Migrate test plugins to Rust and async-ify syscall modules

- Replace Python test plugins (echo, ai_test, claudecode) with Rust
  implementations driven by the plugin SDK
- Convert fs/network/process/timer syscall modules to async/await
- Change Network.OpenConn to return stream ConnEvent (conn_id handed
  to client in first "open" frame for Send/Close routing)
- Bind timer callbacks to plugin identity; stream_call subscriptions
  are identity-checked
- Update docs and regenerate Python SDK protobuf stubs

Verified: cargo build/test/clippy clean; echo + ai_test full syscall
suites pass; hermes & claudecode register and heartbeat; cross-plugin
bridge.call routing and auth denial verified end-to-end.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

plugins/echo/echo_plugin.py

@@ -1,67 +0,0 @@
-"""
-Echo plugin for agentsd - verifies the gRPC syscall chain works.
-Registers as a basic plugin, calls Display.Text and FS.Read.
-"""
-import grpc
-import sys
-import os
-
-# Add SDK path
-sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "_sdk"))
-
-from agentsd_pb2 import (
-    DisplayTextRequest, FsReadRequest, FsPathRequest,
-    MemoryWriteRequest, MemoryReadRequest,
-    PluginInfo, ExportDef, Empty
-)
-from agentsd_pb2_grpc import (
-    DisplayStub, FSStub, MemoryStub, PluginBridgeStub
-)
-
-
-PLUGIN_ID = "echo-test"
-METADATA = (("x-plugin-id", PLUGIN_ID),)
-
-
-def main():
-    channel = grpc.insecure_channel('localhost:50051')
-
-    # Register plugin
-    bridge = PluginBridgeStub(channel)
-    resp = bridge.Register(PluginInfo(
-        id=PLUGIN_ID,
-        name="Echo Test Plugin",
-        version="0.1.0",
-        plugin_type="basic",
-        syscalls=["display.text", "fs.list", "memory.read", "memory.write"],
-        depends=[],
-        exports=[ExportDef(name="echo", description="Echo test")]
-    ))
-    print(f"Register: ok={resp.ok} session={resp.session_id}")
-
-    # Test Display
-    display = DisplayStub(channel)
-    resp = display.Text(DisplayTextRequest(content="Hello from echo plugin!"), metadata=METADATA)
-    print(f"Display.Text: ok={resp.ok}")
-
-    # Test Memory write + read
-    memory = MemoryStub(channel)
-    resp = memory.Write(MemoryWriteRequest(key="test.greeting", value=b"Hello World"), metadata=METADATA)
-    print(f"Memory.Write: ok={resp.ok}")
-
-    resp = memory.Read(MemoryReadRequest(key="test.greeting"), metadata=METADATA)
-    print(f"Memory.Read: found={resp.found} value={resp.value.decode()}")
-
-    # Test FS list
-    fs = FSStub(channel)
-    resp = fs.List(FsPathRequest(path="."), metadata=METADATA)
-    print(f"FS.List: ok={resp.ok} entries={len(resp.entries)}")
-    for entry in resp.entries[:5]:
-        print(f"  {entry.name} {'[dir]' if entry.is_dir else ''}")
-
-    print("\nAll syscalls verified OK!")
-    channel.close()
-
-
-if __name__ == "__main__":
-    main()

plugins/echo/plugin.yaml

@@ -13,4 +13,4 @@ exports:
   - name: echo
     description: Echo test
 
-entry: python echo_plugin.py
+entry: cargo run -p agentsd-plugin-echo