chore: initial scaffolding for SynthesisAgent

Bridge between OpenClaw (multi-channel hub) and interactive Claude Code,
keeping autonomous agent usage on the subscription quota after the
2026-06-15 Agent SDK credit split.

Initial scaffolding only — two submodules with skeletons:

- SynthesisAgent.ClaudePlugin: stdio MCP server registered as a --channels
  source. Declares experimental.claude/channel capability (verified 2026-05-14
  against the official Anthropic discord plugin) and emits
  notifications/claude/channel to push OpenClaw inbound messages into the
  Claude turn loop.

- SynthesisAgent.OpenclawPlugin: process manager + session mapping +
  bridge WebSocket. Currently shaped around a custom ws protocol; will be
  rewritten as a model-provider HTTP server (contractor-agent pattern) so
  OpenClaw routes inbound channel messages through it via /v1/chat/completions.

See STATUS.md for the open punch list and docs/wire-protocol.md for the
(soon-to-change) inter-plugin frame schema.

README.md

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+# SynthesisAgent
+
+Bridge between **OpenClaw** (multi-channel hub) and **Claude Code** (interactive Claude session), letting OpenClaw drive Claude Code as an autonomous worker **without using `claude -p` or the Agent SDK** — so all usage stays on the interactive subscription quota.
+
+## Motivation
+
+Starting 2026-06-15, Claude Agent SDK and `claude -p` usage on Max plans draws from a separate `$100` monthly credit pool. Interactive Claude Code usage continues to draw from the subscription. Today OpenClaw's contractor agents spawn a fresh `claude -p` per external event, which after the cutover will consume credit instead of subscription.
+
+SynthesisAgent moves contractor agents to a model where:
+
+- A **long-lived interactive `claude` process** serves each OpenClaw session.
+- External events (Discord, Telegram, Slack…) flow into that process via the official `notifications/claude/channel` MCP notification protocol, the same one Anthropic's own `discord@claude-plugins-official` plugin uses.
+- The process exposes OpenClaw's tool surface (pcexec, sessions_*, memory_*, wiki_*, canvas, …) back to the model.
+
+## Architecture
+
+```
+        Discord / Telegram / Slack / ...
+                    │
+                    ▼
+            OpenClaw Gateway (existing)
+                    │
+                    ▼
+        ┌──────────────────────────────────────┐
+        │  SynthesisAgent.OpenclawPlugin       │
+        │  - Process Manager (spawn / resume)  │
+        │  - Session Mapping DB                │
+        │  - Bridge WebSocket Server           │
+        └──────────────────────────────────────┘
+              │              ▲
+              │ spawn        │ WebSocket
+              ▼              │
+        ┌──────────────────────────────────────┐
+        │  claude --channels plugin:synthesis  │  (one per OpenClaw session)
+        │  ├─ Claude Code (interactive)        │
+        │  └─ SynthesisAgent.ClaudePlugin      │
+        │       (MCP stdio server)             │
+        │       - notifications/claude/channel │
+        │       - tool proxy → OpenClaw        │
+        │       - permission bridge            │
+        └──────────────────────────────────────┘
+```
+
+## Submodules
+
+| Module                              | Lives in              | Role |
+|-------------------------------------|-----------------------|------|
+| [`SynthesisAgent.OpenclawPlugin`](./SynthesisAgent.OpenclawPlugin/) | OpenClaw process       | Spawns/manages Claude processes per session; bridges Claude `↔` OpenClaw event bus |
+| [`SynthesisAgent.ClaudePlugin`](./SynthesisAgent.ClaudePlugin/) | Each Claude process    | MCP stdio server registered as a `--channels` plugin; receives events from OpenclawPlugin bridge, proxies tool calls back |
+
+## Wire protocol
+
+See [`docs/wire-protocol.md`](./docs/wire-protocol.md) for the message schema between the two plugins.
+
+## Status
+
+Scaffolding only. Nothing wired up. See each submodule's TODO list.
+
+## License
+
+Apache-2.0 (matches the upstream Anthropic Discord channel plugin this work is modeled after).