Add separate migration logging, logmigr callback, and log= override

- Split transaction logger (kanta.changes) and migration logger (kanta.migrations).
- Migrations.apply() now returns MigrationResult instead of logging.
- Kanta.open() emits one info summary per DB and debug transaction per migration.
- Add open(log=...) to suppress/redirect default migration logging.
- Add @kanta.logmigr callback for custom migration logging/summaries.
- Add transaction(log=...) to suppress/redirect transaction logging.
- Update tests for the new MigrationResult API and logging behaviour.

README.md

@@ -53,10 +53,13 @@ asyncio.run(main())
 
 ## Bootstrap and Open Modes
 
-Kanta supports open-time bootstrap callbacks for initializing a brand-new
+When `open()` creates a brand-new database, it always writes a single bootstrap
-database before `open()` returns.
+change record from the initial data object you passed to `Kanta(...)`. The
+simplest bootstrap is therefore the object itself — no extra code is required.
 
-Register bootstrap handlers with a decorator:
+Bootstrap handlers are optional. Use them only when you need to modify the
+initial state at creation time, for example to seed defaults or perform
+expensive/external setup that should happen exactly once:
 
 ```python
 kanta = Kanta("data.kantadb", Data())
@@ -76,9 +79,10 @@ async def bootstrap_async(data) -> None:
     data.counter = 1
 ```
 
-When multiple bootstrap handlers are registered:
+Whether or not handlers are registered, exactly one bootstrap change record is
+written when a new database is created. The record contains the initial object,
+or the state after all bootstrap handlers have run. When handlers are present:
 - they run in registration order,
-- exactly one bootstrap change record is queued,
 - bootstrap metadata (`action`, `user`, `mtime`) is taken from the last
   registration.
 

docs/database.md

@@ -133,7 +133,11 @@ when they have a default value.
 
 #### Bootstrap Callbacks
 
-- Bootstrap callbacks run during `open()` when the database is empty.
+- When `open()` creates a new database, it always writes a single bootstrap
+  `ChangeRecord`.
+- The simplest bootstrap is the initial data object passed to `Kanta(...)`;
+  bootstrap callbacks are optional and only needed when you want to modify or
+  enrich that object at creation time.
 - Register callbacks via:
   - `@kanta.bootstrap`
   - `@kanta.bootstrap(action=..., user=..., mtime=...)`
@@ -146,6 +150,8 @@ when they have a default value.
   - exactly one bootstrap `ChangeRecord` is queued,
   - bootstrap metadata (`action`, `user`, `mtime`) is taken from the last
     callback registration.
+- If no bootstrap callbacks are registered, the bootstrap record still uses
+  `action="bootstrap"` and contains the initial data object.
 - If any bootstrap callback raises, Kanta closes and removes the database file,
   then re-raises the exception.
 

kanta/callbacks.py

@@ -18,6 +18,7 @@ from dataclasses import dataclass
 from typing import Annotated, Any, Union, get_args, get_origin
 
 from kanta.exceptions import DatabaseError
+from kanta.migrations import MigrationResult
 
 DictPre = Annotated[dict, "pre"]
 DictPost = Annotated[dict, "post"]
@@ -59,6 +60,7 @@ class InjectionContext:
     error: DatabaseError | None = None
     previous_state: dict | None = None
     current_state: dict | None = None
+    migration_result: MigrationResult | None = None
 
 
 @dataclass
@@ -98,6 +100,7 @@ class CallbackRegistry:
         self._callbacks: dict[str, list[_CallbackRegistration]] = {
             "bootstrap": [],
             "fatal_error": [],
+            "logmigr": [],
         }
         self._logfmt_callbacks: list[_LogFmtFunctionSpec | _LogFmtClassSpec] = []
 
@@ -446,10 +449,12 @@ class CallbackRegistry:
             return kind == "logfmt"
         if bare is DatabaseError:
             return kind == "fatal_error"
+        if bare is MigrationResult:
+            return kind == "logmigr"
         if self._data_type is not None and bare is self._data_type:
             return kind == "bootstrap"
         if self._kanta_class is not None and bare is self._kanta_class:
-            return kind in {"bootstrap", "fatal_error", "logfmt"}
+            return kind in {"bootstrap", "fatal_error", "logfmt", "logmigr"}
         return False
 
     def _allowed_message(self, kind: str) -> str:
@@ -462,6 +467,8 @@ class CallbackRegistry:
                 parts.append(self._kanta_class.__name__)
         if kind == "fatal_error":
             parts.append("DatabaseError")
+        if kind == "logmigr":
+            parts.append("MigrationResult")
         if kind == "logfmt":
             parts.append("Annotated[dict, 'pre']")
             parts.append("Annotated[dict, 'post']")
@@ -475,6 +482,8 @@ class CallbackRegistry:
             return ctx.current_state
         if bare is DatabaseError:
             return ctx.error
+        if bare is MigrationResult:
+            return ctx.migration_result
         if self._data_type is not None and bare is self._data_type:
             return ctx.data
         if self._kanta_class is not None and bare is self._kanta_class:

kanta/filelock.py

@@ -129,7 +129,9 @@ class LockedFile:
         else:
             self._open_unix(path, create, readonly)
 
-    def open_and_read(self, path: Path, create: bool = False, readonly: bool = False) -> bytes:
+    def open_and_read(
+        self, path: Path, create: bool = False, readonly: bool = False
+    ) -> bytes:
         """Open *path* and read all content.
 
         Combined operation for efficient use with asyncio.to_thread().

kanta/kanta.py

@@ -1,10 +1,11 @@
 """Kanta DB main public API"""
 
 from __future__ import annotations
+import logging
 from datetime import datetime
 from pathlib import Path
 from types import ModuleType, SimpleNamespace
-from typing import Any, Generic, TypeVar
+from typing import Generic, TypeVar
 
 from kanta.kantaimpl import KantaImpl
 from kanta.serialization import JsonSerializer, Serializer
@@ -144,7 +145,13 @@ class Kanta(Generic[T]):
         """
         return self._impl.mtime
 
-    async def open(self, *, create: bool = True, readonly: bool = False) -> None:
+    async def open(
+        self,
+        *,
+        create: bool = True,
+        readonly: bool = False,
+        log: bool | logging.Logger = True,
+    ) -> None:
         """Open the database file and start background persistence.
 
