Implement AI
This commit is contained in:
Chris Chen
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using System.Net.Http.Json;
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using System.Text.Json;
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using Microsoft.EntityFrameworkCore;
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using Microsoft.Extensions.Options;
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using ROLAC.API.Data;
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using ROLAC.API.DTOs.Expense;
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namespace ROLAC.API.Services.Ai;
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/// <summary>
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/// Calls the Google Gemini <c>generateContent</c> API to translate an expense description and
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/// classify it into the church's existing expense category catalog (大項 / 系項). The full active
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/// catalog is sent in the prompt so the model can only choose from real ids; any id it returns is
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/// re-validated against the catalog before being surfaced, so a hallucinated id is dropped, not echoed.
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/// </summary>
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public sealed class GeminiExpenseAiService : IExpenseAiService
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{
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private readonly HttpClient _http;
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private readonly GeminiOptions _options;
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private readonly AppDbContext _db;
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private readonly ILogger<GeminiExpenseAiService> _logger;
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public GeminiExpenseAiService(
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HttpClient http,
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IOptions<GeminiOptions> options,
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AppDbContext db,
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ILogger<GeminiExpenseAiService> logger)
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{
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_http = http;
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_options = options.Value;
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_db = db;
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_logger = logger;
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}
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public async Task<ExpenseAiSuggestion> SuggestAsync(string chineseText, decimal amount, CancellationToken ct = default)
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{
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// Load the active catalog: the allow-list the model must classify into.
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var groups = await _db.ExpenseCategoryGroups
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.AsNoTracking()
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.Where(group => group.IsActive)
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.OrderBy(group => group.SortOrder)
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.Select(group => new
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{
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group.Id,
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group.Name_en,
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group.Name_zh,
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Subs = group.SubCategories
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.Where(sub => sub.IsActive)
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.OrderBy(sub => sub.SortOrder)
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.Select(sub => new { sub.Id, sub.Name_en, sub.Name_zh })
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.ToList(),
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})
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.ToListAsync(ct);
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if (string.IsNullOrWhiteSpace(_options.ApiKey))
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{
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_logger.LogWarning("Gemini API key is not configured; expense AI assist is disabled.");
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return new ExpenseAiSuggestion();
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}
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try
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{
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var catalogJson = JsonSerializer.Serialize(groups);
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var prompt =
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"You are a bookkeeping assistant for a church. Given an expense description (often in " +
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"Traditional Chinese) and its amount, do two things:\n" +
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"1. Translate the description into concise, natural accounting English (a short noun phrase, " +
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"not a full sentence).\n" +
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"2. Choose the single best matching major category (group) and sub-category from the catalog " +
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"below. You MUST pick a groupId and subCategoryId that appear in the catalog, and the " +
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"subCategoryId must belong to that groupId. If nothing fits well, choose the closest " +
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"\"Other / 其他\" option and lower your confidence.\n\n" +
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$"Expense description: {chineseText}\n" +
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$"Amount: {amount}\n\n" +
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$"Category catalog (JSON; each group has an id, English/Chinese names, and its sub-categories):\n{catalogJson}\n\n" +
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"Respond with JSON: englishDescription (string), groupId (integer), subCategoryId (integer), " +
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"confidence (number 0..1).";
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var payload = new
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{
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contents = new[]
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{
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new { parts = new[] { new { text = prompt } } },
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},
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generationConfig = new
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{
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responseMimeType = "application/json",
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responseSchema = new
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{
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type = "object",
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properties = new
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{
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englishDescription = new { type = "string" },
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groupId = new { type = "integer" },
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subCategoryId = new { type = "integer" },
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confidence = new { type = "number" },
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},
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required = new[] { "englishDescription", "groupId", "subCategoryId", "confidence" },
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},
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},
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};
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var url = $"{_options.BaseUrl}/models/{_options.Model}:generateContent";
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using var request = new HttpRequestMessage(HttpMethod.Post, url)
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{
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Content = JsonContent.Create(payload),
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};
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request.Headers.Add("X-goog-api-key", _options.ApiKey);
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using var response = await _http.SendAsync(request, ct);
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if (!response.IsSuccessStatusCode)
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{
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var body = await response.Content.ReadAsStringAsync(ct);
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_logger.LogWarning("Gemini returned {Status}: {Body}", (int)response.StatusCode, body);
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return new ExpenseAiSuggestion();
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}
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// Navigate candidates[0].content.parts[0].text — the model's JSON answer as a string.
