fix(#1264): preserve portable standalone launch

docs/ADMIN-GUIDE/operations/fleet-unattended-first-start.md

@@ -27,7 +27,8 @@ The fleet path never falls back to an interactive wizard. It exits nonzero befor
 when:
 
 - `MOSAIC_AGENT_NAME` is not an exact roster member;
-- an ambient `MOSAIC_AGENT_CLASS` disagrees with that member's canonical class;
+- a defined ambient `MOSAIC_AGENT_CLASS` is blank/whitespace or disagrees with that member's
+  canonical class;
 - a missing destination has no safe regular default source;
 - a source or existing destination is a symlink (including dangling), directory, unavailable, or over the bounded size;
 - the fleet communications helper/roster cannot be validated; or
@@ -56,8 +57,8 @@ The build leg is load-bearing: `dist/` is ignored, so a direct Vitest invocation
 absent or stale CLI output. The gate runs the exact-source built CLI in subprocesses with piped stdin,
 temporary homes, a canonical fixture roster, fake runtime/broker executables, and no provider call. It
 covers no-TTY launch, exact identity,
-private modes, no-clobber, missing/symlink defaults, unknown members, class mismatch,
-standalone wizard preservation, and concurrent first start.
+private modes, no-clobber, missing/symlink defaults, unknown members, blank/mismatched class,
+portable standalone composition/wizard preservation, and concurrent first start.
 
 Do not use this fixture as proof that a real provider credential is present or that a package has
 been deployed. Those require separate environment-specific evidence.