fix: Neptune MCP server respects FASTMCP_LOG_LEVEL (accept common aliases)

[yashx007]

Summary

Fixes the Amazon Neptune MCP server so the stderr Loguru handler respects the FASTMCP_LOG_LEVEL environment variable.
Normalizes common aliases (case-insensitive) so user-friendly short names work as expected:

• WARN → WARNING
• ERR → ERROR
• FATAL → CRITICAL

Unknown/invalid values fall back to INFO.

What changed

• Added get_fastmcp_log_level() helper which:
  • Reads FASTMCP_LOG_LEVEL (defaults to INFO)
  • Normalizes common aliases and uppercases the value
  • Validates against supported Loguru levels and falls back to INFO if unknown
• Updated logger setup to use the helper:

logger.add(sys.stderr, level=get_fastmcp_log_level())

Files changed

• server.py (only)

How tested (local)

Ran unit checks and a small runtime inspection locally to confirm behavior.
Manual checks performed (PowerShell):

# WARN -> WARNING
$env:FASTMCP_LOG_LEVEL='WARN'
python scripts\check_neptune_log_level.py

# ERROR -> ERROR
$env:FASTMCP_LOG_LEVEL='ERROR'
python scripts\check_neptune_log_level.py

# DEBUG -> DEBUG
$env:FASTMCP_LOG_LEVEL='DEBUG'
python scripts\check_neptune_log_level.py

(These confirm the configured handler level matches the normalized value.)

Related issue

Resolves: #1581 (amazon-neptune-mcp-server: StdErr logging forced at INFO level)

Notes for reviewers

The change is intentionally scoped to the Neptune server only.
If maintainers prefer a shared helper across MCP servers, get_fastmcp_log_level() can be extracted into a common utility in a follow-up PR.
Tests used during development were run locally; per request they are not included in this PR to keep it minimal.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of the project license.

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Pull Request Overview

This PR adds dynamic log level configuration through the FASTMCP_LOG_LEVEL environment variable, enabling users to control logging verbosity at runtime instead of using a hardcoded 'INFO' level.

• Introduces a get_fastmcp_log_level() helper function that reads, validates, and normalizes the log level from environment variables
• Maps common log level aliases (WARN, ERR, FATAL) to Loguru's canonical level names
• Falls back to 'INFO' when an invalid level is provided

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