refactor(core): move database schema ownership (#29068)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

packages/opencode/test/session/structured-output-integration.test.ts

@@ -1,4 +1,5 @@
 import { describe, expect, test } from "bun:test"
+import { SessionLegacy } from "@opencode-ai/core/session/legacy"
 import { Effect, Layer } from "effect"
 import { Session } from "@/session/session"
 import { SessionPrompt } from "../../src/session/prompt"
@@ -218,7 +219,7 @@ describe("StructuredOutput Integration", () => {
   )
 
   test("unit test: StructuredOutputError is properly structured", () => {
-    const error = new MessageV2.StructuredOutputError({
+    const error = new SessionLegacy.StructuredOutputError({
       message: "Failed to produce valid structured output after 3 attempts",
       retries: 3,
     })