fix(slack): propagate mediaLocalRoots through Slack send path

Restore Slack local file upload parity with CVE-era local media allowlist enforcement by threading `mediaLocalRoots` through the Slack send call chain.

- pass `ctx.mediaLocalRoots` from Slack channel action adapter into `handleSlackAction`
- add and forward `mediaLocalRoots` in Slack action context/send path
- pass `mediaLocalRoots` into `sendMessageSlack` for upload allowlist enforcement
- add changelog entry with attribution for this behavior fix

Co-authored-by: 2233admin <1497479966@qq.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/agents/tools/slack-actions.ts

@@ -50,6 +50,8 @@ export type SlackActionContext = {
   replyToMode?: "off" | "first" | "all";
   /** Mutable ref to track if a reply was sent (for "first" mode). */
   hasRepliedRef?: { value: boolean };
+  /** Allowed local media directories for file uploads. */
+  mediaLocalRoots?: readonly string[];
 };
 
 /**
@@ -209,6 +211,7 @@ export async function handleSlackAction(
         const result = await sendSlackMessage(to, content ?? "", {
           ...writeOpts,
           mediaUrl: mediaUrl ?? undefined,
+          mediaLocalRoots: context?.mediaLocalRoots,
           threadTs: threadTs ?? undefined,
           blocks,
         });