FEAT-NAMEGEN: GET /names/suggest backend (Gemini, 503 NamesKeyMissing, LitterLetter)

- NameSuggestionService: Gemini via existing OpenAiChatClient, builds
  letter/gender/usages/count prompt, strips markdown fences from response,
  deserialises [{name,meaning,origin}] array; NotConfigured -> 503.
- GET /names/suggest?letter=&gender=&usages=&count= -> Ok<List<NameSuggestion>>
  | 503 {code:NamesKeyMissing} | 502 {code:NamesUpstreamError}.
- Litter.LitterLetter (string?, nullable) + AddLitterLetter migration.
- 17 new tests (prompt assembly, fence strip, parse edge cases,
  503-not-configured, upstream-error); total 157/157 green.
- No Behind-the-Name dependency — Gemini path only (Julian's decision).

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

GerbilManagerWebAPI/Endpoints/NamesEndpoints.cs

@@ -0,0 +1,38 @@
+using GerbilManagerWebAPI.Names;
+
+namespace GerbilManagerWebAPI.Endpoints
+{
+    /// <summary>
+    /// FEAT-NAMEGEN: GET /names/suggest — meaningful gerbil name suggestions via Gemini.
+    ///
+    /// 503 {code:"NamesKeyMissing"} while the AI section is unconfigured — the
+    /// frontend maps exactly this code to its German disabled-state hint.
+    /// </summary>
+    public static class NamesEndpoints
+    {
+        public static IEndpointRouteBuilder MapNamesEndpoints(this IEndpointRouteBuilder app)
+        {
+            app.MapGet("/names/suggest", async (
+                string? letter,
+                string? gender,
+                string? usages,
+                int count,
+                NameSuggestionService service,
+                CancellationToken ct) =>
+            {
+                var result = await service.SuggestAsync(letter, gender, usages, count, ct);
+                return result.Status switch
+                {
+                    NameSuggestionStatus.Ok => Results.Ok(result.Suggestions),
+                    NameSuggestionStatus.NotConfigured => Results.Json(
+                        new { code = "NamesKeyMissing", message = result.Error ?? "" }, statusCode: 503),
+                    _ => Results.Json(
+                        new { code = "NamesUpstreamError", message = result.Error ?? "" }, statusCode: 502),
+                };
+            })
+            .WithTags("Names");
+
+            return app;
+        }
+    }
+}

GerbilManagerWebAPI/Migrations/20260606185411_AddLitterLetter.cs

@@ -0,0 +1,28 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace GerbilManagerWebAPI.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddLitterLetter : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "LitterLetter",
+                table: "Litters",
+                type: "text",
+                nullable: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "LitterLetter",
+                table: "Litters");
+        }
+    }
+}

GerbilManagerWebAPI/Migrations/ApplicationContextModelSnapshot.cs

@@ -905,6 +905,9 @@ namespace GerbilManagerWebAPI.Migrations
                     b.Property<Guid?>("FatherId")
                         .HasColumnType("uuid");
 
+                    b.Property<string>("LitterLetter")
+                        .HasColumnType("text");
+
                     b.Property<Guid?>("MotherId")
                         .HasColumnType("uuid");
 

GerbilManagerWebAPI/Models/Litter.cs

@@ -30,5 +30,9 @@ namespace GerbilManagerWebAPI.Models
         /// nulls allowed for manually-entered litters). Primary idempotency key for re-imports;
         /// Name+Date is the fallback for litters created before this column existed.</summary>
         public string? ExternalRef { get; set; }
+
+        /// <summary>FEAT-NAMEGEN: Wurfbuchstabe (A, B, C … AA, AB …) — alle Welpen dieses
+        /// Wurfs erhalten Namen mit diesem Anfangsbuchstaben (gängige Zuchtkonvention).</summary>
+        public string? LitterLetter { get; set; }
     }
 }

GerbilManagerWebAPI/Names/NameSuggestion.cs

@@ -0,0 +1,5 @@
+namespace GerbilManagerWebAPI.Names
+{
+    /// <summary>FEAT-NAMEGEN: a single name suggestion returned by GET /names/suggest.</summary>
+    public sealed record NameSuggestion(string Name, string Meaning, string Origin);
+}

