diff --git a/src-tauri/src/commands/clipboard.rs b/src-tauri/src/commands/clipboard.rs
index 94fe172..5095a92 100644
--- a/src-tauri/src/commands/clipboard.rs
+++ b/src-tauri/src/commands/clipboard.rs
@@ -15,8 +15,11 @@ pub(crate) const MAX_CLIPBOARD_BYTES: usize = 1024 * 1024;
 /// viewer and transcription preview both have legitimate "copy raw text"
 /// buttons; mirror the secondary-windows capability grant in
 /// `src-tauri/capabilities/secondary-windows.json` so the IPC trust
-/// boundary and the permission set stay in lock-step.
-const CLIPBOARD_ALLOWED_WINDOWS: &[&str] = &["main", "transcript-viewer", "transcription-preview"];
+/// boundary and the permission set stay in lock-step. The mirror
+/// invariant is pinned by
+/// `commands::security::tests_capability_mirror::allowlists_match_capability_jsons`.
+pub(crate) const CLIPBOARD_ALLOWED_WINDOWS: &[&str] =
+    &["main", "transcript-viewer", "transcription-preview"];
 
 /// Copy text to the system clipboard via arboard. Restricted to the
 /// documented "clipboard-capable" windows (main + transcript-viewer +
diff --git a/src-tauri/src/commands/paste.rs b/src-tauri/src/commands/paste.rs
index 289ab35..9feac77 100644
--- a/src-tauri/src/commands/paste.rs
+++ b/src-tauri/src/commands/paste.rs
@@ -26,8 +26,10 @@ use crate::commands::security::{ensure_main_window, ensure_window_in_set};
 /// Windows allowed to invoke `paste_text_replacing`. The
 /// `transcription-preview` window's paste-to-foreground flow legitimately
 /// uses this command; mirror the secondary-windows capability grant in
-/// `src-tauri/capabilities/secondary-windows.json`.
-const PASTE_REPLACING_ALLOWED_WINDOWS: &[&str] = &["main", "transcription-preview"];
+/// `src-tauri/capabilities/secondary-windows.json`. The mirror invariant
+/// is pinned by
+/// `commands::security::tests_capability_mirror::allowlists_match_capability_jsons`.
+pub(crate) const PASTE_REPLACING_ALLOWED_WINDOWS: &[&str] = &["main", "transcription-preview"];
 
 /// Refuse-to-paste limit. Matches `commands::clipboard::MAX_CLIPBOARD_BYTES`
 /// (1 MiB) so paste and copy surfaces share a single rejection rule.
diff --git a/src-tauri/src/commands/security.rs b/src-tauri/src/commands/security.rs
index 8cbccb3..835ac82 100644
--- a/src-tauri/src/commands/security.rs
+++ b/src-tauri/src/commands/security.rs
@@ -66,3 +66,71 @@ mod tests {
         assert!(ensure_window_in_set_label("attacker-popup", allowed).is_err());
     }
 }
+
+/// Pins the invariant flagged in the 12b413d commit message and the
+/// Phase B.6 audit (2026-05-14): every label that the Rust IPC layer
+/// allow-lists for clipboard / paste-replacing must also appear in one
+/// of the Tauri capability JSONs' "windows" arrays. If the two halves
+/// drift, the IPC trust boundary silently disagrees with the permission
+/// grant — either the IPC layer permits a window the capability system
+/// rejects (call dies with a Tauri permission error), or the capability
+/// system permits a window the IPC layer rejects (call dies with the
+/// Lumotia rejection message). Either is a maintenance footgun the
+/// commit message claimed to address but did not actually pin.
+#[cfg(test)]
+mod tests_capability_mirror {
+    use std::collections::HashSet;
+    use std::path::Path;
+
+    /// Read all `"windows"` labels declared across the capability JSONs
+    /// at `src-tauri/capabilities/`. The Tauri permission system uses
+    /// these arrays to scope capability grants per window; the Rust IPC
+    /// `ensure_window_in_set` callers must reference the same labels.
+    fn declared_window_labels() -> HashSet<String> {
+        let manifest_dir = env!("CARGO_MANIFEST_DIR");
+        let capabilities_dir = Path::new(manifest_dir).join("capabilities");
+
+        let mut labels: HashSet<String> = HashSet::new();
+        for filename in ["main.json", "secondary-windows.json"] {
+            let body = std::fs::read_to_string(capabilities_dir.join(filename))
+                .unwrap_or_else(|e| panic!("read {filename}: {e}"));
+            let json: serde_json::Value =
+                serde_json::from_str(&body).unwrap_or_else(|e| panic!("parse {filename}: {e}"));
+            let windows = json["windows"]
+                .as_array()
+                .unwrap_or_else(|| panic!("{filename} missing 'windows' array"));
+            for w in windows {
+                if let Some(label) = w.as_str() {
+                    labels.insert(label.to_string());
+                }
+            }
+        }
+        labels
+    }
+
+    #[test]
+    fn allowlists_match_capability_jsons() {
+        let declared = declared_window_labels();
+
+        for label in crate::commands::clipboard::CLIPBOARD_ALLOWED_WINDOWS {
+            assert!(
+                declared.contains(*label),
+                "CLIPBOARD_ALLOWED_WINDOWS label {label:?} is not declared in any \
+                 capabilities JSON ({}). Either remove the label from the Rust const \
+                 or add the window to capabilities/secondary-windows.json so the IPC \
+                 trust boundary and the capability grant stay in lock-step.",
+                declared.iter().cloned().collect::<Vec<_>>().join(", ")
+            );
+        }
+
+        for label in crate::commands::paste::PASTE_REPLACING_ALLOWED_WINDOWS {
+            assert!(
+                declared.contains(*label),
+                "PASTE_REPLACING_ALLOWED_WINDOWS label {label:?} is not declared in any \
+                 capabilities JSON ({}). Either remove the label from the Rust const \
+                 or add the window to capabilities/secondary-windows.json.",
+                declared.iter().cloned().collect::<Vec<_>>().join(", ")
+            );
+        }
+    }
+}