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using var doc = JsonDocument.Parse(await response.Content.ReadAsStreamAsync(ct));
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var text = doc.RootElement
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.GetProperty("candidates")[0]
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.GetProperty("content")
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.GetProperty("parts")[0]
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.GetProperty("text")
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.GetString();
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if (string.IsNullOrWhiteSpace(text))
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{
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_logger.LogWarning("Gemini response contained no text part.");
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return new ExpenseAiSuggestion();
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}
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var parsed = JsonSerializer.Deserialize<GeminiAnswer>(
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text, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });
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if (parsed is null) return new ExpenseAiSuggestion();
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var suggestion = new ExpenseAiSuggestion
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{
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EnglishDescription = string.IsNullOrWhiteSpace(parsed.EnglishDescription)
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? null
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: parsed.EnglishDescription.Trim(),
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Confidence = parsed.Confidence,
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};
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// Re-validate the returned ids against the catalog; drop anything that doesn't line up.
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var group = groups.FirstOrDefault(candidate => candidate.Id == parsed.GroupId);
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if (group is not null)
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{
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suggestion.GroupId = group.Id;
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suggestion.GroupLabel = Label(group.Name_en, group.Name_zh);
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var sub = group.Subs.FirstOrDefault(candidate => candidate.Id == parsed.SubCategoryId);
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if (sub is not null)
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{
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suggestion.SubCategoryId = sub.Id;
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suggestion.SubLabel = Label(sub.Name_en, sub.Name_zh);
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}
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}
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return suggestion;
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}
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catch (Exception ex)
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{
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_logger.LogError(ex, "Expense AI assist failed.");
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return new ExpenseAiSuggestion();
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}
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}
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/// <summary>Mirror the frontend's bilingual() convention: "English / 中文" (or just English).</summary>
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private static string Label(string nameEn, string? nameZh)
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=> string.IsNullOrWhiteSpace(nameZh) ? nameEn : $"{nameEn} / {nameZh}";
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/// <summary>Shape of the model's JSON answer (constrained by responseSchema).</summary>
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private sealed class GeminiAnswer
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{
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public string? EnglishDescription { get; set; }
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public int GroupId { get; set; }
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public int SubCategoryId { get; set; }
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public double Confidence { get; set; }
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}
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}
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@@ -0,0 +1,10 @@
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namespace ROLAC.API.Services.Ai;
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/// <summary>Google Gemini API settings (bound from the "Gemini" config section).</summary>
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public sealed class GeminiOptions
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{
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/// <summary>API key sent as the <c>X-goog-api-key</c> header. Keep out of source control.</summary>
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public string ApiKey { get; set; } = "";
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public string Model { get; set; } = "gemini-2.5-flash";
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public string BaseUrl { get; set; } = "https://generativelanguage.googleapis.com/v1beta";
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}
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@@ -0,0 +1,14 @@
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using ROLAC.API.DTOs.Expense;
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namespace ROLAC.API.Services.Ai;
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/// <summary>AI assistance for expense entry: translate a description and suggest a category.</summary>
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public interface IExpenseAiService
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{
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/// <summary>
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/// Translate <paramref name="chineseText"/> to concise accounting English and suggest the best
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/// major/sub category from the live catalog, using <paramref name="amount"/> as a hint.
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/// Never throws on an upstream/AI failure — returns a suggestion with null fields instead.
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/// </summary>
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Task<ExpenseAiSuggestion> SuggestAsync(string chineseText, decimal amount, CancellationToken ct = default);
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}
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