GerbilManagerWebAPI/Names/NameSuggestionService.cs

@@ -0,0 +1,107 @@
+using System.Text;
+using System.Text.Json;
+using GerbilManagerWebAPI.Ai;
+using GerbilManagerWebAPI.SaleAd;
+using Microsoft.Extensions.Options;
+
+namespace GerbilManagerWebAPI.Names
+{
+    /// <summary>
+    /// FEAT-NAMEGEN: generates meaningful gerbil name suggestions via Gemini
+    /// (the same OpenAiChatClient used by sale-ads and reply-drafts).
+    /// Returns NotConfigured when the AI section is missing — callers map to 503.
+    /// </summary>
+    public sealed class NameSuggestionService(HttpClient http, IOptions<AiOptions> options)
+    {
+        private readonly OpenAiChatClient _client = new(http, options);
+
+        private static readonly JsonSerializerOptions JsonOpts = new()
+        {
+            PropertyNameCaseInsensitive = true,
+        };
+
+        public async Task<NameSuggestionResult> SuggestAsync(
+            string? letter, string? gender, string? usages, int count,
+            CancellationToken ct = default)
+        {
+            var aiResult = await _client.CompleteAsync(
+                BuildSystemPrompt(),
+                BuildUserPrompt(letter, gender, usages, count),
+                ct);
+
+            if (aiResult.Status == AiCallStatus.NotConfigured)
+                return new NameSuggestionResult(NameSuggestionStatus.NotConfigured, null, aiResult.Error);
+            if (aiResult.Status != AiCallStatus.Ok || aiResult.Text is null)
+                return new NameSuggestionResult(NameSuggestionStatus.UpstreamError, null, aiResult.Error);
+
+            var suggestions = ParseSuggestions(aiResult.Text);
+            return suggestions is null
+                ? new NameSuggestionResult(NameSuggestionStatus.UpstreamError, null, "Ungültiges JSON in KI-Antwort.")
+                : new NameSuggestionResult(NameSuggestionStatus.Ok, suggestions, null);
+        }
+
+        internal static string BuildSystemPrompt() =>
+            "Du bist ein Helfer für Rennmaus-Züchter. " +
+            "Antworte IMMER mit einem reinen JSON-Array — KEINE Markdown-Code-Blöcke, " +
+            "KEINE Erklärungen, KEIN Text außerhalb des Arrays. " +
+            "Jedes Element hat genau die Felder: name, meaning, origin (alle Strings, alle auf Deutsch).";
+
+        internal static string BuildUserPrompt(string? letter, string? gender, string? usages, int count)
+        {
+            var sb = new StringBuilder();
+            sb.Append($"Schlage {count} Rennmaus-Namen vor");
+            if (!string.IsNullOrWhiteSpace(letter))
+                sb.Append($" die mit dem Buchstaben \"{letter.ToUpperInvariant()}\" beginnen");
+            if (!string.IsNullOrWhiteSpace(gender) &&
+                !gender.Equals("any", StringComparison.OrdinalIgnoreCase))
+                sb.Append($", passend für {(gender.Equals("female", StringComparison.OrdinalIgnoreCase) ? "weibliche" : "männliche")} Tiere");
+            if (!string.IsNullOrWhiteSpace(usages))
+                sb.Append($", aus den Kulturkreisen: {usages}");
+            sb.Append(". Jeder Name muss eine echte etymologische Bedeutung und Herkunft haben ");
+            sb.Append("(keine erfundenen oder zufälligen Namen). ");
+            sb.Append($"Antworte mit genau {count} Elementen als reines JSON-Array: ");
+            sb.Append("[{\"name\":\"...\",\"meaning\":\"...\",\"origin\":\"...\"}]");
+            return sb.ToString();
+        }
+
+        /// <summary>
+        /// Strips optional markdown fences (```json ... ```) Gemini sometimes wraps around
+        /// its JSON output, then deserialises the array.
+        /// </summary>
+        internal static List<NameSuggestion>? ParseSuggestions(string raw)
+        {
+            var text = raw.Trim();
+
+            // Strip ```json ... ``` or ``` ... ``` fences.
+            if (text.StartsWith("```", StringComparison.Ordinal))
+            {
+                var firstNewline = text.IndexOf('\n');
+                if (firstNewline >= 0) text = text[(firstNewline + 1)..];
+                if (text.EndsWith("```", StringComparison.Ordinal))
+                    text = text[..^3].TrimEnd();
+            }
+
+            // Find the JSON array bounds defensively.
+            var start = text.IndexOf('[');
+            var end = text.LastIndexOf(']');
+            if (start < 0 || end <= start) return null;
+            text = text[start..(end + 1)];
+
+            try
+            {
+                return JsonSerializer.Deserialize<List<NameSuggestion>>(text, JsonOpts);
+            }
+            catch (JsonException)
+            {
+                return null;
+            }
+        }
+    }
+
+    public enum NameSuggestionStatus { Ok, NotConfigured, UpstreamError }
+
+    public sealed record NameSuggestionResult(
+        NameSuggestionStatus Status,
+        List<NameSuggestion>? Suggestions,
+        string? Error);
+}

GerbilManagerWebAPI/Program.cs

@@ -45,6 +45,9 @@ builder.Services.AddHttpClient<GerbilManagerWebAPI.SaleAd.SaleAdService>(
 // INBOX-2: KI-Antwortentwurf (gleiche AI-Sektion, gleicher Wire-Client).
 builder.Services.AddHttpClient<GerbilManagerWebAPI.Inbox.DraftReplyService>(
     http => http.Timeout = TimeSpan.FromSeconds(60));
+// FEAT-NAMEGEN: Name suggestions via Gemini (same AI section, same wire client).
+builder.Services.AddHttpClient<GerbilManagerWebAPI.Names.NameSuggestionService>(
+    http => http.Timeout = TimeSpan.FromSeconds(60));
 
 // INBOX-0: Gmail inbox. App Password encrypted at rest via Data Protection.
 // AR-3: persist the key ring so encrypted passwords survive image redeployments.
@@ -100,6 +103,7 @@ app.MapSettingsEndpoints();
 app.MapExportEndpoints();
 app.MapCmsEndpoints();
 app.MapRequestEndpoints();
+app.MapNamesEndpoints();
 
 app.Run();