feat(observability): add structured logging

[ditadi]

Summary

• Add comprehensive logging package with structured logging, standardized errors, and request-scoped wide-event tracking
• Implement WideEvent class for collecting rich request metadata (method, path, user, component, execution, stream, error context)
• Add configurable sampling with intelligent defaults (always sample errors, slow requests, and cache info)
• Use AsyncLocalStorage for automatic context propagation across interceptors and nested calls

Details

Standardized Errors

New error hierarchy with AppKitError base class providing:

• Error codes for programmatic handling (code, statusCode, isRetryable)
• Specialized error types: ValidationError, AuthenticationError, ConfigurationError, ConnectionError, ExecutionError, InitializationError, ServerError, TunnelError
• Automatic sensitive field redaction in toJSON() serialization
• Factory methods for common patterns (e.g., ValidationError.missingField("warehouseId"))

Structured Logging

createLogger(scope) returns a logger with:

• debug/info/warn/error levels with printf-style formatting
• Request-aware overloads: logger.info(req, "Processing %s", id) tracks logs in WideEvent
• logger.event(req?) returns the current WideEvent (from AsyncLocalStorage or explicit req)

Wide-Event Tracking (Honeycomb-style)

Request-scoped WideEvent collects:

• Request metadata (method, path, status_code, duration_ms, trace_id)
• Component info (plugin/connector name + operation)
• Execution context (cache_hit, retry_attempts, timeout)
• Stream metadata (events_sent, reconnections)
• Error context (type, code, message, retriable)
• Scoped context for plugin-specific data

Sampling

Configurable via APPKIT_SAMPLE_RATE env var with smart defaults:

• Always sample: errors, status >= 400, duration >= 5s, cache info present
• Deterministic sampling based on request ID hash
• Path exclusions for health checks, static assets, etc.

[MarioCadenas]

if this is what we want to do, we are missing all the error exports in the root index file 😄

[pkosiec]

Nice job overall! A few comments from my side

[pkosiec]

Could you please test a deployed app with OpenTelemetry enabled in Apps runtime? I think it would be great to double-check everything works flawlessly there 👍

From my observations sampling result might differ between local dev and runtime, that's why the AlwaysOnSampler was set before (same as previous default OpenTelemetry config).