Add hierarchical routing processors for document co-location

[atris]

Implements ingest and search pipeline processors to co-locate related
documents based on hierarchical paths (e.g., folder structures). Documents
with same path prefix are routed to same shard, enabling efficient
search within hierarchies.

• HierarchicalRoutingProcessor: Routes documents during indexing
• HierarchicalRoutingSearchProcessor: Routes queries to relevant shards
• Consistent MurmurHash3-based routing between ingest and search
• Configurable anchor depth, path separators, and field mapping

[atris]

RFC and Design Co Author @abhishekpsingh

[atris]

Fixes #18816

[github-actions]

❌ Gradle check result for 72e9306: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[msfroh]

Looks good overall. I left a couple of nitpicky comments.

It looks like one of your tests is failing, and both modules have a test that asserts on what processors are present, so the newly-added processors break that.

[atris]

Looks good overall. I left a couple of nitpicky comments.

It looks like one of your tests is failing, and both modules have a test that asserts on what processors are present, so the newly-added processors break that.

Thanks, fixed both.

[atris]

@msfroh Thanks for reviewing. Updated per comments, please see

[github-actions]

❌ Gradle check result for 9dfe9cc: FAILURE

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[github-actions]

❌ Gradle check result for 85368ab: FAILURE

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[atris]

@msfroh Updated, please see

[github-actions]

❌ Gradle check result for 8194377: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 80db053: FAILURE

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[github-actions]

✅ Gradle check result for 8862c08: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 83.42857% with 29 lines in your changes missing coverage. Please review.

Project coverage is 72.76%. Comparing base (04bf3cb) to head (12c4e99).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...ine/common/HierarchicalRoutingSearchProcessor.java	81.90%	3 Missing and 16 partials ⚠️
...ch/ingest/common/HierarchicalRoutingProcessor.java	85.50%	5 Missing and 5 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #18826      +/-   ##
============================================
+ Coverage     72.75%   72.76%   +0.01%     
- Complexity    68512    68637     +125     
============================================
  Files          5570     5572       +2     
  Lines        314989   315164     +175     
  Branches      45696    45742      +46     
============================================
+ Hits         229165   229340     +175     
+ Misses        67240    67233       -7     
- Partials      18584    18591       +7     

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[github-actions]

❌ Gradle check result for 12c4e99: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 12c4e99: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[atris]

Flaky tests #14509

[github-actions]

✅ Gradle check result for 12c4e99: SUCCESS