Merge feature/fix-import-cycle (FIX-IMPORT-CYCLE P0): break Gerbil<->Litter EF circular dependency on execute

Synth (chart-derived) litters now saved with FatherId/MotherId=null, then a deferred FK-update pass after all gerbils persist -> single-directional Gerbil->Litter dependency in the main save, no cycle. FK guard preserved. Regression: A-mother-is-B + B-mother-is-A cycle (SQLite, FK-enforced) asserts no throw + correct deferred FK. Gate: 158/158 (25/25 import), has-pending=No.

Unblocks the live WIPE+REIMPORT-3.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

GerbilManager.Tests/ImportServiceTests.cs

@@ -261,6 +261,54 @@ namespace GerbilManager.Tests
             finally { try { Directory.Delete(dir, recursive: true); } catch { } }
         }
 
+        [Fact]
+        public async Task Execute_circular_gerbil_litter_dependency_does_not_throw()
+        {
+            // Regression for "Unable to save changes because a circular dependency was detected":
+            // Gerbil [Added] ← FK{MotherId} Litter [Added] ← FK{LitterId} Gerbil [Added].
+            // Triggered when a gerbil is both parent (in one synth litter) and offspring
+            // (LitterId → another synth litter) in the SAME SaveChanges batch — forms a cycle EF
+            // topo-sort cannot resolve. This test encodes the minimal reproducer: A's mother is B,
+            // B's mother is A (artificial genealogical cycle, but triggers the EF cycle reliably).
+            var dir = Path.Combine(Path.GetTempPath(), "cycle-" + Guid.NewGuid().ToString("N"));
+            Directory.CreateDirectory(dir);
+            using var conn = new SqliteConnection("DataSource=:memory:");
+            conn.Open();
+            try
+            {
+                File.WriteAllText(Path.Combine(dir, "litters.json"), "[]");
+                File.WriteAllText(Path.Combine(dir, "animals.json"), """
+                [
+                  {"id":"alpha","name":"Alpha","dob":"01.01.2020","death":"","farbschlag":"",
+                   "genotype":{"mapped8locus":{},"rawGenotype":"","unmappedTokens":[]},"conflict":false,
+                   "parentRefs":[{"name":"Beta","dob":"01.01.2019","roleGuess":"mother","method":"chart-position","confidence":"medium"}]},
+                  {"id":"beta","name":"Beta","dob":"01.01.2019","death":"","farbschlag":"",
+                   "genotype":{"mapped8locus":{},"rawGenotype":"","unmappedTokens":[]},"conflict":false,
+                   "parentRefs":[{"name":"Alpha","dob":"01.01.2020","roleGuess":"mother","method":"chart-position","confidence":"medium"}]}
+                ]
+                """);
+                var opts = new DbContextOptionsBuilder<ApplicationContext>().UseSqlite(conn).Options;
+                using var db = new ApplicationContext(opts);
+                await db.Database.EnsureCreatedAsync();
+
+                // must NOT throw InvalidOperationException (circular dependency)
+                var report = await new ImportService(db, dir, dir).RunAsync(execute: true);
+
+                Assert.Equal(2, await db.Gerbils.CountAsync());
+                var alpha = await db.Gerbils.SingleAsync(g => g.ExternalRef == "alpha");
+                var beta  = await db.Gerbils.SingleAsync(g => g.ExternalRef == "beta");
+                // both should be litter-linked
+                Assert.NotNull(alpha.LitterId);
+                Assert.NotNull(beta.LitterId);
+                // deferred FK update must have set the litter parents correctly
+                var alphaLitter = await db.Litters.SingleAsync(l => l.Id == alpha.LitterId);
+                Assert.Equal(beta.Id, alphaLitter.MotherId);
+                var betaLitter = await db.Litters.SingleAsync(l => l.Id == beta.LitterId);
+                Assert.Equal(alpha.Id, betaLitter.MotherId);
+            }
+            finally { try { Directory.Delete(dir, recursive: true); } catch { } }
+        }
+
         [Fact]
         public async Task Derived_litter_with_quarantined_parent_leaves_FK_null_no_throw()
         {

GerbilManagerWebAPI/Import/ImportService.cs

@@ -289,10 +289,15 @@ namespace GerbilManagerWebAPI.Import
                     litterParents[lid] = (f, m);
                 }
 
-            // PASS 2: stage synthesized litters (parents already guarded above). DO NOT save them
-            // before the animals — the offspring AND the parent gerbils are created in the loop
-            // below, so a single SaveChanges at the end lets EF order parents→litters→offspring
-            // (all FKs are nullable). Saving litters first is exactly what caused the FK fault.
+            // FIX-IMPORT-CYCLE: track deferred synth litter parent FKs (populated in PASS 2 below).
+            // Synth litters are added with null FatherId/MotherId to break the Gerbil↔Litter cycle;
+            // the actual FKs are applied AFTER SaveChanges once all gerbils are persisted.
+            var synthLitterPendingParents = new Dictionary<Guid, (Guid? Father, Guid? Mother)>();
+
+            // PASS 2: stage synthesized litters (parents already guarded above). Litters are added
+            // with FatherId/MotherId = null (deferred) so that the SaveChanges below has only a
+            // one-directional Gerbil→Litter dependency — no Litter→Gerbil FKs in the same batch,
+            // which would cause EF's topo-sort to throw "circular dependency detected".
             if (execute)
             {
                 // reuse an existing litter with the same parents+date instead of duplicating.
@@ -316,13 +321,17 @@ namespace GerbilManagerWebAPI.Import
                         derivedLitters--;
                         continue;
                     }
+                    // Defer FatherId/MotherId: both parent gerbils and offspring gerbils may be [Added]
+                    // in this same batch. Setting them now causes EF circular dependency
+                    // (Gerbil[Added] ← Litter.MotherId [Added] ← Gerbil.LitterId [Added]).
+                    synthLitterPendingParents[sl.Id] = (sl.Father, sl.Mother);
                     _db.Litters.Add(new Litter
                     {
                         Id = sl.Id,
                         Name = $"Wurf (aus Diagramm) {sl.Date:yyyy-MM-dd}".Trim(),
                         Date = sl.Date ?? default,
-                        FatherId = sl.Father,
-                        MotherId = sl.Mother,
+                        FatherId = null,   // deferred — applied after gerbils SaveChanges
+                        MotherId = null,   // deferred — applied after gerbils SaveChanges
                         Notes = $"aus Stammbaum-Diagramm abgeleitet (Konfidenz: {sl.Confidence})",
                     });
                 }
@@ -437,6 +446,20 @@ namespace GerbilManagerWebAPI.Import
             }
             if (execute) await _db.SaveChangesAsync();
 
+            // Apply deferred synth litter parent FKs — all new gerbils are now persisted in the DB,
+            // so no cycle. FK guard already applied above (persisted set); values in the dict are safe.
+            if (execute && synthLitterPendingParents.Count > 0)
+            {
+                foreach (var (litId, (f, m)) in synthLitterPendingParents)
+                {
+                    var row = await _db.Litters.FindAsync(litId);
+                    if (row is null) continue;
+                    if (f is not null) row.FatherId = f;
+                    if (m is not null) row.MotherId = m;
+                }
+                await _db.SaveChangesAsync();
+            }
+
             // ---- back-link Wurfchronik litter parents by name (best effort) ----
             if (execute)
             {