Phase 1: make ORM/migrations Postgres-compatible

Dialect-neutral fixes that keep SQLite behaviour unchanged:
- event_observer: choose INSERT construct by bind dialect so the
  on_conflict upsert works on both SQLite and Postgres
- database: map postgresql:// -> postgresql+asyncpg:// for async sessions
  (was sqlite-only), via a _to_async_url helper
- models: import JSON from sqlalchemy (generic) not the sqlite dialect
- alembic/env: render_as_batch only for SQLite (its ALTER TABLE workaround)

Full SQLite test suite green (1045 passed) and fresh db upgrade builds all
tables; black/flake8/mypy clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

alembic/env.py

@@ -58,7 +58,9 @@ def run_migrations_offline() -> None:
         target_metadata=target_metadata,
         literal_binds=True,
         dialect_opts={"paramstyle": "named"},
-        render_as_batch=True,  # SQLite batch mode for ALTER TABLE
+        # Batch mode is a SQLite-only workaround for its limited ALTER TABLE;
+        # Postgres performs ALTERs directly.
+        render_as_batch=url.startswith("sqlite"),
     )
 
     with context.begin_transaction():

src/meshcore_hub/common/database.py

@@ -11,6 +11,22 @@ from sqlalchemy.orm import Session, sessionmaker
 from meshcore_hub.common.models.base import Base
 
 
+def _to_async_url(database_url: str) -> str:
+    """Map a sync database URL to its async-driver equivalent.
+
+    Leaves an already driver-qualified URL (``dialect+driver://``) untouched so an
+    explicit driver choice is respected.
+    """
+    scheme = database_url.split("://", 1)[0]
+    if "+" in scheme:
+        return database_url
+    if scheme == "sqlite":
+        return database_url.replace("sqlite://", "sqlite+aiosqlite://", 1)
+    if scheme in ("postgresql", "postgres"):
+        return database_url.replace(f"{scheme}://", "postgresql+asyncpg://", 1)
+    return database_url
+
+
 def create_database_engine(
     database_url: str,
     echo: bool = False,
@@ -142,7 +158,7 @@ class DatabaseManager:
 
         from sqlalchemy.ext.asyncio import async_sessionmaker
 
-        async_url = self.database_url.replace("sqlite://", "sqlite+aiosqlite://")
+        async_url = _to_async_url(self.database_url)
         self._async_engine = create_async_engine(async_url, echo=self._echo)
 
         # Apply the same SQLite pragmas as the sync engine (see

src/meshcore_hub/common/models/event_log.py

@@ -3,8 +3,7 @@
 from datetime import datetime
 from typing import Any, Optional
 
-from sqlalchemy import DateTime, ForeignKey, Index, String
-from sqlalchemy.dialects.sqlite import JSON
+from sqlalchemy import DateTime, ForeignKey, Index, JSON, String
 from sqlalchemy.orm import Mapped, mapped_column
 
 from meshcore_hub.common.models.base import Base, TimestampMixin, UUIDMixin, utc_now

src/meshcore_hub/common/models/event_observer.py

@@ -8,13 +8,13 @@ from sqlalchemy import (
     DateTime,
     Float,
     ForeignKey,
+    Insert,
     Integer,
     Index,
     String,
     UniqueConstraint,
     update,
 )
-from sqlalchemy.dialects.sqlite import insert as sqlite_insert
 from sqlalchemy.orm import Mapped, Session, mapped_column, relationship
 
 from meshcore_hub.common.models.base import Base, TimestampMixin, UUIDMixin, utc_now
@@ -122,21 +122,40 @@ def add_event_observer(
 
     now = observed_at or datetime.now(timezone.utc)
 
-    stmt = (
-        sqlite_insert(EventObserver)
-        .values(
-            id=str(uuid4()),
-            event_type=event_type,
-            event_hash=event_hash,
-            observer_node_id=observer_node_id,
-            snr=snr,
-            path_len=path_len,
-            observed_at=now,
-            created_at=now,
-            updated_at=now,
+    # Both SQLite and Postgres expose on_conflict_do_nothing() with the same signature,
+    # but the INSERT construct must come from the matching dialect or it emits SQL for
+    # the wrong backend. Build the statement in each branch (rather than aliasing the
+    # insert() function) so the two dialect-specific Insert types stay distinct.
+    values = {
+        "id": str(uuid4()),
+        "event_type": event_type,
+        "event_hash": event_hash,
+        "observer_node_id": observer_node_id,
+        "snr": snr,
+        "path_len": path_len,
+        "observed_at": now,
+        "created_at": now,
+        "updated_at": now,
+    }
+    conflict_cols = ["event_hash", "observer_node_id"]
+    stmt: Insert
+
+    if session.get_bind().dialect.name == "postgresql":
+        from sqlalchemy.dialects.postgresql import insert as pg_insert
+
+        stmt = (
+            pg_insert(EventObserver)
+            .values(**values)
+            .on_conflict_do_nothing(index_elements=conflict_cols)
+        )
+    else:
+        from sqlalchemy.dialects.sqlite import insert as sqlite_insert
+
+        stmt = (
+            sqlite_insert(EventObserver)
+            .values(**values)
+            .on_conflict_do_nothing(index_elements=conflict_cols)
         )
-        .on_conflict_do_nothing(index_elements=["event_hash", "observer_node_id"])
-    )
     result = session.execute(stmt)
     rowcount = getattr(result, "rowcount", 0)
 

src/meshcore_hub/common/models/raw_packet.py

@@ -3,8 +3,7 @@
 from datetime import datetime
 from typing import Any, Optional
 
-from sqlalchemy import DateTime, Float, ForeignKey, Index, Integer, String, Text
-from sqlalchemy.dialects.sqlite import JSON
+from sqlalchemy import DateTime, Float, ForeignKey, Index, Integer, JSON, String, Text
 from sqlalchemy.orm import Mapped, mapped_column
 
 from meshcore_hub.common.models.base import Base, TimestampMixin, UUIDMixin, utc_now

src/meshcore_hub/common/models/telemetry.py

@@ -3,8 +3,7 @@
 from datetime import datetime
 from typing import Any, Optional
 
-from sqlalchemy import DateTime, ForeignKey, Index, LargeBinary, String
-from sqlalchemy.dialects.sqlite import JSON
+from sqlalchemy import DateTime, ForeignKey, Index, JSON, LargeBinary, String
 from sqlalchemy.orm import Mapped, mapped_column
 
 from meshcore_hub.common.models.base import Base, TimestampMixin, UUIDMixin, utc_now

src/meshcore_hub/common/models/trace_path.py

@@ -3,8 +3,7 @@
 from datetime import datetime
 from typing import Optional
 
-from sqlalchemy import BigInteger, DateTime, ForeignKey, Index, Integer, String
-from sqlalchemy.dialects.sqlite import JSON
+from sqlalchemy import BigInteger, DateTime, ForeignKey, Index, Integer, JSON, String
 from sqlalchemy.orm import Mapped, mapped_column
 
 from meshcore_hub.common.models.base import Base, TimestampMixin, UUIDMixin, utc_now