fix(rb-12): hotkey device filter consults configured HotkeyCombo

try_attach_device was rejecting any device that did not report KEY_A or
KEY_R — a leftover heuristic from the whisper-overlay seed. A user whose
binding was anything else (Ctrl+Shift+D is a common default) would see
no hotkey events from that device even though it supports the key.

Replace the hard-coded check with device_supports_combo(supported,
combo), a pure helper that reads the configured trigger key code from
the HotkeyCombo snapshot. Snapshot is taken from hotkey_rx.borrow()
before opening the device; an unconfigured or shutting-down listener
short-circuits to a non-attach.

Four regression tests in linux::tests cover: supported+D → attach,
unsupported → reject, no reported keys → reject, and the explicit
non-A/non-R case that demonstrates the bug.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/hotkey/src/linux.rs

@@ -13,7 +13,7 @@ use std::collections::HashSet;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
-use evdev::{Device, InputEventKind, Key};
+use evdev::{AttributeSetRef, Device, InputEventKind, Key};
 use notify::{recommended_watcher, EventKind, RecursiveMode, Watcher};
 use tokio::sync::{mpsc, watch, Mutex};
 
@@ -225,6 +225,11 @@ async fn try_attach_device(
         return true;
     }
 
+    let Some(combo) = hotkey_rx.borrow().clone() else {
+        // Listener is unconfigured or shutting down.
+        return false;
+    };
+
     let device = match Device::open(path) {
         Ok(d) => d,
         Err(e) => {
@@ -233,14 +238,7 @@ async fn try_attach_device(
         }
     };
 
-    // Check if this device has the keys we need
-    let supported = device.supported_keys();
-    let has_keys = supported.map_or(false, |keys| {
-        // Must support at least some keyboard keys
-        keys.contains(Key::KEY_A) || keys.contains(Key::KEY_R)
-    });
-
-    if !has_keys {
+    if !device_supports_combo(device.supported_keys(), &combo) {
         return false;
     }
 
@@ -347,3 +345,69 @@ fn is_event_device(path: &Path) -> bool {
         .and_then(|n| n.to_str())
         .map_or(false, |n| n.starts_with("event"))
 }
+
+/// Return true when the device's reported key set includes the combo's
+/// configured trigger key. A device that reports no keys at all (for
+/// example a mouse whose `EV_KEY` capability is buttons only) is rejected.
+fn device_supports_combo(
+    supported: Option<&AttributeSetRef<Key>>,
+    combo: &HotkeyCombo,
+) -> bool {
+    supported.map_or(false, |keys| keys.contains(Key::new(combo.key_code)))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use evdev::AttributeSet;
+
+    fn combo_for(key_code: u16) -> HotkeyCombo {
+        HotkeyCombo {
+            ctrl: false,
+            shift: false,
+            alt: false,
+            super_key: false,
+            key_code,
+            label: "test".to_string(),
+        }
+    }
+
+    const KEY_D: u16 = 32;
+
+    #[test]
+    fn attaches_when_device_supports_configured_trigger() {
+        let mut keys = AttributeSet::<Key>::new();
+        keys.insert(Key::KEY_D);
+        assert!(device_supports_combo(Some(&keys), &combo_for(KEY_D)));
+    }
+
+    #[test]
+    fn rejects_when_device_lacks_configured_trigger() {
+        let mut keys = AttributeSet::<Key>::new();
+        keys.insert(Key::KEY_A);
+        assert!(!device_supports_combo(Some(&keys), &combo_for(KEY_D)));
+    }
+
+    #[test]
+    fn rejects_when_device_reports_no_keys() {
+        assert!(!device_supports_combo(None, &combo_for(KEY_D)));
+    }
+
+    // Regression for RB-12: the original filter hard-coded KEY_A || KEY_R
+    // and would drop a keyboard bound to any other trigger — for example
+    // a user's Ctrl+Shift+D binding on a keyboard that (hypothetically)
+    // reports only KEY_D — even though the device clearly supports it.
+    #[test]
+    fn attaches_for_non_a_non_r_trigger() {
+        let mut keys = AttributeSet::<Key>::new();
+        keys.insert(Key::KEY_D);
+        assert!(device_supports_combo(Some(&keys), &combo_for(KEY_D)));
+
+        // And conversely, a device that only supports KEY_R is correctly
+        // rejected when the binding is KEY_D — the old implementation
+        // would have incorrectly attached.
+        let mut keys = AttributeSet::<Key>::new();
+        keys.insert(Key::KEY_R);
+        assert!(!device_supports_combo(Some(&keys), &combo_for(KEY_D)));
+    }
+}

docs/issues/README.md

@@ -19,7 +19,7 @@ should be mirrored as real GitHub issues on `jakejars/kon`.
 | RB-02 | [c3-migrations-atomicity.md](c3-migrations-atomicity.md) | `crates/storage/migrations.rs` | medium |
 | RB-03 | [c4-transcript-profile-fk.md](c4-transcript-profile-fk.md) | `crates/storage/migrations.rs` + `database.rs` | large |
 
-## MAJOR (9)
+## MAJOR (8 open, 1 resolved)
 
 | # | File | Area | Fix scope |
 |---|---|---|---|
@@ -31,7 +31,12 @@ should be mirrored as real GitHub issues on `jakejars/kon`.
 | RB-09 | [decoder-partial-audio-on-error.md](decoder-partial-audio-on-error.md) | `crates/audio/decode.rs` | medium |
 | RB-10 | [llm-prompt-preflight.md](llm-prompt-preflight.md) | `crates/llm/lib.rs` | medium |
 | RB-11 | [keystore-thread-safety.md](keystore-thread-safety.md) | `crates/cloud-providers/keystore.rs` | medium |
-| RB-12 | [hotkey-linux-device-filter.md](hotkey-linux-device-filter.md) | `crates/hotkey/linux.rs` | small |
+
+## Resolved
+
+| # | File | Area | Resolution |
+|---|---|---|---|
+| RB-12 | [hotkey-linux-device-filter.md](hotkey-linux-device-filter.md) | `crates/hotkey/linux.rs` | Extracted `device_supports_combo` helper; `try_attach_device` now reads the configured `HotkeyCombo` from the watch channel and checks support for that trigger key. Four regression tests land in `linux::tests`. |
 
 ## Dependencies
 

docs/issues/hotkey-linux-device-filter.md

@@ -4,6 +4,24 @@
 **Path:** `crates/hotkey/src/linux.rs:236-241`
 **Source:** [2026-04-22 code review](../code-review-2026-04-22.md)
 **Labels:** release-blocker, major, hotkey, correctness
+**Status:** RESOLVED (2026-04-22)
+
+## Resolution
+
+Extracted `device_supports_combo(supported, combo) -> bool` as a pure helper.
+`try_attach_device` now snapshots the current `HotkeyCombo` from `hotkey_rx`
+(returning early with `false` if the listener is unconfigured) and uses the
+helper to filter devices by the configured trigger key.
+
+Tests in `crates/hotkey/src/linux.rs` (`linux::tests`):
+
+- `attaches_when_device_supports_configured_trigger`
+- `rejects_when_device_lacks_configured_trigger`
+- `rejects_when_device_reports_no_keys`
+- `attaches_for_non_a_non_r_trigger` (direct regression)
+
+Manual verification of the Ctrl+Shift+D binding in Settings remains on the
+ship-gate checklist — code path is correct; runtime GUI check is deferred.
 
 ## Problem