refactor(data): squash the 40 migrations into one InitialCreate

The incremental chain was ~31k lines of generated Designer snapshots for a
schema no shipped database steps through anymore. MigrateAndConfigure now
baselines an existing DB onto the squashed id (pre-EF, or history ending at
AddPrimeActionKind) and throws with a reinstall message for a mid-chain DB.
MigrationBaselineTests covers all three paths with a real Migrate().

tests/ClaudeDo.Data.Tests/MigrationBaselineTests.cs

@@ -0,0 +1,123 @@
+using ClaudeDo.Data.Models;
+using Microsoft.EntityFrameworkCore;
+
+namespace ClaudeDo.Data.Tests;
+
+// The 40 incremental migrations were squashed into one InitialCreate, so every existing database
+// carries a history EF no longer recognises. MigrateAndConfigure re-stamps those instead of
+// re-creating tables — this is the only test covering that path (every other Data.Tests fixture
+// uses EnsureCreated, which skips migrations entirely).
+// Replaces TaskNumberMigrationTests, whose subject (the AddTaskNumbers backfill) was squashed away.
+public sealed class MigrationBaselineTests : IDisposable
+{
+    private const string LastPreSquashMigrationId = "20260825063230_AddPrimeActionKind";
+    private const string SquashedMigrationId = "20260826094154_InitialCreate";
+
+    private readonly string _dbPath;
+    private readonly DbContextOptions<ClaudeDoDbContext> _options;
+
+    public MigrationBaselineTests()
+    {
+        _dbPath = Path.Combine(Path.GetTempPath(), $"claudedo_baseline_{Guid.NewGuid():N}.db");
+        _options = new DbContextOptionsBuilder<ClaudeDoDbContext>()
+            .UseSqlite($"Data Source={_dbPath}")
+            .Options;
+    }
+
+    public void Dispose()
+    {
+        Microsoft.Data.Sqlite.SqliteConnection.ClearAllPools();
+        foreach (var suffix in new[] { "", "-wal", "-shm" })
+            try { File.Delete(_dbPath + suffix); } catch { }
+    }
+
+    [Fact]
+    public void Fresh_database_migrates_and_seeds()
+    {
+        using var ctx = new ClaudeDoDbContext(_options);
+        ClaudeDoDbContext.MigrateAndConfigure(ctx);
+
+        Assert.Equal(new[] { SquashedMigrationId }, ctx.Database.GetAppliedMigrations());
+        Assert.NotEmpty(ctx.Lists);
+    }
+
+    [Fact]
+    public void Fully_migrated_pre_squash_database_is_restamped_and_keeps_its_rows()
+    {
+        SeedCurrentSchemaWithHistory(LastPreSquashMigrationId, taskTitle: "survivor");
+
+        using var ctx = new ClaudeDoDbContext(_options);
+        ClaudeDoDbContext.MigrateAndConfigure(ctx);
+
+        Assert.Equal(new[] { SquashedMigrationId }, ctx.Database.GetAppliedMigrations());
+        Assert.Equal("survivor", ctx.Tasks.Single().Title);
+    }
+
+    [Fact]
+    public void Restamping_is_idempotent()
+    {
+        SeedCurrentSchemaWithHistory(LastPreSquashMigrationId, taskTitle: "survivor");
+
+        using (var first = new ClaudeDoDbContext(_options))
+            ClaudeDoDbContext.MigrateAndConfigure(first);
+        using var second = new ClaudeDoDbContext(_options);
+        ClaudeDoDbContext.MigrateAndConfigure(second);
+
+        Assert.Equal(new[] { SquashedMigrationId }, second.Database.GetAppliedMigrations());
+        Assert.Equal("survivor", second.Tasks.Single().Title);
+    }
+
+    [Fact]
+    public void Database_stuck_mid_chain_fails_loudly_instead_of_being_stamped()
+    {
+        SeedCurrentSchemaWithHistory("20260810115437_AddFailureReason", taskTitle: "stale");
+
+        using var ctx = new ClaudeDoDbContext(_options);
+        var ex = Assert.Throws<InvalidOperationException>(() => ClaudeDoDbContext.MigrateAndConfigure(ctx));
+        Assert.Contains("Reinstall ClaudeDo", ex.Message);
+    }
+
+    [Fact]
+    public void Pre_ef_database_without_history_is_baselined()
+    {
+        SeedCurrentSchemaWithHistory(historyId: null, taskTitle: "legacy");
+
+        using var ctx = new ClaudeDoDbContext(_options);
+        ClaudeDoDbContext.MigrateAndConfigure(ctx);
+
+        Assert.Equal(new[] { SquashedMigrationId }, ctx.Database.GetAppliedMigrations());
+        Assert.Equal("legacy", ctx.Tasks.Single().Title);
+    }
+
+    // EnsureCreated builds today's schema without touching __EFMigrationsHistory, which is exactly
+    // the shape of a database that was fully migrated by the old chain: current tables, old history.
+    private void SeedCurrentSchemaWithHistory(string? historyId, string taskTitle)
+    {
+        using var seed = new ClaudeDoDbContext(_options);
+        seed.Database.EnsureCreated();
+
+        var list = new ListEntity { Id = "l1", Name = "List", CreatedAt = DateTime.UtcNow };
+        seed.Lists.Add(list);
+        seed.Tasks.Add(new TaskEntity
+        {
+            Id = "t1", ListId = list.Id, Title = taskTitle, Number = 1, CreatedAt = DateTime.UtcNow,
+        });
+        seed.SaveChanges();
+
+        if (historyId is null) return;
+
+        var conn = seed.Database.GetDbConnection();
+        conn.Open();
+        using var cmd = conn.CreateCommand();
+        cmd.CommandText = $"""
+            CREATE TABLE "__EFMigrationsHistory" (
+                "MigrationId" TEXT NOT NULL CONSTRAINT "PK___EFMigrationsHistory" PRIMARY KEY,
+                "ProductVersion" TEXT NOT NULL
+            );
+            INSERT INTO "__EFMigrationsHistory" ("MigrationId", "ProductVersion")
+            VALUES ('{historyId}', '8.0.11');
+            """;
+        cmd.ExecuteNonQuery();
+        conn.Close();
+    }
+}