fix: paginate oversized keep-next chains

[jan-kubica]

Summary

• move an oversized keep-with-next chain to a fresh page when it cannot fit the current remainder
• paginate the oversized chain naturally from that fresh page
• retain the populated-page guard that prevents blank-page loops
• add a focused integration regression and core patch changeset

Anonymized parity evidence

• score: 0.2917 → 0.7562
• pages: Word 12; Folio 11 → 12
• pagination findings: 281 → 10
• total findings: 464 → 206

Verification

• 47 focused layout integration tests passed
• bun audit reported no vulnerabilities
• lint and typecheck intentionally delegated to CI

CC on behalf of @jan-kubica

Summary by CodeRabbit

• Bug Fixes

  • Improved pagination for oversized “keep together” content chains.
  • Chains that cannot fit in the remaining space now move to the next page instead of being split unexpectedly.
  • Prevented unnecessary blank pages while preserving the intended sequence of connected content.

• Tests

  • Added coverage for oversized keep-together chains to verify correct page placement during natural pagination.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: ba4f4879-d850-40ce-93e5-a87dfdc1476f

📥 Commits

Reviewing files that changed from the base of the PR and between d452800 and 87fce9d.

📒 Files selected for processing (2)

• packages/core/src/__tests__/layout-pipeline.integration.test.ts
• packages/core/src/layout-engine/index.ts

📝 Walkthrough

Walkthrough

Updates keepNext pagination so oversized chains move to a fresh page when the current page contains fragments. Adds an integration test and a patch changeset entry.

Changes

KeepNext chain pagination

Layer / File(s)	Summary
Oversized chain page-break behavior packages/core/src/layout-engine/index.ts, packages/core/src/__tests__/layout-pipeline.integration.test.ts, .changeset/oversized-keep-next-chain.md	The layout engine breaks before an oversized keepNext chain when the current page has fragments; integration coverage verifies the chain starts on the next page, and a patch changeset records the update.

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

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: fixing pagination for oversized keep-next chains.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/parity-round-21

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[gemini-code-assist]

Code Review

This pull request updates the layout engine to handle oversized 'keep-with-next' chains by moving them to a fresh page before natural pagination. The reviewer identified that the current implementation using 'paginator.forcePageBreak()' is not column-aware and suggested using the existing 'paginator.ensureFits(chainHeight)' abstraction instead, which handles column flow correctly and allows for code simplification.

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[coderabbitai]

🧹 Nitpick comments (1)

packages/core/src/__tests__/layout-pipeline.integration.test.ts (1)

551-567: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Consider asserting the chain paginates across multiple pages.

The test name promises "paginating it naturally" but only verifies the chain moved to page 1. Since 6 blocks × 200 = 1200 likely exceeds a single page, adding an assertion that the chain spans pages 1+ would verify the natural-pagination half of the behavior.

♻️ Optional: add multi-page assertion

     expect(chainStartPage).toBe(1);
     expect(layout.pages[0]?.fragments.map(({ blockId }) => blockId)).toEqual([0]);
+
+    // The oversized chain should paginate naturally across multiple pages.
+    const chainPageCount = layout.pages.filter((page) =>
+      page.fragments.some(({ blockId }) => blockId >= 1 && blockId <= 6),
+    ).length;
+    expect(chainPageCount).toBeGreaterThan(1);

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/core/src/__tests__/layout-pipeline.integration.test.ts` around lines
551 - 567, Add an assertion to the test “moves an oversized keepNext chain
before paginating it naturally” verifying that the chain’s fragments appear
across multiple pages, specifically on page 1 and at least one later page. Keep
the existing assertions for the chain’s starting page and the filler-only first
page.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@packages/core/src/__tests__/layout-pipeline.integration.test.ts`:
- Around line 551-567: Add an assertion to the test “moves an oversized keepNext
chain before paginating it naturally” verifying that the chain’s fragments
appear across multiple pages, specifically on page 1 and at least one later
page. Keep the existing assertions for the chain’s starting page and the
filler-only first page.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: f3eddf1c-9e5f-4ce3-8a10-f197cc53da42

📥 Commits

Reviewing files that changed from the base of the PR and between 95aca77 and d452800.

📒 Files selected for processing (3)

• .changeset/oversized-keep-next-chain.md
• packages/core/src/__tests__/layout-pipeline.integration.test.ts
• packages/core/src/layout-engine/index.ts

[jan-kubica]

Updated the regression to assert the oversized chain spans more than one page, addressing the CodeRabbit nitpick. CC on behalf of @jan-kubica