feat(lifecycle): emit putBucketIndexesFailed metric on index creation errors

[delthas]

Summary

Adds a dedicated metric tag (putBucketIndexesFailed) when the conductor's putBucketIndexes call returns an error. Provides the Prometheus signal that ZENKO-5285's "lifecycle index creation failing repeatedly" alert will hook into.

Why

Today the error callback at LifecycleConductor.js:339-345 just logs a warning and falls back to v1. There's no metric for the failure itself — only putBucketIndexes is emitted (before the call) which counts attempts. No way to alert on a sustained failure rate.

Implementation

One-line change in the conductor's error path, plus a unit test that stubs client.putBucketIndexes to fail and asserts LifecycleMetrics.onLegacyTask is called with the new tag.

The new tag is cause-agnostic — operators can dig into the warn log to find the underlying reason (MongoDB 7.1's IndexBuildKilledByOutOfDiskSpace, duplicate-name conflict, transient infra, etc.). A future ticket can map specific Arsenal errors and emit more granular tags if needed.

Existing tag semantics (unchanged)

• putBucketIndexes — counts attempts
• putBucketIndexesFailed (NEW) — counts failures
• Ratio = failure rate

Related

• BB-783 — this ticket
• ZENKO-5286 — parent ticket that originally tracked the work ("Mongodb index creation error")
• ZENKO-5285 — alert rule that will use the new metric
• ARSN-588 — Arsenal functional test verifying the underlying error catching path (PR #2634)
• ARTESCA-17683 — set indexBuildMinAvailableDiskSpaceMB=10000 in Artesca (PR #5228)
• Parent epic ARTESCA-16740 — Empty bucket feature

Issue: BB-783

[bert-e]

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[bert-e]

Incorrect Jira project

The Jira issue ZENKO-5286 specified in the source
branch name, does not belong to project BB.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.60%. Comparing base (f92d68c) to head (3f906c8).
⚠️ Report is 3 commits behind head on development/9.4.

Additional details and impacted files

Files with missing lines	Coverage Δ
...tensions/lifecycle/conductor/LifecycleConductor.js	86.90% <100.00%> (+0.24%)	⬆️

... and 3 files with indirect coverage changes

Components	Coverage Δ
Bucket Notification	80.22% <ø> (ø)
Core Library	80.61% <ø> (-0.15%)	⬇️
Ingestion	70.63% <ø> (ø)
Lifecycle	79.50% <100.00%> (+0.04%)	⬆️
Oplog Populator	85.83% <ø> (ø)
Replication	59.67% <ø> (-0.04%)	⬇️
Bucket Scanner	85.76% <ø> (ø)

@@                 Coverage Diff                 @@
##           development/9.4    #2750      +/-   ##
===================================================
- Coverage            74.65%   74.60%   -0.06%     
===================================================
  Files                  199      199              
  Lines                13654    13655       +1     
===================================================
- Hits                 10194    10187       -7     
- Misses                3450     3458       +8     
  Partials                10       10              

Flag	Coverage Δ
api:retry	9.12% <0.00%> (-0.01%)	⬇️
api:routes	8.94% <0.00%> (-0.01%)	⬇️
bucket-scanner	85.76% <ø> (ø)
ft_test:queuepopulator	9.08% <0.00%> (-1.05%)	⬇️
ingestion	12.51% <0.00%> (-0.01%)	⬇️
lib	7.74% <0.00%> (-0.01%)	⬇️
lifecycle	18.88% <0.00%> (-0.01%)	⬇️
notification	1.02% <0.00%> (-0.01%)	⬇️
oplogPopulator	0.14% <0.00%> (-0.01%)	⬇️
replication	18.64% <0.00%> (-0.01%)	⬇️
unit	51.34% <100.00%> (+0.01%)	⬆️

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[claude]

LGTM — clean, well-scoped change. The new putBucketIndexesFailed metric follows the existing pattern (matches insufficientDiskSpace at line 323 and putBucketIndexes at line 327), the label is a fixed string with no cardinality concern, and the test properly validates the error path. No issues found.

Review by Claude Code

[claude]

LGTM — one-line metric addition in the existing error path, bounded label cardinality, proper test with spy cleanup via afterEach. No issues found.

Review by Claude Code

[delthas]

Replaced by #2751 after the source branch was renamed (improvement/ZENKO-5286/handle-index-creation-failures → improvement/BB-783/emit-put-bucket-indexes-failed-metric). GitHub auto-closed this PR when the original branch ref was removed.