refactor: replace line-number matching with section-header extraction in verify-protocol-extracts.sh

[michael-wojcik]

Context

Deferred from PACT v3 Phase D. Tracked for v3.1+.

Description

The verify-protocol-extracts.sh script uses hardcoded line ranges (e.g., sed -n '1303,1459p') to extract protocol sections from pact-protocols.md and compare them against source files. This is brittle — any content change above a section shifts all downstream line numbers, requiring manual updates.

Replace with section-header-based extraction that finds sections by their markdown heading (e.g., ## Scope Contract) and extracts content between headings. This would:

• Eliminate line-range maintenance on every protocol change
• Make the verification script resilient to content additions/removals
• Reduce the most common PR friction point (updating line ranges)

Current State

• 16 protocol extracts verified via line ranges
• Line ranges must be manually updated whenever protocol content changes (happened in Phase C, D, and E)
• The script otherwise works reliably — this is a maintainability improvement, not a bug fix

Implementation Notes

• Could use awk or sed with heading pattern matching
• Need to handle nested headings (sections contain ### subsections)
• The --- separator between sections is a reliable boundary marker
• Must preserve the byte-for-byte comparison behavior

Priority

Medium — reduces ongoing maintenance burden.

References

• scripts/verify-protocol-extracts.sh
• pact-plugin/protocols/pact-protocols.md