feat: add JSONBCompat type for cross-database JSON support and implement ActivityType updates

app/models/activity.py

@@ -8,6 +8,7 @@ from typing import Any
 from pydantic import BaseModel, ConfigDict, Field
 from sqlalchemy import DateTime, Enum as SqlEnum, ForeignKey, Integer, func, text
 from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy.types import JSON as GenericJSON, TypeDecorator
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.models.base import Base
@@ -16,10 +17,25 @@ from app.models.base import Base
 class ActivityType(StrEnum):
     COMMENT = "comment"
     STATUS_CHANGED = "status_changed"
+    STAGE_CHANGED = "stage_changed"
     TASK_CREATED = "task_created"
     SYSTEM = "system"
 
 
+class JSONBCompat(TypeDecorator):
+    """Uses JSONB on Postgres and plain JSON elsewhere for testability."""
+
+    impl = JSONB
+    cache_ok = True
+
+    def load_dialect_impl(self, dialect):  # type: ignore[override]
+        if dialect.name == "sqlite":
+            from sqlalchemy.dialects.sqlite import JSON as SQLiteJSON  # local import
+
+            return dialect.type_descriptor(SQLiteJSON())
+        return dialect.type_descriptor(JSONB())
+
+
 class Activity(Base):
     """Represents a timeline event for a deal."""
 
@@ -32,9 +48,9 @@ class Activity(Base):
     )
     type: Mapped[ActivityType] = mapped_column(SqlEnum(ActivityType, name="activity_type"), nullable=False)
     payload: Mapped[dict[str, Any]] = mapped_column(
-        JSONB,
+        JSONBCompat().with_variant(GenericJSON(), "sqlite"),
         nullable=False,
-        server_default=text("'{}'::jsonb"),
+        server_default=text("'{}'"),
     )
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), server_default=func.now(), nullable=False