refactor(db): migrate cover letter history

Move append-only cover letter revisions into an additive provider-aware migration. Preserve manual and AI text, source metadata, ordering, and application cascade semantics.

JobTrackerApi/Migrations/20260830131000_AdoptCoverLetterVersionSchema.cs

@@ -0,0 +1,64 @@
+using System;
+using JobTrackerApi.Data;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace JobTrackerApi.Migrations;
+
+/// <summary>
+/// Moves append-only cover-letter revision history into migration ownership without replacing
+/// manually edited or AI-approved document versions.
+/// </summary>
+[DbContext(typeof(JobTrackerContext))]
+[Migration("20260830131000_AdoptCoverLetterVersionSchema")]
+public sealed class AdoptCoverLetterVersionSchema : Migration
+{
+    protected override void Up(MigrationBuilder migrationBuilder)
+    {
+        if (ActiveProvider.Contains("MySql", StringComparison.OrdinalIgnoreCase))
+        {
+            migrationBuilder.Sql("""
+                CREATE TABLE IF NOT EXISTS `CoverLetterVersions` (
+                    `Id` int NOT NULL AUTO_INCREMENT,
+                    `OwnerUserId` varchar(255) NOT NULL,
+                    `JobApplicationId` int NOT NULL,
+                    `Version` int NOT NULL,
+                    `Text` longtext NOT NULL,
+                    `Source` varchar(32) NOT NULL,
+                    `AiAction` varchar(32) NULL,
+                    `CreatedAtUtc` datetime(6) NOT NULL,
+                    PRIMARY KEY (`Id`),
+                    CONSTRAINT `FK_CoverLetterVersions_JobApplications_JobApplicationId`
+                        FOREIGN KEY (`JobApplicationId`) REFERENCES `JobApplications` (`Id`) ON DELETE CASCADE
+                ) CHARACTER SET=utf8mb4;
+                CREATE INDEX IF NOT EXISTS `IX_CoverLetterVersions_Owner_Job_Version`
+                    ON `CoverLetterVersions` (`OwnerUserId`, `JobApplicationId`, `Version`);
+                """);
+            return;
+        }
+
+        migrationBuilder.Sql("""
+            CREATE TABLE IF NOT EXISTS "CoverLetterVersions" (
+                "Id" INTEGER NOT NULL CONSTRAINT "PK_CoverLetterVersions" PRIMARY KEY AUTOINCREMENT,
+                "OwnerUserId" TEXT NOT NULL,
+                "JobApplicationId" INTEGER NOT NULL,
+                "Version" INTEGER NOT NULL,
+                "Text" TEXT NOT NULL,
+                "Source" TEXT NOT NULL,
+                "AiAction" TEXT NULL,
+                "CreatedAtUtc" TEXT NOT NULL,
+                CONSTRAINT "FK_CoverLetterVersions_JobApplications_JobApplicationId"
+                    FOREIGN KEY ("JobApplicationId") REFERENCES "JobApplications" ("Id") ON DELETE CASCADE
+            );
+            CREATE INDEX IF NOT EXISTS "IX_CoverLetterVersions_Owner_Job_Version"
+                ON "CoverLetterVersions" ("OwnerUserId", "JobApplicationId", "Version");
+            """);
+    }
+
+    protected override void Down(MigrationBuilder migrationBuilder)
+    {
+        // Preserve recoverable document history created before migration ownership.
+    }
+}

JobTrackerApi/Models/CoverLetterVersion.cs

@@ -7,7 +7,7 @@ namespace JobTrackerApi.Models;
 // to be, so an AI rewrite or a bad edit is never destructive. Mirrors CvVariantVersion: restore
 // re-saves an old snapshot as a new version rather than rewinding.
 //
-// Reconciler-owned (docs/infrastructure/database-ownership.md) — its migration is a no-op.
+// Migration-owned; the historical no-op is followed by an additive provider-aware adoption.
 public sealed class CoverLetterVersion
 {
     public int Id { get; set; }

