fix(archive): preserve blank-line runs in code fences

[Marzx13]

Summary

• Preserve internal literal blank-line runs inside backtick and tilde fences recognized by buildCodeFenceMask.
• Keep existing behavior for prose blank-line collapse, ## Requirements boundaries, whitespace-only lines, and exactly one final LF.
• Add apply-path regression coverage for untouched fences in both Purpose and Requirements, plus a patch changeset.

This is not general byte preservation and does not change CRLF/BOM handling or malformed-Markdown policy.

Fixes #1711

Testing

• Baseline red: the new regression failed because both fenced \n\n\n runs collapsed to \n\n.
• Focused serialization tests: 8 passed.
• Archive/specs-apply matrix: 218 passed, 30 skipped.
• Full suite: 4,163 passed, 67 skipped.
• Lint, build, type-checking, changeset validation, and git diff --check: passed.

Risk

Low. Fence recognition remains delegated to the existing shared helper. There are no configuration, dependency, schema, or migration changes.

Codex model gpt-5.6-sol with max reasoning.

Summary by CodeRabbit

• Bug Fixes

  • Preserved intentional blank lines inside untouched fenced code blocks when applying specification changes.
  • Supports both backtick- and tilde-fenced code blocks.
  • Continues collapsing excessive blank lines in surrounding prose for cleaner formatting.
  • Ensures rebuilt specifications maintain consistent final-line formatting.

• Tests

  • Added coverage verifying blank-line preservation and normalization across fenced code blocks and surrounding text.
  • Validated behavior for multiple fence types and consistent trailing line endings.

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Reviewing files that changed from the base of the PR and between 3fb493c and c572572.

📒 Files selected for processing (1)

• .changeset/calm-fences-preserve.md

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

• .changeset/calm-fences-preserve.md

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📝 Walkthrough

Walkthrough

The spec serializer now collapses excessive blank lines outside recognized code fences. Tests verify preservation inside backtick and tilde fences, prose normalization, whitespace-only lines, and one final LF. A changeset documents the fix.

Changes

Fence-aware serialization

Layer / File(s)	Summary
Fence-aware blank-line normalization src/core/specs-apply.ts	buildUpdatedSpec uses collapseExcessiveBlankLinesOutsideFences. The helper preserves blank-line runs inside recognized fences and limits runs outside fences to two newlines.
Serialization behavior validation test/core/specs-apply.serialization.test.ts, .changeset/calm-fences-preserve.md	The test covers backtick and tilde fences, prose blank-line collapsing, whitespace-only prose lines, and the final LF. The changeset declares a patch release.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to c5725

This localized change preserves blank-line runs inside recognized code fences while retaining existing archive behavior; no actionable merge-blocking risk remains after normal checks and review.

Suggested reviewers: alfred-openspec

🚥 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 summarizes the primary change: preserving blank-line runs inside code fences during archive serialization.
Linked Issues check	✅ Passed	The implementation meets issue #1711. It preserves blank-line runs inside recognized backtick and tilde fences while retaining prose normalization, and the regression test covers both fence types.
Out of Scope Changes check	✅ Passed	The changes are limited to the fence-aware serialization fix, focused regression coverage, and its changeset note. No unrelated code changes are present.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files. (1 skipped: 1 …

Full details: Docstring Coverage

Explanation

Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files. (1 skipped: 1 unsupported.)

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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Actionable comments posted: 1

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Inline comments:
In @.changeset/calm-fences-preserve.md:
- Line 7: Update the changelog sentence in calm-fences-preserve.md to hyphenate
the compound modifier, changing the wording to “backtick- and tilde-fenced code
blocks” while preserving the rest of the sentence.

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Fix all unresolved CodeRabbit comments on this PR:

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: 3e9cdacd-d7f4-40c2-8e62-a430419e5ecd

📥 Commits

Reviewing files that changed from the base of the PR and between a0ddb60 and 3fb493c.

📒 Files selected for processing (3)

• .changeset/calm-fences-preserve.md
• src/core/specs-apply.ts
• test/core/specs-apply.serialization.test.ts

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.