fix(packaging): reject ambiguous Snap memory metadata

tools/packaging/verify-linux-frame-copy-runtime.mjs

@@ -546,6 +546,21 @@ export function validateExtractedSnapMetadata(extractionRoot) {
         }
 
         const plugEntries = directYamlMappingEntries(lines, plugs, 2);
+        if (
+            !plugEntries ||
+            plugEntries.some(({ value }) => value.length > 0)
+        ) {
+            errors.push(
+                'Extracted Snap plug declarations must use block mappings.'
+            );
+        }
+        if (
+            plugEntries &&
+            new Set(plugEntries.map(({ key }) => key)).size !==
+                plugEntries.length
+        ) {
+            errors.push('Extracted Snap direct plug keys must be unique.');
+        }
         const sharedMemoryInterfaces =
             plugEntries?.filter((plugEntry) => {
                 const plugFields = directYamlMappingEntries(
@@ -582,12 +597,18 @@ export function validateExtractedSnapMetadata(extractionRoot) {
         lines.length
     );
     let hasSharedMemorySlot = slotsEntries.length > 1;
+    let invalidSlotsShape = slotsEntries.some(
+        ({ value }) => value.length > 0
+    );
     for (const slots of slotsEntries) {
         const slotEntries = directYamlMappingEntries(lines, slots, 2);
         if (!slotEntries) {
-            hasSharedMemorySlot = true;
+            invalidSlotsShape = true;
             continue;
         }
+        invalidSlotsShape ||= slotEntries.some(
+            ({ value }) => value.length > 0
+        );
         hasSharedMemorySlot ||= slotEntries.some((slotEntry) => {
             if (slotEntry.key === 'shared-memory') {
                 return true;
@@ -602,6 +623,11 @@ export function validateExtractedSnapMetadata(extractionRoot) {
             );
         });
     }
+    if (invalidSlotsShape) {
+        errors.push(
+            'Extracted Snap slots must use block mappings with scalar fields.'
+        );
+    }
     if (hasSharedMemorySlot) {
         errors.push(
             'Extracted Snap metadata must not declare a shared-memory slot.'

tools/packaging/verify-linux-frame-copy-runtime.test.mjs

@@ -639,6 +639,27 @@ test('requires a private top-level shared-memory plug used by the Snap app', ()
                     `${contents}slots:\n  shared-memory:\n    interface: shared-memory\n`,
                 /must not declare.*shared-memory slot/i,
             ],
+            [
+                (contents) =>
+                    contents.replace(
+                        '\nplugs:\n',
+                        '\nplugs:\n  other: { interface: shared-memory }\n'
+                    ),
+                /plug declarations.*block mappings/i,
+            ],
+            [
+                (contents) =>
+                    `${contents}slots: { leak: { interface: shared-memory } }\n`,
+                /slots.*block mappings/i,
+            ],
+            [
+                (contents) =>
+                    contents.replace(
+                        '\nplugs:\n',
+                        '\nplugs:\n  network:\n    interface: network\n  network:\n    interface: network\n'
+                    ),
+                /plug keys.*unique/i,
+            ],
             [
                 (contents) =>
                     contents.replace(