Handle finalize and null-path instance config callbacks

[xiangfu0]

Summary

• handle NotificationContext.Type.FINALIZE in ServerGrpcChannelBackoffResetHandler
• fall back to a full scan when Helix does not provide pathChanged
• keep _shuttingDownServers lifecycle-safe instead of assuming every non-init callback is a single-instance update

Why

ServerGrpcChannelBackoffResetHandler currently assumes every non-INIT / non-child-change callback has a populated pathChanged, and it does not clear local state on FINALIZE. That is brittle against Helix callback lifecycle edges.

Validation

• ./mvnw -pl pinot-server -am -Dtest=ServerGrpcChannelBackoffResetHandlerTest test -Dsurefire.failIfNoSpecifiedTests=false

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 63.29%. Comparing base (5cde60a) to head (8cabf74).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...er/helix/ServerGrpcChannelBackoffResetHandler.java	90.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #18173      +/-   ##
============================================
- Coverage     63.30%   63.29%   -0.01%     
+ Complexity     1627     1624       -3     
============================================
  Files          3224     3224              
  Lines        196558   196565       +7     
  Branches      30365    30367       +2     
============================================
- Hits         124426   124421       -5     
- Misses        62177    62178       +1     
- Partials       9955     9966      +11     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (ø)
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	0.00% <ø> (ø)
java-11	63.28% <90.00%> (+<0.01%)	⬆️
java-21	34.94% <90.00%> (-28.34%)	⬇️
temurin	63.29% <90.00%> (-0.01%)	⬇️
unittests	63.29% <90.00%> (-0.01%)	⬇️
unittests1	55.25% <ø> (-0.05%)	⬇️
unittests2	34.97% <90.00%> (+0.02%)	⬆️

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[Copilot]

Pull request overview

Improves ServerGrpcChannelBackoffResetHandler resiliency to Helix callback lifecycle edge cases by explicitly handling FINALIZE events and tolerating callbacks where pathChanged is missing.

Changes:

• Clear tracked shutdown state on NotificationContext.Type.FINALIZE to avoid stale lifecycle state.
• Fall back to a full cluster scan when Helix does not provide context.getPathChanged().
• Add unit tests covering FINALIZE handling and null-pathChanged fallback behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pinot-server/src/main/java/org/apache/pinot/server/starter/helix/ServerGrpcChannelBackoffResetHandler.java	Handles FINALIZE by clearing local state; safely falls back to full scan when pathChanged is absent.
pinot-server/src/test/java/org/apache/pinot/server/starter/helix/ServerGrpcChannelBackoffResetHandlerTest.java	Adds tests validating FINALIZE clears tracked state and that null pathChanged triggers a full scan/reset.