fix(#1264): harden unattended identity bootstrap

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

@@ -27,9 +27,11 @@ 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 missing destination has no safe regular default source;
-- a source or existing destination is a symlink, directory, unavailable, or over the bounded size;
-- the fleet communications helper/roster cannot be validated.
+- 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
+- `USER.md` cannot be securely re-read at the point where its content is composed.
 
 Diagnostics begin with:
 
@@ -45,14 +47,17 @@ not delete or replace an existing personalized `SOUL.md`/`USER.md` merely to cle
 The source gate is:
 
 ```bash
-pnpm --filter @mosaicstack/mosaic exec vitest run \
-  src/commands/launch-first-start.spec.ts
+pnpm --filter @mosaicstack/mosaic... build && \
+  pnpm --filter @mosaicstack/mosaic exec vitest run \
+    src/commands/launch-first-start.spec.ts
 ```
 
-It runs the real 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, standalone wizard preservation,
-and concurrent first start.
+The build leg is load-bearing: `dist/` is ignored, so a direct Vitest invocation could otherwise run
+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.
 
 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.