fix(sender): delete newlines before slots

[advance-hub]

Why

In Chromium, pressing Enter immediately before a non-editable Sender slot creates a new block that starts with <br>. Backspace removes the break node but leaves the block wrapper, so the visual newline cannot be deleted.

Fixes #1889.

What changed

• Detect a collapsed caret at the start of a slot-led block.
• Remove the leading break and unwrap the block into the editor.
• Preserve the slot DOM and restore the caret immediately before it.
• Add a regression test for Enter then Backspace before a slot.

Verification

• Sender slot Jest suite: 23 passed.
• TypeScript --noEmit check passed.
• Biome and git diff --check passed.
• Real Chromium before/after reproduction passed.

Before / After

Before: Backspace removes <br>, but the block wrapper keeps the newline.

before.mp4

After: Backspace merges the line while preserving the slot and caret position.

after.mp4

Changelog: Fix Sender slot mode being unable to delete a newline immediately before a slot.

Summary by CodeRabbit

• Bug 修复
  • 修复编辑器中退格删除操作的问题：光标位于不可编辑插槽前的换行处时，可正确移除换行并合并内容。
  • 优化插槽内容删除后的光标位置与内容变更处理。

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 271ea24c-ad8c-46a1-8222-a2e8c2d0d31a

📥 Commits

Reviewing files that changed from the base of the PR and between 25aad7b and 8d052ad.

📒 Files selected for processing (2)

• packages/x/components/sender/__tests__/slot.test.tsx
• packages/x/components/sender/components/SlotTextArea.tsx

Included review availability: Your plan provides up to 8 included reviews per hour; 4 remain after this review.

---

📝 Walkthrough

Walkthrough

Sender 新增 Chromium 下的退格处理：删除 slot 前的换行块，提升 slot 节点，恢复光标并触发一次 onChange。测试覆盖该行为。

Changes

Sender slot 换行删除

Layer / File(s)	Summary
退格删除换行与测试 packages/x/components/sender/components/SlotTextArea.tsx, packages/x/components/sender/__tests__/slot.test.tsx	当光标位于 slot 前的换行块起始位置时，代码移除 <br>，提升行内节点，恢复光标并阻止默认退格行为。测试验证事件返回 false、换行块被移除、slot 成为根节点直接子节点，并且 onChange 只调用一次。

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

Merge Risk: ⚪ Minimal · up to 8d052

This localized Sender fix removes the unwanted newline before a slot while preserving the slot and caret; no actionable merge-blocking risk remains after normal checks and review.

Poem

小兔按下 Backspace，
换行轻轻跳出框。
slot 越过旧行到根节点，
光标回到清晰位置，
onChange 唤醒一次，
Chromium 也不再迷路。

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	标题准确概括了 Sender slot 前删除换行的主要修复内容，简洁且明确。
Linked Issues check	✅ Passed	代码修复了 Issue #1889 描述的问题：在 slot 前按 Enter 后，Chromium 中按 Backspace 可以删除换行，同时保留 slot 和光标位置。新增回归测试覆盖该场景。
Out of Scope Changes check	✅ Passed	变更仅涉及 Sender 的换行删除逻辑和对应回归测试，均与 Issue #1889 直接相关。未发现无关或超出范围的代码变更。
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2 files.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

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

[nrps9909]

Reviewed exact head 8d052ad against base 25aad7b.

The Chromium newline repair is narrowly gated to a collapsed Backspace selection at offset 0 in a direct child block whose leading nodes are BR plus a registered slot. It removes only that BR and wrapper, preserves the remaining nodes in order, restores the caret immediately before the first slot, and emits one value change.

Validation performed:

• Reverted the new repair branch locally: the submitted regression test failed at the expected event/default-prevention assertion.
• Exact head Sender slot suite: 23/23 passed.
• Temporary complementary probes passed for multiple slots with intervening/trailing text, exact DOM order preservation, caret range at the original line index, one onChange, and non-collapsed selection remaining untouched.
• packages/x TypeScript noEmit passed.
• Biome passed on both changed files.
• git diff --check passed.
• Live PR head rechecked before review and still matches the tested SHA; current remote checks are green.

AI assistance disclosure: Codex was used to inspect the exact diff, run the red/green validation and complementary boundary probes, and draft this review. I verified the reported commands and outcomes.