refactor(desktop): give the rich editor a chip-aware caret insert

`insertPlainTextAtCaret` dropped its text in verbatim, so a caller with
directives in hand had no way to land them as chips. It becomes
`insertComposerContentsAtCaret`, sharing the parse `renderComposerContents`
already uses, and gains a sibling `replaceBeforeCaret` for swapping a
just-typed token for a chip.

apps/desktop/src/app/chat/composer/rich-editor.test.ts

@@ -4,10 +4,11 @@ import { insertInlineRefsIntoEditor } from './inline-refs'
 import {
   composerPlainText,
   deleteSelectionInEditor,
-  insertPlainTextAtCaret,
+  insertComposerContentsAtCaret,
   normalizeComposerEditorDom,
   refChipElement,
   renderComposerContents,
+  replaceBeforeCaret,
   RICH_INPUT_SLOT
 } from './rich-editor'
 
@@ -72,14 +73,14 @@ describe('insertInlineRefsIntoEditor', () => {
   })
 })
 
-describe('insertPlainTextAtCaret', () => {
+describe('insertComposerContentsAtCaret', () => {
   it('inserts multiline text as text nodes + br', () => {
     const editor = document.createElement('div')
     editor.dataset.slot = RICH_INPUT_SLOT
     document.body.append(editor)
     caretIn(editor)
 
-    insertPlainTextAtCaret(editor, 'one\ntwo\nthree')
+    insertComposerContentsAtCaret(editor, 'one\ntwo\nthree')
 
     expect(editor.querySelectorAll('br').length).toBe(2)
     expect(composerPlainText(editor)).toBe('one\ntwo\nthree')
@@ -102,12 +103,76 @@ describe('insertPlainTextAtCaret', () => {
     selection.removeAllRanges()
     selection.addRange(range)
 
-    insertPlainTextAtCaret(editor, 'cd')
+    insertComposerContentsAtCaret(editor, 'cd')
 
     expect(composerPlainText(editor)).toBe('abcdef')
 
     editor.remove()
   })
+
+  it('lands directives in the text as chips', () => {
+    const editor = document.createElement('div')
+    editor.dataset.slot = RICH_INPUT_SLOT
+    document.body.append(editor)
+    caretIn(editor)
+
+    insertComposerContentsAtCaret(editor, 'read @url:`https://example.dev/a` now')
+
+    expect(editor.querySelectorAll('[data-ref-kind="url"]').length).toBe(1)
+    expect(composerPlainText(editor)).toBe('read @url:`https://example.dev/a` now')
+
+    editor.remove()
+  })
+})
+
+describe('replaceBeforeCaret', () => {
+  it('swaps the token before the caret and leaves the caret after the insert', () => {
+    const editor = document.createElement('div')
+    editor.dataset.slot = RICH_INPUT_SLOT
+    editor.textContent = 'see foo'
+    document.body.append(editor)
+
+    const text = editor.firstChild!
+    const selection = window.getSelection()!
+    const range = document.createRange()
+
+    range.setStart(text, 7)
+    range.collapse(true)
+    selection.removeAllRanges()
+    selection.addRange(range)
+
+    const fragment = document.createDocumentFragment()
+    fragment.append(refChipElement('file', '`src/foo.ts`'), document.createTextNode(' '))
+
+    expect(replaceBeforeCaret(editor, 3, fragment)).toBe(true)
+    expect(composerPlainText(editor)).toBe('see @file:`src/foo.ts` ')
+    expect(selection.getRangeAt(0).collapsed).toBe(true)
+
+    editor.remove()
+  })
+
+  it('leaves the editor alone when the caret has no room for the token', () => {
+    const editor = document.createElement('div')
+    editor.dataset.slot = RICH_INPUT_SLOT
+    editor.textContent = 'hi'
+    document.body.append(editor)
+
+    const selection = window.getSelection()!
+    const range = document.createRange()
+
+    range.setStart(editor.firstChild!, 2)
+    range.collapse(true)
+    selection.removeAllRanges()
+    selection.addRange(range)
+
+    const fragment = document.createDocumentFragment()
+    fragment.append(document.createTextNode('x'))
+
+    expect(replaceBeforeCaret(editor, 20, fragment)).toBe(false)
+    expect(composerPlainText(editor)).toBe('hi')
+
+    editor.remove()
+  })
 })
 
 describe('deleteSelectionInEditor', () => {

apps/desktop/src/app/chat/composer/rich-editor.ts

@@ -144,14 +144,15 @@ function composerSelectionRange(editor: HTMLElement) {
   return { range, selection }
 }
 
-/** Insert plain text at the caret (replacing any selection). Pastes use this
- *  instead of `execCommand('insertText')` — Chromium's editing pipeline is
- *  ~O(n²) on large multiline blobs. */
-export function insertPlainTextAtCaret(editor: HTMLElement, text: string) {
+/** Insert text at the caret (replacing any selection), with any `@kind:value`
+ *  directives in it landing as chips. Pastes use this instead of
+ *  `execCommand('insertText')` — Chromium's editing pipeline is ~O(n²) on large
+ *  multiline blobs. */
+export function insertComposerContentsAtCaret(editor: HTMLElement, text: string) {
   const hit = composerSelectionRange(editor)
   const fragment = document.createDocumentFragment()
 
-  appendTextWithBreaks(fragment, text)
+  appendComposerContents(fragment, text)
 
   const tail = fragment.lastChild
 
@@ -172,6 +173,41 @@ export function insertPlainTextAtCaret(editor: HTMLElement, text: string) {
   }
 }
 
+/** Swap the `length` characters immediately before a collapsed caret for
+ *  `fragment`, leaving the caret after it. Returns whether it ran — a caret that
+ *  isn't inside a text node holding the whole token is left alone. */
+export function replaceBeforeCaret(editor: HTMLElement, length: number, fragment: DocumentFragment) {
+  const hit = composerSelectionRange(editor)
+
+  if (!hit?.range.collapsed) {
+    return false
+  }
+
+  const { startContainer, startOffset } = hit.range
+
+  if (startContainer.nodeType !== Node.TEXT_NODE || startOffset < length) {
+    return false
+  }
+
+  const range = document.createRange()
+  const tail = fragment.lastChild
+
+  range.setStart(startContainer, startOffset - length)
+  range.setEnd(startContainer, startOffset)
+  range.deleteContents()
+  range.insertNode(fragment)
+
+  if (tail) {
+    range.setStartAfter(tail)
+  }
+
+  range.collapse(true)
+  hit.selection.removeAllRanges()
+  hit.selection.addRange(range)
+
+  return true
+}
+
 /** Backspace at a collapsed caret immediately after a chip: delete the chip AND
  *  the single trailing space we auto-insert after it, atomically — so removing a
  *  directive never strands an orphaned space (the contenteditable-driven cleanup