refactor(core): select system prompts through plugins (#37181)

packages/core/test/plugin/promise.test.ts

@@ -2,6 +2,8 @@ import { describe, expect } from "bun:test"
 import { Message, SystemPart } from "@opencode-ai/ai"
 import { Effect, Schema } from "effect"
 import { AgentV2 } from "@opencode-ai/core/agent"
+import { Catalog } from "@opencode-ai/core/catalog"
+import { ModelV2 } from "@opencode-ai/core/model"
 import { PluginV2 } from "@opencode-ai/core/plugin"
 import { PluginHooks } from "@opencode-ai/core/plugin/hooks"
 import { PluginHost } from "@opencode-ai/core/plugin/host"
@@ -9,6 +11,7 @@ import { PluginPromise } from "@opencode-ai/core/plugin/promise"
 import { SessionV2 } from "@opencode-ai/core/session"
 import { SessionMessage } from "@opencode-ai/core/session/message"
 import { ToolRegistry } from "@opencode-ai/core/tool/registry"
+import { ProviderV2 } from "@opencode-ai/core/provider"
 import { Plugin } from "@opencode-ai/plugin/v2"
 import type { SessionHooks } from "@opencode-ai/plugin/v2/effect/session"
 import { Model } from "@opencode-ai/schema/model"
@@ -48,6 +51,37 @@ describe("fromPromise", () => {
     }),
   )
 
+  it.effect("forwards direct agent and model reads", () =>
+    Effect.gen(function* () {
+      const agents = yield* AgentV2.Service
+      const catalog = yield* Catalog.Service
+      const plugin = yield* PluginV2.Service
+      const host = yield* PluginHost.make(plugin)
+      yield* agents.transform((draft) =>
+        draft.update(AgentV2.ID.make("reviewer"), (agent) => {
+          agent.description = "Reviews code"
+        }),
+      )
+      yield* catalog.transform((draft) =>
+        draft.model.update(ProviderV2.ID.make("test"), ModelV2.ID.make("alias"), (model) => {
+          model.modelID = ModelV2.ID.make("gpt-5")
+        }),
+      )
+
+      yield* PluginPromise.fromPromise(
+        Plugin.define({
+          id: "promise-direct-reads",
+          setup: async (ctx) => {
+            expect(await ctx.agent.get("reviewer")).toMatchObject({ description: "Reviews code" })
+            expect(await ctx.agent.get("missing")).toBeUndefined()
+            expect(await ctx.catalog.model.get("test", "alias")).toMatchObject({ modelID: "gpt-5" })
+            expect(await ctx.catalog.model.get("test", "missing")).toBeUndefined()
+          },
+        }),
+      ).effect(host)
+    }),
+  )
+
   it.effect("loads a promise plugin and registers a transform hook", () =>
     Effect.gen(function* () {
       const agents = yield* AgentV2.Service