         This loads existing records, applies configured migrations, and starts
@@ -156,6 +163,11 @@ class Kanta(Generic[T]):
             readonly: If True, open the database read-only. No lock is acquired,
                 no background flush task is started, and transactions are
                 rejected. The file is not created if missing.
+            log: Controls migration logging. ``True`` (default) uses the
+                ``kanta.migrations`` logger. ``False`` suppresses the default
+                migration log. A :class:`~logging.Logger` instance writes
+                default migration output to that logger instead. Custom
+                ``@kanta.logmigr`` callbacks run regardless of this setting.
 
         Calling ``open`` more than once on the same instance is not allowed.
 
@@ -163,7 +175,7 @@ class Kanta(Generic[T]):
             kanta.exceptions.DatabaseError: If replay or decoding fails.
             kanta.exceptions.DataIntegrityError: If the instance is already open.
         """
-        await self._impl.open(create=create, readonly=readonly)
+        await self._impl.open(create=create, readonly=readonly, log=log)
 
     async def __aenter__(self) -> Kanta[T]:
         """Enter async context manager and open the database.
@@ -239,6 +251,24 @@ class Kanta(Generic[T]):
             return _register
         return _register(fn)
 
+    def logmigr(self, fn=None):
+        """Register a migration logging callback.
+
+        Can be used as ``@kanta.logmigr``.
+        The callback receives a :class:`kanta.migrations.MigrationResult` and
+        may be sync or async. If registered, it replaces the default migration
+        logger output; the application is responsible for emitting any log
+        messages.
+        """
+
+        def _register(callback):
+            self._impl.add_logmigr(callback)
+            return callback
+
+        if fn is None:
+            return _register
+        return _register(fn)
+
     def logfmt(self, fn=None, *, path: str | None = None):
         """Register a transaction logfmt callback.
 
@@ -266,6 +296,7 @@ class Kanta(Generic[T]):
         *,
         user: str | None = None,
         mtime: bool | datetime = True,
+        log: bool | logging.Logger = True,
     ):
         """Create a transactional mutation context manager.
 
@@ -280,6 +311,10 @@ class Kanta(Generic[T]):
                 system operations that are not considered modifications. A
                 :class:`~datetime.datetime` value sets ``m`` to that explicit
                 time.
+            log: Controls transaction logging. ``True`` (default) uses the
+                ``kanta.changes`` logger. ``False`` suppresses the transaction
+                log. A :class:`~logging.Logger` instance writes output to that
+                logger instead.
 
         Returns:
             A context manager yielding the live state object for mutation.
@@ -294,4 +329,5 @@ class Kanta(Generic[T]):
             action,
             user=user,
             mtime=mtime,
+            log=log,
         )

kanta/kantaimpl.py

@@ -12,7 +12,8 @@ from typing import Any, Generic, TypeVar
 
 from kanta.callbacks import CallbackRegistry, InjectionContext
 from kanta.exceptions import DatabaseError, DataIntegrityError, ReplayError
-from kanta.migrate import MigrationRegistry
+from kanta.logging import log_change, migration_logger
+from kanta.migrations import MigrationResult, Migrations
 from kanta.persistence import PersistenceMixin
 from kanta.serialization import restore_data_in_place, struct_to_dict
 from kanta.serialization.base import replay
@@ -28,18 +29,18 @@ class KantaImpl(PersistenceMixin, Generic[T]):
     def __init__(self, **kwargs: Any):
         self.data_type = kwargs.pop("type")
         self.data: T = kwargs.pop("data")
-        self.migrations = kwargs.pop("migrations", None)
         self._kanta = kwargs.pop("kanta", None)
+        migrations = kwargs.pop("migrations", None)
         self.ctx = SimpleNamespace()
         super().__init__(**kwargs)
-        self.migration_registry: MigrationRegistry | None = None
+        self.migrations: Migrations | None = None
-        if self.migrations is not None:
+        if migrations is not None:
             module = (
-                importlib.import_module(self.migrations)
+                importlib.import_module(migrations)
-                if isinstance(self.migrations, str)
+                if isinstance(migrations, str)
-                else self.migrations
+                else migrations
             )
-            self.migration_registry = MigrationRegistry.from_module(module)
+            self.migrations = Migrations.from_module(module)
 
         self.in_transaction = False
         self.transaction_snapshot: dict[str, Any] | None = None
@@ -55,9 +56,7 @@ class KantaImpl(PersistenceMixin, Generic[T]):
         )
 
         self.statedict = struct_to_dict(self.data, serializer=self.serializer)
-        self.version = (
+        self.version = self.migrations.dbver if self.migrations is not None else 0
-            self.migration_registry.dbver if self.migration_registry is not None else 0
-        )
 
     def add_bootstrap(
         self,
@@ -77,7 +76,64 @@ class KantaImpl(PersistenceMixin, Generic[T]):
         """Register one transaction logfmt callback."""
         self.callback_registry.register("logfmt", callback, path=path)
 
-    async def open(self, *, create: bool = True, readonly: bool = False) -> None:
+    def add_logmigr(self, callback) -> None:
+        """Register one migration logging callback."""
+        self.callback_registry.register("logmigr", callback)
+
+    async def _handle_migration_log(
+        self,
+        migration_result: MigrationResult,
+        previous_version: int,
+        log: bool | logging.Logger,
+    ) -> None:
+        """Route migration logging to callback or default logger."""
+        assert isinstance(migration_result, MigrationResult)
+
+        if self.callback_registry.has("logmigr"):
+            await self.callback_registry.invoke(
+                "logmigr",
+                InjectionContext(
+                    kanta=self._kanta,
+                    migration_result=migration_result,
+                ),
+            )
+            return
+
+        if log is False:
+            return
+
+        migration_log = log if isinstance(log, logging.Logger) else migration_logger
+
+        changed = [m for m in migration_result.migrations if m.changed]
+        if not changed:
+            return
+
+        for info in changed:
+            if info.diff:
+                log_change(
+                    info.name,
+                    info.diff,
+                    previous=info.before,
+                    logger=migration_log,
+                    level=logging.DEBUG,
+                )
+
+        descriptions = [f"{m.name} ({m.description})" for m in changed]
+        migration_log.info(
+            "Migrated %s v%s -> v%s: %s",
+            self.filename,
+            previous_version,
+            migration_result.version,
+            ", ".join(descriptions),
+        )
+
+    async def open(
+        self,
+        *,
+        create: bool = True,
+        readonly: bool = False,
+        log: bool | logging.Logger = True,
+    ) -> None:
         """Open the database: load from disk, apply migrations, start background task."""
         if self.opened:
             raise DataIntegrityError(
@@ -112,6 +168,9 @@ class KantaImpl(PersistenceMixin, Generic[T]):
                 action="open",
             )
 
