Add pre-merge-check skill and improve PR review workflow

[igerber]

Summary

• Create /pre-merge-check skill for automated checks before submitting PRs
  • Pattern checks for NaN handling issues (if se > 0 else 0.0 anti-pattern)
  • Test coverage verification (methodology file → test file mapping)
  • Context-specific checklists based on changed files
• Update PR review prompt with edge case checklist learned from PR Add base_period parameter to CallawaySantAnna for pre-treatment effects #97 analysis
  • Empty result set handling
  • NaN/Inf propagation through all inference fields
  • Parameter interaction verification with aggregation/bootstrap
  • Control group logic validation
  • Pattern consistency checks for bug fixes
• Add Task Implementation Workflow section to CLAUDE.md
  • 4-phase workflow: Planning, Implementation, Pre-Merge Review, Submit
  • Quick reference grep commands for common pattern checks

Methodology references (required if estimator / math changes)

• Method name(s): N/A - no methodology changes
• Paper / source link(s): N/A
• Any intentional deviations from the source (and why): None

Validation

• Tests added/updated: No test changes (workflow/documentation only)
• Backtest / simulation / notebook evidence (if applicable): N/A

Security / privacy

• Confirm no secrets/PII in this PR: Yes

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Generated with Claude Code

[github-actions]

Overall Assessment

• ⚠️ Needs changes

Executive Summary

• P1: pre-merge change detection can miss committed PR changes, which can skip critical checks.
• P2: NaN division pattern check likely never matches due to \b usage without PCRE.
• No estimator/math/variance behavior changes; updates are workflow/docs only.

Methodology

• No findings; no methodology or estimator code changes in this diff.

Code Quality

• Severity: P1 | Impact: pre-merge check may ignore committed changes and return an empty file list on clean branches, skipping pattern/test checks | Fix: diff against the PR base (e.g., git diff --name-only <base>...HEAD or git diff --name-only $(git merge-base HEAD <base>) HEAD) and keep git ls-files --others --exclude-standard for untracked | Location: .claude/commands/pre-merge-check.md:L14-L20
• Severity: P2 | Impact: grep -n "/ se\b" uses BRE where \b is a backspace, so the heuristic likely never matches and can miss issues | Fix: switch to grep -n -P "/\s*se\b" or grep -n -E "/[[:space:]]*se\>" | Location: .claude/commands/pre-merge-check.md:L38-L39

Performance

• No findings.

Maintainability

• No findings.

Tech Debt

• No findings.

Security

• No findings.

Documentation/Tests

• No findings; doc-only changes are consistent with scope.