diff --git a/roboco/runtime/orchestrator.py b/roboco/runtime/orchestrator.py
index 38626e69..a970b5f2 100644
--- a/roboco/runtime/orchestrator.py
+++ b/roboco/runtime/orchestrator.py
@@ -4626,11 +4626,20 @@ class AgentOrchestrator:
         """
         from roboco.db.base import get_session_factory
         from roboco.services.task import TaskService
-        from roboco.utils.converters import require_uuid
+        from roboco.utils.converters import InvalidIdentifierError, require_uuid
 
         try:
             task_id = require_uuid(task_id_str)
-        except Exception:
+        except InvalidIdentifierError as exc:
+            # A malformed task_id_str is a bad identifier, not a transient
+            # failure — log it so the drop is visible instead of swallowed,
+            # then no-op (nothing to release). Other exceptions still fall
+            # through to the broad catch below (#25).
+            logger.warning(
+                "stopped agent claim had malformed task id",
+                task_id_str=task_id_str,
+                error=str(exc),
+            )
             return
         try:
             factory = get_session_factory()
diff --git a/roboco/utils/converters.py b/roboco/utils/converters.py
index 72d7a0a2..81adc629 100644
--- a/roboco/utils/converters.py
+++ b/roboco/utils/converters.py
@@ -8,6 +8,16 @@ from typing import Any
 from uuid import UUID as PythonUUID
 
 
+class InvalidIdentifierError(ValueError):
+    """A malformed/None identifier reached UUID coercion.
+
+    A ``ValueError`` subclass so existing ``except ValueError`` callers keep
+    working, but typed so a caller can distinguish a bad identifier from any
+    other exception instead of broad-catching and silently swallowing it
+    (#25).
+    """
+
+
 def require_uuid(value: Any) -> PythonUUID:
     """
     Convert SQLAlchemy UUID to Python UUID, raising if None.
@@ -19,13 +29,19 @@ def require_uuid(value: Any) -> PythonUUID:
         Python UUID
 
     Raises:
-        ValueError: If value is None or cannot be converted
+        InvalidIdentifierError: If value is None or cannot be parsed as a UUID.
+            A ``ValueError`` subclass, so existing ``except ValueError`` /
+            ``except Exception`` callers are unaffected, but typed so callers
+            can handle a bad identifier distinctly instead of swallowing it.
     """
     if value is None:
-        raise ValueError("UUID value cannot be None")
+        raise InvalidIdentifierError("UUID value cannot be None")
     if isinstance(value, PythonUUID):
         return value
-    return PythonUUID(str(value))
+    try:
+        return PythonUUID(str(value))
+    except (ValueError, AttributeError, TypeError) as exc:
+        raise InvalidIdentifierError(f"invalid UUID identifier: {value!r}") from exc
 
 
 def repo_key(git_url: str) -> str:
diff --git a/tests/unit/utils/test_converters.py b/tests/unit/utils/test_converters.py
index fad25f8f..8b98f7c5 100644
--- a/tests/unit/utils/test_converters.py
+++ b/tests/unit/utils/test_converters.py
@@ -6,6 +6,7 @@ from uuid import uuid4
 
 import pytest
 from roboco.utils.converters import (
+    InvalidIdentifierError,
     require_uuid,
     to_python_uuid,
     to_python_uuid_list,
@@ -27,6 +28,27 @@ def test_require_uuid_raises_for_none() -> None:
         require_uuid(None)
 
 
+def test_require_uuid_none_raises_typed_identifier_error() -> None:
+    """#25: a None identifier raises the typed InvalidIdentifierError (a
+    ValueError subclass), not a bare ValueError, so callers can distinguish a
+    bad identifier from any other exception instead of broad-catching."""
+    with pytest.raises(InvalidIdentifierError, match="cannot be None"):
+        require_uuid(None)
+
+
+def test_require_uuid_unparseable_raises_typed_identifier_error() -> None:
+    """#25: an unparseable identifier raises InvalidIdentifierError, not a bare
+    ValueError — the dropped-identifier pattern must surface as a typed error."""
+    with pytest.raises(InvalidIdentifierError, match="invalid UUID identifier"):
+        require_uuid("not-a-uuid")
+
+
+def test_invalid_identifier_error_is_value_error() -> None:
+    """Back-compat: InvalidIdentifierError subclasses ValueError so existing
+    `except ValueError` callers keep catching it."""
+    assert issubclass(InvalidIdentifierError, ValueError)
+
+
 def test_to_python_uuid_returns_none_for_none() -> None:
     assert to_python_uuid(None) is None