+        # From this point the file is open and must be closed via close().
+        self.opened = True
+
         if content:
             try:
                 rr = replay(
@@ -141,12 +200,33 @@ class KantaImpl(PersistenceMixin, Generic[T]):
                     cause_type=type(e).__name__,
                 ) from e
 
-            if self.migration_registry is not None:
+            migration_result = None
-                rr.version = self.migration_registry.apply(
+            state_before_migrations = None
+            previous_version = rr.version
+            if self.migrations is not None:
+                state_before_migrations = copy.deepcopy(rr.state)
+                migration_result = self.migrations.apply(
                     rr.state, rr.version, self._kanta
                 )
+                rr.version = migration_result.version
 
-            self.statedict = copy.deepcopy(rr.state)
+            migrations_ran = rr.version != previous_version
+            migration_state_changed = (
+                state_before_migrations is not None
+                and state_before_migrations != rr.state
+            )
+
+            self.snapshot.ts = (
+                datetime.fromtimestamp(rr.last_snapshot_mtime, UTC)
+                if rr.last_snapshot_mtime is not None
+                else None
+            )
+
+            self.statedict = copy.deepcopy(
+                state_before_migrations
+                if state_before_migrations is not None
+                else rr.state
+            )
             self.data = restore_data_in_place(
                 self.data,
                 rr.state,
@@ -159,34 +239,53 @@ class KantaImpl(PersistenceMixin, Generic[T]):
             if self.readonly:
                 self.statedict = copy.deepcopy(normalized)
             else:
-                self.queue_change("migrate:msgspec", normalized, mtime=False)
+                if migrations_ran and migration_state_changed:
-            self.snapshot.ts = (
+                    self.queue_change(
-                datetime.fromtimestamp(rr.last_snapshot_mtime, UTC)
+                        f"migrate:v{self.version}",
-                if rr.last_snapshot_mtime is not None
+                        rr.state,
-                else None
+                        mtime=False,
-            )
+                    )
+                msgspec_record = self.queue_change(
+                    "migrate:msgspec", normalized, mtime=False
+                )
+                if migrations_ran or msgspec_record is not None:
+                    self.snapshot.request_force()
+                    await self.flush()
+                    self.snapshot.maybe_write(
+                        self.file, self.version, self.statedict, m=self.mtime
+                    )
+
+                if migrations_ran and migration_result is not None:
+                    await self._handle_migration_log(
+                        migration_result, previous_version, log
+                    )
         elif self.readonly:
+            self.opened = False
             self.file.close()
             raise DataIntegrityError(
                 "Cannot open empty database in read-only mode",
                 db_path=self.filename,
                 action="open",
             )
-        elif self.callback_registry.has("bootstrap"):
+        else:
             try:
-                await self.callback_registry.invoke(
+                if self.callback_registry.has("bootstrap"):
-                    "bootstrap",
+                    await self.callback_registry.invoke(
-                    InjectionContext(data=self.data, kanta=self._kanta),
+                        "bootstrap",
-                )
+                        InjectionContext(data=self.data, kanta=self._kanta),
+                    )
 
+                self.statedict = {}
                 current = struct_to_dict(self.data, serializer=self.serializer)
                 self.queue_change(
                     self.bootstrap_action,
                     current,
                     user=self.bootstrap_user,
                     mtime=self.bootstrap_mtime,
+                    force=True,
                 )
             except Exception:
+                self.opened = False
                 self.file.close()
                 try:
                     await asyncio.to_thread(self.filename.unlink, missing_ok=True)
@@ -194,8 +293,6 @@ class KantaImpl(PersistenceMixin, Generic[T]):
                     pass
                 raise
 
-        self.opened = True
-
         if not self.readonly:
             self.background_task = asyncio.create_task(self._background_loop())
 

kanta/logging.py

@@ -10,7 +10,8 @@ import sys
 from collections.abc import Callable
 from typing import Any
 
-logger = logging.getLogger("kanta.changes")
+changes_logger = logging.getLogger("kanta.changes")
+migration_logger = logging.getLogger("kanta.migrations")
 
 # Pattern to match control characters and bidirectional overrides
 _UNSAFE_CHARS = re.compile(
@@ -274,6 +275,9 @@ def log_change(
     user: str | None = None,
     previous: dict | None = None,
     logfmt: Callable[[Any, str], str | None] | None = None,
+    *,
+    logger: logging.Logger = changes_logger,
+    level: int = logging.INFO,
 ) -> None:
     """Log a database change with pretty-printed diff.
 
@@ -283,27 +287,29 @@ def log_change(
         user: Optional already-formatted user name to show in the header.
         previous: The previous state dict (for determining add vs update).
         logfmt: Optional formatter callable ``(value, path) -> str | None``.
+        logger: Logger to write to. Defaults to the ``kanta.changes`` logger.
+        level: Log level to use. Defaults to ``logging.INFO``.
     """
     header = format_action_header(action, user)
     diff_lines = format_diff(diff, previous, logfmt)
 
     if not diff_lines:
-        logger.info(header)
+        logger.log(level, header)
         return
 
     if len(diff_lines) == 1:
-        logger.info(f"{header}{diff_lines[0]}")
+        logger.log(level, f"{header}{diff_lines[0]}")
     else:
-        logger.info(header)
+        logger.log(level, header)
         for line in diff_lines:
-            logger.info(line)
+            logger.log(level, line)
 
 
 def configure_logging() -> None:
     """Configure the database logger to output to stderr without prefix."""
-    if not logger.handlers:
+    if not changes_logger.handlers:
         handler = logging.StreamHandler(sys.stderr)
         handler.setFormatter(logging.Formatter("%(message)s"))
-        logger.addHandler(handler)
+        changes_logger.addHandler(handler)
-    logger.setLevel(logging.INFO)
+    changes_logger.setLevel(logging.INFO)
-    logger.propagate = False
+    changes_logger.propagate = False

