Background

In crates/outline/src/combined_extractor.rs, CombinedExtractors::extract currently uses an explicit pre-order (DFS) traversal via a stack to match top-level outline items and skip their descendants once matched.

Task

Explore whether switching to a level-order (BFS) traversal would be faster in practice. Potential advantages of BFS:

• Outline items (functions, classes, etc.) tend to cluster near the top levels of the AST, so BFS might find matches earlier and avoid allocating deep stack frames.
• The "skip descendants once matched" semantics may integrate naturally with a queue-based approach.

Potential drawbacks:

• BFS requires a queue/deque, which may have higher allocation overhead for deeply nested or wide ASTs.
• Pre-order with early skip may already be near-optimal for typical AST shapes.

Suggested investigation

• Benchmark both approaches on representative source files (Rust, TypeScript, Go) with the existing outline rules.
• Measure allocation count and throughput.

References

• PR: Outline extractor execution #2729
• Comment: Outline extractor execution #2729 (comment)

Requested by @HerringtonDarkholme.