Add declarative TableSpec API with preload and fail-fast; fix shared-connection race

CHANGELOG.md

@@ -6,6 +6,24 @@ All notable changes to this project will be documented in this file.
 
 ---
 
+## [1.16.0] - 2026-06-11
+
+### Added
+- **Declarative table specs — `CachingEngine(tables=[TableSpec(...)])`** — declare each cached table up front (columns, indexes, refresh strategy, datetime columns, preload) instead of letting the engine learn columns lazily from queries. New public types `TableSpec`, `TTL`, `Delta` (a friendly alias of `DeltaConfig`) and exception `UndeclaredError`.
+  - **Background preload** — `preload=True` tables are loaded at startup (on the background thread by default, so startup isn't blocked; `blocking_startup_refresh=True` loads them synchronously). A copy already fresh in the persistent cache is skipped via the same double-checked locking added in 1.15.0, so a warm restart is instant.
+  - **Fail-fast on undeclared access** — in declarative mode a query referencing a table that has no `TableSpec`, or a column outside a spec's declared `columns` (including `SELECT *` on a column-restricted table), raises `UndeclaredError` instead of silently triggering an expensive lazy load / column-expansion. Declare `columns=None` to cache the whole table and allow any column.
+  - **Solves the lazy second-reload** — because columns are declared, a first query for a previously unseen column no longer forces a full re-fetch.
+- `executor.ensure_loaded(table, columns)` — preloads a table into the cache (reusing the full load path: delta/index augmentation, registry, watermark, double-checked locking) without materializing any rows.
+
+### Fixed
+- **Race on the shared cache connection** — the metadata reads (`is_table_cached`, `is_table_full`, `seconds_since_refresh`, `get_table_columns`, `get_last_synced_at`, `max_value`, `count_rows`) touched the single shared SQLite connection without the connection lock, so a query thread reading while the background refresh/preload thread wrote could raise `sqlite3.InterfaceError`. These reads now take the lock. More likely to surface now that startup preload adds background-thread activity.
+
+### Changed
+- `pyproject.toml` — bumped version to `1.16.0`.
+- **Fully backward compatible** — omit `tables=` and the legacy `delta=`/`ttl=`/`indexes=`/`datetime_columns=` kwargs behave exactly as before (lazy mode, no fail-fast). Passing both `tables=` and any of those kwargs raises `ValueError`; `tables=` is internally converted to the same config.
+
+---
+
 ## [1.15.0] - 2026-06-11
 
 ### Fixed

README.md

@@ -238,6 +238,41 @@ Each value is a list of index definitions: a string is a single-column index, a
 - Indexes are **recreated after every (re)load** — full loads, TTL reloads, and `invalidate()` + re-fetch all rebuild them — so they're always present, and they persist in `cache.db` across restarts.
 - Delta-tracked tables already get a unique index on their key columns; secondary indexes are independent and can be combined with `delta` or `ttl`.
 