kanta/migrate.py

@@ -1,122 +0,0 @@
-"""Database schema migration framework.
-
-Migrations are numbered functions discovered automatically via a decorator
-or by prefix. Each runs exactly once based on the current version.
-"""
-
-from __future__ import annotations
-
-import importlib
-import inspect
-import logging
-from types import ModuleType
-from typing import Any
-
-_logger = logging.getLogger(__name__)
-
-
-class MigrationRegistry:
-    """Registry of schema migration functions.
-
-    Usage::
-
-        registry = MigrationRegistry()
-
-        @registry.register
-        def migrate_v1(d: dict, kanta) -> None:
-            d.setdefault("version", 1)
-            kanta.ctx.note = "migrated"
-
-        @registry.register
-        def migrate_v2(d: dict) -> None:
-            d.setdefault("version", 2)
-
-        new_version = registry.apply(state, current_version=0, kanta=kanta)
-
-    Or load from a module::
-
-        registry = MigrationRegistry.from_module("myapp.migrations")
-        new_version = registry.apply(state, current_version=0, kanta=kanta)
-    """
-
-    def __init__(self) -> None:
-        self._migrations: dict[int, Any] = {}
-
-    @staticmethod
-    def _migration_version(fn: Any) -> int:
-        name = getattr(fn, "__name__", "")
-        if not name.startswith("migrate_v"):
-            raise ValueError(f"Invalid migration function name: {name!r}")
-        suffix = name.removeprefix("migrate_v")
-        if not suffix.isdigit() or int(suffix) <= 0:
-            raise ValueError(f"Invalid migration version in function name: {name!r}")
-        return int(suffix)
-
-    def register(self, fn):
-        """Decorator to register a migration function."""
-        version = self._migration_version(fn)
-        self._migrations[version] = fn
-        return fn
-
-    @classmethod
-    def from_module(cls, module: str | ModuleType) -> MigrationRegistry:
-        """Create a registry by scanning a module for ``migrate_vN`` functions.
-
-        Args:
-            module: A module name (string) or an imported module object.
-        """
-        reg = cls()
-        if isinstance(module, str):
-            mod = importlib.import_module(module)
-        else:
-            mod = module
-
-        for name in dir(mod):
-            if name.startswith("migrate_v"):
-                fn = getattr(mod, name)
-                if callable(fn):
-                    version = reg._migration_version(fn)
-                    reg._migrations[version] = fn
-        return reg
-
-    @property
-    def dbver(self) -> int:
-        """Current schema version (= highest discovered migration, or 0)."""
-        return max(self._migrations.keys(), default=0)
-
-    @staticmethod
-    def _call_migration(fn: Any, data_dict: dict[str, Any], kanta: Any) -> None:
-        """Call *fn* with the data dict and, if accepted, the Kanta instance."""
-        try:
-            inspect.signature(fn).bind(data_dict, kanta)
-        except TypeError:
-            fn(data_dict)
-        else:
-            fn(data_dict, kanta)
-
-    def apply(
-        self,
-        data_dict: dict[str, Any],
-        current_version: int,
-        kanta: Any,
-        *,
-        silent: bool = False,
-    ) -> int:
-        """Apply pending migrations to *data_dict* in place.
-
-        Returns the new version after all migrations.
-        """
-        while current_version < self.dbver:
-            next_version = current_version + 1
-            fn = self._migrations.get(next_version)
-            if fn is None:
-                raise ValueError(
-                    f"Missing migration step migrate_v{next_version} "
-                    f"(highest discovered is v{self.dbver})"
-                )
-            self._call_migration(fn, data_dict, kanta)
-            current_version = next_version
-            if not silent:
-                desc = (fn.__doc__ or fn.__name__).split("\n")[0].rstrip(".")
-                _logger.info("Applied migration %s: %s", fn.__name__, desc)
-        return current_version

