fix(mime): text/plain falls through to Text Editor on live (#119)

A singleton default naming code.desktop left the live ISO with no text
handler — GIO skips missing .desktop files and offers nothing. Prefer
vscode when present, then org.gnome.TextEditor.desktop. Live also gains
mpv (video defaults had the same hole; free via the template pin).

checks.live-baseline-apps now requires every Default Applications key
to resolve to a present .desktop on live (HM + system path) and on the
default template install. Proved to fail on a vscode-only text/plain.

Verified: V2 (live-baseline-apps green + prove-to-fail); V0 flake check.

agent/JOURNAL.md

@@ -19,6 +19,26 @@ Template:
 
 ---
 
+## 2026-07-15 — #119: mime defaults must name a present .desktop (this commit)
+- **Task:** BACKLOG #119 — `text/plain` named vscode, which the live ISO never
+  ships (same GIO-skip trap as #94, one key over).
+- **Did:** `text/plain` is now an ordered fallback
+  `code.desktop` → `org.gnome.TextEditor.desktop` (HM tries the next when the
+  preferred is missing). Live profile gains `mpv` too — video mime defaults
+  had the same hole and the package is free via the template pin. Extended
+  `checks.live-baseline-apps` so every `[Default Applications]` key has at
+  least one listed `.desktop` on **live** (HM path + system path for thunar)
+  and on the **default template install**.
+- **Verified:** **V2** — check green; mimeapps.list renders
+  `text/plain=code.desktop;org.gnome.TextEditor.desktop`; **proved to fail**
+  when `text/plain` is a vscode-only singleton. V0 flake check green.
+- **Pending:** V3 launch of a `.txt` on the Acer is covered by the existing
+  #103 HARDWARE-QUEUE entry (now expects Text Editor for text files). Opting
+  out of *both* vscode and Text Editor still leaves no handler — that is the
+  delete-the-line convention, not a silent live-ISO bug.
+- **Next suggestion:** #95 (Ghostty does not open) or #94 residual
+  (test-install chromium launch).
+
 ## 2026-07-14 — #118: smartd self-gates; the doctor was right all along (this commit)
 - **Task:** BACKLOG #118 — Bernardo's live ISO showed a red Waybar health icon
   reporting smartd.