Category/overall spend + transaction-count intents

[rghvgrv]

Parent

#145 — Ask Splitzy: personal spending chatbot (self-hosted LLM)

What to build

Extend the chat router and query layer from #146 with three more fixed intents: category spend totals, overall spend totals, and transaction counts — each distinguishing "my share of the split" from "what I paid". Adds the grocery/groceries → ExpenseCategory.Food synonym mapping the router uses to resolve informal category words.

Implementation Steps

1. Router prompt update — Extend the router prompt (backend/splitzy-dotnet/Services/Chat/Prompts/) and RouterResult intent enum from Chat foundation: streaming balance intent + router skeleton #146 with CategoryTotal, OverallTotal, TransactionCount, each carrying params { Metric: share|paid, Category?, From, To }. Add a category synonym map to the prompt (e.g. "grocery"/"groceries" → Food) covering the existing ExpenseCategory enum values in backend/splitzy-dotnet/Models/Expense.cs. [HITL]: confirm the grocery→Food mapping with product — flag it as a comment in the prompt template so it's easy to change later.
2. Category total query — Add Task<decimal> CategoryTotal(int userId, SpendMetric metric, ExpenseCategory category, DateTime from, DateTime to) to IChatQueryService/ChatQueryService (backend/splitzy-dotnet/Services/Chat/). share sums ExpenseSplit.OwedAmount where UserId = userId joined to Expense.Category; paid sums Expense.Amount where PaidByUserId = userId and Category matches. Both filter Expense.CreatedAt within [from, to].
3. Overall total + transaction count queries — Add Task<decimal> OverallTotal(int userId, SpendMetric metric, DateTime from, DateTime to) (same share/paid distinction, no category filter) and Task<int> TransactionCount(int userId, ExpenseCategory? category, DateTime from, DateTime to) to the same service.
4. Orchestrator dispatch — Update ChatOrchestrator.AskAsync (from Chat foundation: streaming balance intent + router skeleton #146) to dispatch the three new intents to the corresponding ChatQueryService methods before synthesis.
5. Tests — Extend backend/spllitzy-dotnet-tests/ChatControllerTests.cs (or a new ChatQueryServiceTests.cs following the same NUnit + TestHelper.CreateTestContext() pattern): category total correctness for both share and paid metrics against seeded fixture data, overall total correctness, transaction count correctness, and a router test proving "how much did I spend on groceries" resolves to CategoryTotal with Category = Food.

Agent Routing

agent_routing:
  complexity_hint: medium
  required_capability: balanced
  parallel_safe: false
  cost_preference: balanced
  speed_preference: balanced
  ownership_scope:
    - backend/splitzy-dotnet/Services/Chat/
    - backend/spllitzy-dotnet-tests/
  verification:
    - dotnet test backend/spllitzy-dotnet-tests
    - Manual Swagger call: "how much did I spend on groceries this month" and "how much have I paid overall this year"

Technical Context Snapshot

Current stack in scope

• Same backend stack as Chat foundation: streaming balance intent + router skeleton #146 (ASP.NET Core 8, EF Core 8 + Npgsql). This slice is additive to the Services/Chat/ module created there — no new infrastructure.
• Reuses ExpenseCategory enum (backend/splitzy-dotnet/Models/Expense.cs), ExpenseSplit.OwedAmount, Expense.Amount/Expense.PaidByUserId/Expense.CreatedAt.

Dependencies in scope

• Reuse only: EF Core LINQ querying, no new packages.
• New dependency additions allowed for this slice: no.

Architecture alignment

• Extends IChatQueryService/ChatQueryService and the router/orchestrator from Chat foundation: streaming balance intent + router skeleton #146 rather than introducing parallel structures.
• userId continues to be resolved server-side only, never taken from router/LLM output.
• create-git-issue provides routing hints only; it must not assign concrete agent/model names.
• run-with-it remains the final runtime routing authority.

Integration touchpoints

• No new endpoints — same POST /api/chat/stream contract from Chat foundation: streaming balance intent + router skeleton #146.
• No schema/migration changes; all data already exists in Expense/ExpenseSplit.

Acceptance criteria

• "How much did I spend on groceries this month" returns the correct Food-category share total for the authenticated user.
• "How much have I paid overall this year" returns the correct paid-total (not share-total) figure.
• Transaction count queries return the correct count for a given category/date range.

Blocked by

• Chat foundation: streaming balance intent + router skeleton #146