refactor(discord): one liveness-knob resolver; int knobs reject inf and fractions

`_finite_positive_config_float` and `_config_int` were the same shape with the warn call
pasted six times and asymmetric sign checks. Collapse both onto `_liveness_knob(key, default,
cast)`: usable iff finite, >= 0 and exact for the cast; else warn and return 0; explicit 0
stays silent.

Two int-path holes closed on the way: `websocket_liveness_failure_threshold: .inf` raised
OverflowError inside `DiscordAdapter.__init__`, and `0.5` truncated to 0 and disabled the
probe silently — the bug class this PR exists to remove. `2.0` / `"2"` still resolve to 2.

plugins/platforms/discord/adapter.py

@@ -1115,40 +1115,30 @@ class DiscordAdapter(DiscordMediaMixin, BasePlatformAdapter):
             self.name, key, raw,
         )
 
+    def _liveness_knob(self, key: str, default: Any, cast: type, *, env_key: Optional[str] = None):
+        """Resolve a liveness knob: usable iff finite, >= 0 and exact for ``cast``; else warn and return 0.
+
+        ``0`` is the documented opt-out and stays silent. Bools, unparsable strings, nan/inf,
+        negatives and (for int knobs) fractional values all disable the probe WITH a warning.
+        """
+        raw = self._config_value(key, default, env_key=env_key)
+        try:
+            value = None if isinstance(raw, bool) else float(raw)
+        except (TypeError, ValueError):
+            value = None
+        if value is not None and math.isfinite(value) and value >= 0 and cast(value) == value:
+            return cast(value)
+        if value != 0:
+            self._warn_liveness_config_disabled(key, raw)
+        return cast(0)
+
     def _finite_positive_config_float(
         self, key: str, default: float, *, env_key: Optional[str] = None
     ) -> float:
-        """Resolve a finite positive liveness duration; invalid values disable it (with a warning)."""
-        raw = self._config_value(key, default, env_key=env_key)
-        if isinstance(raw, bool):
-            self._warn_liveness_config_disabled(key, raw)
-            return 0.0
-        try:
-            value = float(raw)
-        except (TypeError, ValueError):
-            self._warn_liveness_config_disabled(key, raw)
-            return 0.0
-        if math.isfinite(value) and value > 0:
-            return value
-        if value != 0:
-            self._warn_liveness_config_disabled(key, raw)
-        return 0.0
+        return self._liveness_knob(key, default, float, env_key=env_key)
 
     def _config_int(self, key: str, default: int, *, env_key: Optional[str] = None) -> int:
-        """Resolve a positive liveness count; invalid values disable it (with a warning)."""
-        raw = self._config_value(key, default, env_key=env_key)
-        if isinstance(raw, bool):
-            self._warn_liveness_config_disabled(key, raw)
-            return 0
-        try:
-            value = int(raw)
-        except (TypeError, ValueError):
-            self._warn_liveness_config_disabled(key, raw)
-            return 0
-        if value < 0:
-            self._warn_liveness_config_disabled(key, raw)
-            return 0
-        return value
+        return self._liveness_knob(key, default, int, env_key=env_key)
 
     def _handle_bot_task_done(self, task: asyncio.Task) -> None:
         """Surface post-startup discord.py task exits as a retryable fatal so GatewayRunner

tests/gateway/test_discord_liveness.py

@@ -124,6 +124,8 @@ class _BrokenWebSocket:
         ("websocket_max_latency_seconds", "_max_latency_seconds", "-inf"),
         ("websocket_max_latency_seconds", "_max_latency_seconds", True),
         ("websocket_max_latency_seconds", "_max_latency_seconds", "15s"),
+        ("websocket_liveness_failure_threshold", "_liveness_failure_threshold", 2.5),
+        ("websocket_liveness_failure_threshold", "_liveness_failure_threshold", float("inf")),
     ],
 )
 def test_nonfinite_liveness_config_disables_that_probe_dimension(monkeypatch, key, attribute, raw):
@@ -149,6 +151,7 @@ def test_unusable_liveness_config_warns_instead_of_disabling_silently(caplog):
                     "websocket_liveness_interval_seconds": "15s",
                     "websocket_max_latency_seconds": True,
                     "websocket_liveness_failure_threshold": -1,
+                    "websocket_heartbeat_ack_max_age_seconds": "nan",
                 },
             )
         )
@@ -156,8 +159,10 @@ def test_unusable_liveness_config_warns_instead_of_disabling_silently(caplog):
     assert adapter._liveness_interval_seconds == 0.0
     assert adapter._max_latency_seconds == 0.0
     assert adapter._liveness_failure_threshold == 0
+    assert adapter._heartbeat_ack_max_age_seconds == 0.0
     warned = [r.getMessage() for r in caplog.records if "liveness knob" in r.getMessage()]
-    assert len(warned) == 3
+    assert len(warned) == 4
+    assert any("websocket_heartbeat_ack_max_age_seconds='nan'" in w for w in warned)
     assert any("websocket_liveness_interval_seconds='15s'" in w for w in warned)
     assert any("websocket_max_latency_seconds=True" in w for w in warned)
     assert any("websocket_liveness_failure_threshold=-1" in w for w in warned)
@@ -170,11 +175,16 @@ def test_explicit_zero_liveness_knob_disables_without_warning(caplog):
             PlatformConfig(
                 enabled=True,
                 token="test-token",
-                extra={"websocket_liveness_interval_seconds": 0, "websocket_liveness_failure_threshold": 0},
+                extra={
+                    "websocket_liveness_interval_seconds": 0,
+                    "websocket_max_latency_seconds": "0",
+                    "websocket_liveness_failure_threshold": 0,
+                },
             )
         )
 
     assert adapter._liveness_interval_seconds == 0.0
+    assert adapter._max_latency_seconds == 0.0
     assert adapter._liveness_failure_threshold == 0
     assert not [r for r in caplog.records if "liveness knob" in r.getMessage()]