subprocess.run(["ps", "-p", str(pid), "-o", "lstart="], capture_output=True, text=True,