fix(extensions): synthesize mediaLocalRoots propagation across sendMedia adapters

Restore deterministic mediaLocalRoots propagation through extension sendMedia adapters and add coverage for local/remote media handling in Google Chat.

Synthesis of #33581, #33545, #33540, #33536, #33528.

Co-authored-by: bmendonca3 <bmendonca3@users.noreply.github.com>

extensions/imessage/src/channel.outbound.test.ts

@@ -63,4 +63,33 @@ describe("imessagePlugin outbound", () => {
     );
     expect(result).toEqual({ channel: "imessage", messageId: "m-media" });
   });
+
+  it("forwards mediaLocalRoots on direct sendMedia adapter path", async () => {
+    const sendIMessage = vi.fn().mockResolvedValue({ messageId: "m-media-local" });
+    const sendMedia = imessagePlugin.outbound?.sendMedia;
+    expect(sendMedia).toBeDefined();
+    const mediaLocalRoots = ["/tmp/workspace"];
+
+    const result = await sendMedia!({
+      cfg,
+      to: "chat_id:88",
+      text: "caption",
+      mediaUrl: "/tmp/workspace/pic.png",
+      mediaLocalRoots,
+      accountId: "acct-1",
+      deps: { sendIMessage },
+    });
+
+    expect(sendIMessage).toHaveBeenCalledWith(
+      "chat_id:88",
+      "caption",
+      expect.objectContaining({
+        mediaUrl: "/tmp/workspace/pic.png",
+        mediaLocalRoots,
+        accountId: "acct-1",
+        maxBytes: 3 * 1024 * 1024,
+      }),
+    );
+    expect(result).toEqual({ channel: "imessage", messageId: "m-media-local" });
+  });
 });

extensions/imessage/src/channel.ts

@@ -54,6 +54,7 @@ async function sendIMessageOutbound(params: {
   to: string;
   text: string;
   mediaUrl?: string;
+  mediaLocalRoots?: readonly string[];
   accountId?: string;
   deps?: { sendIMessage?: IMessageSendFn };
   replyToId?: string;
@@ -69,6 +70,7 @@ async function sendIMessageOutbound(params: {
   });
   return await send(params.to, params.text, {
     ...(params.mediaUrl ? { mediaUrl: params.mediaUrl } : {}),
+    ...(params.mediaLocalRoots?.length ? { mediaLocalRoots: params.mediaLocalRoots } : {}),
     maxBytes,
     accountId: params.accountId ?? undefined,
     replyToId: params.replyToId ?? undefined,
@@ -239,12 +241,13 @@ export const imessagePlugin: ChannelPlugin<ResolvedIMessageAccount> = {
       });
       return { channel: "imessage", ...result };
     },
-    sendMedia: async ({ cfg, to, text, mediaUrl, accountId, deps, replyToId }) => {
+    sendMedia: async ({ cfg, to, text, mediaUrl, mediaLocalRoots, accountId, deps, replyToId }) => {
       const result = await sendIMessageOutbound({
         cfg,
         to,
         text,
         mediaUrl,
+        mediaLocalRoots,
         accountId: accountId ?? undefined,
         deps,
         replyToId: replyToId ?? undefined,