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/slack/src/channel.test.ts

@@ -108,6 +108,33 @@ describe("slackPlugin outbound", () => {
     );
     expect(result).toEqual({ channel: "slack", messageId: "m-media" });
   });
+
+  it("forwards mediaLocalRoots for sendMedia", async () => {
+    const sendSlack = vi.fn().mockResolvedValue({ messageId: "m-media-local" });
+    const sendMedia = slackPlugin.outbound?.sendMedia;
+    expect(sendMedia).toBeDefined();
+    const mediaLocalRoots = ["/tmp/workspace"];
+
+    const result = await sendMedia!({
+      cfg,
+      to: "C999",
+      text: "caption",
+      mediaUrl: "/tmp/workspace/image.png",
+      mediaLocalRoots,
+      accountId: "default",
+      deps: { sendSlack },
+    });
+
+    expect(sendSlack).toHaveBeenCalledWith(
+      "C999",
+      "caption",
+      expect.objectContaining({
+        mediaUrl: "/tmp/workspace/image.png",
+        mediaLocalRoots,
+      }),
+    );
+    expect(result).toEqual({ channel: "slack", messageId: "m-media-local" });
+  });
 });
 
 describe("slackPlugin config", () => {

extensions/slack/src/channel.ts

@@ -371,7 +371,17 @@ export const slackPlugin: ChannelPlugin<ResolvedSlackAccount> = {
       });
       return { channel: "slack", ...result };
     },
-    sendMedia: async ({ to, text, mediaUrl, accountId, deps, replyToId, threadId, cfg }) => {
+    sendMedia: async ({
+      to,
+      text,
+      mediaUrl,
+      mediaLocalRoots,
+      accountId,
+      deps,
+      replyToId,
+      threadId,
+      cfg,
+    }) => {
       const { send, threadTsValue, tokenOverride } = resolveSlackSendContext({
         cfg,
         accountId: accountId ?? undefined,
@@ -381,6 +391,7 @@ export const slackPlugin: ChannelPlugin<ResolvedSlackAccount> = {
       });
       const result = await send(to, text, {
         mediaUrl,
+        mediaLocalRoots,
         threadTs: threadTsValue != null ? String(threadTsValue) : undefined,
         accountId: accountId ?? undefined,
         ...(tokenOverride ? { token: tokenOverride } : {}),