docs(backlog): gate item 35 on 41 (no windowrule infra yet); rec pwvucontrol

Investigating the right-click mixer showed the config has zero
windowrules today, so the float rule needs the infrastructure item 41 is
meant to design list-first. Recorded the gate + the mixer recommendation
(pwvucontrol, app-id com.saivert.pwvucontrol) so the research is not lost.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -259,17 +259,30 @@ today, each needs a per-theme handle width/colour. Payoff is V3-only
 
 ### 35. Right-click volume → audio control app
 (Raised by Bernardo, 2026-07-07 — item 5.) Right-click the Waybar
-`pulseaudio` module to open a mixer (e.g. pavucontrol) in a floating
-window. Wire `on-click-right` in `waybar.nix` AND the whole-swap jsoncs
-(parity rule); add a Hyprland `windowrulev2 = float` for the mixer.
-Ship the mixer in the template's `home.packages`. Pairs with item 41.
+`pulseaudio` module to open a mixer in a floating window. Wire
+`on-click-right` in `waybar.nix` AND the whole-swap jsoncs (parity rule);
+add a Hyprland `windowrulev2 = float` for the mixer. Ship the mixer in
+the template's `home.packages`.
+_Scoped 2026-07-07 (held for item 41):_ the on-click-right wiring is
+trivial, but the float rule needs the windowrule infrastructure that
+**does not exist yet** — there are currently **zero** `windowrule`s in
+the whole config, and item 41 is where that set gets designed list-first
+(Bernardo's call). So this is gated on 41, not independently shippable
+without inverting his 41→35 plan. **Mixer recommendation:** `pwvucontrol`
+(PipeWire-native, GTK4/libadwaita → themes via the portal color-scheme
+like Amberol; the distro is already wpctl/PipeWire). app-id for the float
+rule: `com.saivert.pwvucontrol`. (`pavucontrol` is the GTK3 fallback.)
 
 ### 41. Floating-window audit
 (Raised by Bernardo, 2026-07-07 — item 11.) Decide which windows should
-open floating by default (config dialogs, pavucontrol, file-chooser
-portals, calculators, etc.) and add the `windowrulev2 = float` rules in
+open floating by default (config dialogs, mixer, file-chooser portals,
+calculators, etc.) and add the `windowrulev2 = float` rules in
 `hyprland.nix`. Enables items 35/36b. Produce the list first, then the
 rules.
+_Note 2026-07-07:_ this establishes the **first** windowrule block in the
+config (none exist today) — so it also owns the decision of where the
+rules live and their format. Once the pattern's set, 35's mixer float and
+36b fall out of it.