Sources/App/SystemTelemetryStore.swift

@@ -702,7 +702,9 @@ public final class SystemTelemetryStore {
                 freeBytes: $0.freeBytes,
                 freePercent: $0.totalBytes > 0
                     ? Double($0.freeBytes) / Double($0.totalBytes) * 100.0
-                    : 0
+                    : 0,
+                totalBytes: $0.totalBytes,
+                isReadOnly: $0.isReadOnly
             )
         }
         context.batteryLevel = self.batteryHealth.maxCapacity > 0

Sources/Intelligence/AlertEngine.swift

@@ -163,7 +163,10 @@ public final class AlertEngine {
 
         // 4. Low storage space (per mounted volume)
         if cfg.storageEnabled {
-            for volume in ctx.volumes {
+            // Skip read-only mounts (DMGs, snapshots) and trivially small
+            // volumes where free-space thresholds are meaningless.
+            let minTotalBytes: UInt64 = 1_073_741_824 // 1 GB
+            for volume in ctx.volumes where !volume.isReadOnly && volume.totalBytes >= minTotalBytes {
                 let freeGB = Double(volume.freeBytes) / (1024 * 1024 * 1024)
                 if freeGB < cfg.storageFreeGBThreshold || volume.freePercent < cfg.storageFreePercentThreshold {
                     alerts.append(SystemAlert(

Sources/Intelligence/AlertModels.swift

@@ -70,12 +70,18 @@ public struct StorageVolumeContext: Equatable, Sendable {
     public let volumeName: String
     public let freeBytes: UInt64
     public let freePercent: Double
+    public let totalBytes: UInt64
+    /// Read-only mounts (DMG images, snapshots) are excluded from alerting.
+    public let isReadOnly: Bool
 
-    public init(mountPoint: String, volumeName: String, freeBytes: UInt64, freePercent: Double) {
+    public init(mountPoint: String, volumeName: String, freeBytes: UInt64, freePercent: Double,
+                totalBytes: UInt64 = 0, isReadOnly: Bool = false) {
         self.mountPoint = mountPoint
         self.volumeName = volumeName
         self.freeBytes = freeBytes
         self.freePercent = freePercent
+        self.totalBytes = totalBytes
+        self.isReadOnly = isReadOnly
     }
 }
 

Tests/MMAlertsTests.swift

@@ -128,8 +128,10 @@ final class MMAlertsTests: XCTestCase {
 
     func testStorageRuleTriggersPerVolume() {
         let volumes = [
-            StorageVolumeContext(mountPoint: "/", volumeName: "Macintosh HD", freeBytes: 5 * 1_073_741_824, freePercent: 5),
-            StorageVolumeContext(mountPoint: "/Volumes/Data", volumeName: "Data", freeBytes: 500 * 1_073_741_824, freePercent: 50)
+            StorageVolumeContext(mountPoint: "/", volumeName: "Macintosh HD", freeBytes: 5 * 1_073_741_824,
+                                 freePercent: 5, totalBytes: 500 * 1_073_741_824),
+            StorageVolumeContext(mountPoint: "/Volumes/Data", volumeName: "Data", freeBytes: 500 * 1_073_741_824,
+                                 freePercent: 50, totalBytes: 1_000_000_000_000)
         ]
         engine.evaluate(context(volumes: volumes))
         XCTAssertEqual(engine.activeAlerts.count, 1)
@@ -137,11 +139,32 @@ final class MMAlertsTests: XCTestCase {
     }
 
     func testStorageRuleTriggersOnLowPercent() {
-        let volumes = [StorageVolumeContext(mountPoint: "/Volumes/Big", volumeName: "Big", freeBytes: 200 * 1_073_741_824, freePercent: 4)]
+        let volumes = [StorageVolumeContext(mountPoint: "/Volumes/Big", volumeName: "Big",
+                                            freeBytes: 200 * 1_073_741_824, freePercent: 4,
+                                            totalBytes: 2_000_000_000_000)]
         engine.evaluate(context(volumes: volumes))
         XCTAssertEqual(engine.activeAlerts.count, 1)
     }
 
+    func testStorageRuleSkipsReadOnlyVolumes() {
+        // A read-only DMG mount (e.g. an app running from a mounted image)
+        // with ~0% free must not alert — issue #33 false positive.
+        let volumes = [StorageVolumeContext(mountPoint: "/Volumes/Ghostty", volumeName: "Ghostty",
+                                            freeBytes: 1_048_576, freePercent: 0.1,
+                                            totalBytes: 500_000_000_000, isReadOnly: true)]
+        engine.evaluate(context(volumes: volumes))
+        XCTAssertTrue(engine.activeAlerts.isEmpty)
+        XCTAssertTrue(engine.history.isEmpty)
+    }
+
+    func testStorageRuleSkipsTinyVolumes() {
+        let volumes = [StorageVolumeContext(mountPoint: "/Volumes/Small", volumeName: "Small",
+                                            freeBytes: 1_048_576, freePercent: 0.5,
+                                            totalBytes: 200_000_000, isReadOnly: false)]
+        engine.evaluate(context(volumes: volumes))
+        XCTAssertTrue(engine.activeAlerts.isEmpty)
+    }
+
     // MARK: Battery
 
     func testBatteryRuleTriggersOnlyWhileDischarging() {