SubMiner/backlog/tasks/task-36 - Add-structured-logging-with-configurable-verbosity-levels.md

id, title, status, assignee, created_date, updated_date, labels, dependencies, priority

id	title	status	assignee	created_date	updated_date	labels	dependencies	priority
TASK-36	Add structured logging with configurable verbosity levels	Done		2026-02-14 00:59	2026-02-17 04:16	infrastructure developer-experience observability		medium

Description

Replace ad-hoc console.log/console.error calls throughout the codebase with a lightweight structured logger that supports configurable verbosity levels (debug, info, warn, error).

Motivation

• TASK-33 (restrict mpv socket logs) is a symptom of a broader problem: no log-level filtering
• Debugging production issues requires grepping through noisy output
• Users report log spam in normal operation
• No way to enable verbose logging for bug reports without code changes

Scope

1. Create a minimal logger module (no external dependencies needed) with debug, info, warn, error levels
2. Add a config option for log verbosity (default: info)
3. Add a CLI flag to control logging verbosity (--log-level) while keeping --debug as app/dev mode.
4. Migrate existing console.log/error calls to use the logger
5. Include context tags (service name, operation) in log output for filterability

Design constraints

• Zero external dependencies — use a simple wrapper over console methods
• Must not impact hot-path performance (subtitle rendering, tokenization)
• Log level should be changeable at runtime via config hot-reload if that feature exists
• TASK-33 becomes trivial once this lands (mpv socket logs become debug level)

Acceptance Criteria

• #1 A logger module exists with debug/info/warn/error levels.
• #2 Config option controls default verbosity level.
• #3 CLI --log-level override config.
• #4 Existing console.log/error calls in core services are migrated to structured logger.
• #5 MPV socket connection logs use debug level (resolves TASK-33 implicitly).
• #6 Log output includes source context (service/module name).
• #7 No performance regression on hot paths (rendering, tokenization).

Implementation Plan

1. Audit remaining runtime console calls and classify by target (core runtime vs help/UI/test-only).
2. Keep --debug scoped to Electron app/dev mode only; --log-level controls logging verbosity.
3. Add tests for parsing and startup to keep logging override behavior stable.
4. Migrate remaining non-user-facing console.* calls in core paths (especially tokenization, jimaku, config generation, electron-backend/notifications) to logger and include context via child loggers.
5. Ensure mpv-related connection/reconnect messages use debug level; keep user-facing success/failure outputs when intended.
6. Run focused test updates for impacted files, update task notes/acceptance criteria, and finalize task state.

Implementation Notes

Updated logging override semantics so --debug stays an app/dev-only flag and --log-level is the CLI logging control.

Migrated remaining non-user-facing runtime console.* calls in core paths (notification, config-gen, electron-backend, jimaku, tokenizer) to structured logger

Moved MPV socket lifecycle chatter to debug-level in mpv-service so default info is less noisy

Updated help text and CLI parsing/tests for logging via --log-level while keeping --debug app/dev-only.

Validated with focused test run: node --test dist/cli/args.test.js dist/core/services/startup-bootstrap-service.test.js dist/core/services/cli-command-service.test.js

Build still passes via pnpm run build

Final Summary

TASK-36 is now complete; structured logging is consistently used in core runtime paths, with CLI log verbosity controlled by --log-level, while --debug remains an Electron app/dev-mode toggle.

Backlog task moved to Done after verification of build and focused tests.