test(data): assert migrated schema matches EF model (schema-drift guard)

Sibling migrations branched off the same parent have silently dropped
each other's columns during a SQLite table rebuild before, and every
other Data.Tests fixture uses EnsureCreated, which skips the migration
chain entirely and would never catch that.

tests/ClaudeDo.Data.Tests/MigrationSchemaDriftTests.cs

@@ -0,0 +1,96 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Data.Sqlite;
+
+namespace ClaudeDo.Data.Tests;
+
+// Sibling migrations branched off the same parent have silently dropped each other's columns
+// during a SQLite table rebuild before (see docs/explore-notes). Every other Data.Tests fixture
+// uses EnsureCreated, which skips the migration chain entirely, so nothing else in the suite
+// would catch that. This compares the schema the migration chain actually produces against the
+// schema EnsureCreated builds from today's model.
+public sealed class MigrationSchemaDriftTests : IDisposable
+{
+    private readonly string _migratedDbPath;
+    private readonly string _modelDbPath;
+
+    public MigrationSchemaDriftTests()
+    {
+        _migratedDbPath = Path.Combine(Path.GetTempPath(), $"claudedo_drift_migrated_{Guid.NewGuid():N}.db");
+        _modelDbPath = Path.Combine(Path.GetTempPath(), $"claudedo_drift_model_{Guid.NewGuid():N}.db");
+    }
+
+    public void Dispose()
+    {
+        SqliteConnection.ClearAllPools();
+        foreach (var path in new[] { _migratedDbPath, _modelDbPath })
+            foreach (var suffix in new[] { "", "-wal", "-shm" })
+                try { File.Delete(path + suffix); } catch { }
+    }
+
+    [Fact]
+    public void Migrated_schema_has_the_same_columns_as_the_current_model()
+    {
+        using (var migrated = new ClaudeDoDbContext(OptionsFor(_migratedDbPath)))
+            ClaudeDoDbContext.MigrateAndConfigure(migrated);
+        using (var model = new ClaudeDoDbContext(OptionsFor(_modelDbPath)))
+            model.Database.EnsureCreated();
+
+        var migratedColumns = ReadColumnsByTable(_migratedDbPath);
+        var modelColumns = ReadColumnsByTable(_modelDbPath);
+
+        var mismatches = new List<string>();
+        foreach (var (table, expectedColumns) in modelColumns)
+        {
+            if (!migratedColumns.TryGetValue(table, out var actualColumns))
+            {
+                mismatches.Add($"{table}: missing from migrated schema entirely");
+                continue;
+            }
+
+            var missingInMigrated = expectedColumns.Except(actualColumns).ToList();
+            var extraInMigrated = actualColumns.Except(expectedColumns).ToList();
+            if (missingInMigrated.Count > 0 || extraInMigrated.Count > 0)
+            {
+                mismatches.Add(
+                    $"{table}: missing-in-migrated=[{string.Join(", ", missingInMigrated)}] " +
+                    $"extra-in-migrated=[{string.Join(", ", extraInMigrated)}]");
+            }
+        }
+
+        Assert.True(mismatches.Count == 0, "Schema drift between migrated DB and current model:\n" + string.Join("\n", mismatches));
+    }
+
+    private static DbContextOptions<ClaudeDoDbContext> OptionsFor(string dbPath) =>
+        new DbContextOptionsBuilder<ClaudeDoDbContext>()
+            .UseSqlite($"Data Source={dbPath}")
+            .Options;
+
+    private static Dictionary<string, HashSet<string>> ReadColumnsByTable(string dbPath)
+    {
+        using var conn = new SqliteConnection($"Data Source={dbPath}");
+        conn.Open();
+
+        var tables = new List<string>();
+        using (var cmd = conn.CreateCommand())
+        {
+            cmd.CommandText = "SELECT name FROM sqlite_master WHERE type='table' AND name != '__EFMigrationsHistory' AND name NOT LIKE 'sqlite_%'";
+            using var reader = cmd.ExecuteReader();
+            while (reader.Read())
+                tables.Add(reader.GetString(0));
+        }
+
+        var result = new Dictionary<string, HashSet<string>>();
+        foreach (var table in tables)
+        {
+            var columns = new HashSet<string>();
+            using var cmd = conn.CreateCommand();
+            cmd.CommandText = $"PRAGMA table_info(\"{table}\")";
+            using var reader = cmd.ExecuteReader();
+            while (reader.Read())
+                columns.Add(reader.GetString(reader.GetOrdinal("name")));
+            result[table] = columns;
+        }
+
+        return result;
+    }
+}