diff --git a/canvas/src/components/tabs/chat/__tests__/uploads.test.ts b/canvas/src/components/tabs/chat/__tests__/uploads.test.ts
index 54a298a16..da703dd99 100644
--- a/canvas/src/components/tabs/chat/__tests__/uploads.test.ts
+++ b/canvas/src/components/tabs/chat/__tests__/uploads.test.ts
@@ -113,6 +113,31 @@ describe("resolveAttachmentHref — platform-pending: scheme (poll-mode uploads)
   });
 });
 
+describe("resolveAttachmentHref — legacy platform content URLs", () => {
+  const chatWs = "chat-ws-aaaaaaaa";
+  const sourceWs = "d76977b1-d620-4f42-a57e-111111111111";
+  const fileID = "e2dfaf2e-1111-4abc-9999-222222222222";
+
+  it("rewrites /workspaces/<ws>/content/<file>/content to the authenticated pending-upload endpoint", () => {
+    const url = resolveAttachmentHref(
+      chatWs,
+      `/workspaces/${sourceWs}/content/${fileID}/content`,
+    );
+    expect(url).toContain(`/workspaces/${sourceWs}/pending-uploads/${fileID}/content`);
+    expect(url).not.toContain(`/workspaces/${chatWs}/`);
+  });
+
+  it("treats legacy content URLs as platform attachments so previews fetch with auth headers", () => {
+    expect(isPlatformAttachment(`/workspaces/${sourceWs}/content/${fileID}/content`)).toBe(true);
+  });
+
+  it("passes malformed legacy content URLs through unchanged", () => {
+    const malformed = `/workspaces/${sourceWs}/content//content`;
+    expect(resolveAttachmentHref(chatWs, malformed)).toBe(malformed);
+    expect(isPlatformAttachment(malformed)).toBe(false);
+  });
+});
+
 describe("isPlatformAttachment", () => {
   it("returns true for platform-pending: URIs", () => {
     expect(isPlatformAttachment("platform-pending:abc/file")).toBe(true);
diff --git a/canvas/src/components/tabs/chat/uploads.ts b/canvas/src/components/tabs/chat/uploads.ts
index 430991102..102a9e7e1 100644
--- a/canvas/src/components/tabs/chat/uploads.ts
+++ b/canvas/src/components/tabs/chat/uploads.ts
@@ -125,6 +125,8 @@ export async function uploadChatFiles(
  *    - `/workspace/...` (bare absolute path inside the container)
  *    - `platform-pending:<wsid>/<file_id>` (poll-mode upload, staged
  *      on platform side; resolves to /pending-uploads/<file_id>/content)
+ *    - `/workspaces/<wsid>/content/<file_id>/content` (legacy platform
+ *      content URL; normalizes to the same pending-upload endpoint)
  *  Everything that looks like an allowed-root container path is
  *  rewritten to the authenticated /chat/download endpoint. HTTP(S)
  *  URIs pass through unchanged so we can also render links to
@@ -163,6 +165,11 @@ export function resolveAttachmentHref(
     }
     return uri;
   }
+  const legacy = parseLegacyPlatformContentUri(uri);
+  if (legacy) {
+    const [wsid, fileID] = legacy;
+    return `${PLATFORM_URL}/workspaces/${encodeURIComponent(wsid)}/pending-uploads/${encodeURIComponent(fileID)}/content`;
+  }
   const containerPath = normalizeWorkspaceUri(uri);
   if (containerPath) {
     return `${PLATFORM_URL}/workspaces/${workspaceId}/chat/download?path=${encodeURIComponent(containerPath)}`;
@@ -175,6 +182,7 @@ export function resolveAttachmentHref(
  *  downloadChatFile rather than letting the browser navigate. */
 export function isPlatformAttachment(uri: string): boolean {
   if (uri.startsWith("platform-pending:")) return true;
+  if (parseLegacyPlatformContentUri(uri)) return true;
   return normalizeWorkspaceUri(uri) !== null;
 }
 
@@ -183,6 +191,12 @@ export function isPlatformAttachment(uri: string): boolean {
  *  mirror the server's `allowedRoots` allowlist. */
 const ALLOWED_CONTAINER_ROOTS = ["/configs", "/workspace", "/home", "/plugins"];
 
+function parseLegacyPlatformContentUri(uri: string): [string, string] | null {
+  const m = uri.match(/^\/workspaces\/([^/]+)\/content\/([^/]+)\/content(?:[?#].*)?$/);
+  if (!m || !m[1] || !m[2]) return null;
+  return [m[1], m[2]];
+}
+
 function normalizeWorkspaceUri(uri: string): string | null {
   let path: string | null = null;
   if (uri.startsWith("workspace:")) {