+## Declarative initialization (`tables=`)
+
+Instead of the lazy "learn columns from queries" mode, you can **declare every table up front** with `tables=[TableSpec(...)]` — its columns, indexes, refresh strategy and which columns are datetimes — and have the engine preload them and reject anything undeclared:
+
+```python
+from sqlmem import CachingEngine, TableSpec, Delta, TTL
+
+engine = CachingEngine(
+    base_engine,
+    tables=[
+        TableSpec(
+            name="VW_P_PRATVALUES",
+            columns=["PRODUCT_PRODUCTNR", "PRAT_NAME", "PRATVALUE", "CHANGE_DATE"],
+            indexes=["PRODUCT_PRODUCTNR", "PRAT_NAME", "CHANGE_DATE"],
+            refresh=Delta(change_column="CHANGE_DATE", key_columns=["PRATVALUE_ID"]),
+            datetime_columns=["CHANGE_DATE"],
+            preload=True,
+        ),
+        TableSpec(
+            name="VW_PRODUCTS_ASSIGNED_E",
+            columns=["PRODUCT_PRODUCTNR", "ELEMENT_NAME", "ELEMENT_ID"],
+            indexes=["PRODUCT_PRODUCTNR"],
+            refresh=TTL(seconds=1800),
+            preload=True,
+        ),
+    ],
+    pragmas={"mmap_size": 32 * 1024**3, "page_size": 8192},
+)
+```
+
+- **Preload** — `preload=True` tables are loaded at startup (on the background thread by default, so startup isn't blocked; pass `blocking_startup_refresh=True` to load them synchronously before serving). A copy already fresh in the persistent cache is **skipped**, so a warm restart is instant. During warm-up a table reports `TableState.LOADING` in [`stats`](#runtime-statistics) — handy for gating a `503` until it's `ready`.
+- **Fail-fast** — a query for a table without a `TableSpec`, or for a column outside a spec's declared `columns` (including `SELECT *` on a column-restricted table), raises `UndeclaredError` instead of silently kicking off an expensive lazy load. Use `columns=None` to cache the whole table and allow any column.
+- `refresh=` takes a `Delta(change_column=…, key_columns=…)` (same as `DeltaConfig`) or `TTL(seconds=…)`, or `None` for a static table.
+- **Backward compatible** — omit `tables=` and the legacy `delta=`/`ttl=`/`indexes=`/`datetime_columns=` kwargs work exactly as before (lazy mode, no fail-fast). Passing both raises `ValueError`.
+
 ## Persistence
 
 By default the cache lives in an **in-memory SQLite** and is persisted to `cache.db` on disk:
@@ -413,9 +448,10 @@ By default the **startup catch-up** (delta pulls and TTL reloads for tables rest
 |---|---|
 | `ReadOnlyError` | INSERT, UPDATE, or DELETE statement |
 | `UnsupportedQueryError` | non-SELECT statement, `SELECT` without `FROM`, or an unqualified column in a multi-table query |
+| `UndeclaredError` | in [declarative mode](#declarative-initialization-tables) (`tables=`): a query references a table or column that was not declared |
 
 ```python
-from sqlmem import ReadOnlyError, UnsupportedQueryError
+from sqlmem import ReadOnlyError, UnsupportedQueryError, UndeclaredError
 ```
 
 ## Logging

project.md

@@ -225,10 +225,11 @@ SQLMEM_DEBUG=true   # DEBUG level — podrobný výpis každého dotazu, cache o
 - [x] **`vacuum(incremental=True)` varuje bez `auto_vacuum=INCREMENTAL`**: dřív tichý no-op; teď zaloguje warning (a jak to opravit) a vrátí se.
 - [x] **`Stats.db_size_bytes`**: velikost cache souboru na disku (0 v memory módu) ve `stats` pro monitoring.
 - [x] **Ochrana proti cache stampede**: `load_table` dělá double-checked locking — po získání `_load_lock` znovu ověří, zda tabulku mezitím nenahrál souběžný loader (cached + sloupce + ne-stale), a redundantní reload přeskočí. Bez toho druhý dotaz během studeného loadu velké tabulky spustil druhý plný reload (212M řádků = +2 h).
+- [x] **Deklarativní inicializace (`tables=[TableSpec(...)]`)**: předem se deklaruje každá tabulka (`TableSpec(name, columns, indexes, refresh=Delta(...)|TTL(...), datetime_columns, preload)`). `preload=True` se na pozadí (nebo blokujícně) přednahraje při startu; co je v persistentní cache čerstvé, se přeskočí (warm restart = instant). Nedeklarovaná tabulka/sloupec (i `SELECT *` na sloupcově omezené tabulce) → `UndeclaredError` (fail-fast) místo tichého líného loadu; `columns=None` = celá tabulka + libovolný sloupec. Plně zpětně kompatibilní: bez `tables=` fungují staré `delta=/ttl=/indexes=/datetime_columns=` jako dřív (kombinace obojího → `ValueError`).
 
