fix: Enter key not creating new line in memo mode

[devin-ai-integration]

Summary

Fixes #4964 — Enter key doesn't create a new line in the session editor's memo (raw) mode.

Two changes in apps/desktop/src/editor/session/index.tsx:

1. Add missing prosemirror-view/style/prosemirror.css import — The chat editor already imports this, but the session editor was missing it. This CSS provides baseline ProseMirror functional styles (white-space: break-spaces, position: relative, etc.) that the @handlewithcare/react-prosemirror library expects to be present.

2. Remove redundant state management in dispatchTransaction — The old handler manually called this.state.applyTransaction(tr) and this.updateState(newState), duplicating what useEditor from @handlewithcare/react-prosemirror already does internally. This double state application can cause conflicts between React state and the ProseMirror view state, potentially preventing transactions (like splitBlock from Enter) from taking effect.

Review & Testing Checklist for Human

• Verify Enter key works in memo mode — Open a session note, switch to memo/raw mode, type some text, and press Enter. A new line should be created without needing Cmd+Enter.
• Verify Enter key still works in list modes — In bullet list, ordered list, and task list modes, Enter should still split list items (and lift empty items as before).
• Verify Cmd+Enter still inserts hard breaks — The hard break shortcut should remain functional.
• Check for visual regressions — The new prosemirror-view/style/prosemirror.css import adds styles like .ProseMirror-selectednode { outline: 2px solid #8cf } and selection-related styles that may affect the editor's visual appearance.
• Verify onUpdate (save) still fires correctly — The simplified dispatchTransaction now checks tr.docChanged instead of transactions.some(t => t.docChanged). Confirm that edits are still being persisted.

Notes

• The fix was identified by comparing the working chat editor (src/editor/chat/index.tsx) with the broken session editor — both use @handlewithcare/react-prosemirror but the session editor was missing the CSS import and had a more complex dispatchTransaction.
• This is a Tauri desktop app, so the fix could not be tested end-to-end in this environment. Manual testing on the desktop app is strongly recommended.

Link to Devin session: https://app.devin.ai/sessions/078f377777df476b8a230c16b3a77899
Requested by: @ComputelessComputer

[devin-ai-integration]

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