chore: initial scaffolding for SynthesisAgent.OpenclawPlugin

OpenClaw plugin that manages long-lived interactive Claude Code processes
per OpenClaw session. Process manager + session-mapping persistence +
bridge WebSocket server skeleton.

Will be rewritten to follow the contractor-agent HTTP model-provider pattern
(register as `synthesis-claude-bridge` provider, receive /v1/chat/completions,
dispatch to channel notification on the bound Claude process). See parent
repo's STATUS.md for the punch list.

openclaw.plugin.json

@@ -0,0 +1,52 @@
+{
+  "id": "synthesis-agent",
+  "name": "SynthesisAgent",
+  "description": "Manages long-lived interactive Claude Code processes per OpenClaw session; bridges OpenClaw events <-> SynthesisAgent.ClaudePlugin",
+  "activation": {
+    "onStartup": true
+  },
+  "commandAliases": [
+    { "name": "synthesis" }
+  ],
+  "configSchema": {
+    "type": "object",
+    "additionalProperties": false,
+    "properties": {
+      "bridgePort": {
+        "type": "number",
+        "default": 18801,
+        "description": "TCP port the bridge WebSocket server binds on (127.0.0.1)"
+      },
+      "bridgeToken": {
+        "type": "string",
+        "default": "synthesis-local",
+        "description": "Shared secret each ClaudePlugin instance must present in its hello frame"
+      },
+      "claudePluginRef": {
+        "type": "string",
+        "default": "plugin:synthesis-claude@local",
+        "description": "The --channels argument passed to claude on spawn"
+      },
+      "permissionMode": {
+        "type": "string",
+        "default": "acceptEdits",
+        "description": "Claude Code permission mode for spawned sessions"
+      },
+      "idleKillMs": {
+        "type": "number",
+        "default": 3600000,
+        "description": "Idle time after which a session's claude process is killed; next message resumes it"
+      },
+      "maxProcesses": {
+        "type": "number",
+        "default": 16,
+        "description": "Hard cap on concurrent claude processes; new sessions beyond this evict the oldest idle one"
+      },
+      "mappingDbPath": {
+        "type": "string",
+        "default": "~/.openclaw/synthesis/sessions.json",
+        "description": "Where openclaw_session <-> claude_session UUID mapping is persisted"
+      }
+    }
+  }
+}