Stop writing the schema version on database open

CHANGELOG.md

@@ -1,6 +1,10 @@
 # Changelog
 ## [Unreleased]
 
+### Fixed
+
+- Opening a database no longer writes to it: reads no longer rewrite the stored embedding settings or change the stored version, and the version is never downgraded.
+
 ## [0.54.0] - 2026-06-04
 
 ### Added

haiku_rag_slim/haiku/rag/store/engine.py

@@ -12,6 +12,7 @@ import lancedb
 import pyarrow as pa
 from lancedb.index import FTS, BTree, IvfPq
 from lancedb.pydantic import LanceModel, Vector
+from packaging.version import parse
 from pydantic import Field
 
 from haiku.rag.config import AppConfig, Config
@@ -509,7 +510,7 @@ class Store:
         await self.set_haiku_version(metadata.version("haiku.rag-slim"))
 
     async def _check_migrations(self) -> None:
-        """Check if migrations are pending and error or update version accordingly.
+        """Raise if migrations are pending. Opening never writes the version.
 
         Raises:
             MigrationRequiredError: If migrations are pending.
@@ -529,10 +530,6 @@ class Store:
                 "Run 'haiku-rag migrate' to upgrade."
             )
 
-        # No pending migrations - update version silently if needed (writable only)
-        if not self._read_only and db_version != current_version:
-            await self.set_haiku_version(current_version)
-
     async def migrate(self) -> list[str]:
         """Run pending database migrations.
 
@@ -551,8 +548,9 @@ class Store:
 
         applied = await run_pending_upgrades(self, db_version)
 
-        # Update version after successful migration
-        if applied or db_version != current_version:
+        # Advance the schema marker only forward — never downgrade a database
+        # opened with an older build than last stamped it.
+        if parse(current_version) > parse(db_version):
             await self.set_haiku_version(current_version)
 
         return applied

tests/store/test_migrations.py

@@ -38,21 +38,19 @@ class TestMigrationCheck:
             pass
 
     @pytest.mark.asyncio
-    async def test_version_bump_without_pending_migrations_updates_silently(
-        self, temp_db_path
-    ):
-        """When version is outdated but no migrations pending, update version silently."""
+    async def test_open_does_not_change_version(self, temp_db_path):
+        """Opening a database never writes the version, even when it differs.
+
+        A version newer than all upgrade steps has no pending migrations, so the
+        open succeeds; the stored version must be left untouched (no downgrade,
+        no bump) because opening is a pure read.
+        """
         async with Store(temp_db_path, create=True) as store:
-            # Set an older version that has no pending migrations
-            # (newer than all current upgrade steps)
             await store.set_haiku_version("100.0.0")
 
-        # Re-open - should update version silently, no error
+        # Re-open writable - no error, version unchanged
         async with Store(temp_db_path) as store:
-            # Version should now be current
-            version = await store.get_haiku_version()
-            expected = metadata.version("haiku.rag-slim")
-            assert version == expected
+            assert await store.get_haiku_version() == "100.0.0"
 
     @pytest.mark.asyncio
     async def test_pending_migrations_raises_error(self, temp_db_path):
@@ -160,6 +158,21 @@ class TestMigrateMethod:
             applied = await store.migrate()
             assert applied == []
 
+    @pytest.mark.asyncio
+    async def test_migrate_does_not_downgrade_future_version(self, temp_db_path):
+        """migrate() must not move the version backwards.
+
+        Running an older build's migrate against a DB stamped with a newer
+        version (no pending upgrades) leaves the stored version untouched.
+        """
+        async with Store(temp_db_path, create=True) as store:
+            await store.set_haiku_version("100.0.0")
+
+        async with Store(temp_db_path, skip_migration_check=True) as store:
+            applied = await store.migrate()
+            assert applied == []
+            assert await store.get_haiku_version() == "100.0.0"
+
     @pytest.mark.asyncio
     async def test_migrate_raises_read_only_error(self, temp_db_path):
         """Store.migrate() should raise ReadOnlyError in read-only mode."""