 ## TODO — budoucí funkce
 
-- [ ] **Deklarativní inicializace (`tables=[TableSpec(...)]`)** — předem deklarovat sloupce/indexy/strategii každé tabulky, background preload, fail-fast na nedeklarované sloupce. Řeší líznou expanzi sloupců (druhý reload) a dělá z `execute()` čistě read-only. Plán pro 1.16.0.
+- _(zatím žádné otevřené položky)_
 
 ---
 

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "sqlmem"
-version = "1.15.0"
+version = "1.16.0"
 description = ""
 authors = [
     {name = "jan.doubravsky@gmail.com"}

src/sqlmem/__init__.py

@@ -7,7 +7,8 @@ from ._coerce import to_sqlite_datetime as datetime_to_epoch_us
 from .config import DEBUG
 from .delta import DeltaConfig
 from .engine import CachingEngine
-from .exceptions import ReadOnlyError, UnsupportedQueryError
+from .exceptions import ReadOnlyError, UndeclaredError, UnsupportedQueryError
+from .spec import TTL, Delta, TableSpec
 from .stats import Stats, TableStats
 
 _DEFAULT_FORMAT = (
@@ -59,8 +60,12 @@ def add_sink(sink: Any, *, level: str | None = None, **kwargs: Any) -> None:
 __all__ = [
     "CachingEngine",
     "DeltaConfig",
+    "Delta",
+    "TTL",
+    "TableSpec",
     "ReadOnlyError",
     "UnsupportedQueryError",
+    "UndeclaredError",
     "Stats",
     "TableStats",
     "add_sink",

src/sqlmem/cache.py

@@ -311,6 +311,7 @@ class CacheManager:
         return dict(self._last_run)
 
     def is_table_cached(self, table: str) -> bool:
+        with self._lock:  # the shared _conn must not be read while a writer uses it
             row = self._conn.execute(
                 "SELECT 1 FROM _sqlmem_tables WHERE table_name = ?", (table,)
             ).fetchone()
@@ -318,6 +319,7 @@ class CacheManager:
 
     def is_table_full(self, table: str) -> bool:
         """True if the whole table (all columns) is cached — a SELECT * cache hit."""
+        with self._lock:
             row = self._conn.execute(
                 "SELECT is_full FROM _sqlmem_tables WHERE table_name = ?", (table,)
             ).fetchone()
@@ -325,6 +327,7 @@ class CacheManager:
 
     def seconds_since_refresh(self, table: str) -> float | None:
         """Age of a cached table in seconds, or None if it is not cached."""
+        with self._lock:
             row = self._conn.execute(
                 "SELECT last_refresh_at FROM _sqlmem_tables WHERE table_name = ?", (table,)
             ).fetchone()
@@ -576,6 +579,7 @@ class CacheManager:
 
     def get_table_columns(self, table: str) -> list[str]:
         """Authoritative ordered column list of a cached table (via PRAGMA)."""
+        with self._lock:
             rows = self._conn.execute(f"PRAGMA table_info({quote(table)})").fetchall()
         return [r[1] for r in rows]
 
@@ -590,6 +594,7 @@ class CacheManager:
             self._conn.commit()
 
     def get_last_synced_at(self, table: str) -> str | None:
+        with self._lock:
             row = self._conn.execute(
                 "SELECT last_synced_at FROM _sqlmem_tables WHERE table_name = ?", (table,)
             ).fetchone()
@@ -610,6 +615,7 @@ class CacheManager:
 
