test: adapt main's diagnostics tests to the merged designs

cli-lock asserts typed ServerLockError (errno + lock path) instead of
the log-and-return shape the merge didn't keep, dropping only the one
duplicate of server-lock-errors coverage; the liveness tripwire exempts
error-handling.ts as the sanctioned tasklist site; snapshot and
compare-board wrappers pass the now-mandatory browser-manager arg;
background.js's test pins that the retired sidebar-command type is
rejected pre-gate with no response fields.

browse/test/gstack-config.test.ts

@@ -15,12 +15,20 @@ const SCRIPT = join(import.meta.dir, '..', '..', 'bin', 'gstack-config');
 let stateDir: string;
 
 function run(args: string[] = [], extraEnv: Record<string, string> = {}) {
+  // The script resolves its state dir as GSTACK_STATE_ROOT > GSTACK_HOME >
+  // GSTACK_STATE_DIR > $HOME/.gstack. Strip the higher-precedence vars so a
+  // stray value in the harness env (another test file's leftovers, operator
+  // shell) can never outrank the per-test GSTACK_STATE_DIR isolation.
+  const env: Record<string, string | undefined> = {
+    ...process.env,
+    GSTACK_STATE_DIR: stateDir,
+  };
+  delete env.GSTACK_STATE_ROOT;
+  delete env.GSTACK_HOME;
+  Object.assign(env, extraEnv); // per-test overrides always win, deliberately
+
   const result = Bun.spawnSync(['bash', SCRIPT, ...args], {
-    env: {
-      ...process.env,
-      GSTACK_STATE_DIR: stateDir,
-      ...extraEnv,
-    },
+    env,
     stdout: 'pipe',
     stderr: 'pipe',
   });