feat(taskflow): add core task API, storage persistence, csv export, stats page, and test coverage

app/storage/models.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+from datetime import datetime
+from uuid import UUID
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+DATA_FORMAT_VERSION = 1
+
+
+class StoredTask(BaseModel):
+    model_config = ConfigDict(extra="forbid", frozen=True)
+
+    id: UUID
+    title: str = Field(..., min_length=1, max_length=100)
+    created_at: datetime
+    started_at: datetime | None = None
+    done_at: datetime | None = None
+
+
+class StoragePayloadV1(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    version: int = Field(default=DATA_FORMAT_VERSION)
+    tasks: list[StoredTask] = Field(default_factory=list)
+
+
+class StoragePayload(BaseModel):
+    """
+    Canonical in-memory storage payload.
+    This model allows safe parsing of the top-level version field
+    before delegating to a concrete versioned schema.
+    """
+
+    model_config = ConfigDict(extra="allow")
+
+    version: int
+
+
+def upgrade_payload(raw_data: dict) -> StoragePayloadV1:
+    """
+    Upgrade any supported payload version to the latest schema.
+    """
+    payload = StoragePayload.model_validate(raw_data)
+
+    if payload.version == 1:
+        parsed_v1 = StoragePayloadV1.model_validate(raw_data)
+        return StoragePayloadV1(
+            version=DATA_FORMAT_VERSION,
+            tasks=parsed_v1.tasks,
+        )
+
+    raise ValueError(
+        f"Unsupported storage payload version: {payload.version}. "
+        f"Supported versions: 1..{DATA_FORMAT_VERSION}",
+    )
+