kanta/migrations.py

@@ -0,0 +1,184 @@
+"""Database schema migration framework.
+
+Migrations are numbered functions discovered automatically via a decorator
+or by prefix. Each runs exactly once based on the current version.
+"""
+
+from __future__ import annotations
+
+import copy
+import importlib
+import inspect
+from dataclasses import dataclass
+from types import ModuleType
+from typing import Any
+
+from kanta.diff import compute_diff
+from kanta.exceptions import DatabaseError
+
+# Cache registries by imported module object so that many Kanta instances using
+# the same migrations module do not re-scan it each time.
+_module_registry_cache: dict[ModuleType, Migrations] = {}
+
+
+@dataclass
+class MigrationInfo:
+    """Information about a single migration that ran."""
+
+    name: str
+    description: str
+    version: int
+    changed: bool
+    diff: dict | None = None
+    before: dict | None = None
+
+
+@dataclass
+class MigrationResult:
+    """Result of applying migrations."""
+
+    version: int
+    migrations: list[MigrationInfo]
+
+
+class Migrations:
+    """Registry of schema migration functions.
+
+    Usage::
+
+        migrations = Migrations()
+
+        @migrations.register
+        def migrate_v1(d: dict, kanta) -> None:
+            d.setdefault("version", 1)
+            kanta.ctx.note = "migrated"
+
+        @migrations.register
+        def migrate_v2(d: dict) -> None:
+            d.setdefault("version", 2)
+
+        result = migrations.apply(state, current_version=0, kanta=kanta)
+        new_version = result.version
+
+    Or load from a module::
+
+        migrations = Migrations.from_module("myapp.migrations")
+        result = migrations.apply(state, current_version=0, kanta=kanta)
+    """
+
+    def __init__(self) -> None:
+        self._migrations: dict[int, Any] = {}
+
+    @staticmethod
+    def _migration_version(fn: Any) -> int:
+        name = getattr(fn, "__name__", "")
+        if not name.startswith("migrate_v"):
+            raise ValueError(f"Invalid migration function name: {name!r}")
+        suffix = name.removeprefix("migrate_v")
+        if not suffix.isdigit() or int(suffix) <= 0:
+            raise ValueError(f"Invalid migration version in function name: {name!r}")
+        return int(suffix)
+
+    def register(self, fn):
+        """Decorator to register a migration function."""
+        version = self._migration_version(fn)
+        self._migrations[version] = fn
+        return fn
+
+    @classmethod
+    def from_module(cls, module: str | ModuleType) -> Migrations:
+        """Create or retrieve a cached registry by scanning a module.
+
+        Args:
+            module: A module name (string) or an imported module object.
+        """
+        if isinstance(module, str):
+            mod = importlib.import_module(module)
+        else:
+            mod = module
+
+        try:
+            return _module_registry_cache[mod]
+        except KeyError:
+            pass
+
+        reg = cls()
+        for name in dir(mod):
+            if name.startswith("migrate_v"):
+                fn = getattr(mod, name)
+                if callable(fn):
+                    version = reg._migration_version(fn)
+                    reg._migrations[version] = fn
+        _module_registry_cache[mod] = reg
+        return reg
+
+    @property
+    def dbver(self) -> int:
+        """Current schema version (= highest discovered migration, or 0)."""
+        return max(self._migrations.keys(), default=0)
+
+    @property
+    def minver(self) -> int:
+        """Minimum supported current version (first migration minus 1, or 0)."""
+        return min(self._migrations.keys(), default=1) - 1
+
+    @staticmethod
+    def _call_migration(fn: Any, data_dict: dict[str, Any], kanta: Any) -> None:
+        """Call *fn* with the data dict and, if accepted, the Kanta instance."""
+        try:
+            inspect.signature(fn).bind(data_dict, kanta)
+        except TypeError:
+            fn(data_dict)
+        else:
+            fn(data_dict, kanta)
+
+    def apply(
+        self,
+        data_dict: dict[str, Any],
+        current_version: int,
+        kanta: Any,
+    ) -> MigrationResult:
+        """Apply pending migrations to *data_dict* in place.
+
+        Missing intermediate migration steps are silently skipped.
+
+        Raises:
+            DatabaseError: If the database version is newer than the highest
+                supported version or older than the minimum supported version.
+
+        Returns a :class:`MigrationResult` describing the new version and every
+        migration that ran.
+        """
+        if current_version > self.dbver:
+            raise DatabaseError(
+                f"Database version v{current_version} is newer than the "
+                f"highest supported version v{self.dbver}"
+            )
+        if current_version < self.minver:
+            raise DatabaseError(
+                f"Database version v{current_version} is older than the "
+                f"minimum supported version v{self.minver}"
+            )
+
+        migrations: list[MigrationInfo] = []
+        for version in sorted(self._migrations.keys()):
+            if version <= current_version:
+                continue
+            fn = self._migrations[version]
+            before = copy.deepcopy(data_dict)
+            self._call_migration(fn, data_dict, kanta)
+            current_version = version
+            changed = before != data_dict
+            diff = compute_diff(before, data_dict) if changed else None
+            desc = (fn.__doc__ or f"v{version}").split("\n")[0].rstrip(".")
+            migrations.append(
+                MigrationInfo(
+                    name=fn.__name__,
+                    description=desc,
+                    version=version,
+                    changed=changed,
+                    diff=diff,
+                    before=before,
+                )
+            )
+        return MigrationResult(version=current_version, migrations=migrations)

kanta/persistence.py

@@ -109,6 +109,7 @@ class PersistenceMixin:
         *,
         user: str | None = None,
         mtime: bool | datetime = True,
+        force: bool = False,
     ) -> ChangeRecord | None:
         """Queue a change record internally (thread-safe).
 
@@ -121,9 +122,11 @@ class PersistenceMixin:
                 previous modification time remains in effect; this is used for
                 system operations that are not considered modifications. A
                 :class:`~datetime.datetime` value sets ``m`` to that explicit time.
+            force: If ``True``, queue the record even when the diff is empty.
 
         Returns:
-            The queued :class:`ChangeRecord`, or ``None`` if the diff was empty.
+            The queued :class:`ChangeRecord`, or ``None`` if the diff was empty
+            and *force* is ``False``.
         """
         now = datetime.now(UTC)
 
@@ -138,7 +141,9 @@ class PersistenceMixin:
 
         diff = compute_diff(self.statedict, current)
         if not diff:
-            return None
+            if not force:
+                return None
+            diff = {}
 
         record = ChangeRecord(
             ts=now,

kanta/snapshot.py

@@ -41,15 +41,16 @@ class SnapshotState:
         self, file, version: int, state: dict, m: datetime | None = None
     ) -> None:
         """Write snapshot when thresholds/time policy allows it."""
-        if self.changes < self._min_diffs:
-            return
         force = self._force_pending
         now = datetime.now(UTC)
-        if not force and now.weekday() != 6:  # 6 = Sunday
+        if not force:
-            return
+            if self.changes < self._min_diffs:
-        sunday_midnight = now.replace(hour=0, minute=0, second=0, microsecond=0)
+                return
-        if not force and self.ts is not None and self.ts >= sunday_midnight:
+            if now.weekday() != 6:  # 6 = Sunday
-            return
+                return
+            sunday_midnight = now.replace(hour=0, minute=0, second=0, microsecond=0)
+            if self.ts is not None and self.ts >= sunday_midnight:
+                return
         if not file.is_open:
             return
         try:

kanta/structs.py

@@ -23,7 +23,7 @@ class ChangeRecord(msgspec.Struct, omit_defaults=True, kw_only=True):
     v: int = 0
     u: str | None = None
     m: datetime | None = None
-    diff: dict
+    diff: dict = {}
 
 
 class Snapshot(msgspec.Struct, omit_defaults=True):

kanta/transaction.py

@@ -9,7 +9,7 @@ from datetime import datetime
 from kanta.diff import compute_diff
 from kanta.exceptions import DataIntegrityError
 from kanta.callbacks import InjectionContext
-from kanta.logging import _USER_PATH, log_change
+from kanta.logging import _USER_PATH, changes_logger, log_change
 from kanta.serialization import restore_data_in_place, struct_to_dict
 
