chore(sonar): fix CA1859 concrete types + CA1826 indexable collections

[thomasluizon]

What

SonarCloud smell burn-down (thomasluizon_orbit-api), two Roslyn performance rules, all behavior-preserving:

Rule	Count	Fix
external_roslyn:CA1859	29	Change interface-typed private locals/fields/params/returns to the concrete type Sonar named (List<T>, Dictionary<K,V>, int[], MemoryCache, MemoryDistributedCache, SystemPromptBuilder) where no polymorphism is needed.
external_roslyn:CA1826	11	Replace .FirstOrDefault() on IReadOnlyList<T> repository results with a Count/indexer check (x.Count > 0 ? x[0] : null); the null-conditional Results?.FirstOrDefault() becomes a { Count: > 0 } pattern.

Notes

• Only Sonar-flagged members were retyped. Where a rule fired on some overloads/methods but not others (e.g. CreateChallengeCommand.VerifyInvitedFriendsAsync, MoveHabitParentCommand.GetSubtreeHeight, ExportUserDataQuery freshStreakValues), the un-flagged declarations were left as-is to keep the diff surgical.
• Verified every caller already flows a concrete type and that no return-type change introduces a new CA1859 on a caller (all call sites use var or pass the result directly).
• dotnet build — 0 errors (13 pre-existing warnings, unrelated: NU1608/RS1038/CS9057/CS0618).
• dotnet test — 5284 passed, 0 failed, 0 skipped.

Refs thomasluizon/orbit-ui-mobile#243

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
89.2% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[claude]

Code Review: PR #388

Scope: chore(sonar): fix CA1859 concrete types + CA1826 indexable collections
Recommendation: APPROVE

Summary

Mechanical SonarCloud smell burn-down: 29 CA1859 interface→concrete-type retypes and 11 CA1826 FirstOrDefault()→indexer rewrites across 24 Orbit.Application/Orbit.Infrastructure files plus 8 matching test-file updates. No DTOs/Controllers/routes/auth/validation touched. Every retype was traced to its call site; every FirstOrDefault()→Count > 0 ? x[0] : null rewrite was verified against the source collection's actual return type (IGenericRepository<T>.FindAsync/FindTrackedIgnoringFiltersAsync return Task<IReadOnlyList<T>>, guaranteeing Count/indexer support) — semantically identical to FirstOrDefault().

A dedicated security review of the three highest-risk files independently confirmed:

• AgentTargetOwnershipService.AllOwnedAsync — ids retyped IReadOnlyCollection<Guid> → List<Guid>; the ownedCount == ids.Count / ids.Count == 0 checks are untouched; CollectGuids still returns List<Guid>. No authorization-bypass risk.
• ContentModerationService — payload?.Results is { Count: > 0 } results ? results[0] : null is behaviorally identical to the prior FirstOrDefault(); fail-open-only-on-empty-results semantics preserved, no swallowing of a flagged result.
• GetPublicProfileQuery, GetFriendProfileQuery, FriendGraphService lookup rewrites all filter on unique keys (Id, PublicProfileSlug, normalized Handle, ReferralCode); matches[0] selection is equivalent to the old FirstOrDefault(), no ordering-dependence introduced.

Findings

Critical

None.

High

None.

Medium

None.

Low / Info

• [Info] src/Orbit.Infrastructure/Services/PushNotificationService.cs:72 — subs as List<T> ?? subs.ToList() — subs is already declared List<Domain.Entities.PushSubscription>, so the cast always succeeds and the ?? subs.ToList() fallback is unreachable. Pre-existing (previously subs as IList<T>), not introduced by this diff. No action needed.

Deferred / N/A dimensions

• Build/test (dotnet): N/A — CI runs Build/Unit Tests/SonarCloud as separate required checks; PR body states 0 build errors, 5284/5284 tests passed.
• Contract-aligner / cross-repo parity: N/A — no DTO, Controller route, or packages/shared type touched; sibling orbit-ui-mobile repo not checked out regardless.
• Backend hard rules (timezone/authz/validation/logging/transactions): gated in, confirmed untouched — diff surface is type retyping only.

What's good

• Every retype verified compile-safe by checking the caller already produces the narrower concrete type, rather than trusting the "0 build errors" claim blindly.
• FirstOrDefault()→indexer rewrites backed by the repository interface contract (IReadOnlyList<T>), provably behavior-identical.
• No narration comments, TODO/FIXME/HACK, or dead code introduced.
• PR description is precise about scope and states verified build/test results.

Recommendation

Approve as-is. Clean, well-scoped, behavior-preserving Sonar cleanup with no correctness, security, or contract regressions found.