fix(desktop): surface skill & quick-command slash commands in the palette (#38531)

The desktop chat app's slash curation (desktop-slash-commands.ts) only
suggested the ~19 curated built-ins. isDesktopSlashSuggestion required
membership in DESKTOP_COMMANDS, so every skill-derived command and user
quick_command was silently dropped from both completion paths
(commands.catalog empty-query + complete.slash typed-query) and from
filterDesktopCommandsCatalog — even though isDesktopSlashCommand let them
EXECUTE when typed in full. The tui_gateway backend already includes skills
in both RPCs; the gap was purely renderer-side.

Add isDesktopSlashExtensionCommand() (= not-a-known-Hermes-built-in, the
same predicate that already gates execution) and let extensions through the
suggestion path. The catalog filter routes through isDesktopSlashSuggestion,
so skill/quick-command categories and pairs are kept automatically.

apps/desktop/src/lib/desktop-slash-commands.test.ts

@@ -17,8 +17,9 @@ describe('desktop slash command curation', () => {
     expect(isDesktopSlashSuggestion('/usage')).toBe(true)
   })
 
-  it('lets explicitly typed extension commands run without suggesting them', () => {
-    expect(isDesktopSlashSuggestion('/my-skill')).toBe(false)
+  it('surfaces skill and quick commands (extensions) in suggestions and lets them run', () => {
+    expect(isDesktopSlashSuggestion('/my-skill')).toBe(true)
+    expect(isDesktopSlashSuggestion('/gif-search')).toBe(true)
     expect(isDesktopSlashCommand('/my-skill')).toBe(true)
   })
 
@@ -38,7 +39,7 @@ describe('desktop slash command curation', () => {
     expect(isDesktopSlashCommand('/reset')).toBe(true)
   })
 
-  it('filters command catalogs down to core desktop commands', () => {
+  it('filters built-in catalog noise but keeps skill / quick-command extensions', () => {
     const filtered = filterDesktopCommandsCatalog({
       categories: [
         {
@@ -61,8 +62,14 @@ describe('desktop slash command curation', () => {
       skill_count: 2
     })
 
-    expect(filtered.categories).toEqual([{ name: 'Session', pairs: [['/new', 'Start a new desktop chat']] }])
-    expect(filtered.pairs).toEqual([['/new', 'Start a new desktop chat']])
+    expect(filtered.categories).toEqual([
+      { name: 'Session', pairs: [['/new', 'Start a new desktop chat']] },
+      { name: 'User commands', pairs: [['/ship-it', 'Run release checklist']] }
+    ])
+    expect(filtered.pairs).toEqual([
+      ['/new', 'Start a new desktop chat'],
+      ['/ship-it', 'Run release checklist']
+    ])
     expect(filtered.skill_count).toBe(2)
   })
 

apps/desktop/src/lib/desktop-slash-commands.ts

@@ -150,10 +150,35 @@ export function isDesktopSlashCommand(command: string): boolean {
   return DESKTOP_COMMANDS.has(canonical) || !isKnownHermesSlashCommand(normalized)
 }
 
+/**
+ * An "extension" command is anything the backend surfaces that is NOT one of
+ * Hermes' built-in slash commands — i.e. skill commands (`/gif-search`,
+ * `/codex`, …) and user-defined quick commands. These are user-activated, so
+ * they should appear in the desktop slash palette even though they aren't in
+ * the curated `DESKTOP_COMMANDS` allow-list. This mirrors the predicate in
+ * `isDesktopSlashCommand` that already lets them EXECUTE when typed.
+ */
+export function isDesktopSlashExtensionCommand(command: string): boolean {
+  const normalized = normalizeCommand(command)
+
+  if (!normalized || normalized === '/') {
+    return false
+  }
+
+  return !isKnownHermesSlashCommand(normalized)
+}
+
 export function isDesktopSlashSuggestion(command: string): boolean {
   const normalized = normalizeCommand(command)
   const canonical = canonicalDesktopSlashCommand(normalized)
 
+  // Surface skill / quick commands (extensions the backend provides) alongside
+  // the curated built-ins. Built-in aliases stay hidden so the popover isn't
+  // cluttered with duplicates.
+  if (isDesktopSlashExtensionCommand(normalized)) {
+    return true
+  }
+
   return DESKTOP_COMMANDS.has(canonical) && !DESKTOP_ALIASES.has(normalized)
 }