fix(#2823): auto-migrate legacy plugin name and warn users at startup

- logLegacyPluginStartupWarning now emits console.warn (visible to user,
  not just log file) when oh-my-opencode is detected in opencode.json
- Auto-migrates opencode.json plugin entry from oh-my-opencode to
  oh-my-openagent (with backup)
- plugin-config.ts: add console.warn when loading legacy config filename
- test: 10 tests covering migration, console output, edge cases

src/hooks/legacy-plugin-toast/auto-migrate.test.ts

@@ -0,0 +1,127 @@
+import { afterEach, beforeEach, describe, expect, it } from "bun:test"
+import { mkdirSync, readFileSync, rmSync, writeFileSync } from "node:fs"
+import { tmpdir } from "node:os"
+import { join } from "node:path"
+import { autoMigrateLegacyPluginEntry } from "./auto-migrate"
+
+describe("autoMigrateLegacyPluginEntry", () => {
+  let testConfigDir = ""
+
+  beforeEach(() => {
+    testConfigDir = join(tmpdir(), `omo-legacy-migrate-${Date.now()}-${Math.random().toString(36).slice(2)}`)
+    mkdirSync(testConfigDir, { recursive: true })
+    process.env.OPENCODE_CONFIG_DIR = testConfigDir
+  })
+
+  afterEach(() => {
+    rmSync(testConfigDir, { recursive: true, force: true })
+    delete process.env.OPENCODE_CONFIG_DIR
+  })
+
+  describe("#given opencode.json has a bare legacy plugin entry", () => {
+    it("#then replaces oh-my-opencode with oh-my-openagent", () => {
+      // given
+      writeFileSync(
+        join(testConfigDir, "opencode.json"),
+        JSON.stringify({ plugin: ["oh-my-opencode"] }, null, 2) + "\n",
+      )
+
+      // when
+      const result = autoMigrateLegacyPluginEntry()
+
+      // then
+      expect(result.migrated).toBe(true)
+      expect(result.from).toBe("oh-my-opencode")
+      expect(result.to).toBe("oh-my-openagent")
+      const saved = JSON.parse(readFileSync(join(testConfigDir, "opencode.json"), "utf-8"))
+      expect(saved.plugin).toEqual(["oh-my-openagent"])
+    })
+  })
+
+  describe("#given opencode.json has a version-pinned legacy entry", () => {
+    it("#then preserves the version suffix", () => {
+      // given
+      writeFileSync(
+        join(testConfigDir, "opencode.json"),
+        JSON.stringify({ plugin: ["oh-my-opencode@3.10.0"] }, null, 2) + "\n",
+      )
+
+      // when
+      const result = autoMigrateLegacyPluginEntry()
+
+      // then
+      expect(result.migrated).toBe(true)
+      expect(result.from).toBe("oh-my-opencode@3.10.0")
+      expect(result.to).toBe("oh-my-openagent@3.10.0")
+      const saved = JSON.parse(readFileSync(join(testConfigDir, "opencode.json"), "utf-8"))
+      expect(saved.plugin).toEqual(["oh-my-openagent@3.10.0"])
+    })
+  })
+
+  describe("#given both canonical and legacy entries exist", () => {
+    it("#then removes legacy entry and keeps canonical", () => {
+      // given
+      writeFileSync(
+        join(testConfigDir, "opencode.json"),
+        JSON.stringify({ plugin: ["oh-my-openagent", "oh-my-opencode"] }, null, 2) + "\n",
+      )
+
+      // when
+      const result = autoMigrateLegacyPluginEntry()
+
+      // then
+      expect(result.migrated).toBe(true)
+      const saved = JSON.parse(readFileSync(join(testConfigDir, "opencode.json"), "utf-8"))
+      expect(saved.plugin).toEqual(["oh-my-openagent"])
+    })
+  })
+
+  describe("#given no config file exists", () => {
+    it("#then returns migrated false", () => {
+      // given - empty dir
+
+      // when
+      const result = autoMigrateLegacyPluginEntry()
+
+      // then
+      expect(result.migrated).toBe(false)
+      expect(result.from).toBeNull()
+    })
+  })
+
+  describe("#given opencode.jsonc has comments and a legacy entry", () => {
+    it("#then preserves comments and replaces entry", () => {
+      // given
+      writeFileSync(
+        join(testConfigDir, "opencode.jsonc"),
+        '{\n  // my config\n  "plugin": ["oh-my-opencode"]\n}\n',
+      )
+
+      // when
+      const result = autoMigrateLegacyPluginEntry()
+
+      // then
+      expect(result.migrated).toBe(true)
+      const content = readFileSync(join(testConfigDir, "opencode.jsonc"), "utf-8")
+      expect(content).toContain("// my config")
+      expect(content).toContain("oh-my-openagent")
+      expect(content).not.toContain("oh-my-opencode")
+    })
+  })
+
+  describe("#given only canonical entry exists", () => {
+    it("#then returns migrated false and leaves file untouched", () => {
+      // given
+      const original = JSON.stringify({ plugin: ["oh-my-openagent"] }, null, 2) + "\n"
+      writeFileSync(join(testConfigDir, "opencode.json"), original)
+
+      // when
+      const result = autoMigrateLegacyPluginEntry()
+
+      // then
+      expect(result.migrated).toBe(false)
+      const content = readFileSync(join(testConfigDir, "opencode.json"), "utf-8")
+      expect(content).toBe(original)
+    })
+  })
+})