fix(opencode): tests drop XDG_DATA_HOME, status reads the adapter's db, the version probe runs in a home of its own (Issue #60, review 2)

- Review 8a485fa0 B1 / c9d06e85 / c4e96018 (blocking): the adapter now
  follows the caller's XDG_DATA_HOME for its own home, but the tests did not
  drop it: a sandbox that sets HOME resolved the runner's real data dir.
  XDG_DATA_HOME joins _agent_home_guard.DROPPED_VARS (dropped per test), and
  the session guard watches <XDG_DATA_HOME>/opencode when it is set.
  Checked with XDG_DATA_HOME set to a separate dir: the opencode modules
  pass and nothing is written there.
- status.sh asks the adapter for the db (`debug paths`, XDG-aware) instead
  of a fixed ~/.local/share/opencode (8a485fa0 N1).
- The opt-in test's `opencode --version` probe ran with the real HOME at
  import and appended to the real opencode log; it runs in a temporary home
  now (8a485fa0 N2).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

tests/_agent_home_guard.py

@@ -18,7 +18,7 @@ import tempfile
 
 # The pane-inherited variables conftest._isolate_agent_homes drops for every
 # test, so HOME (which the tests set) governs, as it does in a plain shell.
-DROPPED_VARS = ("HOME_DIR", "CLAUDE_PROJECT_DIR", "CLAUDE_CONFIG_DIR", "CODEX_HOME", "LOCAL_BIN")
+DROPPED_VARS = ("HOME_DIR", "CLAUDE_PROJECT_DIR", "CLAUDE_CONFIG_DIR", "CODEX_HOME", "XDG_DATA_HOME", "LOCAL_BIN")
 # Read by the code under test but left alone, on purpose: HOME is where the
 # real herdr tests and the shim bootstrap find the server socket, and it is
 # what the suite's own tests set for an isolated home; XDG_CONFIG_HOME and
@@ -45,7 +45,8 @@ def watch_dirs(ambient):
              for d in ("conversations", "cache", "brain", "annotations", "presence")]
     dirs += [("codex", os.path.join(codex, "sessions")),
              ("grok", os.path.join(home, ".grok", "sessions")),
-             ("opencode", os.path.join(home, ".local", "share", "opencode")),
+             ("opencode", os.path.join(ambient.get("XDG_DATA_HOME") or os.path.join(home, ".local", "share"),
+                                       "opencode")),
              ("hermes", os.path.join(home, ".hermes"))]
     return dirs