Initial commit: Crafter.DB

Header-only C++26 module library for typed, file-backed tables with
schema reflection, migrations, queries, and crash-safe commits.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

interfaces/Crafter.DB-Error.cppm

@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: LGPL-3.0-only
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+export module Crafter.DB:Error;
+import std;
+
+export namespace Crafter::DB {
+    // Root of every exception the library throws. Catch this to handle
+    // "the table is unusable" uniformly; catch the subclasses to react.
+    class Error : public std::runtime_error {
+    public:
+        using std::runtime_error::runtime_error;
+    };
+
+    // A system call failed. `code` carries errno, `path` the file involved.
+    class IOError : public Error {
+    public:
+        IOError(std::string_view what, std::error_code code, std::filesystem::path path)
+            : Error(std::format("{}: {} ({})", path.string(), what, code.message())), code(code), path(std::move(path)) {}
+
+        std::error_code code;
+        std::filesystem::path path;
+    };
+
+    // The file is not a Crafter.DB table or its header/commit records fail
+    // validation (bad magic, both commit CRCs wrong, extents outside the file).
+    class CorruptError : public Error {
+    public:
+        using Error::Error;
+    };
+
+    // The compiled struct and the file disagree: same version but a different
+    // fingerprint (struct changed without bumping `version`), a file newer
+    // than the code, or no `Previous` chain reaching the file's version.
+    class SchemaError : public Error {
+    public:
+        using Error::Error;
+    };
+
+    // A migration is needed but cannot run: the table was opened read-only or
+    // with `migrate = false`.
+    class MigrationError : public Error {
+    public:
+        using Error::Error;
+    };
+
+    // Another process (or another Table object in this process) holds the
+    // file lock in a conflicting mode.
+    class LockedError : public Error {
+    public:
+        using Error::Error;
+    };
+
+    // A write would break the order of the `orderedBy` column.
+    class OrderError : public Error {
+    public:
+        using Error::Error;
+    };
+
+    // A write was attempted on a table opened with `readOnly = true`.
+    class ReadOnlyError : public Error {
+    public:
+        using Error::Error;
+    };
+}