feat(sync): add SyncConfig construction validation (#425)

Co-authored-by: wphillipmoore-claude <255925739+wphillipmoore-claude@users.noreply.github.com>

Author: wphillipmoore

src/pymqrest/sync.py

@@ -27,6 +27,15 @@ class SyncConfig:
     timeout_seconds: float = 30.0
     poll_interval_seconds: float = 1.0
 
+    def __post_init__(self) -> None:
+        """Validate that both fields are positive."""
+        if self.timeout_seconds <= 0:
+            msg = f"timeout_seconds must be positive, got {self.timeout_seconds}"
+            raise ValueError(msg)
+        if self.poll_interval_seconds <= 0:
+            msg = f"poll_interval_seconds must be positive, got {self.poll_interval_seconds}"
+            raise ValueError(msg)
+
 
 class SyncOperation(enum.Enum):
     """Operation performed by a synchronous wrapper.

tests/pymqrest/test_sync.py

@@ -134,6 +134,22 @@ def test_frozen(self) -> None:
         with pytest.raises(AttributeError):
             sync_config.timeout_seconds = 99.0  # type: ignore[misc]
 
+    def test_zero_timeout_raises(self) -> None:
+        with pytest.raises(ValueError, match="timeout_seconds must be positive"):
+            SyncConfig(timeout_seconds=0.0)
+
+    def test_negative_timeout_raises(self) -> None:
+        with pytest.raises(ValueError, match="timeout_seconds must be positive"):
+            SyncConfig(timeout_seconds=-1.0)
+
+    def test_zero_poll_interval_raises(self) -> None:
+        with pytest.raises(ValueError, match="poll_interval_seconds must be positive"):
+            SyncConfig(poll_interval_seconds=0.0)
+
+    def test_negative_poll_interval_raises(self) -> None:
+        with pytest.raises(ValueError, match="poll_interval_seconds must be positive"):
+            SyncConfig(poll_interval_seconds=-1.0)
+
 
 # ---------------------------------------------------------------------------
 # SyncOperation enum