 _logger = logging.getLogger(__name__)
@@ -22,6 +22,7 @@ def transaction(
     *,
     user: str | None = None,
     mtime: bool | datetime = True,
+    log: bool | logging.Logger = True,
 ):
     """Wrap writes in a transaction and yield the live db object."""
     if impl.readonly:
@@ -80,7 +81,16 @@ def transaction(
                     resolved = logfmt(user, _USER_PATH)
                     if resolved is not None:
                         formatted_user = resolved
-                log_change(action, record.diff, formatted_user, previous, logfmt)
+                if log is not False:
+                    logger = log if isinstance(log, logging.Logger) else changes_logger
+                    log_change(
+                        action,
+                        record.diff,
+                        formatted_user,
+                        previous,
+                        logfmt,
+                        logger=logger,
+                    )
     except Exception:
         _logger.warning("Transaction '%s' failed, rolling back changes", action)
         if impl.transaction_snapshot is not None:

tests/support.py

@@ -7,7 +7,7 @@ from uuid import UUID
 import msgspec
 
 from kanta.kanta import Kanta
-from kanta.structs import ChangeRecord
+from kanta.structs import ChangeRecord, Snapshot
 
 
 class User(msgspec.Struct):
@@ -70,6 +70,18 @@ def change_actions(path: Path, format_config) -> list[str]:
     return actions
 
 
+def read_changes(path: Path, format_config) -> list[ChangeRecord]:
+    _, serializer_cls = format_config
+    serializer = serializer_cls()
+    framer = serializer.framer_cls()
+    records: list[ChangeRecord] = []
+    for is_snapshot, payload, _, _ in framer.iter_records(path.read_bytes(), 0):
+        if is_snapshot:
+            continue
+        records.append(serializer.decode(payload, type=ChangeRecord))
+    return records
+
+
 def make_migrations_module(name: str, fn_name: str, fn):
     mod = ModuleType(name)
     mod.__dict__[fn_name] = fn
@@ -77,6 +89,17 @@ def make_migrations_module(name: str, fn_name: str, fn):
     return mod
 
 
+def read_last_snapshot(path: Path, format_config) -> Snapshot | None:
+    _, serializer_cls = format_config
+    serializer = serializer_cls()
+    framer = serializer.framer_cls()
+    data = path.read_bytes()
+    payload, _, _ = framer.scan_last_snapshot(data)
+    if payload is None:
+        return None
+    return serializer.decode(payload, type=Snapshot)
+
+
 def fixed_change(action: str, diff: dict, *, version: int = 0) -> ChangeRecord:
     return ChangeRecord(
         ts=datetime(2026, 1, 1, tzinfo=UTC), a=action, v=version, diff=diff

tests/test_kanta_integration.py

@@ -1,4 +1,5 @@
 import asyncio
+import logging
 import sys
 from datetime import UTC, datetime
 from uuid import uuid4
@@ -6,6 +7,7 @@ from uuid import uuid4
 import pytest
 
 from kanta.exceptions import DatabaseError, DataIntegrityError, FileLockError
+from kanta.migrations import MigrationResult
 from kanta.serialization import struct_to_dict
 
 from .support import (
@@ -17,6 +19,9 @@ from .support import (
     change_actions,
     fixed_change,
     make_kanta,
+    make_migrations_module,
+    read_changes,
+    read_last_snapshot,
     seed_single_change,
 )
 
@@ -30,6 +35,63 @@ async def test_load_empty(tmp_path, format_config):
     await kanta.close()
 
 
+@pytest.mark.asyncio
+async def test_new_file_writes_bootstrap_record_without_handlers(
+    tmp_path, format_config
+):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+    await kanta.open()
+    await kanta.close()
+
+    records = read_changes(path, format_config)
+    assert len(records) == 1
+    assert records[0].a == "bootstrap"
+    assert records[0].diff == {"$replace": {"users": {}, "counter": 0}}
+
+
+@pytest.mark.asyncio
+async def test_new_file_persists_initial_state_for_roundtrip(tmp_path, format_config):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(
+        path, Data(counter=5, users={"alice": User(name="Alice")}), format_config
+    )
+    await kanta.open()
+    await kanta.close()
+
+    records = read_changes(path, format_config)
+    assert len(records) == 1
+    assert records[0].a == "bootstrap"
+    assert records[0].diff == {
+        "$replace": {"users": {"alice": {"name": "Alice", "age": 0}}, "counter": 5}
+    }
+
+    kanta2 = make_kanta(path, Data, format_config)
+    await kanta2.open()
+    assert kanta2.data.counter == 5
+    assert kanta2.data.users["alice"].name == "Alice"
+    await kanta2.close()
+
+
+@pytest.mark.asyncio
+async def test_reopen_without_changes_does_not_force_snapshot(tmp_path, format_config):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data(counter=5), format_config)
+    await kanta.open()
+    await kanta.close()
+
+    # No snapshot should exist after the initial bootstrap and close.
+    assert read_last_snapshot(path, format_config) is None
+
+    kanta2 = make_kanta(path, Data, format_config)
+    await kanta2.open()
+    assert kanta2.data.counter == 5
+    await kanta2.close()
+
+    # Re-opening without migrations or normalization changes must not force one.
+    assert read_last_snapshot(path, format_config) is None
+
+
 @pytest.mark.asyncio
 async def test_open_overwrites_caller_owned_root_data(tmp_path, format_config):
     path = tmp_path / "test.db"
@@ -434,6 +496,203 @@ async def test_msgspec_normalization_logs_migration(tmp_path, format_config):
     assert "migrate:msgspec" in change_actions(path, format_config)
 
