fix: bound external calls — Discord-429 storm + Musical-Taste hang

[LucasSantana-Dev]

Converged resilience hotfixes (Track A of the logging-hardening ADR + the Musical-Taste perf ADR). All three share one root cause — unbounded external calls + caches gated on a decommissioned Redis — so they're fixed together with shared utilities.

What & why

Shared foundation

• withTimeout(promise, ms, label) + delay(ms) (@lucky/shared/utils/async) — bound any external call so a hung promise becomes a logged, recoverable error instead of an invisible forever-pending request.
• TtlCache (@lucky/shared/utils/cache) — bounded in-memory TTL cache, the replacement for Redis read-through caches of regenerable/external-API data (single-instance; per the Redis-removal ADRs).

Discord-429 guild-context (fixes the /moderation/cases + /logs "weird UI" — they were degraded by a 429 storm, not a UX bug)

• GuildAccessService: guild-list cache moved off Redis (an unhealthy client meant a miss on every request → per-request /users/@me/guilds → 429 storm) into a bounded TtlCache; 429-fallback now logged at WARN (was INFO, invisible).
• DiscordOAuthService.getUserGuilds: parses Retry-After with bounded backoff + a 10s timeout.

Musical-Taste Discover hang (the forever-spinner)

• ArtistSuggestionService.getSuggestions: each tier (incl. the Postgres read) runs under a ~5s deadline; on timeout the tier is skipped and whatever was collected is returned — the endpoint always responds.
• Both suggestion caches moved off Redis → bounded in-memory; prewarmCache populates the in-memory fallback at startup.

Frontend

• Discover/search feed hides artists already saved as preferred (operator request) — matched on Spotify id + normalized name key.

Tests

• shared 663/663, backend 854/854, frontend page 25/25. New coverage for withTimeout, TtlCache, the 429 retry path, in-memory cache semantics, and the dedupe. Redis-mock tests reworked to in-memory.

ADRs

• docs/decisions/2026-06-01-musical-taste-discover-performance.md
• docs/decisions/2026-06-01-logging-observability-hardening.md

Deferred (per the logging ADR): silent-catch sweep + ESLint rule, frontend→Sentry, PII scrubbing (Track B); request-id/pino (Track C, gated); metrics (per ADR 2026-05-30).

Summary by CodeRabbit

• Bug Fixes

  • Resolved Musical Taste Discover tab hanging by implementing timeouts for all data-fetching tiers and replacing Redis caching with bounded in-memory storage.

• New Features

  • Discover feed now filters out artists already saved as preferences.
  • Improved Discord API resilience with automatic retry on rate limits.

• Documentation

  • Added architectural decision records documenting observability hardening and performance improvements.

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lucky	Ready	Preview, Comment	Jun 1, 2026 11:56pm

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Size Change: +28 B (+0.01%)

Total Size: 424 kB

📦 View Changed

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📥 Commits

Reviewing files that changed from the base of the PR and between e3e31b2 and e67df17.

📒 Files selected for processing (2)

• docs/decisions/2026-06-01-logging-observability-hardening.md
• docs/decisions/2026-06-01-musical-taste-discover-performance.md

📝 Walkthrough

Walkthrough

This PR harderns the observability and resilience of artist suggestion and Discord guild access by introducing bounded execution timeouts, in-memory caching to replace Redis, and rate-limit retry logic. It adds shared async utilities (withTimeout, delay, TtlCache), updates Discord OAuth to retry on 429 with Retry-After backoff, migrates guild caching from Redis to synchronized TTL cache, applies per-tier timeouts to suggestion generation, and refactors the frontend to filter already-preferred artists from the discover feed.

