diff --git a/context/open-questions.md b/context/open-questions.md
index 9049553..5cde9c8 100644
--- a/context/open-questions.md
+++ b/context/open-questions.md
@@ -88,6 +88,16 @@ authentic path scoped.
 - **MechControlsMapper look/eyepoint commit** — reconstructed but its offsets collide with declared
   members; arbitrate before enabling (no port consumer yet). The fire-trigger-through-mapper is
   still the `gBTWeaponTrigger` bring-up.
+- **Weapon groups / per-button fire channels (decomp-anchored 2026-07-09)** — MechWeapon message
+  handlers id 9 **`ConfigureMappables`** (`FUN_004b9550`) and id 10 **`ChooseButton`**
+  (`FUN_004b95b8`), table @0x511860 region: ConfigureMappables binds the weapon's
+  `fireImpulse`@0x31C to mapper fire-channel #N (msg value 1-based; <1 unbinds; mapper = roster
+  slot 0, vtable +0x38 register / +0x3c unregister; weapon+0x110 = the bound-state), ChooseButton
+  re-binds (vtable +0x44) — the pod's in-cockpit weapon→button GROUPING. Weapons sharing a button
+  fire together; grouping was a PILOT choice (heat management: alpha vs split). The port's
+  SPACE=all-energy / CTRL=missiles split is a stand-in default; the authentic system needs the
+  mapper channel registration + who SENDS the default ConfigureMappables (mission/player setup —
+  not yet traced). Payoff: authentic weapon groups + a path to chain-fire.
 - **Myomers authentic coupling** — the structural un-stub is INERT (mover feed + heat-gen no-op).
   Real coupling needs the advanced-damage gate (`OwnerAdvancedDamage`/`FUN_004ad7d4` → the owning
   **BTPlayer** `mech+0x190`+0x260, NOT 0xBD3 — see the mech+0x190 item above) + `MoverAttach` routing