The playbook system had a nice text insertion effect — characters first, then words, then progressively larger chunks, so text appears to accelerate onto the page. The problem: it existed as two independent implementations. command-executor.ts had progressiveInsert for rich editors. playbook-handler.ts had progressiveFill for form inputs. Same algorithm, different consumers, diverging over time.
I extracted the core into pages-editor-core as two functions. progressiveEmit is the low-level version — takes a callback, calls it with each chunk at the right timing. progressiveInsert wraps that for EditableText consumers. Both existing callers now import from the shared module.
The interesting part came when we tried it in the Milkdown editor. Every chunk rendered as its own paragraph — three words, new paragraph, three words, new paragraph. The Milkdown bridge’s insertText() runs each chunk through the markdown parser, which wraps plain text in <p> blocks. Correct behaviour for the parser; wrong behaviour for character-by-character insertion.
The fix was insertRawText — an optional method on the EditableText interface that bypasses markdown parsing and uses ProseMirror’s tr.insertText() directly. progressiveInsert prefers it when available, falls back to insertText for editors that don’t implement it. The Milkdown bridge implements it; the CodeMirror bridge doesn’t need to because CodeMirror’s insertText doesn’t parse markdown.
The API layering ended up clean: progressiveEmit (callback) → progressiveInsert (typed interface) → insertRawText (parser bypass). Each level serves a distinct consumer. Any new editor that implements EditableText gets progressive insertion for free.