feat(agents): Phase 4 — ProductWatch Agent

[NavneetHegde]

Summary

• Implements the ProductWatchWorker BackgroundService that polls every 15s for active watches and finds matching products
• Adds MockProductSource (10-item catalog with ±15% price jitter and 70% availability simulation) registered as IProductSource
• Adds MatchingService — pure static helper filtering listings by price and optional preferred sellers
• Adds 31 unit tests across a new AgentPayWatch.Agents.ProductWatch.Tests project

Test plan

• All 31 new unit tests pass
• All existing unit tests continue to pass
• Start system via Aspire, create a watch for "iPhone" with maxPrice 999, wait 15-30s, confirm status transitions to Matched
• Check Aspire traces for Cosmos write and Service Bus publish on product-match-found

🤖 Generated with Claude Code

[NavneetHegde]

🔍 Phase 4 Code Review — ProductWatch Agent

Commits

• 7735ce4 feat(agents): implement Phase 4 — ProductWatch agent

Files Changed

File	Description
src/.../Mocks/MockProductSource.cs	New — 10-product hardcoded catalog; deterministic per-minute seed with ±15% price jitter and 70% availability filter
src/.../MatchingService.cs	New — pure static match evaluator (price ≤ maxPrice + optional seller filter, case-insensitive)
src/.../ProductWatchWorker.cs	New — BackgroundService polling every 15s; scan → match → persist ProductMatch → update WatchRequest → publish ProductMatchFound
src/.../Program.cs	Wired up AddInfrastructureServices() and AddHostedService<ProductWatchWorker>()
src/.../appsettings.json	New — PollIntervalSeconds: 15, Debug log level for agent namespace
src/AgentPayWatch.Infrastructure/DependencyInjection.cs	Registers MockProductSource as IProductSource singleton
AgentPayWatch.slnx	New test project added to solution
tests/.../Fakes.cs	Hand-written fakes for all 4 interfaces (no mocking library)
tests/.../MatchingServiceTests.cs	8 unit tests — price boundaries, seller filtering, case sensitivity
tests/.../MockProductSourceTests.cs	7 unit tests — known/unknown search terms, listing shape, URL format, price jitter bounds, 3-result cap
tests/.../ProductWatchWorkerTests.cs	10 unit tests — no watches, no listings, price filtering, match creation, status transition, event publishing, lowest-price selection, preferred sellers, multi-watch, expiry
tests/.../*.csproj	New test project targeting net10.0, xUnit 2.9.3, coverlet

Test Results

• ✅ Unit tests: 70 passed, 0 failed (8 skipped — integration tests requiring live emulators)
• ✅ Integration tests: 2 skipped (emulator not running — expected in CI without infrastructure)
• ✅ Build: 0 errors, 0 warnings
• ✅ New tests added: 31 new unit tests
• ✅ Branch up to date with main

Code Quality

• ✅ No Console.Write / debug statements
• ✅ No hardcoded secrets or API keys
• ✅ No TODO / FIXME comments
• ✅ No unused imports detected
• ✅ Error handling in ProductWatchWorker: per-watch exceptions are caught and logged, scan continues; scan-level exception is caught and retried next interval; graceful shutdown via OperationCanceledException

Potential Issues

• ⚠️ MockProductSource registered globally — IProductSource is registered in DependencyInjection.cs (shared Infrastructure DI), meaning all three agent projects will get the mock. This is fine for the current phase but should be swapped for a real implementation later. Consider a comment noting this is temporary.
• ⚠️ ProductWatchWorker timing test — ProductWatchWorkerTests uses Task.Delay(300ms) to let one scan cycle complete before StopAsync. This is reliable with synchronous fakes but could be flaky in heavily loaded CI environments. An internal-exposed scan method + InternalsVisibleTo would make these tests fully deterministic if that becomes a concern.
• ℹ️ No end-to-end test — Phase 5 will consume ProductMatchFound; integration coverage spans across phases. This is expected and acceptable at this stage.

Recommendation

✅ Ready to merge — implementation matches the Phase 4 spec exactly, all unit tests pass, no blocking issues. The two notes above are low-priority and can be addressed in later phases.