Fix node_16::grow() missing 128 offset in node_48 index population

[Copilot]

Recreates PR #26 with co-author attribution for bowling233.

node_16::grow() populates node_48::indexes_[] without the required 128 offset, causing child lookups to fail after growth. All other node_48 operations consistently use indexes_[128 + partial_key] for byte-to-index mapping.

Changes

• include/art/node_16.hpp: Add 128 offset when populating node_48::indexes_[] during growth

  // Before
  new_node->indexes_[(uint8_t) this->keys_[i]] = i;
  
  // After
  new_node->indexes_[128 + (uint8_t) this->keys_[i]] = i;

• test/node_16.cpp: Add test case that grows node_16 to node_48 and verifies child accessibility and iterator navigation

• .gitignore: Exclude _codeql_detected_source_root

Impact

Without this fix, children inserted before growth become unreachable, iterator navigation returns incorrect keys, and data is effectively corrupted after any node_16→node_48 transition.

Related to PR #20.

Co-authored-by: bowling233 zhubaolin228@gmail.com

Original prompt

recreate PR 26 but this time make sure you add co-author bowling233 <zhubaolin228@gmail.com>

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[Copilot]

Pull request overview

This PR fixes a critical bug in node_16::grow() that caused data corruption when a node_16 transitions to node_48. The fix ensures children remain accessible after node growth by correctly applying the 128 offset required by node_48's indexes_[] array, which maps signed char partial keys (-128 to 127) to array indices (0 to 255).

Key Changes:

• Fixed node_16::grow() to use indexes_[128 + partial_key] instead of indexes_[partial_key], making it consistent with all other node_48 operations
• Added comprehensive test case that verifies children remain accessible after growth and that iteration (next_partial_key/prev_partial_key) works correctly
• Updated .gitignore to exclude CodeQL temporary file

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
include/art/node_16.hpp	Adds 128 offset when populating node_48's indexes_ array during node growth, fixing the data corruption bug
test/node_16.cpp	Adds test case that verifies children accessibility and iteration after node_16→node_48 growth, but has a SUBCASE placement bug causing memory safety issues
.gitignore	Excludes CodeQL-generated temporary file _codeql_detected_source_root

[rafaelkallis]

lgtm