 
+@pytest.mark.asyncio
+async def test_empty_migration_writes_snapshot_and_is_not_reapplied(
+    tmp_path, format_config
+):
+    path = tmp_path / "test.db"
+    seed_single_change(
+        path, fixed_change("init", {"counter": 0, "users": {}}), format_config
+    )
+
+    def migrate_v1(d, kanta):
+        """No-op migration that only bumps the schema version."""
+        pass
+
+    mod = make_migrations_module("empty_migration_mod", "migrate_v1", migrate_v1)
+
+    try:
+        kanta = make_kanta(path, Data, format_config, migrations=mod)
+        await kanta.open()
+        assert kanta.version == 1
+        await kanta.close()
+
+        # Empty migrations must not produce empty change records.
+        records = read_changes(path, format_config)
+        migration_records = [r for r in records if r.a.startswith("migrate")]
+        assert not migration_records
+
+        # The version bump is persisted via a snapshot instead.
+        snap = read_last_snapshot(path, format_config)
+        assert snap is not None
+        assert snap.v == 1
+        assert snap.state == {"counter": 0, "users": {}}
+
+        kanta2 = make_kanta(path, Data, format_config, migrations=mod)
+        await kanta2.open()
+        assert kanta2.version == 1
+        await kanta2.close()
+
+        # Re-opening must not create additional migration records or snapshots.
+        records2 = read_changes(path, format_config)
+        assert not [r for r in records2 if r.a.startswith("migrate")]
+    finally:
+        sys.modules.pop("empty_migration_mod", None)
+
+
+@pytest.mark.asyncio
+async def test_migration_with_changes_records_diff_and_snapshot(
+    tmp_path, format_config
+):
+    path = tmp_path / "test.db"
+    seed_single_change(path, fixed_change("init", {"counter": 0}), format_config)
+
+    mod = type(sys)("test_migrations_changes")
+
+    def migrate_v1(d, kanta):
+        d["counter"] = 2
+
+    mod.__dict__["migrate_v1"] = migrate_v1
+
+    kanta = make_kanta(path, Data, format_config, migrations=mod)
+    await kanta.open()
+    assert kanta.version == 1
+    assert kanta.data.counter == 2
+    await kanta.close()
+
+    records = read_changes(path, format_config)
+    migration_records = [r for r in records if r.a.startswith("migrate")]
+    assert len(migration_records) == 2
+    assert migration_records[0].a == "migrate:v1"
+    assert migration_records[0].v == 1
+    assert migration_records[0].diff == {"counter": 2}
+    assert migration_records[1].a == "migrate:msgspec"
+    assert migration_records[1].v == 1
+    assert migration_records[1].diff == {"users": {}}
+
+    snap = read_last_snapshot(path, format_config)
+    assert snap is not None
+    assert snap.v == 1
+    assert snap.state == {"counter": 2, "users": {}}
+
+
+@pytest.mark.asyncio
+async def test_migration_summary_log_includes_filename(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    seed_single_change(path, fixed_change("init", {"counter": 0}), format_config)
+
+    mod = type(sys)("test_migrations_log")
+
+    def migrate_v1(d, kanta):
+        """Bump counter."""
+        d["counter"] = 2
+
+    mod.__dict__["migrate_v1"] = migrate_v1
+
+    with caplog.at_level(logging.INFO, logger="kanta.migrations"):
+        kanta = make_kanta(path, Data, format_config, migrations=mod)
+        await kanta.open()
+        assert kanta.version == 1
+        await kanta.close()
+
+    info_messages = [r.message for r in caplog.records if r.levelno == logging.INFO]
+    assert len(info_messages) == 1
+    assert str(path) in info_messages[0]
+    assert "v0 -> v1" in info_messages[0]
+    assert "migrate_v1 (Bump counter)" in info_messages[0]
+
+
+@pytest.mark.asyncio
+async def test_open_log_false_suppresses_migration_log(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    seed_single_change(path, fixed_change("init", {"counter": 0}), format_config)
+
+    mod = type(sys)("test_migrations_silent")
+
+    def migrate_v1(d, kanta):
+        d["counter"] = 2
+
+    mod.__dict__["migrate_v1"] = migrate_v1
+
+    with caplog.at_level(logging.INFO, logger="kanta.migrations"):
+        kanta = make_kanta(path, Data, format_config, migrations=mod)
+        await kanta.open(log=False)
+        await kanta.close()
+
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert not info_messages
+
+
+@pytest.mark.asyncio
+async def test_logmigr_callback_replaces_default_logging(
+    tmp_path, format_config, caplog
+):
+    path = tmp_path / "test.db"
+    seed_single_change(path, fixed_change("init", {"counter": 0}), format_config)
+
+    mod = type(sys)("test_migrations_callback")
+
+    def migrate_v1(d, kanta):
+        """Bump counter."""
+        d["counter"] = 2
+
+    mod.__dict__["migrate_v1"] = migrate_v1
+
+    summaries = []
+
+    kanta = make_kanta(path, Data, format_config, migrations=mod)
+
+    @kanta.logmigr
+    def collect(summary: MigrationResult):
+        summaries.append(summary)
+
+    with caplog.at_level(logging.INFO, logger="kanta.migrations"):
+        await kanta.open()
+        await kanta.close()
+
+    assert len(summaries) == 1
+    assert summaries[0].version == 1
+    assert summaries[0].migrations[0].name == "migrate_v1"
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert not info_messages
+
+
+@pytest.mark.asyncio
+async def test_transaction_log_false_suppresses_log(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+    await kanta.open()
+
+    with caplog.at_level(logging.INFO, logger="kanta.changes"):
+        with kanta.transaction(action="inc", log=False) as data:
+            data.counter = 1
+
+    await kanta.close()
+
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert not info_messages
+
+
+@pytest.mark.asyncio
+async def test_transaction_log_custom_logger(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+    await kanta.open()
+
+    custom_logger = logging.getLogger("custom.transaction")
+    custom_logger.setLevel(logging.INFO)
+
+    with caplog.at_level(logging.INFO, logger="custom.transaction"):
+        with kanta.transaction(action="inc", log=custom_logger) as data:
+            data.counter = 1
+
+    await kanta.close()
+
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert len(info_messages) >= 1
+    assert "inc" in info_messages[0].message
+
+
 @pytest.mark.asyncio
 async def test_open_locked_file_raises_filelock_error(tmp_path, format_config):
     path = tmp_path / "test.db"

tests/test_logging.py

@@ -1,16 +1,15 @@
 import logging
 
-from kanta.logging import configure_logging, log_change
+from kanta.logging import changes_logger, configure_logging, log_change
-from kanta.logging import logger
 
 
 def test_configure_logging():
     configure_logging()
-    assert logger.level == logging.INFO
+    assert changes_logger.level == logging.INFO
 
 
 def test_log_change_no_diff(capsys):
-    logger.handlers.clear()
+    changes_logger.handlers.clear()
     configure_logging()
     log_change("test", {})
     captured = capsys.readouterr()

tests/test_migrations.py

@@ -1,6 +1,9 @@
 from types import ModuleType, SimpleNamespace
 
-from kanta.migrate import MigrationRegistry
+import pytest
+
+from kanta.exceptions import DatabaseError
+from kanta.migrations import Migrations
 
 
 class _DummyKanta:
@@ -9,7 +12,7 @@ class _DummyKanta:
 
 
 def test_register_and_apply():
-    reg = MigrationRegistry()
+    reg = Migrations()
     kanta = _DummyKanta()
 
