docs(reorder-buffer): correct insert complexity and add micro-bench

[nh13]

Summary

• Fix a misleading complexity claim in ReorderBuffer's docstring. It said "O(1) insert and pop operations," but insert_with_size runs a while self.buffer.len() <= index { push_back(None) } loop, so insert is O(gap) when a sequence number arrives ahead of the current buffer end. Pop remains O(1). The docstring now states the actual contract.
• Add a criterion micro-bench at benches/reorder_buffer.rs covering four realistic insert patterns — purely in-order (k=0) and leading-gap (k=1, 8, 64) — over a 256-insert fill+drain cycle per iteration. Bench target registered in Cargo.toml mirroring the existing core_functions block with harness = false.

The bench exists so future data-structure swaps (BTreeMap, BinaryHeap, fixed-capacity ring buffer) can be measured honestly against the current sparse-VecDeque behavior, including the O(gap) path the corrected doc now advertises.

No functional change; no API change.

Test plan

• cargo build --release --bench reorder_buffer
• cargo ci-fmt
• cargo ci-lint
• cargo bench --bench reorder_buffer -- --test
• Reviewer: spot-check bench output is stable across runs

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: eddbb366-b9f4-4655-823a-477c08906775

📥 Commits

Reviewing files that changed from the base of the PR and between 072f8c7 and fb77c7a.

📒 Files selected for processing (3)

• Cargo.toml
• benches/reorder_buffer.rs
• src/lib/reorder_buffer.rs

📝 Walkthrough

Walkthrough

This change adds a Criterion benchmark for the ReorderBuffer::insert_with_size operation. A new benchmark target is configured in Cargo.toml, and the corresponding benchmark file measures insertion performance across two workload patterns: in-order insertions and insertions with leading gaps of varying sizes (k=1, 8, 64). The benchmark performs sequential inserts followed by drains to measure throughput. Documentation in the reorder buffer module is updated to clarify complexity characteristics: pop operations are O(1) via VecDeque, while insert operations are O(1) for in-order sequences but O(gap) when creating sentinel entries for missing slots.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	Title clearly summarizes the main changes: correcting documentation complexity and adding a benchmark for ReorderBuffer insert operations.
Description check	✅ Passed	Description directly relates to the changeset, explaining the docstring fix and benchmark additions with clear rationale and test plan.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch nh/reorder-buffer-doc-bench

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.87%. Comparing base (25ede93) to head (fb77c7a).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #265      +/-   ##
==========================================
+ Coverage   89.84%   89.87%   +0.03%     
==========================================
  Files         120      120              
  Lines       61359    61416      +57     
==========================================
+ Hits        55127    55197      +70     
+ Misses       6232     6219      -13     

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[nh13]

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[nh13]

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Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@benches/reorder_buffer.rs`:
- Around line 53-70: The benchmark currently computes chunks = batch_size /
chunk which drops the remainder and understates per-batch work; change the loop
to process the full batch_size by computing total_chunks = (batch_size + chunk -
1) / chunk (or loop while processed < batch_size), and for each iteration
compute this_chunk = min(chunk, remaining) so you only insert that many slots:
insert the far slot only if this_chunk > 0, then insert min(k, this_chunk - 1)
near slots (use buffer.insert_with_size), drain with
buffer.try_pop_next_with_size as before, and advance base by this_chunk instead
of always chunk; update references: chunk, batch_size, k, base,
buffer.insert_with_size, buffer.try_pop_next_with_size.
- Line 13: Add a file-level deny for unsafe code in benches/reorder_buffer.rs by
adding the attribute #![deny(unsafe_code)] at the top of the file (adjacent to
or replacing the existing #![allow(clippy::cast_possible_truncation)] line) so
this bench target is compiled with the crate policy; ensure the deny attribute
appears before any module items to apply at file scope.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 1d0c4a08-dff5-4c67-bdca-46f528feb668

📥 Commits

Reviewing files that changed from the base of the PR and between 25ede93 and 072f8c7.

📒 Files selected for processing (3)

• Cargo.toml
• benches/reorder_buffer.rs
• src/lib/reorder_buffer.rs

[nh13]

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