fix: use bundled OpenCode path in isolation tests

Linux release CI could not start OpenCode because the isolation test assumed a platform-specific npm executable name. Reuse the production runtime path resolver, which matches the installed bin/opencode.exe on all platforms.

Validation: nine focused tests, typecheck, lint, and bilingual release-note verification passed. Product behavior, versions, and release notes remain unchanged; main-branch CI must pass before tagging.

docs/development/release-preparation-0.13.12.md

@@ -107,3 +107,31 @@ Follow-up validation: the seven selected IPC/UI regression cases and all seven
 OpenCode isolation cases passed locally. Type checks and lint passed. Full
 remote CI and the production build still require a new approved commit; these
 focused results do not satisfy that release gate.
+
+## Linux Executable Path Follow-up
+
+On 2026-09-23, local `main` was fast-forwarded from `163e245` to
+`073aa45a30efe99fab7a92f8aee2a36087db9c2a` after inspecting the four intervening
+commits. They update only the community QR codes in the two README files.
+The user authorized retaining these changes, fixing CI, pushing both remotes,
+and publishing Desktop `v0.13.12` and Agent `agent-v0.13.3` after successful
+candidate CI without another approval round. No LoongArch preview is requested.
+
+[Desktop CI 35854792610](https://github.com/mesalogo/goodbuddy/actions/runs/35854792610)
+reported 5,004 passing tests, three failures, and 43 skipped tests. All three
+failures were in the real OpenCode isolation test. It constructed
+`opencode-ai/bin/opencode` on Linux, but OpenCode 1.18.29 installs its npm
+executable as `bin/opencode.exe` on every platform. The test now reuses
+`resolveBundledRuntimePaths`, the existing production resolver, instead of
+constructing a platform-specific filename. Production Runtime code and both
+release-note files are unchanged.
+
+Local follow-up validation passed all nine tests in
+`opencode-selection-isolation.test.ts` and `bundled-runtimes.test.ts`, including
+the existing Linux development-path assertion, plus full type checks and lint.
+Release-note and package/lockfile version validation passed. The isolation
+tests made two requests to their local mock endpoint and zero real model
+requests. No full local suite, production build, package, or real-Host check
+was run for this test-only fix; it changes neither deployed Agent code nor
+the Desktop-to-Agent production path. Successful Linux main-branch CI and
+its production build remain required before tagging.

src/main/agent/opencode-selection-isolation.test.ts

@@ -10,6 +10,7 @@ import { runtimeSettingsInputSchema } from '../../shared/contracts'
 import { RuntimeSettingsStore } from '../runtime-settings-store'
 import { applyRuntimeSelection } from './runtime-selection'
 import { OpenCodeRuntime } from './opencode-runtime'
+import { resolveBundledRuntimePaths } from './bundled-runtimes'
 
 const cipher = {
   isAvailable: () => false,
@@ -103,8 +104,9 @@ describe('OpenCode isolated configuration paths', () => {
       }))
       let launchEnvironment: NodeJS.ProcessEnv = {}
       let serverUrl = ''
-      const binaryPath = join(process.cwd(), 'node_modules', 'opencode-ai', 'bin',
+      const binaryPath = resolveBundledRuntimePaths({
-        process.platform === 'win32' ? 'opencode.exe' : 'opencode')
+        appPath: process.cwd(), resourcesPath: process.cwd(), packaged: false
+      }).opencode
       const runtime = new OpenCodeRuntime({
         embedded: true, binaryPath, defaultWorkspace: root,
         configPath: source === 'native-empty' ? '' : configPath,