         Returns an ``int`` for a datetime column stored as INTEGER µs, else the
         ISO ``TEXT`` string."""
+        with self._lock:
             row = self._conn.execute(
                 f"SELECT MAX({quote(column)}) FROM {quote(table)}"
             ).fetchone()
@@ -629,6 +635,7 @@ class CacheManager:
             self._conn.commit()
 
     def count_rows(self, table: str) -> int:
+        with self._lock:
             row = self._conn.execute(f"SELECT COUNT(*) FROM {quote(table)}").fetchone()
         return int(row[0]) if row else 0
 

src/sqlmem/engine.py

@@ -18,12 +18,50 @@ from .config import (
     SQL_DIALECT,
 )
 from .delta import DeltaConfig, DeltaRefresher, ResolvedDelta
+from .exceptions import UndeclaredError
 from .executor import QueryExecutor
-from .parser import Params, parse
+from .parser import Params, ParsedQuery, parse
 from .registry import ColumnRegistry
+from .spec import TTL, TableSpec
 from .stats import Stats, StatsCollector, TableState, TableStats
 
 
+def _specs_to_config(
+    tables: list[TableSpec],
+) -> tuple[
+    dict[str, DeltaConfig],
+    dict[str, int],
+    dict[str, list[str | list[str]]],
+    dict[str, list[str]],
+    dict[str, list[str] | None],
+]:
+    """Convert declarative ``TableSpec``s into the engine's internal config dicts.
+
+    Returns ``(delta, ttl, indexes, datetime_columns, declared)`` — the first four
+    mirror the legacy kwargs; ``declared`` maps each table to its allowed columns
+    (``None`` = whole table / any column) for fail-fast query checking.
+    """
+    delta: dict[str, DeltaConfig] = {}
+    ttl: dict[str, int] = {}
+    indexes: dict[str, list[str | list[str]]] = {}
+    datetime_columns: dict[str, list[str]] = {}
+    declared: dict[str, list[str] | None] = {}
+    for spec in tables:
+        if spec.name in declared:
+            raise ValueError(f"Duplicate TableSpec for table {spec.name!r}.")
+        declared[spec.name] = list(spec.columns) if spec.columns is not None else None
+        if spec.indexes:
+            indexes[spec.name] = list(spec.indexes)
+        if spec.datetime_columns:
+            datetime_columns[spec.name] = list(spec.datetime_columns)
+        refresh = spec.refresh
+        if isinstance(refresh, TTL):
+            ttl[spec.name] = refresh.seconds
+        elif isinstance(refresh, DeltaConfig):
+            delta[spec.name] = refresh
+    return delta, ttl, indexes, datetime_columns, declared
+
+
 class _LazySource:
     """A source connection opened on first ``execute`` and shared across one query.
 
@@ -68,9 +106,25 @@ class CachingEngine:
         pragmas: dict[str, str | int] | None = None,
         datetime_columns: dict[str, list[str]] | None = None,
         return_datetime: bool = True,
+        tables: list[TableSpec] | None = None,
         blocking_startup_refresh: bool = False,
     ) -> None:
         self._source_engine = source_engine
+
+        # Declarative mode: a list of TableSpecs is converted to the same internal
+        # config the legacy delta=/ttl=/indexes=/datetime_columns= kwargs produce,
+        # plus a declared-columns allowlist (for fail-fast) and preload set.
+        self._declared: dict[str, list[str] | None] | None = None
+        self._preload_specs: list[TableSpec] = []
+        if tables is not None:
+            if any(x is not None for x in (delta, ttl, indexes, datetime_columns)):
+                raise ValueError(
+                    "Pass either tables=[TableSpec(...)] or the legacy "
+                    "delta=/ttl=/indexes=/datetime_columns= kwargs, not both."
+                )
+            delta, ttl, indexes, datetime_columns, self._declared = _specs_to_config(tables)
+            self._preload_specs = [s for s in tables if s.preload]
+
         use_memory = IN_MEMORY if in_memory is None else in_memory
         self._dialect = dialect if dialect is not None else SQL_DIALECT
         self._refresh_interval = (
@@ -101,12 +155,14 @@ class CachingEngine:
                 "reload), not both."
             )
 
