fix(core): avoid torn Yjs plugin state during fork merge by nperez0111 · Pull Request #3136 · TypeCellOS/BlockNote

nperez0111 · 2026-09-28T16:00:25Z

Summary

Fixes #3135. This closes the cursor crash left after #2952.

Give the replacement ySync and yUndo plugins fresh state during an off-view reconfiguration, then update the view once. This keeps the sync type, doc, and binding consistent when y-prosemirror rerenders synchronously and the remote cursor plugin initializes.
Preserve original-document undo and redo stacks across fork/merge while isolating fork undo history. Remove the post-swap ySync rebinding transaction.
Add regression coverage for Accept and Discard with a remote awareness cursor, plus undo/redo history isolation. Both cursor cases reproduced the reported nodeSize exception without this change.

Verification

vp run test in packages/core: 792 passed, 9 skipped
vp run lint in packages/core: clean

Out of scope

Undoing an accepted merge is a separate existing behavior: Y.applyUpdate uses the editor as the update origin, which the Yjs undo manager does not track. This PR leaves that origin unchanged.

Summary by CodeRabbit

Bug Fixes
- Merging a fork while a remote cursor is present no longer causes an error, and the cursor remains visible.
- Undo and redo history now behaves consistently when editing, merging, or discarding fork changes, preserving the expected document content.

vercel · 2026-09-28T16:00:31Z

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coderabbitai · 2026-09-28T16:00:45Z

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: a940b80d-5f99-46f1-945e-0683c6f07f33

📥 Commits

Reviewing files that changed from the base of the PR and between 660f8a2 and 591b983.

📒 Files selected for processing (3)

packages/core/src/editor/managers/ExtensionManager/index.ts
packages/core/src/yjs/extensions/ForkYDoc.test.ts
packages/core/src/yjs/extensions/ForkYDoc.ts

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📝 Walkthrough

Walkthrough

replaceExtension now supports resetting selected ProseMirror plugin state during replacement. ForkYDocExtension uses this when switching between original and forked documents, preserves undo and redo stacks, and adds tests for remote cursors and history.

Changes

Forked document plugin state

Layer / File(s)	Summary
Selected plugin state reset `packages/core/src/editor/managers/ExtensionManager/index.ts`	`replaceExtension` accepts an optional list of plugin keys to reset. The update removes matching keyed plugins from an intermediate state before reconfiguring with the updated plugins.
Fork and merge plugin state `packages/core/src/yjs/extensions/ForkYDoc.ts`, `packages/core/src/yjs/extensions/ForkYDoc.test.ts`	Fork and merge reset ySync and yUndo plugin state. ForkYDoc saves the original undo and redo stacks and restores them after merge. Tests cover merging with remote cursors for both `keepChanges` values and restoring history after undo.

Priority: ➖ Normal

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

Change: Bug fix · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant ForkYDocExtension
  participant ExtensionManager
  participant EditorState
  participant UndoManager
  ForkYDocExtension->>UndoManager: Save original undo and redo stacks
  ForkYDocExtension->>ExtensionManager: replaceExtension with resetPluginStateFor
  ExtensionManager->>EditorState: Reconfigure plugins with selected state reset
  ForkYDocExtension->>ExtensionManager: replaceExtension during merge with resetPluginStateFor
  ExtensionManager->>EditorState: Reconfigure plugins with selected state reset
  ForkYDocExtension->>UndoManager: Restore saved undo and redo stacks

Merge Risk: ⚪ Minimal · up to 591b9

The fork and merge changes are mergeable after normal checks; the saved undo and redo history remains available when the old manager is destroyed.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 591b9

The change improves collaboration-state consistency without an established new security exposure. Failure recovery and concurrent-edit behavior remain insufficiently verified.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

inferred — The directly affected state is the editor’s fork and its configured original collaboration document; accept retains the pre-existing path for propagating changes to that document. No broader service or tenant exposure is established by the available evidence.

Security Findings and Attack Paths

inferred — Tracing the supplied update through fork and merge found no PR-added route into the original document: discard does not apply it, while accept uses the existing explicit update path. Caller authorization is not defined in this source.

Trust Boundaries and Controls

observed — Fork omits the awareness cursor plugin; merge reinstalls it with the original collaboration options. The remote-cursor regression checks its restoration, not provider-level identity or authorization.

Resilience and Maintainability Implications

inferred — An exception between plugin replacement and final store-state updates could leave the visible fork status inconsistent with plugin or document ownership. This is an unverified recovery limitation, not an established new security finding.

Hardening Proposals

proposed — Exercise replacement and merge-update failures, retries, and concurrent remote content edits; define how plugin, history, and fork-status ownership is restored after an interrupted transition.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the primary change: preventing torn Yjs plugin state during fork merge.
Description check	✅ Passed	The description provides a clear summary, rationale, implementation details, testing results, and out-of-scope behavior. It does not use all template headings and omits the checklist, but the required…
Linked Issues check	✅ Passed	The PR addresses [`#3135`]. `replaceExtension` can reset `ySyncPluginKey` and `yUndoPluginKey` state during the single plugin reconfiguration. `ForkYDocExtension` uses this option for both fork and merg…
Out of Scope Changes check	✅ Passed	The changes stay within [`#3135`]. The `ExtensionManager` option provides the atomic state reset required by the fork and merge fix. The `ForkYDoc` changes remove the torn-state rebinding step and prese…

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_{A rabbit checks the cursor’s place,
Then watches forked changes race.
The plugins reset; the stacks stay near,
Undo and redo both appear.
The remote cursor finds its way,
And hops through merge without delay.}

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

pkg-pr-new · 2026-09-28T16:08:26Z

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commit: 591b983

github-actions · 2026-09-28T16:11:08Z

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fix(core): initialize Yjs plugin state before fork merge view swap

591b983

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fix(core): avoid torn Yjs plugin state during fork merge - #3136

fix(core): avoid torn Yjs plugin state during fork merge#3136
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fix-issue-3135-collaboration-cursor-merge-crash

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