v1.0.0

Fixed

• A transition with no news posted an empty message. Any state change
  outside the three handled cases fell through with msg still an empty
  string, and that empty payload was sent to Slack. Those transitions are now
  logged and skipped.
• A rejected message looked like a delivered one. The response status was
  printed and then ignored, so a rotated webhook returning 403 left alerting
  silently dead. The handler now raises, which surfaces as a Lambda error
  metric you can alarm on.
• A composite or metric-math alarm crashed the function. The first trigger
  dimension was read unconditionally, and those alarms carry none.

Added

• The webhook URL comes from the SLACK_WEBHOOK_URL environment variable.
  It used to be a literal in the source, which is how a webhook ends up in a
  public fork.
• Retries with backoff on 429 and 5xx answers from Slack.
• tests/test_handler.py: six cases against recorded SNS events with the
  HTTP layer stubbed, covering each alarm transition, the skip path, a
  dimensionless alarm, and a Slack rejection. CI runs it on every push.

Upgrading

Take the new script. Both the parameters and the defaults are documented in the README, and the first run should use -WhatIf (PowerShell) or the test suite (Python) before anything is scheduled.

Full history in CHANGELOG.md.