-        if self._delta or self._ttl:
-            # The startup catch-up (deltas/TTL reloads for tables restored from
-            # disk) can take a while on a cold start. By default it runs on the
-            # background thread so it never blocks application startup; callers
-            # who need the cache fully fresh before serving can opt back in.
+        if self._delta or self._ttl or self._preload_specs:
+            # Startup work (preload of declared tables + delta/TTL catch-up for
+            # tables restored from disk) can take a while on a cold start. By
+            # default it runs on the background thread so it never blocks
+            # application startup; callers who need the cache fully warm before
+            # serving can opt back in.
             if blocking_startup_refresh:
+                self._preload()
                 self._run_refresh()
             self._start_refresh_thread(initial_catch_up=not blocking_startup_refresh)
 
@@ -199,13 +255,8 @@ class CachingEngine:
             )
         return replace(table_stats, tracking=tracking, state=state, last_refresh=last_refresh)
 
-    def execute(self, sql: str, params: Params = None) -> list[dict]:
-        parsed = parse(sql, params, dialect=self._dialect)
-        # The source connection is opened lazily — a pure cache hit never touches
-        # the source and never occupies a pool slot.
-        source = _LazySource(self._source_engine)
-        try:
-            executor = QueryExecutor(
+    def _make_executor(self, source: Any) -> QueryExecutor:
+        return QueryExecutor(
             self._cache,
             self._registry,
             source,
@@ -214,7 +265,57 @@ class CachingEngine:
             self._ttl,
             self._index_columns,
         )
-            return executor.execute(parsed)
+
+    def _check_declared(self, parsed: ParsedQuery) -> None:
+        """In declarative mode, reject any table/column not declared up front."""
+        if self._declared is None:
+            return
+        for table in parsed.tables:
+            if table not in self._declared:
+                raise UndeclaredError(
+                    f"Table {table!r} is not declared in tables=[TableSpec(...)]. "
+                    "Add a TableSpec for it (declarative mode is a strict allowlist)."
+                )
+            allowed = self._declared[table]
+            if allowed is None:
+                continue  # whole table declared — any column is fine
+            if table in parsed.wildcard_tables:
+                raise UndeclaredError(
+                    f"SELECT * on {table!r} is not allowed: only columns {allowed} "
+                    "are declared. List the columns explicitly or declare "
+                    "columns=None for the whole table."
+                )
+            unknown = [c for c in parsed.columns_by_table.get(table, []) if c not in allowed]
+            if unknown:
+                raise UndeclaredError(
+                    f"Column(s) {unknown} of {table!r} are not declared "
+                    f"(declared: {allowed})."
+                )
+
+    def execute(self, sql: str, params: Params = None) -> list[dict]:
+        parsed = parse(sql, params, dialect=self._dialect)
+        self._check_declared(parsed)
+        # The source connection is opened lazily — a pure cache hit never touches
+        # the source and never occupies a pool slot.
+        source = _LazySource(self._source_engine)
+        try:
+            return self._make_executor(source).execute(parsed)
+        finally:
+            source.close()
+
+    def _preload(self) -> None:
+        """Load declared ``preload=True`` tables into the cache (skipping fresh copies)."""
+        if not self._preload_specs:
+            return
+        source = _LazySource(self._source_engine)
+        try:
+            executor = self._make_executor(source)
+            for spec in self._preload_specs:
+                try:
+                    logger.info(f"Preloading {spec.name!r}…")
+                    executor.ensure_loaded(spec.name, spec.columns)
+                except Exception as e:
+                    logger.error(f"Preload failed for {spec.name!r}: {e}")
         finally:
             source.close()
 
