forgeproof(#9): Add priority validation to Task

.forgeproof/chain-9.json

@@ -0,0 +1,134 @@
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+  {
+    "index": 0,
+    "timestamp": "2026-07-06T04:27:28.973771+00:00",
+    "action": "genesis",
+    "data": {
+      "issue": 9,
+      "title": "Feature: Add priority levels to Task",
+      "requirements": [
+        "REQ-1: Each Task has a priority attribute with allowed values low, medium, high; default is medium",
+        "REQ-2: Creating or setting a Task with any other priority value raises ValueError",
+        "REQ-3: TaskStore has a filter_by_priority(priority) method returning tasks matching the given priority",
+        "REQ-4: Existing behavior (creation, completion, serialization) is unchanged for tasks that never set a priority"
+      ]
+    },
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+    "index": 3,
+    "timestamp": "2026-07-06T04:28:14.273994+00:00",
+    "action": "decision",
+    "data": {
+      "context": "How to enforce priority validation on both construction and later assignment for a mutable dataclass",
+      "choice": "Override Task.__setattr__ to validate the priority field, coercing valid strings ('low'/'medium'/'high') to Priority enum members and raising ValueError otherwise",
+      "rationale": "Dataclass __init__ assigns fields via __setattr__, so one override covers both creation and mutation without switching to frozen dataclass or properties; string coercion keeps the public API forgiving while guaranteeing the stored value is always a Priority member so to_dict/from_dict behavior is unchanged"
+    },
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+    "timestamp": "2026-07-06T04:28:38.280927+00:00",
+    "action": "file-edit",
+    "data": {
+      "path": "tests/test_priority.py",
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+  {
+    "index": 5,
+    "timestamp": "2026-07-06T04:28:38.374432+00:00",
+    "action": "decision",
+    "data": {
+      "context": "REQ-3 asks TaskStore to gain filter_by_priority, but the method already exists in src/task_store.py",
+      "choice": "Leave src/task_store.py unchanged and cover the existing method with new tests",
+      "rationale": "The existing implementation already satisfies the requirement; ForgeProof rules call for focused, minimal changes rather than rewriting working code"
+    },
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+  },
+  {
+    "index": 6,
+    "timestamp": "2026-07-06T04:28:59.838656+00:00",
+    "action": "test-result",
+    "data": {
+      "suite": "pytest",
+      "passed": 44,
+      "failed": 0,
+      "coverage": {
+        "REQ-1": [
+          "test_priority_defaults_to_medium",
+          "test_priority_accepts_all_allowed_values",
+          "test_priority_accepts_allowed_strings"
+        ],
+        "REQ-2": [
+          "test_invalid_priority_string_at_creation_raises",
+          "test_invalid_priority_type_at_creation_raises",
+          "test_invalid_priority_on_assignment_raises",
+          "test_valid_priority_on_assignment",
+          "test_invalid_priority_in_from_dict_raises"
+        ],
+        "REQ-3": [
+          "test_filter_by_priority_returns_matches",
+          "test_filter_by_priority_no_match"
+        ],
+        "REQ-4": [
+          "test_untouched_priority_creation_and_completion",
+          "test_untouched_priority_serialization_round_trip"
+        ]
+      },
+      "failed_tests": []
+    },
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+  },
+  {
+    "index": 7,
+    "timestamp": "2026-07-06T04:29:10.976253+00:00",
+    "action": "lint-result",
+    "data": {
+      "tool": "ruff",
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+  }
+]

src/task.py

@@ -32,6 +32,23 @@ class Task:
     completed_at: datetime | None = None
     due_date: datetime | None = None
 
