fix(dropbox): correct shared_link_already_exists JSON path

The prior fix read data.error.shared_link_already_exists.metadata, which
is wrong per Stone's own JSON serialization rules: a union member whose
payload is a struct (SharedLinkMetadata) flattens that struct's fields
alongside ".tag" rather than nesting under a wrapper key. The real shape
is data.error.shared_link_already_exists directly (with an extra ".tag"
field mixed in) - there is no nested .metadata key, so the existing-link
fast path never fired before this fix.

Also marks list_shared_links' expires output optional, matching every
other optional field in this PR and the SharedLinkMetadata spec.

Author: waleedlatif1

apps/sim/tools/dropbox/create_shared_link.ts

@@ -90,7 +90,9 @@ export const dropboxCreateSharedLinkTool: ToolConfig<
     if (!response.ok) {
       // A link may already exist for this path - Dropbox includes its metadata in the error
       // when the requested settings match the existing link, so surface it as a success.
-      const existingLink = data.error?.shared_link_already_exists?.metadata
+      // Per Stone's JSON rules, a union member whose payload is a struct (SharedLinkMetadata)
+      // flattens that struct's fields alongside ".tag" - there is no nested "metadata" key.
+      const existingLink = data.error?.shared_link_already_exists
       if (existingLink) {
         return {
           success: true,

apps/sim/tools/dropbox/list_shared_links.ts

@@ -104,7 +104,7 @@ export const dropboxListSharedLinksTool: ToolConfig<
             description: 'Lowercase path of the shared item',
             optional: true,
           },
-          expires: { type: 'string', description: 'Expiration date if set' },
+          expires: { type: 'string', description: 'Expiration date if set', optional: true },
         },
       },
     },