Changes

Observability hardening across suggestion, guild, and Discord services

Layer / File(s)	Summary
Shared async timing and caching utilities packages/shared/src/utils/async.ts, packages/shared/src/utils/async.spec.ts, packages/shared/src/utils/cache.ts, packages/shared/src/utils/cache.spec.ts, packages/shared/src/utils/index.ts	TimeoutError, withTimeout(), and delay() primitives for bounding async operations; TtlCache<V> for bounded in-memory storage with automatic expiry and max-entry eviction; full Jest test coverage.
Discord OAuth timeout and rate-limit retry packages/backend/src/services/DiscordOAuthService.ts, packages/backend/tests/unit/services/DiscordOAuthService.test.ts	getUserGuilds wraps fetch in withTimeout and implements retry loop on HTTP 429 using parsed Retry-After header; new test cases verify retry success and exhaustion scenarios.
Guild cache migration from Redis to in-memory TTL packages/backend/src/services/GuildAccessService.ts, packages/backend/tests/unit/services/GuildAccessService.test.ts	Replaces Redis read-through with synchronized TtlCache keyed by access token fingerprint; fallback logging level changed from infoLog to warnLog; tests validate cache reuse and multi-call consolidation without re-fetching from Discord.
Artist suggestion per-tier timeouts and in-memory caches packages/backend/src/services/artistSuggestion.ts, packages/backend/src/routes/artists.ts, packages/backend/tests/unit/services/artistSuggestion.test.ts, packages/backend/tests/unit/routes/artists.test.ts	Per-tier hard timeouts prevent hanging across DB/Spotify/fallback tiers; Redis caches replaced with bounded TtlCache for user-specific and global artist lists; service instance exported for test cache isolation; new tests cover uncached fetch paths and cache warmth assertions.
Frontend discover feed filters already-preferred artists packages/frontend/src/pages/PreferredArtists.tsx, packages/frontend/src/pages/PreferredArtists.test.tsx	Computes preferredSpotifyIds and preferredKeys lookup sets to filter discover feed results; refactors tab buttons via .map() and updates grid rendering for clarity; test mocks framer-motion with explicit React.forwardRef and verifies discover excludes already-saved artists.
Architecture Decision Records docs/decisions/2026-06-01-logging-observability-hardening.md, docs/decisions/2026-06-01-musical-taste-discover-performance.md	Documents three-track observability hardening plan (urgent hotfixes, P1 standard, gated P2) and Musical Taste Discover fix including per-tier timeout strategy, Redis-to-in-memory migration, per-tier observability, and frontend AbortController timeout matching backend bounds.

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant DiscordOAuthService
  participant Discord
  Client->>DiscordOAuthService: getUserGuilds()
  loop retry up to maxRateLimitRetries
    DiscordOAuthService->>DiscordOAuthService: withTimeout(fetch, restTimeoutMs)
    DiscordOAuthService->>Discord: fetch user guilds
    alt HTTP 429 (rate limited)
      Discord-->>DiscordOAuthService: 429 + Retry-After header
      DiscordOAuthService->>DiscordOAuthService: delay(parseRetryAfterMs)
    else HTTP 200 (success)
      Discord-->>DiscordOAuthService: 200 + guild list
      DiscordOAuthService-->>Client: parsed and normalized guilds
    else timeout or other error
      DiscordOAuthService-->>Client: throw error
    end
  end

Loading

flowchart TD
  getSuggestions["getSuggestions()"]
  runTier["runTier(tier, timeout)"]
  tierDB["Tier 1: Preferred artists from DB"]
  tierSpotify["Tier 2: User top Spotify artists<br/>from userTopArtistsCache"]
  tierPopular["Tier 3: Popular fallback<br/>from fallbackCache"]
  collectResults["Collect non-empty results"]
  return200["Return 200 with results + message"]
  
  getSuggestions --> runTier
  runTier --> tierDB
  tierDB -->|timeout/error| collectResults
  tierDB -->|success| collectResults
  collectResults --> tierSpotify
  tierSpotify -->|timeout/error| collectResults
  tierSpotify -->|success| collectResults
  collectResults --> tierPopular
  tierPopular -->|timeout/error| return200
  tierPopular -->|success| return200

Loading

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

Possibly related PRs

• LucasSantana-Dev/Lucky#980: Earlier updates to ArtistSuggestionService caching and suggestion generation flow that directly inform the per-tier timeout and in-memory cache refactoring in this PR.
• LucasSantana-Dev/Lucky#1078: Modifies GuildAccessService caching behavior around fetchUserGuilds, closely related to this PR's migration from Redis to in-memory TTL cache.
• LucasSantana-Dev/Lucky#630: Adds the initial /api/artists/suggestions endpoint and frontend default-suggestions behavior that this PR now hardens with per-tier timeouts and in-memory caching.