+    def __setattr__(self, name: str, value: object) -> None:
+        if name == "priority":
+            if isinstance(value, str):
+                try:
+                    value = Priority(value)
+                except ValueError:
+                    raise ValueError(
+                        f"invalid priority: {value!r}; allowed values are "
+                        f"{', '.join(p.value for p in Priority)}"
+                    ) from None
+            elif not isinstance(value, Priority):
+                raise ValueError(
+                    f"invalid priority: {value!r}; allowed values are "
+                    f"{', '.join(p.value for p in Priority)}"
+                )
+        super().__setattr__(name, value)
+
     def complete(self) -> None:
         """Mark the task as done. No-op if already done."""
         if self.status == Status.DONE:

tests/test_priority.py

@@ -0,0 +1,111 @@
+"""Tests for Task priority levels (issue #9)."""
+
+import pytest
+
+from src.task import Priority, Status, Task
+from src.task_store import TaskStore
+
+
+# REQ-1: priority attribute with allowed values low, medium, high; default medium
+
+
+def test_priority_defaults_to_medium():
+    task = Task(title="No priority given")
+    assert task.priority == Priority.MEDIUM
+
+
+def test_priority_accepts_all_allowed_values():
+    for priority in (Priority.LOW, Priority.MEDIUM, Priority.HIGH):
+        task = Task(title="Explicit priority", priority=priority)
+        assert task.priority == priority
+
+
+def test_priority_accepts_allowed_strings():
+    for value in ("low", "medium", "high"):
+        task = Task(title="String priority", priority=value)
+        assert task.priority == Priority(value)
+
+
+# REQ-2: any other priority value raises ValueError
+
+
+def test_invalid_priority_string_at_creation_raises():
+    with pytest.raises(ValueError):
+        Task(title="Bad", priority="urgent")
+
+
+def test_invalid_priority_type_at_creation_raises():
+    with pytest.raises(ValueError):
+        Task(title="Bad", priority=3)
+
+
+def test_invalid_priority_on_assignment_raises():
+    task = Task(title="Good")
+    with pytest.raises(ValueError):
+        task.priority = "banana"
+
+
+def test_valid_priority_on_assignment():
+    task = Task(title="Good")
+    task.priority = Priority.HIGH
+    assert task.priority == Priority.HIGH
+    task.priority = "low"
+    assert task.priority == Priority.LOW
+
+
+def test_invalid_priority_in_from_dict_raises():
+    data = {
+        "title": "Bad",
+        "priority": "critical",
+        "status": "todo",
+        "tags": [],
+        "created_at": "2026-01-01T00:00:00+00:00",
+        "completed_at": None,
+    }
+    with pytest.raises(ValueError):
+        Task.from_dict(data)
+
+
+# REQ-3: TaskStore.filter_by_priority returns tasks matching the given priority
+
+
+def test_filter_by_priority_returns_matches():
+    store = TaskStore()
+    low_id = store.add(Task(title="Low", priority=Priority.LOW))
+    store.add(Task(title="Medium"))
+    high_id = store.add(Task(title="High", priority=Priority.HIGH))
+
+    high_tasks = store.filter_by_priority(Priority.HIGH)
+    assert [(tid, t.title) for tid, t in high_tasks] == [(high_id, "High")]
+
+    low_tasks = store.filter_by_priority(Priority.LOW)
+    assert [(tid, t.title) for tid, t in low_tasks] == [(low_id, "Low")]
+
+
+def test_filter_by_priority_no_match():
+    store = TaskStore()
+    store.add(Task(title="Medium only"))
+    assert store.filter_by_priority(Priority.HIGH) == []
+
+
+# REQ-4: existing behavior unchanged for tasks that never set a priority
+
+
+def test_untouched_priority_creation_and_completion():
+    task = Task(title="Plain task", description="desc", tags=["a"])
+    assert task.priority == Priority.MEDIUM
+    assert task.status == Status.TODO
+    task.complete()
+    assert task.status == Status.DONE
+    assert task.completed_at is not None
+
+
+def test_untouched_priority_serialization_round_trip():
+    original = Task(title="Plain task")
+    original.complete()
+    d = original.to_dict()
+    assert d["priority"] == "medium"
+    rebuilt = Task.from_dict(d)
+    assert rebuilt.priority == Priority.MEDIUM
+    assert rebuilt.status == original.status
+    assert rebuilt.completed_at == original.completed_at