     @reg.register
@@ -21,13 +24,13 @@ def test_register_and_apply():
         d["version"] = 2
 
     state = {}
-    new_ver = reg.apply(state, current_version=0, kanta=kanta, silent=True)
+    result = reg.apply(state, current_version=0, kanta=kanta)
-    assert new_ver == 2
+    assert result.version == 2
     assert state["version"] == 2
 
 
 def test_no_migrations_needed():
-    reg = MigrationRegistry()
+    reg = Migrations()
     kanta = _DummyKanta()
 
     @reg.register
@@ -35,8 +38,8 @@ def test_no_migrations_needed():
         d["x"] = 1
 
     state = {"x": 1}
-    new_ver = reg.apply(state, current_version=1, kanta=kanta, silent=True)
+    result = reg.apply(state, current_version=1, kanta=kanta)
-    assert new_ver == 1
+    assert result.version == 1
 
 
 def test_from_module():
@@ -52,17 +55,17 @@ def test_from_module():
     mod.__dict__["migrate_v1"] = migrate_v1
     mod.__dict__["migrate_v2"] = migrate_v2
 
-    reg = MigrationRegistry.from_module(mod)
+    reg = Migrations.from_module(mod)
     assert reg.dbver == 2
 
     state = {}
-    new_ver = reg.apply(state, current_version=0, kanta=kanta, silent=True)
+    result = reg.apply(state, current_version=0, kanta=kanta)
-    assert new_ver == 2
+    assert result.version == 2
     assert state["v"] == 2
 
 
 def test_migrations_can_use_kanta_ctx():
-    reg = MigrationRegistry()
+    reg = Migrations()
     kanta = _DummyKanta()
 
     @reg.register
@@ -71,14 +74,14 @@ def test_migrations_can_use_kanta_ctx():
         d["source"] = kanta.ctx.source
 
     state = {}
-    new_ver = reg.apply(state, current_version=0, kanta=kanta, silent=True)
+    result = reg.apply(state, current_version=0, kanta=kanta)
-    assert new_ver == 1
+    assert result.version == 1
     assert state["source"] == "migration"
     assert kanta.ctx.source == "migration"
 
 
 def test_migration_can_omit_kanta_argument():
-    reg = MigrationRegistry()
+    reg = Migrations()
     kanta = _DummyKanta()
 
     @reg.register
@@ -86,6 +89,120 @@ def test_migration_can_omit_kanta_argument():
         d["x"] = 1
 
     state = {}
-    new_ver = reg.apply(state, current_version=0, kanta=kanta, silent=True)
+    result = reg.apply(state, current_version=0, kanta=kanta)
-    assert new_ver == 1
+    assert result.version == 1
     assert state["x"] == 1
+
+
+def test_version_too_new():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v1(d):
+        d["x"] = 1
+
+    with pytest.raises(
+        DatabaseError,
+        match="Database version v2 is newer than the highest supported version v1",
+    ):
+        reg.apply({}, current_version=2, kanta=kanta)
+
+
+def test_version_too_old():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v3(d):
+        d["x"] = 3
+
+    with pytest.raises(
+        DatabaseError,
+        match="Database version v1 is older than the minimum supported version v2",
+    ):
+        reg.apply({}, current_version=1, kanta=kanta)
+
+
+def test_missing_middle_migration_is_skipped():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v1(d):
+        d["x"] = 1
+
+    @reg.register
+    def migrate_v3(d):
+        d["y"] = 3
+
+    state = {"x": 1}
+    result = reg.apply(state, current_version=1, kanta=kanta)
+    assert result.version == 3
+    assert state["x"] == 1
+    assert state["y"] == 3
+
+
+def test_old_migrations_deleted_current_supported():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v3(d):
+        d["x"] = 3
+
+    state = {"x": 2}
+    result = reg.apply(state, current_version=2, kanta=kanta)
+    assert result.version == 3
+    assert state["x"] == 3
+
+
+def test_apply_returns_change_information():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v1(d):
+        """Set x."""
+        d["x"] = 1
+
+    @reg.register
+    def migrate_v2(d):
+        """No-op."""
+        pass
+
+    @reg.register
+    def migrate_v3(d):
+        """Set y."""
+        d["y"] = 3
+
+    result = reg.apply({}, current_version=0, kanta=kanta)
+    assert result.version == 3
+    assert len(result.migrations) == 3
+
+    assert result.migrations[0].name == "migrate_v1"
+    assert result.migrations[0].description == "Set x"
+    assert result.migrations[0].changed is True
+    assert result.migrations[0].diff == {"$replace": {"x": 1}}
+
+    assert result.migrations[1].name == "migrate_v2"
+    assert result.migrations[1].description == "No-op"
+    assert result.migrations[1].changed is False
+    assert result.migrations[1].diff is None
+
+    assert result.migrations[2].name == "migrate_v3"
+    assert result.migrations[2].description == "Set y"
+    assert result.migrations[2].changed is True
+    assert result.migrations[2].diff == {"y": 3}
+
+
+def test_description_defaults_to_version_when_no_docstring():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v1(d):
+        d["x"] = 1
+
+    result = reg.apply({}, current_version=0, kanta=kanta)
+    assert result.migrations[0].description == "v1"

tests/test_mtime.py

@@ -82,8 +82,9 @@ async def test_transaction_mtime_false_preserves_mtime(tmp_path, format_config):
             continue
         records.append(serializer.decode(payload, type=ChangeRecord))
 
-    assert records[0].m == first_m
+    assert records[0].a == "bootstrap"
-    assert records[1].m is None
+    assert records[1].m == first_m
+    assert records[2].m is None
     assert kanta.mtime == first_m
 
 

tests/test_snapshot.py

@@ -32,3 +32,20 @@ def test_force_writes():
     f = FakeFile()
     ss.maybe_write(f, 1, {"x": 1})
     assert len(f.written) == 1
+
+
+def test_force_bypasses_min_diffs():
+    class FakeFile:
+        def __init__(self):
+            self.written = []
+            self.is_open = True
+
+        def write(self, data: bytes):
+            self.written.append(data)
+
+    ss = SnapshotState(min_diffs=100)
+    ss.record_changes(5)
+    ss.request_force()
+    f = FakeFile()
+    ss.maybe_write(f, 1, {"x": 1})
+    assert len(f.written) == 1