refactor: Replace in-process Inventory calls with HTTP client to inventory-service

[devin-ai-integration]

Summary

Decouples the Inventory module from the OrderManager monolith by replacing direct EF Core database access (InventoryService) with HTTP calls to the new standalone inventory microservice (InventoryHttpClient).

Key changes:

• Deleted InventoryService.cs (direct DB), InventoryItem.cs model, InventoryItems DbSet, seed data, and Product.Inventory navigation property
• Deleted Clients/InventoryServiceClient.cs — removed dead duplicate HTTP client class
• Added InventoryHttpClient (in Services/) — typed HTTP client calling the inventory microservice REST API for all inventory operations
• Updated InventoryController to proxy through InventoryHttpClient
• Updated OrderService.CreateOrderAsync to call DeductStockAsync over HTTP instead of mutating local InventoryItems (returns null on insufficient stock / 409)
• Updated ProductService to remove .Include(p => p.Inventory) from all queries
• Registered InventoryHttpClient via AddHttpClient<> in Program.cs with configurable InventoryService:BaseUrl (default http://localhost:5001)
• Updated tests with MockHttpMessageHandler to simulate inventory-service responses

Updates since last revision

• Removed dead Clients/InventoryServiceClient.cs and fixed namespace imports across InventoryController, OrderService, and Program.cs (were importing OrderManager.Api.Clients but class lives in OrderManager.Api.Services)
• Removed CheckStockAsync and StockCheckResult — the inventory microservice has no /check endpoint. OrderService.CreateOrderAsync now calls DeductStockAsync directly; a null return (from 409 Conflict) means insufficient stock
• Verified end-to-end integration locally: monolith on port 5000 + inventory-service on port 8080 — GET /api/inventory returns data from microservice, POST /api/orders deducts stock via HTTP, stock confirmed decremented on microservice

Review & Testing Checklist for Human

• No compensation for multi-item order failures: CreateOrderAsync loops over items calling DeductStockAsync for each. If deduction succeeds for item N but fails for item N+1 (or if SaveChangesAsync fails after all deductions), previously deducted items are not rolled back on the microservice. The old code did this atomically in a single DB transaction. Evaluate whether this is acceptable for workshop scope or if a saga/compensation pattern is needed.
• No HTTP resilience policies: No retry, circuit breaker, or fallback on InventoryHttpClient. If the inventory-service is unreachable, CreateOrderAsync throws unhandled HttpRequestException (raw 500 to client). The 30s timeout is the only safeguard. Consider adding Polly policies before production use.
• InventoryController.Restock has no error handling: If the inventory-service returns an error, the raw HttpRequestException propagates as an unhandled 500. Other controller endpoints have the same issue.
• End-to-end test: Start the inventory-service (port 8080 or configure InventoryService:BaseUrl) and the monolith on its default port. Verify: GET /api/inventory returns data, POST /api/orders deducts stock on the microservice, and ordering more than available stock returns a clear error (not an unhandled 500).

Notes

• The InventoryItems table will remain in existing SQLite databases (no drop migration generated) but is no longer read or written by the monolith.
• Test coverage is reduced: old tests verified actual inventory DB mutations; new tests only verify behavior against mocked HTTP responses. InventoryHttpClient methods are not virtual or behind an interface, making them harder to mock for unit testing.
• The companion inventory microservice PR is app_dotnet-angular-microservices PR #8 on the workshop-mason branch.

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/26a7c9b49dfb4214b6f9e3970bc9abf3

[devin-ai-integration]

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