@@ -250,6 +351,7 @@ class CachingEngine:
     def _start_refresh_thread(self, initial_catch_up: bool = True) -> None:
         def loop() -> None:
             if initial_catch_up:
+                self._preload()      # off-main-thread declared-table preload
                 self._run_refresh()  # off-main-thread startup catch-up
             event = threading.Event()
             while not event.wait(self._refresh_interval):

src/sqlmem/exceptions.py

@@ -4,3 +4,13 @@ class ReadOnlyError(Exception):
 
 class UnsupportedQueryError(Exception):
     """Raised when a query uses unsupported features (JOIN, SELECT *)."""
+
+
+class UndeclaredError(Exception):
+    """Raised in declarative mode (``tables=[TableSpec(...)]``) when a query
+    references a table or column that was not declared up front.
+
+    Fail-fast by design: an undeclared table/column would otherwise trigger a
+    silent (potentially multi-hour) lazy load/column-expansion, so it is surfaced
+    immediately instead.
+    """

src/sqlmem/executor.py

@@ -42,6 +42,20 @@ class QueryExecutor:
             self._ensure_table(table, parsed)
         return self._run_in_memory(parsed)
 
+    def ensure_loaded(self, table: str, columns: list[str] | None) -> None:
+        """Preload *table* into the cache without running a query.
+
+        ``columns=None`` loads the whole table (``SELECT *`` semantics); otherwise
+        only the listed columns. Reuses the same load path as a real query — delta
+        key/change + index columns are augmented, the registry and watermark are
+        updated, and double-checked locking skips a copy already fresh in the
+        cache — but never materializes any rows (unlike :meth:`execute`).
+        """
+        if columns is None:
+            self._ensure_full(table)
+        else:
+            self._ensure_columns(table, columns)
+
     def _ensure_table(self, table: str, parsed: ParsedQuery) -> None:
         if table in parsed.wildcard_tables:
             self._ensure_full(table)

src/sqlmem/spec.py

@@ -0,0 +1,49 @@
+"""Declarative table specs for ``CachingEngine(tables=[...])``.
+
+Instead of the lazy "learn columns from queries" mode, an application can declare
+each table up front — its columns, indexes, refresh strategy and datetime columns —
+so the engine preloads them and rejects anything undeclared (fail-fast) rather than
+silently triggering an expensive lazy load. The legacy ``delta=/ttl=/indexes=``
+kwargs keep working; ``tables=`` is converted to the same internal config.
+"""
+
+from dataclasses import dataclass, field
+
+from .delta import DeltaConfig
+
+# Friendly alias for the declarative API; ``Delta`` and ``DeltaConfig`` are the
+# same type (``change_column`` + ``key_columns``), so either may be used as a
+# ``TableSpec.refresh`` strategy.
+Delta = DeltaConfig
+
+
+@dataclass(frozen=True)
+class TTL:
+    """Time-based refresh strategy: full-reload the table when older than *seconds*."""
+
+    seconds: int
+
+
+@dataclass(frozen=True)
+class TableSpec:
+    """Declarative specification of one cached table.
+
+    *columns* lists the columns to cache; leave it ``None`` to cache the whole
+    table (``SELECT *`` semantics) and allow any column. When columns are listed,
+    a query asking for a column outside the list raises
+    :class:`~sqlmem.exceptions.UndeclaredError`.
+
+    *refresh* is a :class:`Delta` (change-column incremental sync) or :class:`TTL`
+    (time-based full reload), or ``None`` for a static table loaded once.
+
+    *preload=True* loads the table at startup (in the background by default) so the
+    first query is a cache hit instead of paying a cold load; a copy already fresh
+    in the persistent cache is skipped.
+    """
+
+    name: str
+    columns: list[str] | None = None
+    indexes: list[str | list[str]] = field(default_factory=list)
+    refresh: DeltaConfig | TTL | None = None
+    datetime_columns: list[str] = field(default_factory=list)
+    preload: bool = False

