fix(backend): eliminate N+1 query patterns in portfolio and projects #1420

[ifygreg01-best]

Summary

Closes #1420

Audited the four modules called out in the issue (grants, projects, contributor-feed, portfolio). Grants and contributor-feed are pure in-memory (no DB/RPC calls in loops). The five worst patterns were all in portfolio and projects.

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Five Worst Endpoints — Before / After

#	Endpoint	Before (10 items)	After	Fix
1	POST /portfolio/snapshots (primary path)	10 price calls	1	getAssetValuesUsd() batch
2	POST /portfolio/snapshots (fallback path)	10 price calls	1	getAssetValuesUsd() batch
3	GET /portfolio/account/:key	10 price calls	1	getAssetValuesUsd() batch
4	GET /portfolio/allocation	10 price calls	1	getAssetValuesUsd() batch
5	GET /projects + refreshMaterializedSnapshots	N sequential RPC calls	concurrent + capped at 10	Preloaded states + Promise.allSettled

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Changes

Batch price fetching (fixes #1, 2, 3, 4)

• PriceService.getPricesForAssets(codes[]) — single batched lookup; when a real price-feed API is wired in, this is the only place to change
• StellarBalanceService.getAssetValuesUsd(assets[]) — replaces four independent Promise.all(items.map(getPrice)) patterns with one call
• portfolio.service.ts — createSnapshot, getPortfolioSummaryForAccount, getAssetAllocation all updated

Projects list fix (fix #5a)

• projects.service.ts listProjects: preload all on-chain states with a single concurrent Promise.all before mapping, instead of one fetchOnChainState per row inside a .map()

Sequential refresh loop fix (fix #5b)

• refreshMaterializedSnapshots: replace sequential for loop with Promise.allSettled batches (concurrency cap = 10)

Query profiling middleware (off by default)

• Extended QueryProfilerService with AsyncLocalStorage-based per-request call counter (trackCall, runInContext)
• New QueryCountMiddleware wraps each request and logs the final call count
• Registered in AppModule behind QUERY_PROFILING=true — zero overhead in production
• ProfilingModule updated to export new middleware

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Tests

New regression test: src/portfolio/portfolio-n-plus-one.spec.ts

Spies on getPricesForAssets and asserts it is called exactly once regardless of portfolio size:

PASS src/portfolio/portfolio-n-plus-one.spec.ts
  PortfolioService – N+1 regression guard
    createSnapshot – price call count is O(1) not O(N)
      ✓ portfolio with 1 asset(s) → exactly 1 batch price call
      ✓ portfolio with 5 asset(s) → exactly 1 batch price call
      ✓ portfolio with 10 asset(s) → exactly 1 batch price call
      ✓ call count does NOT grow with portfolio size (O(1) assertion)
    getAssetAllocation – price call count is O(1) not O(N)
      ✓ 1 aggregated asset(s) → exactly 1 batch price call
      ✓ 5 aggregated asset(s) → exactly 1 batch price call
      ✓ 10 aggregated asset(s) → exactly 1 batch price call

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Documentation

apps/backend/QUERY_PROFILING.md — covers how to enable profiling mode, what gets logged, the middleware architecture, the five fixed endpoints with before/after counts, and how to run the regression test.

Enable with:

QUERY_PROFILING=true npm run start:dev

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[Cedarich]

lgtm