Describe the bug

When an agent response contains both text and a MEDIA: URL, and block streaming is disabled (the default — blockStreamingDefault is "off" unless explicitly set), the text is silently discarded. Only the image is delivered to the channel; the accompanying text is never sent.

To Reproduce

1. Leave blockStreamingDefault at its default ("off")
2. Have an agent produce a response like:

   here's something interesting
   
   MEDIA:https://example.com/photo.jpg

3. The channel receives only the image. The text is never delivered — not as a caption, not as a preceding message, not at all.

Expected behavior

Text accompanying a MEDIA: URL should be delivered — either as the image caption or as a preceding/following message, depending on what the channel supports.

Root cause

In agent-runner (createBlockReplyDeliveryHandler), when blockStreamingEnabled is false and the payload contains media, text is explicitly stripped before calling onBlockReply:

} else if (blockHasMedia) {
    params.directlySentBlockKeys.add(createBlockReplyContentKey(blockPayload)); // key includes text
    await params.onBlockReply({
        ...blockPayload,
        text: void 0   // ← text dropped here
    });
}

The content key is computed from blockPayload (which includes the text), so the final delivery pass correctly identifies this payload as already sent and skips it. The text is lost at both stages.

Proposed fix

Remove the text: void 0 override — pass blockPayload directly:

} else if (blockHasMedia) {
    params.directlySentBlockKeys.add(createBlockReplyContentKey(blockPayload));
    await params.onBlockReply(blockPayload);
}

The content key logic is unchanged, so deduplication still works correctly. Channels that support captions receive the text as the image caption. Channels that don't support inline captions (e.g., QQBot) already handle this gracefully via sendTextAfterMedia, which sends text as a follow-up if text?.trim() is non-empty.

Additional context

This is compounded by the fact that disableBlockStreaming: true is hardcoded in at least one gateway handler, meaning blockStreamingDefault: "on" in agent config cannot override it. Even users who discover and set blockStreamingDefault: "on" as a workaround will find it has no effect.