fix(archive): preserve blank lines inside code fences

[dwin-gharibi]

Closes #1797.

Why

The final assembly in buildUpdatedSpec normalises blank lines across the whole
rebuilt document:

.join('\n\n')
.replace(/\n{3,}/g, '\n\n')   // whole-document, fence-unaware

That normalisation exists to tidy the seams between the four slices being
rejoined, but it also rewrites the inside of fenced code blocks. A requirement
documenting a sample with two or more consecutive blank lines has that sample
silently edited on archive, and re-edited on every subsequent archive.

It matters for whitespace-significant content — YAML block scalars, Python,
expected-output fixtures, Markdown-in-Markdown examples. Every other structural
pass in this module is already fence-aware via buildCodeFenceMask; this one
was not.

What Changes

• Replaced the whole-document regex with collapseBlankRunsOutsideFences, which
  walks the assembled document with buildCodeFenceMask and collapses blank
  runs only outside fenced blocks.
• Semantics outside fences are byte-identical to before: only a truly empty
  line counts as blank, exactly as /\n{3,}/ did, so a line of spaces is still
  never a collapse boundary.

Testing

test/core/specs-apply.fence-preservation.test.ts — 8 tests, written first and
watched fail (5 failed / 3 passed before, 8 passed after).

Edge cases covered:

• two blank lines, and a longer run, inside a backtick fence
• a tilde (~~~) fence
• indentation-sensitive Python content inside a fence
• blank runs outside fences still collapse (no \n{3,} survives)
• a spec with no fences is byte-identical to the previous output (asserted
  against the full expected string, not a substring)
• a whitespace-only line is still not collapsed, matching the old regex exactly
• fenced blank lines carried in from the existing main spec (not just the
  delta) are preserved

Full suite green on this branch.

Changeset

Not added. Per .changeset/README.md the default path is the normal release
cadence; happy to run pnpm changeset if a maintainer wants dedicated release
notes.

Summary by CodeRabbit

• Bug Fixes

  • Preserved multiple blank lines inside fenced code samples during specification updates.
  • Continued collapsing excessive blank lines outside fenced sections.
  • Maintained existing behavior for specifications without fenced code.
  • Preserved indentation-sensitive and whitespace-significant content within fenced samples.

• Tests

  • Added coverage for backtick- and tilde-fenced samples, indentation-sensitive content, whitespace-only lines, and existing specification content.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Team

Run ID: 2f452435-a839-448f-a8ea-86674e404516

📥 Commits

Reviewing files that changed from the base of the PR and between 3de67b3 and 36f135c.

📒 Files selected for processing (1)

• test/core/specs-apply.fence-preservation.test.ts

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

• test/core/specs-apply.fence-preservation.test.ts

Included review availability: Your plan provides up to 10 included reviews per hour; 7 remain after this review.

---

📝 Walkthrough

Walkthrough

The spec assembly now collapses blank-line runs only outside fenced code blocks. The change adds fence-aware normalization and tests for backtick fences, tilde fences, indentation-sensitive content, whitespace-only lines, and existing spec content.

Changes

Spec normalization

Layer / File(s)	Summary
Fence-aware normalization src/core/specs-apply.ts	buildUpdatedSpec now uses collapseBlankRunsOutsideFences. The helper collapses empty-line runs outside fences and preserves content inside backtick and tilde fences.
Normalization coverage test/core/specs-apply.fence-preservation.test.ts	Tests verify fenced blank-line preservation, outside-fence collapsing, no-fence compatibility, whitespace-only lines, indentation-sensitive content, and fenced content from the existing main spec.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 36f13

The change preserves blank lines in fenced code blocks while retaining existing normalization outside fences, with no current merge-blocking risk identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly states the primary change: preserving blank lines inside code fences during archive processing.
Linked Issues check	✅ Passed	The changes address issue #1797. buildUpdatedSpec now preserves consecutive blank lines inside backtick and tilde fences while retaining blank-line normalization outside fences. Tests cover the requ…
Out of Scope Changes check	✅ Passed	The changes are limited to fence-aware normalization in src/core/specs-apply.ts and focused regression tests. No unrelated changes are present.
Docstring Coverage	✅ Passed	Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}