feat: add shared call-time isConductor() helper

Single source of truth for Conductor host detection in TS consumers
(CONDUCTOR_WORKSPACE_PATH / CONDUCTOR_PORT). Reads the passed env at
call time, not a module-load snapshot, so unit tests can pin the env
inline without Bun --preload (esm-hoist-breaks-env-pin-bootstrap).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/is-conductor.ts

@@ -0,0 +1,19 @@
+/**
+ * Conductor host detection — single source of truth for TS consumers.
+ *
+ * Conductor (the Mac app that runs many coding agents in parallel) sets
+ * CONDUCTOR_WORKSPACE_PATH / CONDUCTOR_PORT in the session env. The same two
+ * vars are what `bin/gstack-session-kind` keys on (it collapses Conductor into
+ * `interactive`, so it can't be reused to distinguish Conductor specifically —
+ * hence this dedicated helper).
+ *
+ * IMPORTANT: detection is a CALL-TIME read of the passed-in env (default
+ * `process.env`), never a module-load-time snapshot. ESM hoists static imports
+ * above any in-file `process.env.X = ...`, so a load-time read can't be pinned
+ * by a test without Bun --preload. Reading at call time lets unit tests set
+ * `process.env.CONDUCTOR_WORKSPACE_PATH` inline before invoking. See the
+ * `esm-hoist-breaks-env-pin-bootstrap` learning.
+ */
+export function isConductor(env: NodeJS.ProcessEnv = process.env): boolean {
+  return !!(env.CONDUCTOR_WORKSPACE_PATH || env.CONDUCTOR_PORT);
+}