otel: Value Updates and Logging

[schloerke]

Goal: Log reactive value updates as OTel log events.

Tasks

• Add logging helper to shiny/otel/_core.py:
  • emit_otel_log(body, severity, attributes) - Emit OTel log record
• Modify Value._set() to log value updates
• Store value name at creation time for logging
• Include session ID in log attributes
• Add comprehensive tests
• Create example application

Acceptance Criteria

• Value updates logged when SHINY_OTEL_COLLECT >= reactivity
• Logs include value name (e.g., "Set reactiveVal myValue")
• Logs include session.id attribute
• No logs when collection level insufficient
• No-op when OTel SDK not configured

Implementation

Completed in PR #2169:

• Added emit_otel_log() helper function (renamed from emit_log for clarity)
• Value updates log with DEBUG severity
• Namespace support for module-scoped values
• Standalone values log as <unnamed>
• 12 comprehensive tests
• Example application demonstrating functionality

Files Modified

• shiny/otel/_core.py - Added emit_otel_log() helper
• shiny/otel/__init__.py - Export emit_otel_log
• shiny/reactive/_reactives.py - Log in Value._set() method
• shiny/session/_session.py - Set value names in Inputs
• tests/pytest/test_otel_value_logging.py - 12 tests
• examples/otel-value-logging/ - Demo application