Suggested labels

backend, frontend, shared, size/xl

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title precisely summarizes the main changes: bounding external calls to fix Discord 429 storms and Musical-Taste Discover hanging—the core resilience improvements across the changeset.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Create PR with unit tests
• Commit unit tests in branch fix/resilience-timeouts-429-discover

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Actionable comments posted: 1

🧹 Nitpick comments (3)

packages/backend/src/services/DiscordOAuthService.ts (1)

227-278: 💤 Low value

Consider consuming the 429 response body before retrying.

When a 429 response is received (lines 244–256), the response body is not consumed before the next retry. In contrast, the error path at line 259 does consume it with await response.text(). While modern fetch implementations handle unconsumed bodies gracefully, explicitly consuming or discarding the body before retrying is a best practice that can help release HTTP connections more promptly.

🔄 Suggested fix

                 if (
                     response.status === 429 &&
                     attempt < this.maxRateLimitRetries
                 ) {
+                    // Consume the response body to release the connection
+                    await response.text().catch(() => {})
                     const retryAfterMs = this.parseRetryAfterMs(response)
                     warnLog({
                         message:
                             'Discord rate-limited the user guilds fetch; backing off',
                         data: { endpoint, attempt: attempt + 1, retryAfterMs },
                     })
                     await delay(retryAfterMs)
                     continue
                 }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/backend/src/services/DiscordOAuthService.ts` around lines 227 - 278,
In getUserGuilds, when handling a 429 retry path you should consume the response
body before awaiting the backoff so connections are released; after detecting
response.status === 429 (inside the attempt loop) call and await a body consumer
(e.g. await response.text() or response.arrayBuffer()) before logging and
awaiting delay(retryAfterMs), then continue; keep the existing warnLog and
parseRetryAfterMs usage so behavior is unchanged except the body is explicitly
drained before retrying.

packages/backend/tests/unit/routes/artists.test.ts (1)

36-44: ⚡ Quick win

Remove stale redisClient mock.

The mock for redisClient is no longer needed since Redis caching has been removed from the artist suggestion flow.

🧹 Suggested cleanup

 jest.mock('`@lucky/shared/services`', () => ({
     spotifyLinkService: {
         getValidAccessToken: jest.fn(),
     },
-    redisClient: {
-        get: jest.fn().mockResolvedValue(null),
-        setex: jest.fn().mockResolvedValue('OK'),
-    },
 }))

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/backend/tests/unit/routes/artists.test.ts` around lines 36 - 44, The
test mock in artists.test.ts still defines a stale redisClient mock inside the
jest.mock call; remove the redisClient property (including get and setex mocks)
from the mocked module so only spotifyLinkService.getValidAccessToken remains
mocked. Update the jest.mock block that currently returns { spotifyLinkService:
{...}, redisClient: {...} } to omit redisClient and adjust any imports/uses in
the test that assumed redisClient to avoid unused/mock references.

packages/backend/src/services/artistSuggestion.ts (1)

37-44: 💤 Low value

Stale docstring mentions Redis caching.

The class docstring still says "Handles Redis caching to minimize Spotify API calls" but Redis has been replaced with in-memory caching.

