Fix flaky CKEditor caret placement in e2e tests (Firefox mid-word failure on master)

[bartekplus]

Summary

Master failed in E2E Full (firefox, 2/2):
CKEditor inline preview hides trailing word chars when caret is mid-word timed out waiting for the inline preview.

Root cause

The test seeds "The dog walked the street", sets the caret with a DOM selection at "Th|e", and types "r" at once.

CKEditor 5 copies a DOM selection into its model only when the next selectionchange event arrives, which is asynchronous. If the key arrives first (a slow runner), CKEditor inserts the "r" at its old model caret, offset 0 after setData. The new failure dump shows exactly this:

CKEditor state: {"dom":"rThe dog walked the street","model":"<p>rThe dog walked the street</p>","caret":1,...}

"rThe" is not the mid-word case, so FluentTyper correctly shows no preview, and the test times out. This is a race in the test, not a product bug. It is also not caused by #472: this test runs in the same shard, after the same tests, as before. It failed 1 time in the last 24 runs of that shard.

Fix

• New helper setCkEditorCaret(page, paragraph, offset | "end"). It focuses the editing view and sets the caret with editor.model.change(writer => writer.setSelection(...)). CKEditor renders the model selection to the DOM, so the model and the DOM agree before the key is typed.
• It replaces the DOM-selection caret code in all three CKEditor tests that had the same race:
  • CKEditor inline preview hides trailing word chars when caret is mid-word
  • CKEditor preserves paragraph break when accepting suggestion at line end
  • CKEditor grammar/text-edit replacement applies in active second paragraph
• When the mid-word preview times out, the test now reports the editor state (DOM text, model text, caret, focus, FluentTyper attributes).

Evidence

A temporary probe workflow ran on this PR (it is removed in the last commit):

Run	Setup	Result
Before the fix, normal load	6 × Firefox shard 2/2, plus 10 runs of the test alone	all passed (the flake is rare)
Before the fix, all CPU cores busy	8 jobs × 15 runs	every job failed, several runs each, always with "dom":"rThe dog…"
After the fix, all CPU cores busy	8 jobs × 15 runs × the 3 changed tests	all 360 test runs passed

Locally: all CKEditor e2e tests pass in Chrome, and bun run check passes. Firefox does not start on my machine (Firefox 156 cannot create a profile on this macOS version), so CI is the Firefox check.

🤖 Generated with Claude Code

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.
To continue using code reviews, you can upgrade your account or add credits to your account and enable them for code reviews in your settings.