feat(agent): unify MCP tools and adopt Responses delivery

Move project and host queries into native MCP with host-owned OAuth/context,
while retaining memory, skills, actions and publication plugins. Add nearby-model
queries and explicit chat/task/learning model defaults.

Adopt Responses HTTP/SSE and native steer/queue inbox delivery, preserving scoped
session ownership, pending input edits and investigation communication.

Disable local-provider discovery: Server /health allowed native vLLM to probe
/v1/models on port 8000. A native before/after regression prevents recurrence.

Validation: 170 focused Bun tests; service/plugin typechecks; native discovery,
provider-discovery and input-inbox smoke checks; no paid model inference.

.opencode/agent-messages.ts

@@ -0,0 +1,30 @@
+import { z } from "zod";
+import { getInternalBridgeConfig } from "./internalBridge.js";
+import { tool, type ToolContext } from "./tool.js";
+
+type Operation = "send" | "reply";
+
+// This helper is not a model-facing tool. Each registered tool fixes its operation
+// and input contract; the bridge resolves identity, project, run and thread scope.
+export function agentMessageTool<Args extends z.ZodRawShape>(operation: Operation, definition: {
+  description: string;
+  args: Args;
+}) {
+  const inputSchema = z.object(definition.args).strict();
+  return tool({
+    ...definition,
+    async execute(args, context: ToolContext) {
+      const input = inputSchema.parse(args);
+      const { baseUrl, internalToken } = getInternalBridgeConfig();
+      const response = await fetch(`${baseUrl}/internal/agent-messages/${operation}`, {
+        method: "POST",
+        headers: { "Content-Type": "application/json", "x-agent-internal-token": internalToken },
+        signal: context.signal,
+        body: JSON.stringify({ session_id: context.sessionID, input }),
+      });
+      const text = await response.text();
+      if (!response.ok) throw new Error(`agent message ${operation} failed (${response.status}): ${text}`);
+      return text;
+    },
+  });
+}