refactor(backend): migrate to structured logging with createLogger

[test3207]

Summary

Migrate all backend logging to the unified structured format defined in #249. This ensures all logs follow a consistent structure with proper traceId for Loki/Grafana observability.

Changes

Logger Core (backend/src/lib/logger.ts)

• Add generateTraceId() using crypto.randomUUID() for system logs without request context
• Update createLogger(c?: Context) to auto-generate traceId when no Context provided
• Update RequestLogger.warn to accept ErrorLogParams (for logging warnings with error objects)

Route Handlers (5 files)

• routes/songs.ts - Song search, CRUD, streaming logs
• routes/playlists.ts - Playlist management logs
• routes/libraries.ts - Library management logs
• routes/player.ts - Playback state logs
• routes/user.ts - User preferences logs

Service Layer (4 files)

• services/library.service.ts - Library operations
• services/song.service.ts - Song operations
• services/player.service.ts - Player state operations
• services/upload.service.ts - Upload processing

Infrastructure (5 files)

• lib/prisma.ts - Database connection logs
• lib/redis.ts - Redis connection logs
• lib/minio-client.ts - MinIO storage logs
• lib/jwt.ts - JWT token logs
• lib/auth-middleware.ts - Authentication logs

Startup/Shutdown (index.ts)

• Shared startupTraceId for correlated startup logs

Demo Module (2 files)

• lib/demo/storage-tracker.ts - Storage tracking logs
• lib/demo/reset-service.ts - Reset service logs

Test Updates (4 files)

• Update logger mocks to include createLogger export

Log Structure

All logs now follow this unified structure:

log.info({
  source: 'filename.functionName',  // e.g., 'songs.search'
  col1: 'category',                 // system, auth, library, playlist, song, player, upload, user, demo
  col2: 'action',                   // login, create, delete, update, search, etc.
  col3: 'entityId',                 // optional: songId, libraryId, playlistId
  raw: { ... },                     // optional: debug data
  message: 'Human readable message'
});

Testing

• ✅ TypeScript: No errors
• ✅ ESLint: No errors
• ✅ Backend Tests: 160/160 passed
• ✅ Frontend Tests: 411/411 passed
• ✅ Build: Success

Related

Closes #249

Parent Epic: #190

[github-actions]

Coverage after merging refactor/backend-structured-logging into main will be

60.62%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
	100%	100%	100%	100%
src/lib
events.ts	100%	100%	100%	100%
logger-client.ts	40.67%	33.33%	48.39%	46.49%	129, 136–138, 138, 138–139, 145, 145, 145–146, 146, 146–147, 149, 171, 176, 182–183, 185, 190, 190, 190, 192, 192, 192, 194, 196, 196, 196–199, 199, 199, 205, 205, 205–207, 209, 221, 224–225, 225, 225–226, 228, 228, 228, 228–229, 229, 229–230, 234, 236, 242, 242, 246, 246–247, 247–248, 248–249, 249–250, 250–251, 251, 258–259, 259, 259–260, 265, 265, 265, 267–269, 275, 275, 275–276, 279, 298–299, 306–307, 310–311, 316, 318–319, 324, 326–327, 346, 346, 346–349, 353, 361, 361, 361, 365, 372, 375–376, 376, 376, 382–383, 383, 383, 389–390, 390, 390, 395, 395, 395, 397–398, 401, 401, 404, 407–408, 41, 411, 411, 46, 46–47, 47, 47, 51, 55
shared.ts	100%	100%	100%	100%
src/lib/api
config.ts	75%	62.50%	100%	85.71%	17, 22, 22–23
multi-region.ts	2.21%	0%	0%	3.81%	103–104, 104, 104, 106, 109–110, 110, 110, 114, 116–119, 121–122, 126, 126, 126, 126, 126–127, 129–130, 130, 130, 132–133, 143, 145–146, 148–150, 154, 156, 156, 156, 158–159, 161, 172, 172, 172–173, 176, 179, 179, 179–180, 182–183, 187, 189, 189, 189–191, 191, 191–194, 196, 203, 203, 203, 203, 203–205, 208, 208, 208–209, 211–212, 216–218, 220, 220, 220–223, 229–230, 233, 240, 240, 240, 244, 244, 244–245, 247, 255, 266, 266, 266, 269, 269, 269–271, 275, 277, 279–281, 283, 283, 283, 283, 283–285, 289–290, 292, 296, 304–305, 50, 50, 50, 52, 56, 56, 56–57, 57, 57–59, 61, 65, 65, 65, 68, 68, 68, 68, 68, 70, 77, 85, 85, 85, 87–89, 89, 89, 91–92, 92, 92, 94
src/lib/audio
media-session.ts	74.84%	90.91%	71.43%	65.12%	107–108, 126, 137–139, 146–148, 150, 157–159, 161, 169–171, 173, 180–182, 184, 200, 214, 228, 241, 249–250, 263, 44–45, 78, 88–89, 95
queue.ts	86.15%	82.54%	92%	86.92%	210–211, 223, 225, 225, 225–226, 228, 249–252, 303, 313, 313, 313–314, 316, 37–38, 54–55, 72, 76–77
src/lib/cache
metadata-cache.ts	1%	0%	0%	1.47%	101–103, 106, 106, 108, 108, 123–124, 127–129, 131, 131, 131–133, 136–137, 139–140, 153–154, 157, 160, 163, 170–171, 173–174, 183–186, 188–189, 201–204, 204, 204–205, 207, 207, 207–209, 212, 214–215, 24–25, 25, 25, 32, 40–42, 44–45, 54–56, 58–59, 68–70, 72–73, 82–84, 86–87, 97–99
response-cache.ts	0%	0%	0%	0%	100, 32–33, 33, 33–34, 38–39, 39, 39, 41, 44, 46–47, 50, 50, 50, 50, 50–51, 54, 57, 57, 57, 57, 59, 59, 59–61, 61, 61–62, 64, 67, 67, 67–69, 69, 69–70, 72, 75, 75, 75–77, 77, 77, 79, 79, 79, 79, 79–81, 83–84, 84, 84, 86, 89, 92, 97
src/lib/offline-proxy/routes
libraries.ts	42.23%	24.32%	57.14%	51.69%	127–128, 213, 253, 266–268, 271, 273, 273, 273–274, 283, 283, 283, 283, 283–284, 293–294, 296, 296, 296–297, 301, 304–305, 308, 310, 310, 310, 312, 316, 316–317, 317, 321, 325, 328, 331, 331, 331–332, 343, 346, 349, 349, 349, 349, 349–350, 352, 357, 361, 364, 366, 369, 369–370, 370–371, 371–372, 372–373, 373–374, 374, 374, 374–375, 375–376, 376, 378, 378, 378, 378, 381, 381, 393–394, 397, 402, 402, 402–404, 404, 410, 420–421, 427–430, 430, 430, 432, 434, 434, 434, 434, 434–435, 445, 448, 450, 455, 66, 95, 95–96
player.ts	47.26%	35%	57.14%	55.70%	102, 138, 150–151, 154, 159, 161, 165, 167, 167, 167–169, 171, 171, 171–172, 180, 180–181, 181, 195, 200–201,

[Copilot]

Pull request overview

This PR migrates backend logging from the legacy pino logger syntax to a unified structured format using createLogger(). The migration implements the specification from issue #249 to enable better observability with traceId correlation for Loki/Grafana.

Key Changes:

• Enhanced logger core with generateTraceId() function and auto-generated traceIds for system logs
• Updated RequestLogger.warn to accept ErrorLogParams for error object logging
• Migrated 5 route handlers, 4 service modules, 5 infrastructure modules, startup/shutdown code, and 2 demo modules to structured logging format
• Updated test mocks to export createLogger function

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
backend/src/lib/logger.ts	Added generateTraceId(), updated createLogger() to auto-generate traceId when no Context provided, extended warn() to accept ErrorLogParams
backend/src/routes/songs.ts	Migrated to createLogger(c) with structured log format for search, CRUD, and streaming operations
backend/src/routes/playlists.ts	Migrated playlist management logs to structured format
backend/src/routes/libraries.ts	Migrated library operations and upload processing logs
backend/src/routes/player.ts	Migrated playback state logs to structured format
backend/src/routes/user.ts	Migrated user preferences logs
backend/src/services/library.service.ts	Migrated file and song creation logs
backend/src/services/song.service.ts	Migrated file deletion logs
backend/src/services/player.service.ts	Migrated playback seed, preferences, and progress logs
backend/src/services/upload.service.ts	Migrated upload processing, metadata extraction, and cleanup logs
backend/src/lib/prisma.ts	Migrated database connection logs with createLogger()
backend/src/lib/redis.ts	Migrated Redis connection logs
backend/src/lib/minio-client.ts	Migrated MinIO initialization logs
backend/src/lib/jwt.ts	Migrated JWT configuration warning logs
backend/src/lib/auth-middleware.ts	Migrated authentication verification logs
backend/src/index.ts	Migrated startup/shutdown logs with shared startupTraceId for correlation
backend/src/lib/demo/storage-tracker.ts	Migrated demo storage tracking logs
backend/src/lib/demo/reset-service.ts	Migrated demo reset service logs with resetTraceId correlation
backend/src/test/routes/*.test.ts	Updated logger mocks to export createLogger function