fix(slack): improve rate limit error handling and logging

[aminghadersohi]

SUMMARY

Fixes the issue where Slack API rate limit errors (HTTP 429) were being swallowed or masked by generic error messages in the slack-sdk library's retry handler. This change improves observability and reliability of Slack integrations by adding explicit error detection and detailed logging.

Root Cause: The RateLimitErrorRetryHandler in the slack-sdk library can re-raise errors without proper context when certain conditions are met. When these errors bubble up to generic exception handlers, they get logged as "Failed to send a request to Slack API server" instead of clearly indicating a rate limit issue.

Changes:

• Increased retry count from 2 to 4 to provide more buffer before failure
• Added explicit error handling for HTTP 429 rate limit responses in get_channels()
• Enhanced logging to include:
  • Retry-After header value from Slack API
  • Indication that retry handler may have failed or exhausted retries
  • Full error context for debugging
• Added client initialization logging for debugging
• Fixed edge case where ex.response could be a string instead of response object using hasattr() check

Impact: Rate limit errors will now be clearly visible in monitoring systems like Datadog with actionable information (Retry-After values, retry counts), making it much easier to diagnose and respond to Slack API rate limiting issues.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A - Backend logging improvement

TESTING INSTRUCTIONS

1. All existing unit tests pass: pytest tests/unit_tests/utils/slack_test.py
2. Pre-commit hooks pass: pre-commit run --files superset/utils/slack.py
3. To manually test rate limiting:
   • Configure Slack integration in Superset
   • Trigger multiple rapid Slack API calls (e.g., by editing multiple alert configurations)
   • Observe error logs - they should now clearly indicate "Slack API rate limit exceeded (HTTP 429)" with Retry-After information instead of generic errors

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[korbit-ai]

I've completed my review and didn't find any issues.

Files scanned

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File Path	Reviewed
superset/utils/slack.py	✅

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[codecov]

Codecov Report

❌ Patch coverage is 10.52632% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.85%. Comparing base (ff80d4f) to head (c517358).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
superset/utils/slack.py	10.52%	17 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #35588       +/-   ##
===========================================
+ Coverage        0   71.85%   +71.85%     
===========================================
  Files           0      589      +589     
  Lines           0    43608    +43608     
  Branches        0     4718     +4718     
===========================================
+ Hits            0    31335    +31335     
- Misses          0    11035    +11035     
- Partials        0     1238     +1238     

Flag	Coverage Δ
hive	46.26% <0.00%> (?)
mysql	70.88% <10.52%> (?)
postgres	70.94% <10.52%> (?)
presto	49.97% <0.00%> (?)
python	71.82% <10.52%> (?)
sqlite	70.53% <10.52%> (?)
unit	100.00% <ø> (?)

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