⚡ Bolt: optimize trie normalization and prefix collection

[gregyjames]

Implemented performance optimizations in src/hypertrie/src/trie.rs:

1. Storing bit_idx directly in normalization buffers avoids + b'a' addition during normalization and - b'a' subtraction during Trie node lookup in insert and contains.
2. Using trailing_zeros bit-twiddling (TZCNT) on children_mask in collect_words_from_node skips empty branches and iterates directly to active child nodes.

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PR created automatically by Jules for task 17268167718362437021 started by @gregyjames

Summary by CodeRabbit

• Performance Improvements
  • Improved word and prefix lookup efficiency.
  • Reduced unnecessary processing during trie insertion and traversal.
  • Maintained readable letter output in debugging views.

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Review details

⚙️ Run configuration

Configuration used: defaults

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📥 Commits

Reviewing files that changed from the base of the PR and between a872b11 and 2f63ee4.

📒 Files selected for processing (1)

• src/hypertrie/src/trie.rs

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Reviewing files that changed from the base of the PR and between 22ccc67 and a872b11.

📒 Files selected for processing (1)

• src/hypertrie/src/trie.rs

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📝 Walkthrough

Walkthrough

Trie normalization now stores alphabet indices from 0 through 25. Insertion and lookup use these indices directly. Debug output restores letters for display. Prefix traversal visits only set child bits.

Changes

Trie index optimization

Layer / File(s)	Summary
Direct alphabet index representation src/hypertrie/src/trie.rs	Insertion and lookup use direct alphabet indices. Debug output converts indices to lowercase ASCII letters.
Set-bit word traversal src/hypertrie/src/trie.rs	Word collection iterates set bits in children_mask instead of scanning all 26 alphabet positions.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to a872b

This localized performance optimization introduces no identified correctness or production risk at the current head; no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the two main changes: optimized trie normalization and prefix collection.
Docstring Coverage	✅ Passed	Docstring check was indeterminate for this PR — some files could not be analyzed in time. Not blocking.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch bolt-trie-bitmask-normalization-opt-17268167718362437021

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.21%. Comparing base (d35e0e1) to head (2f63ee4).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #61      +/-   ##
==========================================
+ Coverage   95.83%   98.21%   +2.37%     
==========================================
  Files           3        3              
  Lines         600      615      +15     
  Branches      600      615      +15     
==========================================
+ Hits          575      604      +29     
+ Misses         19        5      -14     
  Partials        6        6              

Flag	Coverage Δ
rust	98.21% <100.00%> (+2.37%)	⬆️

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