Introduce log levels with slog

[Copilot]

Replaces logrus with Go's standard library log/slog for structured logging with configurable log levels. Debug logs are now enabled via DEBUG=1 environment variable.

Implementation

• New logging abstraction (pkg/logging/)

  • SlogLogger: Wraps log/slog, implements Logger interface
  • LogrusAdapter: Maintains compatibility for existing logrus usage
  • Logger interface: Implementation-agnostic (no longer tied to *logrus.Entry)

• Main initialization (main.go)

  • Added initLogger() to configure log level from DEBUG env var
  • Sets slog.LevelDebug when DEBUG=1, otherwise slog.LevelInfo

• Updated dependencies

  • ClientConfig.Logger now uses logging.Logger interface
  • Removed hardcoded logrus level manipulation in pkg/metrics
  • All tests updated to use new interface

Usage

# Enable debug logging
DEBUG=1 ./model-runner

# Docker
docker run -e DEBUG=1 docker/model-runner:latest

Log output format:

time=2025-11-12T15:55:44.435Z level=INFO msg="Successfully initialized store" component=model-manager
time=2025-11-12T15:55:44.435Z level=DEBUG msg="Loading model from cache" model=llama-3

Structured logging still supported:

log.WithFields(map[string]interface{}{
    "component": "backend",
    "model": "llama-3",
}).Debug("Model loaded")

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Introduce log levels with slog</issue_title>
<issue_description>There is a library in stdlib that is ideal for this, --debug should print all the debug-level logs:

https://pkg.go.dev/log/slog</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Introduce log levels with slog docker/model-runner#384

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