JobTrackerApi/Services/StartupInitializationExtensions.cs

@@ -712,25 +712,6 @@ public static class StartupInitializationExtensions
                     EnsureColumn(c, "AiInteractions", "EstimatedTokenCount", "ALTER TABLE AiInteractions ADD COLUMN EstimatedTokenCount INTEGER NOT NULL DEFAULT 0;");
                 }
 
-                // Phase 5.4: append-only cover letter history.
-                static void EnsureCoverLetterVersionsTable(DbConnection c)
-                {
-                    Exec(c, """
-        CREATE TABLE IF NOT EXISTS "CoverLetterVersions" (
-            "Id" INTEGER NOT NULL CONSTRAINT "PK_CoverLetterVersions" PRIMARY KEY AUTOINCREMENT,
-            "OwnerUserId" TEXT NOT NULL,
-            "JobApplicationId" INTEGER NOT NULL,
-            "Version" INTEGER NOT NULL,
-            "Text" TEXT NOT NULL,
-            "Source" TEXT NOT NULL,
-            "AiAction" TEXT NULL,
-            "CreatedAtUtc" TEXT NOT NULL,
-            CONSTRAINT "FK_CoverLetterVersions_JobApplications_JobApplicationId" FOREIGN KEY ("JobApplicationId") REFERENCES "JobApplications" ("Id") ON DELETE CASCADE
-        );
-        """);
-                    Exec(c, """CREATE INDEX IF NOT EXISTS "IX_CoverLetterVersions_Owner_Job_Version" ON "CoverLetterVersions" ("OwnerUserId", "JobApplicationId", "Version");""");
-                }
-
                 // Phase 5.5: user-owned interview preparation (not the AI cache InterviewPrepNote).
                 static void EnsureInterviewPrepItemsTable(DbConnection c)
                 {
@@ -756,7 +737,6 @@ public static class StartupInitializationExtensions
                 ReconcileGmailConnectionColumns(conn);
                 EnsureCareerProfileTables(conn);
                 ReconcileAiInteractionUsageColumns(conn);
-                EnsureCoverLetterVersionsTable(conn);
                 EnsureInterviewPrepItemsTable(conn);
 
                 // Once the base app tables exist, provision this reconciler-owned schema set and
@@ -1151,24 +1131,6 @@ public static class StartupInitializationExtensions
                     DropMalformedMySqlTable(conn, "CoverLetterVersions", "CreatedAtUtc", "datetime");
                     DropMalformedMySqlTable(conn, "InterviewPrepItems", "CreatedAtUtc", "datetime");
 
-                    if (!HasMySqlTable(conn, "CoverLetterVersions") && HasMySqlTable(conn, "JobApplications"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = @"CREATE TABLE IF NOT EXISTS `CoverLetterVersions` (
-        `Id` int NOT NULL AUTO_INCREMENT,
-        `OwnerUserId` varchar(255) NOT NULL,
-        `JobApplicationId` int NOT NULL,
-        `Version` int NOT NULL,
-        `Text` longtext NOT NULL,
-        `Source` varchar(32) NOT NULL,
-        `AiAction` varchar(32) NULL,
-        `CreatedAtUtc` datetime(6) NOT NULL,
-        PRIMARY KEY (`Id`),
-        CONSTRAINT `FK_CoverLetterVersions_JobApplications_JobApplicationId` FOREIGN KEY (`JobApplicationId`) REFERENCES `JobApplications` (`Id`) ON DELETE CASCADE
-        );";
-                        cmd.ExecuteNonQuery();
-                    }
-
                     if (!HasMySqlTable(conn, "InterviewPrepItems") && HasMySqlTable(conn, "JobApplications"))
                     {
                         using var cmd = conn.CreateCommand();

JobTrackerApi/Services/StartupSchemaOwnership.cs

@@ -18,6 +18,7 @@ internal static class StartupSchemaOwnership
         "Attachments",
         "Companies",
         "Correspondences",
+        "CoverLetterVersions",
         "CvExtractionRuns",
         "CvUploadArtifacts",
         "CvVariants",
@@ -60,7 +61,6 @@ internal static class StartupSchemaOwnership
         "CareerProfileVersions",
         "CareerProjects",
         "CareerSkills",
-        "CoverLetterVersions",
         "InterviewPrepItems",
     };