OrderHub — Order Processing (.NET 8)

Modernised replacement for the legacy .NET Framework 4.7 OrderProcessor order flow. See MIGRATION.md for the zero-downtime migration plan.

Layout

src/OrderHub.Orders/
  Models.cs                      Typed request/result (replaces "FAIL: ..." strings)
  Abstractions.cs                Seams: school, catalog, stock, payment, notification
  Pricing/PricingService.cs      Tier discount + embroidery rules (pure, unit-tested)
  OrderProcessor.cs              Async orchestration
  Infrastructure/                Parameterised SQL, HttpClientFactory payment, SMTP
tests/OrderHub.Orders.Tests/
  PricingServiceTests.cs         Characterisation tests pinning the pricing rule

What the legacy slice got wrong, and where it's fixed

Legacy problem	Why it hurts in August	Fix
SQL built by string concatenation	Injectable from the public order form	Parameterised queries (Infrastructure/SqlStores.cs)
.PostAsync(...).Result	Sync-over-async → thread-pool starvation at peak	async end-to-end
new HttpClient() per order	Socket exhaustion under load	IHttpClientFactory-managed client
catch { /* swallow */ } on email	Parents pay, never hear back, nobody knows	Logged, alertable — still never fails a paid order
"OK" / "FAIL: ..." strings	Callers parse prose; typos become logic bugs	OrderResult with typed failure reasons
Pricing buried in if/else mid-method	Untestable; the rule most likely to drift in a rewrite	Extracted pure PricingService
No rounding on money	Sub-penny amounts sent to payment provider	Round per unit, 2 dp, away from zero

Deliberately out of scope for this first cut

• Stock reservation vs. stock check. The legacy code only checks stock, so two simultaneous orders can both pass and oversell. Preserved for behavioural parity; fixing it is an inventory-service concern (see Q4 decomposition) and changes business behaviour, so it needs a product decision, not a silent fix.
• EF Core / Dapper. ADO.NET kept close to the legacy queries makes the diff reviewable during migration. ORM adoption is a later, low-risk phase.
• Transactions / outbox. Arrives with the Q4 decomposition where the order gets persisted state.

Run the tests

dotnet test

The shipped test pins the rule I consider most important: tier discount is applied before the embroidery surcharge, and embroidery is never discounted. It's the money calculation, it's boundary-heavy (the 3-character embroidery threshold), and it's exactly the kind of rule that silently drifts during a rewrite.