fix: report PLATFORM_NOT_SUPPORTED instead of PERM_DENIED on stub adapters

The default SystemOps::permission_report returned accessibility Denied,
so the CLI preflight short-circuited before dispatch and told Windows
and Linux users they had a permissions problem. They do not; those
adapters are unimplemented, and the suggested fix does not exist.

An adapter that never overrides the probe has not measured permissions
at all, which is a different fact from a user denying one. Reporting
Unknown lets preflight pass so the call reaches the adapter and surfaces
the honest PLATFORM_NOT_SUPPORTED.

The skills reference assertion is gated to macOS because the macOS
reference document is itself cfg-gated into the binary.

crates/core/src/adapter/system.rs

@@ -15,11 +15,13 @@ pub trait SystemOps: Send + Sync {
         Err(AdapterError::not_supported("acquire_interaction_lease"))
     }
 
+    /// An adapter that never overrides this has not probed permissions at all,
+    /// which is not the same fact as a user denying one. `Unknown` routes through
+    /// `unknown_accessibility_means_unsupported` to `PLATFORM_NOT_SUPPORTED`
+    /// rather than the misleading `PERM_DENIED`.
     fn permission_report(&self, _deadline: Deadline) -> Result<PermissionReport, AdapterError> {
         Ok(PermissionReport {
-            accessibility: PermissionState::Denied {
-                suggestion: "Platform adapter not available".into(),
-            },
+            accessibility: PermissionState::Unknown,
             screen_recording: PermissionState::Unknown,
             automation: PermissionState::NotRequired,
         })

crates/core/src/adapter/system_tests.rs

@@ -18,6 +18,17 @@ fn default_surfaces_fail_closed() {
     assert!(DefaultOnly.supported_surfaces().is_empty());
 }
 
+#[test]
+fn default_permission_report_is_unknown_not_denied() {
+    let report = DefaultOnly
+        .permission_report(crate::Deadline::standard().unwrap())
+        .expect("default permission report must not error");
+
+    assert_eq!(report.accessibility, crate::PermissionState::Unknown);
+    assert!(!report.accessibility_denied());
+    assert!(DefaultOnly.unknown_accessibility_means_unsupported());
+}
+
 #[test]
 fn default_open_session_is_explicitly_unsupported() {
     let affinity = crate::SessionAffinity {

crates/core/src/commands/skills_tests.rs

@@ -30,7 +30,9 @@ fn get_full_inlines_references() {
     .expect("get full");
     let content = v["content"].as_str().expect("string");
     assert!(content.contains("--- references/workflows.md ---"));
-    assert!(content.contains("--- references/macos.md ---"));
+    if cfg!(target_os = "macos") {
+        assert!(content.contains("--- references/macos.md ---"));
+    }
     assert!(content.contains("@s8f3k2p9:e1"));
     assert!(content.contains("session start` does not activate later processes"));
     assert!(content.contains("session-owned ref still requires the same `--session`"));