tests/test_spec.py

@@ -0,0 +1,221 @@
+import sqlite3
+import time
+from datetime import datetime, timezone
+
+import pytest
+from sqlalchemy import create_engine
+
+from sqlmem import (
+    TTL,
+    CachingEngine,
+    Delta,
+    DeltaConfig,
+    TableSpec,
+    UndeclaredError,
+)
+
+
+@pytest.fixture
+def spec_source(tmp_path):
+    db = tmp_path / "src.db"
+    conn = sqlite3.connect(db)
+    conn.execute("CREATE TABLE products (id TEXT, name TEXT, price TEXT, changed TEXT)")
+    conn.executemany(
+        "INSERT INTO products VALUES (?, ?, ?, ?)",
+        [
+            ("1", "Widget", "9.99", "2026-06-01T10:00:00"),
+            ("2", "Gadget", "19.99", "2026-06-02T10:00:00"),
+        ],
+    )
+    conn.execute("CREATE TABLE orders (order_id TEXT, qty TEXT)")
+    conn.executemany("INSERT INTO orders VALUES (?, ?)", [("101", "2")])
+    conn.commit()
+    conn.close()
+    se = create_engine(f"sqlite:///{db}")
+    yield se
+    se.dispose()
+
+
+# --- back-compat / validation -----------------------------------------------
+
+
+def test_tables_and_legacy_kwargs_are_mutually_exclusive(spec_source):
+    with pytest.raises(ValueError):
+        CachingEngine(
+            spec_source,
+            tables=[TableSpec("products", ["id"])],
+            delta={"products": DeltaConfig("changed", ["id"])},
+        )
+
+
+def test_duplicate_tablespec_raises(spec_source):
+    with pytest.raises(ValueError):
+        CachingEngine(
+            spec_source,
+            tables=[TableSpec("products", ["id"]), TableSpec("products", ["name"])],
+        )
+
+
+def test_delta_alias_is_deltaconfig():
+    assert Delta is DeltaConfig
+
+
+# --- preload ----------------------------------------------------------------
+
+
+def test_preload_blocking_caches_before_first_query(spec_source, tmp_path):
+    ce = CachingEngine(
+        spec_source,
+        cache_db_path=tmp_path / "c.db",
+        tables=[TableSpec("products", ["id", "name"], preload=True)],
+        blocking_startup_refresh=True,
+    )
+    # Cached at construction time — no execute() needed.
+    assert ce._cache.is_table_cached("products") is True
+    rows = ce.execute("SELECT id, name FROM products")
+    assert {r["id"] for r in rows} == {"1", "2"}
+    ce.close()
+
+
+def test_preload_non_blocking_eventually_caches(spec_source, tmp_path):
+    ce = CachingEngine(
+        spec_source,
+        cache_db_path=tmp_path / "c.db",
+        tables=[TableSpec("products", ["id", "name"], preload=True)],
+    )
+    deadline = time.time() + 5
+    while not ce._cache.is_table_cached("products") and time.time() < deadline:
+        time.sleep(0.05)
+    assert ce._cache.is_table_cached("products") is True
+    ce.close()
+
+
+def test_non_preload_table_is_not_loaded_at_startup(spec_source, tmp_path):
+    ce = CachingEngine(
+        spec_source,
+        cache_db_path=tmp_path / "c.db",
+        tables=[TableSpec("products", ["id", "name"], preload=False)],
+        blocking_startup_refresh=True,
+    )
+    assert ce._cache.is_table_cached("products") is False  # loads lazily on first query
+    ce.execute("SELECT id, name FROM products")
+    assert ce._cache.is_table_cached("products") is True
+    ce.close()
+
+
+# --- fail-fast on undeclared tables / columns -------------------------------
+
+
+def test_fail_fast_undeclared_table(spec_source):
+    ce = CachingEngine(spec_source, tables=[TableSpec("products", ["id", "name"])])
+    with pytest.raises(UndeclaredError):
+        ce.execute("SELECT order_id FROM orders")
+    ce.close()
+
+
+def test_fail_fast_undeclared_column(spec_source):
