feat(deploy): per-agent base_url and workspace_path routing

- AgentDefinition gains base_url and workspace_path fields (optional)
- load_agent_registry parses them from matrix-agents.yaml
- _build_platform_from_env uses agent.base_url per agent (falls back to AGENT_BASE_URL)
- _agent_workspace_root() resolves workspace per agent from registry
- _materialize_incoming_attachments saves files to agent workspace_path/incoming/
- send_outgoing accepts workspace_root param; reads outgoing files from agent workspace_path
- dispatch loop computes workspace_root from room agent_id and passes to _send_all
- config/matrix-agents.yaml and example updated with base_url and workspace_path

adapter/matrix/agent_registry.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 from collections.abc import Mapping
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from pathlib import Path
 
 import yaml
@@ -15,6 +15,8 @@ class AgentRegistryError(ValueError):
 class AgentDefinition:
     agent_id: str
     label: str
+    base_url: str = field(default="")
+    workspace_path: str = field(default="")
 
 
 class AgentRegistry:
@@ -47,6 +49,15 @@ def _required_text(entry: Mapping[str, object], key: str) -> str:
     return text
 
 
+def _optional_text(entry: Mapping[str, object], key: str) -> str:
+    value = entry.get(key)
+    if value is None:
+        return ""
+    if not isinstance(value, str):
+        raise AgentRegistryError(f"agent entry field '{key}' must be a string")
+    return value.strip()
+
+
 def _load_registry_data(path: str | Path) -> dict[str, object]:
     try:
         raw = yaml.safe_load(Path(path).read_text(encoding="utf-8"))
@@ -72,10 +83,19 @@ def load_agent_registry(path: str | Path) -> AgentRegistry:
             raise AgentRegistryError("each agent entry requires id and label")
         agent_id = _required_text(entry, "id")
         label = _required_text(entry, "label")
+        base_url = _optional_text(entry, "base_url")
+        workspace_path = _optional_text(entry, "workspace_path")
         if agent_id in seen:
             raise AgentRegistryError(f"duplicate agent id: {agent_id}")
         seen.add(agent_id)
-        agents.append(AgentDefinition(agent_id=agent_id, label=label))
+        agents.append(
+            AgentDefinition(
+                agent_id=agent_id,
+                label=label,
+                base_url=base_url,
+                workspace_path=workspace_path,
+            )
+        )
 
     user_agents = raw.get("user_agents")
     if user_agents is not None: