Add snippet metadata panel, duplicate, and immediate-load preview (M4.5)

docs/architecture/10-interaction-and-feedback.md

@@ -252,6 +252,29 @@ Not features to add later — the baseline every surface is built on.
 
 ---
 
+## 7. Revealed actions & destructive affordances
+
+How row/list actions appear, and how dangerous ones signal themselves. (Pairs with the
+iconography contract, [arch 09 §5](09-visual-design.md).)
+
+- **Reveal-on-hover is a per-surface choice, not a default.** Hiding a control until hover
+  cuts clutter in a **dense, repeated** list the user inevitably traverses (the snippet-row
+  delete) — there, arrival is guaranteed, so discoverability isn't lost. But a **rare or
+  load-bearing** action must stay **always-visible**, or it becomes effectively unreachable
+  (NN/g #6 — recognition over recall; a feature you can't see you can't use). Decide per
+  surface; when in doubt, show it.
+- **A hover-revealed control must also reveal on keyboard focus.** Gate visibility on
+  `:hover` **and** `:focus-within`/`:focus-visible`, never hover alone — otherwise the
+  action is mouse-only and invisible to keyboard users (WCAG 2.1.1). The snippet row reveals
+  its delete on `.item:hover` _and_ `.delete:focus-visible`.
+- **Destructive controls signal danger on hover _and_ focus.** A delete/remove affordance
+  reddens to `--support-error` on both `:hover` and `:focus-visible` — not colour-by-mouse
+  only — so the warning reaches keyboard users at parity. Colour is a _reinforcement_ here,
+  never the sole signal: the control still carries its label/`aria-label` and the
+  consequential ones still route through a confirm dialog (§4).
+
+---
+
 ## Do / Don't
 
 **Do**