docs(benchmarking): drop the 3% default band; a gain is outside the declared variation criterion

[bompus]

hr-benchmarking no longer has a 3% default band for "no clear change". There is no minimum gain size: a difference counts as a gain when it is outside the variation criterion declared before the first run (the comparison's own run-to-run spread) and the outputs are identical.

Before, the skill said to use 3% as the default no-clear-change band and to widen it only when the declared variation threshold was larger. That made a real, repeatable gain smaller than 3% read as "no clear change" even when the comparison's own spread was far smaller. The criterion each comparison already declares before its first run is now the only line.

What changes:

• A gap inside the declared variation criterion is still reported as no clear change, with the statistic and threshold named beside it. A gap outside it, with identical outputs, is a gain.
• Memory and CPU costs are reported beside the gain.
• If the criterion cannot support a percentage, the result stays separate and unsupported differences are inconclusive (unchanged).
• hr-writing-pr: the benefit chart script no longer defaults band to 0.03. The spec must give band, the declared criterion as a fraction of the baseline; a spec without one now exits with a message. The skill text, thread-visuals.md and the upstream-contributions rule say "declared variation criterion" instead of "reporting band".

Kept, on purpose: rules/core.md and hr-what-next/references/reporting.md ("label changes inside the noise band 'no clear change'") carry no number, and "noise band" still means the comparison's measured variation. The "skip the chart when the one row moved by less than 10%" rule in hr-writing-pr is a chart-size choice, not an acceptance threshold. The evals/end-of-reply/screen/benefit-column.md fixture mentions "noise band about 3%" in a tool result, which is test data. The CHANGELOG.md line about the 3% band under 0.11.0 is history.

Checks: bun test skills/hr-writing-pr (8 pass, including a new test for the required band); node --test on the composer, reference-link and rule-reference tests (46 pass); pinned oxfmt --check and oxlint clean. The full suites run in CI. Not landed; the maintainer decides. A CHANGELOG.md entry is under Unreleased.

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Summary by cubic

hr-benchmarking no longer has a 3% default band for "no clear change". A favorable difference counts as a gain when it lies outside the variation criterion declared before the first run and the outputs are identical; an unfavorable one outside it is a regression labeled worsening. A change at or inside the criterion is still no clear change, with the statistic and threshold named beside the result, and memory and CPU costs are reported beside the gain.

• hr-writing-pr's benefit chart script now requires the spec's band (the declared criterion as a fraction of the baseline, a finite non-negative number) and exits with a message when it is missing or invalid, including booleans, instead of defaulting to 0.03. When the criterion cannot be a fraction of the baseline, the chart is skipped and the result labeled inconclusive.
• Skill text, thread-visuals.md, and the upstream-contributions rule now reference the declared variation criterion instead of a reporting band, and thread-visuals.md also requires identical outputs.
• Changelog entry added under Unreleased.

^{Written for commit a22ca9f. Summary will update on new commits.}

Summary by CodeRabbit

• New Features
  • Benchmark reports classify favorable results outside the predeclared variation criterion as gains when outputs are identical, and similarly unfavorable results as regressions. Differences within or equal to the criterion are reported as “no clear change.”
  • Reports show memory and CPU costs alongside gains and mark unsupported percentage comparisons as inconclusive.
• Documentation
  • Benefit-chart specifications require a finite, non-negative variation band; there is no default band or minimum gain size. Charts are skipped when the criterion cannot be represented as a band, and invalid or missing values produce an error. Guidance consistently refers to the declared variation criterion.

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• skills/hr-writing-pr/scripts/benefit-chart.py
• skills/hr-writing-pr/test/benefit-chart.test.ts

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📝 Walkthrough

Benchmarking guidance now classifies results using the declared variation criterion. Benefit-chart specifications require a top-level band, which chart and table output validate.

Changes: Benchmark reporting

Layer / File(s)	Summary
Define benchmark reporting criterion skills/hr-benchmarking/SKILL.md, rules/modifiers/upstream-contributions.md, rules/references/thread-visuals.md, CHANGELOG.md	The guidance removes the default 3% reporting band and uses the declared variation criterion to classify results. A gain requires identical outputs. Differences within the criterion are “no clear change.” The guidance also specifies memory and CPU costs alongside gains and updates related measured-result references.
Require chart band skills/hr-writing-pr/SKILL.md, skills/hr-writing-pr/scripts/benefit-chart.py, skills/hr-writing-pr/test/benefit-chart.test.ts	Chart guidance requires band to represent the declared variation criterion as a fraction of the baseline. The script rejects missing or invalid values and uses the validated value for chart and table output. Tests cover existing fixtures, invalid values, and changes equal to the band.

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to a22ca

Benchmark classifications follow the declared variation criterion, and chart output requires an explicit threshold. The equality case is covered; no material merge risk remains in the reviewed changes.

### Architecture Summary

Architecture risk: 🔵 Low · up to a22ca

The change affects 3 systems.

Changed systems: skills, rules, CHANGELOG.md

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — skills (service) was modified; 4 changed files map to changed impact.
• observed — rules (service) was modified; 2 changed files map to changed impact.
• observed — CHANGELOG.md (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in rules/modifiers/upstream-contributions.md: The benchmark condition for using a figure changes from being outside the reporting band with the variation criterion met to being outside the declared variation criterion.
• observed — Modified behavior in CHANGELOG.md: Adds Unreleased notes on benchmarking result classification, required band configuration and its validation failure, and terminology updates in related guidance.
• observed — Modified behavior in rules/references/thread-visuals.md: The qualified measured-result condition changes from being outside the reporting band while meeting the declared variation criterion to being outside the declared variation criterion with identical outputs.
• observed — Modified behavior in skills/hr-benchmarking/SKILL.md: The instruction changes from calling a gap within run-to-run variation “inconclusive” to calling it “no clear change.”

Pre-merge checks: 6

Passed checks: 6 passed

Check name	Status	Explanation
Title check		The title clearly identifies the primary change: removing the 3% default band and using the declared variation criterion for gains.
Description check		The description explains the motivation, behavior changes, affected components, validation results, and changelog update. It does not reproduce the required checklist, but it provides evidence for the…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Suppressions Explained		No changed line adds or broadens a lint, type-check, or formatter suppression directive. The pull request changes documentation, Python validation logic, and tests only. No lint or formatter config fi…
Rule Changes Documented		The diff modifies rules/modifiers/upstream-contributions.md and the existing skills/hr-benchmarking/SKILL.md and skills/hr-writing-pr/SKILL.md. CHANGELOG.md adds a matching entry under `## Unr…

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @skills/hr-writing-pr/scripts/benefit-chart.py:
- Line 76: Update the threshold comparison in judge so changes whose absolute
value equals band are classified as “no change,” including zero change with a
zero band. Add tests for both boundary cases and preserve directional labels for
changes outside the band.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: Repository YAML (base), Organization UI (inherited)
• Review profile: CHILL
• Plan: Advanced
• Run ID: ce262bf2-7063-4419-bc32-97e41ddbc782

📥 Commits

Reviewing files that changed from the base of the PR and between ca09d54 and 0500869.

📒 Files selected for processing: 6

• CHANGELOG.md
• rules/references/thread-visuals.md
• skills/hr-benchmarking/SKILL.md
• skills/hr-writing-pr/SKILL.md
• skills/hr-writing-pr/scripts/benefit-chart.py
• skills/hr-writing-pr/test/benefit-chart.test.ts

🚧 Files skipped from review as they are similar to previous changes: 1

• CHANGELOG.md

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All reported issues were addressed across 6 files (changes from recent commits).

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