fix(opencode): use cross-platform data directory (#10362)

* fix(opencode): use cross-platform data directory

* fix(opencode): honor in-memory database override

* fix(opencode): harden database discovery coverage

* test(opencode): reproduce Windows session discovery

---------

Co-authored-by: OrcaWin <alpha-eng@stably.ai>
Co-authored-by: OrcaWin <293788423+OrcaWin@users.noreply.github.com>

src/main/opencode/opencode-data-directory.ts

@@ -0,0 +1,17 @@
+import { homedir } from 'node:os'
+import { join } from 'node:path'
+
+export function resolveOpenCodeDataDirectory(
+  environment: NodeJS.ProcessEnv = process.env,
+  homeDirectory = homedir()
+): string {
+  const xdgDataHome = environment.XDG_DATA_HOME?.trim()
+  return join(xdgDataHome || join(homeDirectory, '.local', 'share'), 'opencode')
+}
+
+export function resolveOpenCodeStorageDirectory(
+  environment: NodeJS.ProcessEnv = process.env,
+  homeDirectory = homedir()
+): string {
+  return join(resolveOpenCodeDataDirectory(environment, homeDirectory), 'storage')
+}