[Rajan-vish]

Closes #716

What

SmartRetryMiddleware sent a different delay progression depending on whether schedule_source was configured.
Without schedule_source, on_send re-kicks the task with with_labels(delay=delay), overwriting labels["delay"] with the newly computed delay. On subsequent errors, make_delay read that updated label back as the base delay rather than the initial configured delay.

This caused:

1. Backoff with use_delay_exponent=True without schedule_source to compound factorially (base * n!) instead of linearly (base * n), quickly hitting max_delay_exponent.
2. Jitter to accumulate into subsequent retry base delays on each retry.
3. Divergent retry intervals between direct broker execution and schedule_source.

Fix

• Added _get_initial_delay(message) to resolve and preserve the initial base delay in a private _initial_delay label on the kicker across retries.
• make_delay() now computes the delay from _initial_delay (falling back to delay or default_delay), ensuring consistent retry intervals across both broker and schedule_source paths.
• Added comprehensive unit tests in tests/middlewares/test_smart_retry.py covering:
  • Delay exponent progression without schedule_source (base * n).
  • Exact consistency between broker path and schedule_source path.
  • Jitter non-accumulation across retry attempts.
  • Initial custom delay label preservation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.67%. Comparing base (f08a54a) to head (f89cc07).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #719      +/-   ##
==========================================
+ Coverage   85.48%   85.67%   +0.18%     
==========================================
  Files          68       68              
  Lines        2660     2667       +7     
==========================================
+ Hits         2274     2285      +11     
+ Misses        386      382       -4     

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[s3rius]

Please run pre-commit.

[Rajan-vish]

Done! Ran pre-commit / prek run and resolved the import sorting in tests/middlewares/test_smart_retry.py in commit 2060494. All hooks (ruff, black, mypy, check-ast, typos, etc.) now pass cleanly.