fix(email): preserve draft send identity

Persist and export each draft's idempotency UUID so refresh and edits cannot create a fresh delivery identity. Add reversible provider-specific migration SQL.

JobTrackerApi/Controllers/BackupController.cs

@@ -100,6 +100,7 @@ namespace JobTrackerApi.Controllers
                     draft.Subject,
                     draft.BodyText,
                     draft.ThreadId,
+                    draft.ClientRequestId,
                     draft.Revision,
                     draft.CreatedAtUtc,
                     draft.UpdatedAtUtc))

JobTrackerApi/Controllers/EmailDraftsController.cs

@@ -25,6 +25,7 @@ public sealed class EmailDraftsController(
         string Subject,
         string BodyText,
         string? ThreadId,
+        string ClientRequestId,
         long Revision,
         DateTime CreatedAtUtc,
         DateTime UpdatedAtUtc);
@@ -41,15 +42,17 @@ public sealed class EmailDraftsController(
 
     [HttpGet]
     public async Task<ActionResult<IReadOnlyList<DraftDto>>> List(
-        [FromQuery] int jobApplicationId,
+        [FromQuery] int? jobApplicationId,
         CancellationToken cancellationToken)
     {
         var ownerUserId = GetOwnerUserId();
         if (ownerUserId is null) return Unauthorized();
-        if (jobApplicationId <= 0) return BadRequest("A valid job application is required.");
+        if (jobApplicationId is <= 0) return BadRequest("A valid job application is required.");
 
-        return Ok(await db.EmailDrafts.AsNoTracking()
-            .Where(draft => draft.OwnerUserId == ownerUserId && draft.JobApplicationId == jobApplicationId)
+        var query = db.EmailDrafts.AsNoTracking().Where(draft => draft.OwnerUserId == ownerUserId);
+        if (jobApplicationId.HasValue)
+            query = query.Where(draft => draft.JobApplicationId == jobApplicationId.Value);
+        return Ok(await query
             .OrderByDescending(draft => draft.UpdatedAtUtc)
             .Select(draft => new DraftDto(
                 draft.Id,
@@ -59,6 +62,7 @@ public sealed class EmailDraftsController(
                 draft.Subject,
                 draft.BodyText,
                 draft.ThreadId,
+                draft.ClientRequestId,
                 draft.Revision,
                 draft.CreatedAtUtc,
                 draft.UpdatedAtUtc))
@@ -103,6 +107,7 @@ public sealed class EmailDraftsController(
             Subject = subject,
             BodyText = bodyText,
             ThreadId = threadId,
+            ClientRequestId = Guid.NewGuid().ToString("D"),
             Revision = 1,
             CreatedAtUtc = now,
             UpdatedAtUtc = now,
@@ -193,6 +198,7 @@ public sealed class EmailDraftsController(
         draft.Subject,
         draft.BodyText,
         draft.ThreadId,
+        draft.ClientRequestId,
         draft.Revision,
         draft.CreatedAtUtc,
         draft.UpdatedAtUtc);