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/test-fixtures/mcp-call-plugin.ts

@@ -0,0 +1,32 @@
+import { Plugin, Rpc } from "@opencode/plugin";
+import { z } from "zod";
+
+// Loaded only by the opt-in isolated smoke script, never by the Agent service.
+export default Plugin.define({
+  id: "tjwater.mcp-fixture",
+  async setup(ctx) {
+    await ctx.websearch.transform((editor) => {
+      editor.add({ id: "fixture-search", name: "Isolated search fixture", execute: async ({ query }) => [
+        { url: "https://example.test/search-result", title: "Fixture result", content: query, time: {} },
+      ] });
+    });
+    // Materialize the native session toolbox, then stop before any model call.
+    await ctx.session.hook("context", () => { throw new Error("MCP fixture stops before model request"); });
+    const evaluated: string[] = [];
+    await ctx.permission.hook("evaluate", (event) => { evaluated.push(event.action); });
+    await ctx.rpc.register(Rpc.define({
+      id: "tjwater.mcp-fixture", events: {}, methods: {
+        call: { input: z.object({ session_id: z.string(), tool: z.enum(["mcp_stdio_echo", "mcp_http_write", "mcp_tjwater_session_search", "mcp_tjwater_todoread", "mcp_tjwater_run_simulation", "websearch"]), value: z.string().optional(), arguments: z.record(z.string(), z.unknown()).optional() }), output: z.object({ content: z.unknown(), evaluated: z.array(z.string()), error: z.string().optional() }) },
+      },
+    }), {
+      call: async (input, context) => {
+        const tool = (await ctx.tool.list()).find((tool) => tool.id === input.tool);
+        if (!tool) throw new Error("fixture tool missing");
+        try {
+          const result = await tool.execute(input.arguments ?? { value: input.value }, { sessionID: input.session_id as never, id: "call-mcp-fixture" as never, messageID: "msg-mcp-fixture" as never, agent: "instruction" as never, signal: context.signal, progress: async () => {} });
+          return { content: result.content ?? [], evaluated };
+        } catch (error) { return { content: [], evaluated, error: String(error) }; }
+      },
+    });
+  },
+});

.opencode/test-fixtures/task-agent-probe-plugin/index.ts

@@ -0,0 +1,15 @@
+// Loaded only by the opt-in isolated task-agent smoke test, never by the service.
+import { Plugin, Rpc } from "@opencode/plugin";
+import * as Schema from "effect/Schema";
+import { z } from "zod";
+
+export default Plugin.define({ id: "test.task-agent-probe", async setup(ctx) {
+  await ctx.rpc.register(Rpc.define({ id: "test.task-agent-probe", methods: {
+    subagent_input: { input: z.object({}), output: z.array(z.string()) },
+  }, events: {} }), { subagent_input: async () => {
+    const tool = (await ctx.tool.list()).find((item) => item.id === "subagent");
+    if (!tool) throw new Error("native subagent tool missing");
+    const input = Schema.isSchema(tool.input) ? Schema.toJsonSchemaDocument(tool.input).schema : tool.input;
+    return Object.keys((input as { properties?: Record<string, unknown> }).properties ?? {});
+  } });
+} });

.opencode/test-fixtures/task-agent-probe-plugin/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "tjwater-task-agent-probe-plugin",
+  "version": "1.0.0",
+  "private": true,
+  "type": "module",
+  "exports": "./index.ts"
+}