fix(native-chat): cover footnote definitions and correct the doc comment

GFM adds a second definition construct. `[^note]: I meant this literally` was
still rendering an empty bubble on a user row — the same total content loss,
one construct over — so disable `gfmFootnoteDefinition` alongside `definition`.

The comment claimed reference links survive. Measured, they do not: they resolve
*against* the definitions this removes, so `[d]`, `[d][]` and `![alt][d]` now
render literally. That is the right reading for prose, but the comment said the
opposite. Also pin that the untouched-content cases render something, since
comparing the two prop values to each other is trivially true if the plugin
ever stops attaching.

src/renderer/src/components/sidebar/remark-disable-definitions.test.tsx

@@ -22,6 +22,12 @@ describe('disableLinkDefinitions', () => {
     ['inside a bullet', '- [Image #1]: /tmp/a.png', '[Image #1]: /tmp/a.png'],
     ['inside an ordered item', '1. [Image #1]: /tmp/a.png', '[Image #1]: /tmp/a.png'],
     ['inside a blockquote', '> [Image #1]: /tmp/a.png', '[Image #1]: /tmp/a.png'],
+    // GFM adds a second definition construct that swallows prose the same way.
+    [
+      'as a footnote definition',
+      '[^note]: I meant this literally',
+      '[^note]: I meant this literally'
+    ],
     // A link label may span lines, so the swallow is not a single-line shape.
     [
       'with a wrapped label',
@@ -49,6 +55,10 @@ describe('disableLinkDefinitions', () => {
     '~~~\ncode\n```\n[Image #1]: /tmp/a.png\n~~~',
     '| a | b |\n| - | - |\n| 1 | 2 |'
   ])('leaves content the pipeline already rendered untouched', (typed) => {
+    // Why the second assertion: comparing the two prop values to each other is
+    // trivially true if the plugin ever stops attaching, so pin that these
+    // render something before trusting that they render the same thing.
+    expect(rendered(typed, true)).not.toBe('')
     expect(rendered(typed, true)).toBe(rendered(typed, false))
   })
 

src/renderer/src/components/sidebar/remark-disable-definitions.ts

@@ -1,19 +1,24 @@
 import type { Processor } from 'unified'
 
 /**
- * Stop CommonMark from reading `[label]: /some/target` as a link reference
- * definition.
+ * Stop the parser from reading `[label]: /some/target` (and its GFM footnote
+ * sibling `[^label]: text`) as a definition.
  *
- * Definitions render to nothing at all, so on content that is prose rather than
- * authored Markdown — a chat turn the user typed — such a line silently deletes
- * itself. Escaping the bracket in the source text only reaches lines at the top
- * level; a definition inside a list item or blockquote, or one whose label wraps
- * across lines, is still swallowed. Turning the construct off covers every
- * container, and leaves inline links, reference *links*, and GFM intact.
+ * A definition renders to nothing at all, so on content that is prose rather
+ * than authored Markdown — a chat turn the user typed — such a line silently
+ * deletes itself. Escaping the bracket in the source text only reaches lines at
+ * the top level; a definition inside a list item or blockquote, or one whose
+ * label wraps across lines, is still swallowed. Turning the constructs off
+ * covers every container without rewriting a byte of what the user wrote.
+ *
+ * Inline links and the rest of GFM are untouched. Reference links necessarily
+ * render literally, because they resolve *against* the definitions this removes
+ * — which is the right reading for prose, where `[d]` is far more likely to be
+ * a bracket the user typed than a link they meant to define.
  */
 export function remarkDisableDefinitions(this: Processor): undefined {
   const data = this.data()
   const extensions = (data.micromarkExtensions ??= [])
-  extensions.push({ disable: { null: ['definition'] } })
+  extensions.push({ disable: { null: ['definition', 'gfmFootnoteDefinition'] } })
   return undefined
 }