docs: add WhisperGate architecture and implementation plan

README.md

@@ -2,6 +2,30 @@
 
 Rule-based no-reply gate for OpenClaw.
 
-## Status
+## What it does
 
-Initial scaffold.
+WhisperGate adds a deterministic gate **before model selection**:
+
+1. If message is not from Discord → skip gate
+2. If sender is in bypass user list → skip gate
+3. If message ends with configured end-symbol → skip gate
+4. Otherwise switch this turn to a no-reply model/provider
+
+The no-reply provider returns `NO_REPLY` for any input.
+
+---
+
+## Repo layout
+
+- `plugin/` — OpenClaw plugin (before_model_resolve hook)
+- `no-reply-api/` — OpenAI-compatible minimal API that always returns `NO_REPLY`
+- `docs/` — rollout and configuration notes
+
+---
+
+## Development plan (incremental commits)
+
+- [x] Task 1: project docs + structure
+- [ ] Task 2: no-reply API MVP
+- [ ] Task 3: plugin MVP with rule chain
+- [ ] Task 4: sample config + quick verification scripts