+    ce = CachingEngine(spec_source, tables=[TableSpec("products", ["id", "name"])])
+    with pytest.raises(UndeclaredError):
+        ce.execute("SELECT price FROM products")
+    ce.close()
+
+
+def test_declared_columns_query_succeeds(spec_source):
+    ce = CachingEngine(spec_source, tables=[TableSpec("products", ["id", "name"])])
+    rows = ce.execute("SELECT id, name FROM products")
+    assert len(rows) == 2
+    ce.close()
+
+
+def test_columns_none_allows_wildcard_and_any_column(spec_source):
+    ce = CachingEngine(spec_source, tables=[TableSpec("products", columns=None)])
+    assert len(ce.execute("SELECT * FROM products")) == 2
+    assert len(ce.execute("SELECT price FROM products")) == 2  # any column allowed
+    ce.close()
+
+
+def test_wildcard_on_column_restricted_table_fails(spec_source):
+    ce = CachingEngine(spec_source, tables=[TableSpec("products", ["id", "name"])])
+    with pytest.raises(UndeclaredError):
+        ce.execute("SELECT * FROM products")
+    ce.close()
+
+
+def test_lazy_mode_has_no_fail_fast(spec_source):
+    """Without tables=, undeclared columns/tables load lazily as before."""
+    ce = CachingEngine(spec_source)
+    rows = ce.execute("SELECT order_id FROM orders")
+    assert len(rows) == 1
+    ce.close()
+
+
+# --- refresh strategies via TableSpec ---------------------------------------
+
+
+def test_tablespec_delta_tracking(spec_source, tmp_path):
+    ce = CachingEngine(
+        spec_source,
+        cache_db_path=tmp_path / "c.db",
+        tables=[
+            TableSpec(
+                "products",
+                ["id", "name", "changed"],
+                refresh=Delta(change_column="changed", key_columns=["id"]),
+                preload=True,
+            )
+        ],
+        blocking_startup_refresh=True,
+    )
+    assert ce.stats.tables["products"].tracking == "delta"
+    ce.close()
+
+
+def test_tablespec_ttl_tracking(spec_source, tmp_path):
+    ce = CachingEngine(
+        spec_source,
+        cache_db_path=tmp_path / "c.db",
+        tables=[TableSpec("products", ["id", "name"], refresh=TTL(seconds=1800), preload=True)],
+        blocking_startup_refresh=True,
+    )
+    assert ce.stats.tables["products"].tracking == "ttl"
+    ce.close()
+
+
+def test_tablespec_datetime_columns_roundtrip(spec_source, tmp_path):
+    ce = CachingEngine(
+        spec_source,
+        cache_db_path=tmp_path / "c.db",
+        tables=[
+            TableSpec("products", ["id", "changed"], datetime_columns=["changed"], preload=True)
+        ],
+        blocking_startup_refresh=True,
+    )
+    rows = ce.execute("SELECT id, changed FROM products WHERE changed > ?", ("2026-06-01T12:00:00",))
+    assert [r["id"] for r in rows] == ["2"]  # param coercion via datetime_columns
+    assert rows[0]["changed"] == datetime(2026, 6, 2, 10, 0, 0, tzinfo=timezone.utc)
+    ce.close()
+
+
+# --- warm restart: preload skips a copy already fresh on disk ---------------
+
+
+def test_warm_restart_preload_skips_reload(spec_source, tmp_path):
+    path = tmp_path / "c.db"
+
+    def make() -> CachingEngine:
+        return CachingEngine(
+            spec_source,
+            cache_db_path=path,
+            in_memory=False,
+            tables=[TableSpec("products", ["id", "name"], preload=True)],
+            blocking_startup_refresh=True,
+        )
+
+    ce1 = make()
+    assert ce1.stats.misses >= 1  # cold preload had to load from source
+    ce1.close()
+
+    ce2 = make()
+    assert ce2._cache.is_table_cached("products") is True
+    assert ce2.stats.misses == 0  # warm: preload was a cache hit, no redundant reload
+    ce2.close()