fix(auto-reply): allow image-only messages to reach the agent (openclaw#12352) thanks @arosstale

Verified:
- pnpm build
- pnpm check
- pnpm test

Co-authored-by: arosstale <117890364+arosstale@users.noreply.github.com>
Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

CHANGELOG.md

@@ -40,6 +40,7 @@ Docs: https://docs.openclaw.ai
 - Security/Link understanding: block loopback/internal host patterns and private/mapped IPv6 addresses in extracted URL handling to close SSRF bypasses in link CLI flows. (#15604) Thanks @AI-Reviewer-QS.
 - Android/Nodes: harden `app.update` by requiring HTTPS and gateway-host URL matching plus SHA-256 verification, stream URL camera downloads to disk with size guards to avoid memory spikes, and stop signing release builds with debug keys. (#13541) Thanks @smartprogrammer93.
 - Auto-reply/Threading: auto-inject implicit reply threading so `replyToMode` works without requiring model-emitted `[[reply_to_current]]`, while preserving `replyToMode: "off"` behavior for implicit Slack replies and keeping block-streaming chunk coalescing stable under `replyToMode: "first"`. (#14976) Thanks @Diaspar4u.
+- Auto-reply/Media: allow image-only inbound messages (no caption) to reach the agent instead of short-circuiting as empty text, and preserve thread context in queued/followup prompt bodies for media-only runs. (#11916) Thanks @arosstale.
 - Sandbox: pass configured `sandbox.docker.env` variables to sandbox containers at `docker create` time. (#15138) Thanks @stevebot-alive.
 - Gateway/Restart: clear stale command-queue and heartbeat wake runtime state after SIGUSR1 in-process restarts to prevent zombie gateway behavior where queued work stops draining. (#15195) Thanks @joeykrug.
 - Onboarding/CLI: restore terminal state without resuming paused `stdin`, so onboarding exits cleanly after choosing Web UI and the installer returns instead of appearing stuck.