📝 Suggested fix

 /**
  * Service to fetch artist suggestions through a three-tier lookup strategy:
  * 1. User's saved preferred artists (from database)
  * 2. User's Spotify top artists (if Spotify is linked)
  * 3. Popular artists fallback (static list)
  *
- * Handles Redis caching to minimize Spotify API calls.
+ * Handles in-memory caching to minimize Spotify API calls.
  */

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/backend/src/services/artistSuggestion.ts` around lines 37 - 44, The
module docstring still claims "Handles Redis caching to minimize Spotify API
calls" even though Redis was replaced by an in-memory cache; update the header
comment for the artist suggestion service to reflect the current implementation
(e.g., "Uses in-memory caching to minimize Spotify API calls") and remove any
remaining references to Redis in the same file (including comments above the
class/ArtistSuggestionService and the fetchArtistSuggestions function) so
documentation matches the actual use of the in-memory Map/cache.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docs/decisions/2026-06-01-logging-observability-hardening.md`:
- Around line 75-79: The "Deferred (unchanged)" paragraph conflicts with
Musical-Taste ADR (§3) because it forbids adding failure-mode metrics now;
update that section to explicitly permit per-tier or scoped incident metrics
(e.g., 429/timeout/slow-query/feature-toggle-health) required by the
Musical-Taste ADR while keeping broad/platform-level metrics and OTel
deferred—refer to the "Failure-mode metrics" phrase and the "Deferred
(unchanged)" heading and change the wording to: allow immediate, scoped per-tier
incident metrics as required by Musical-Taste ADR §3, but defer cross-platform
or full OTel rollout until the planned revisit date.

---

Nitpick comments:
In `@packages/backend/src/services/artistSuggestion.ts`:
- Around line 37-44: The module docstring still claims "Handles Redis caching to
minimize Spotify API calls" even though Redis was replaced by an in-memory
cache; update the header comment for the artist suggestion service to reflect
the current implementation (e.g., "Uses in-memory caching to minimize Spotify
API calls") and remove any remaining references to Redis in the same file
(including comments above the class/ArtistSuggestionService and the
fetchArtistSuggestions function) so documentation matches the actual use of the
in-memory Map/cache.

In `@packages/backend/src/services/DiscordOAuthService.ts`:
- Around line 227-278: In getUserGuilds, when handling a 429 retry path you
should consume the response body before awaiting the backoff so connections are
released; after detecting response.status === 429 (inside the attempt loop) call
and await a body consumer (e.g. await response.text() or response.arrayBuffer())
before logging and awaiting delay(retryAfterMs), then continue; keep the
existing warnLog and parseRetryAfterMs usage so behavior is unchanged except the
body is explicitly drained before retrying.

In `@packages/backend/tests/unit/routes/artists.test.ts`:
- Around line 36-44: The test mock in artists.test.ts still defines a stale
redisClient mock inside the jest.mock call; remove the redisClient property
(including get and setex mocks) from the mocked module so only
spotifyLinkService.getValidAccessToken remains mocked. Update the jest.mock
block that currently returns { spotifyLinkService: {...}, redisClient: {...} }
to omit redisClient and adjust any imports/uses in the test that assumed
redisClient to avoid unused/mock references.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: dd6377f3-3882-460a-a2f9-d79660264ca7

📥 Commits

Reviewing files that changed from the base of the PR and between d4fdd98 and e3e31b2.

📒 Files selected for processing (17)

• docs/decisions/2026-06-01-logging-observability-hardening.md
• docs/decisions/2026-06-01-musical-taste-discover-performance.md
• packages/backend/src/routes/artists.ts
• packages/backend/src/services/DiscordOAuthService.ts
• packages/backend/src/services/GuildAccessService.ts
• packages/backend/src/services/artistSuggestion.ts
• packages/backend/tests/unit/routes/artists.test.ts
• packages/backend/tests/unit/services/DiscordOAuthService.test.ts
• packages/backend/tests/unit/services/GuildAccessService.test.ts
• packages/backend/tests/unit/services/artistSuggestion.test.ts
• packages/frontend/src/pages/PreferredArtists.test.tsx
• packages/frontend/src/pages/PreferredArtists.tsx
• packages/shared/src/utils/async.spec.ts
• packages/shared/src/utils/async.ts
• packages/shared/src/utils/cache.spec.ts
• packages/shared/src/utils/cache.ts
• packages/shared/src/utils/index.ts

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[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
93.2% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud