feat(lifecycle): alert when index creation fails

[delthas]

Summary

• Add LifecycleIndexCreationFailed Prometheus alert (monitoring/lifecycle/alerts.yaml) wired to the s3_lifecycle_legacy_tasks_total{status="putBucketIndexesFailed"} counter introduced by BB-783 (feat(lifecycle): emit putBucketIndexesFailed metric on index creation errors #2751).
• Fires on any failure in a 5m window with severity warning — mirrors the CircuitBreakerError shape: the conductor falls back to v1 full-scan, so this is recoverable but always warrants investigation (typically a disk-fill / indexBuildMinAvailableDiskSpaceMB refusal).
• Companion fixture added to alerts.test.yaml.

Part of the Empty bucket feature epic. A symmetric MongoDB-side createIndexes-failed alert lives in the Zenko chart under ZENKO-5285.

Issue: BB-784

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.85%. Comparing base (6223d3e) to head (5514c80).

Additional details and impacted files

see 4 files with indirect coverage changes

Components	Coverage Δ
Bucket Notification	80.22% <ø> (ø)
Core Library	81.24% <ø> (+0.03%)	⬆️
Ingestion	70.63% <ø> (ø)
Lifecycle	79.46% <ø> (-0.04%)	⬇️
Oplog Populator	85.83% <ø> (ø)
Replication	59.67% <ø> (ø)
Bucket Scanner	85.76% <ø> (ø)

@@               Coverage Diff                @@
##           development/9.4    #2753   +/-   ##
================================================
  Coverage            74.84%   74.85%           
================================================
  Files                  199      199           
  Lines                13657    13657           
================================================
+ Hits                 10222    10223    +1     
+ Misses                3425     3424    -1     
  Partials                10       10           

Flag	Coverage Δ
api:retry	9.14% <ø> (ø)
api:routes	8.96% <ø> (ø)
bucket-scanner	85.76% <ø> (ø)
ft_test:queuepopulator	10.93% <ø> (+0.58%)	⬆️
ingestion	12.53% <ø> (ø)
lib	7.76% <ø> (-0.01%)	⬇️
lifecycle	18.93% <ø> (-0.01%)	⬇️
notification	1.02% <ø> (ø)
oplogPopulator	0.14% <ø> (ø)
replication	18.66% <ø> (ø)
unit	51.34% <ø> (ø)

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[claude]

LGTM — alert rule follows the existing CircuitBreakerError pattern (increase(...[5m]) > 0, no For clause, warning severity). Test fixture covers pre-increment silence (1m, 4m), firing window (5m, 9m), and post-window resolution (10m), plus a negative series (noIndex status) to confirm no false trigger. Description is clear and actionable.

Review by Claude Code