diff --git a/src/cli/config-manager/add-plugin-to-opencode-config.ts b/src/cli/config-manager/add-plugin-to-opencode-config.ts
index 208abd56a..23c398873 100644
--- a/src/cli/config-manager/add-plugin-to-opencode-config.ts
+++ b/src/cli/config-manager/add-plugin-to-opencode-config.ts
@@ -79,12 +79,8 @@ export async function addPluginToOpenCodeConfig(currentVersion: string): Promise
 
     const normalizedPlugins = [...otherPlugins]
 
-    if (canonicalEntries.length > 0) {
-      normalizedPlugins.push(canonicalEntries[0])
-    } else if (legacyEntries.length > 0) {
-      const versionMatch = legacyEntries[0].match(/@(.+)$/)
-      const preservedVersion = versionMatch ? versionMatch[1] : null
-      normalizedPlugins.push(preservedVersion ? `${PLUGIN_NAME}@${preservedVersion}` : pluginEntry)
+    if (canonicalEntries.length > 0 || legacyEntries.length > 0) {
+      normalizedPlugins.push(pluginEntry)
     } else {
       normalizedPlugins.push(pluginEntry)
     }
diff --git a/src/cli/config-manager/plugin-detection.test.ts b/src/cli/config-manager/plugin-detection.test.ts
index e03e63357..fcd6109f9 100644
--- a/src/cli/config-manager/plugin-detection.test.ts
+++ b/src/cli/config-manager/plugin-detection.test.ts
@@ -1,4 +1,4 @@
-import { afterEach, beforeEach, describe, expect, it } from "bun:test"
+import { afterEach, beforeEach, describe, expect, it, spyOn } from "bun:test"
 import { mkdirSync, readFileSync, rmSync, writeFileSync } from "node:fs"
 import { tmpdir } from "node:os"
 import { join } from "node:path"
@@ -6,6 +6,7 @@ import { join } from "node:path"
 import { resetConfigContext } from "./config-context"
 import { detectCurrentConfig } from "./detect-current-config"
 import { addPluginToOpenCodeConfig } from "./add-plugin-to-opencode-config"
+import * as pluginNameWithVersion from "./plugin-name-with-version"
 
 describe("detectCurrentConfig - single package detection", () => {
   let testConfigDir = ""
@@ -109,17 +110,19 @@ describe("addPluginToOpenCodeConfig - single package writes", () => {
     expect(savedConfig.plugin).toEqual(["oh-my-openagent"])
   })
 
-  it("upgrades a version-pinned legacy entry to canonical", async () => {
+  it("updates a version-pinned legacy entry to the requested version", async () => {
     // given
-    writeFileSync(testConfigPath, JSON.stringify({ plugin: ["oh-my-opencode@3.10.0"] }, null, 2) + "\n", "utf-8")
+    const getPluginNameWithVersionSpy = spyOn(pluginNameWithVersion, "getPluginNameWithVersion").mockResolvedValue("oh-my-openagent@3.16.0")
+    writeFileSync(testConfigPath, JSON.stringify({ plugin: ["oh-my-opencode@3.15.0"] }, null, 2) + "\n", "utf-8")
 
     // when
-    const result = await addPluginToOpenCodeConfig("3.11.0")
+    const result = await addPluginToOpenCodeConfig("3.16.0")
 
     // then
     expect(result.success).toBe(true)
     const savedConfig = JSON.parse(readFileSync(testConfigPath, "utf-8"))
-    expect(savedConfig.plugin).toEqual(["oh-my-openagent@3.10.0"])
+    expect(savedConfig.plugin).toEqual(["oh-my-openagent@3.16.0"])
+    getPluginNameWithVersionSpy.mockRestore()
   })
 
   it("removes stale legacy entry when canonical and legacy entries both exist", async () => {
@@ -135,17 +138,36 @@ describe("addPluginToOpenCodeConfig - single package writes", () => {
     expect(savedConfig.plugin).toEqual(["oh-my-openagent"])
   })
 
-  it("preserves a canonical entry when it already exists", async () => {
+  it("preserves a canonical entry when the same version is re-installed", async () => {
     // given
+    const getPluginNameWithVersionSpy = spyOn(pluginNameWithVersion, "getPluginNameWithVersion").mockResolvedValue("oh-my-openagent@3.10.0")
     writeFileSync(testConfigPath, JSON.stringify({ plugin: ["oh-my-openagent@3.10.0"] }, null, 2) + "\n", "utf-8")
 
     // when
-    const result = await addPluginToOpenCodeConfig("3.11.0")
+    const result = await addPluginToOpenCodeConfig("3.10.0")
 
     // then
     expect(result.success).toBe(true)
     const savedConfig = JSON.parse(readFileSync(testConfigPath, "utf-8"))
     expect(savedConfig.plugin).toEqual(["oh-my-openagent@3.10.0"])
+    getPluginNameWithVersionSpy.mockRestore()
+  })
+
+  it("blocks a downgrade for a version-pinned canonical entry", async () => {
+    // given
+    const getPluginNameWithVersionSpy = spyOn(pluginNameWithVersion, "getPluginNameWithVersion").mockResolvedValue("oh-my-openagent@3.15.0")
+    writeFileSync(testConfigPath, JSON.stringify({ plugin: ["oh-my-openagent@3.16.0"] }, null, 2) + "\n", "utf-8")
+
+    // when
+    const result = await addPluginToOpenCodeConfig("3.15.0")
+
+    // then
+    expect(result.success).toBe(false)
+    expect(result.error).toContain("Downgrade")
+
+    const savedConfig = JSON.parse(readFileSync(testConfigPath, "utf-8"))
+    expect(savedConfig.plugin).toEqual(["oh-my-openagent@3.16.0"])
+    getPluginNameWithVersionSpy.mockRestore()
   })
 
   it("rewrites quoted jsonc plugin field in place", async () => {