v0.91.0 — the DR tier can no longer be applied and dead at the same time (R-39 + R-50b(a))

Closes the agent half of R-39's fleet fix. Requires hub >=0.68.0 for the re-arm signal;
that hub is safe for 0.90.0 agents (unknown key dropped), so it deploys first.

Three compounding defects let a box report `applied` while every PBS request 401'd:

1. The re-key was INVISIBLE. An ep0 re-issue rotates the secret of an existing token, so
   token_id/fingerprint/datastore/namespace come back byte-identical and the descriptor
   content hash never moved — the converged agent short-circuited and never consumed the
   fresh secret. WirePBSDR.SecretGeneration (field-exact with the hub) is what moves the
   hash now, because descriptorHash marshals this struct.

2. The agent could not READ its own credential. It writes /etc/pve/priv/storage/<id>.pw
   through the root wrapper, but that dir is 0700 root:www-data and the wrapper had no
   read verb — so the target resolver got "permission denied" every cycle, warned, and
   skipped. The one loop that could have caught the 401 was blind BY CONSTRUCTION. Adds a
   narrow `read` verb (+ exactly one sudoers line, + a pbsdr-read capability row): one
   secret to stdout, no network, no mutation, never in argv (sudo logs argv), traversal
   refused by the id grammar, the dir allowlist AND a resolved-path prefix assertion.

3. Nothing probed AUTHENTICATION. pbs.ProbeAuth (GET /version + an ErrUnauthorized
   sentinel) runs on the 15-minute collect path and its verdict becomes a loud
   `auth_failed` the hub escalates to a fresh mint. /version needs no datastore, namespace
   or privilege, so a 401 means the CREDENTIAL is bad; 403 is deliberately NOT treated as
   unauthorized, since re-keying a too-narrow token would mint forever without fixing
   anything. A transport error is UNKNOWN, never a rejection — otherwise every network
   blip burns a credential. Recovery self-clears.

R-50b(a): the report now carries the installed wrapper's sha256 so drift against the
vouched manifest value is answerable. Empty = unknown, never drift.

Three red-proofs, all at the assertion level. Removing SecretGeneration fails the re-arm
test with "consume calls=1, want 2". Swallowing the probe result leaves State:applied
AuthFailed:false — the July-18 shape exactly. Notably, deleting the wrapper's id charset
guard alone does NOT open a traversal hole (readlink + the prefix assertion still catch
it), so the isolating red-proof removes BOTH and shows the out-of-tree secret printed —
the layering is real, and a single-guard red-proof would have passed vacuously.

configs/felhom-agent.sudoers

@@ -216,10 +216,18 @@ Cmnd_Alias FELHOM_SSHD = \
 # token secret rides the wrapper's STDIN — sudo logs argv, so it must never appear here. The
 # agent fine-validates every field (charset + descriptor equality) before exec; these globs are
 # the coarse allowlist.
+#
+# `read` (R-39 leg b, agent v0.91.0) is the ONE added verb. It prints a token secret to stdout and
+# performs no mutation. It exists because the agent writes that file through this wrapper but could
+# never read it back (/etc/pve/priv is 0700 root:www-data), leaving its PBS verify loop permanently
+# blind to an `applied`-but-401 tier. It is NOT a general file-read: the wrapper pins the directory
+# and prefix-asserts the resolved path, and the id grammar admits no slash. The secret goes to
+# STDOUT, never argv — sudo logs argv.
 Cmnd_Alias FELHOM_PBSDR = \
   /usr/local/sbin/felhom-pbs-apply create *, \
   /usr/local/sbin/felhom-pbs-apply reconcile *, \
-  /usr/local/sbin/felhom-pbs-apply grant *
+  /usr/local/sbin/felhom-pbs-apply grant *, \
+  /usr/local/sbin/felhom-pbs-apply read *
 
 # OOB nft belt (TASK H1). The STATIC table `inet felhom_oob` is installed once by host-install; the
 # agent mutates ONLY its two SETS — @operator_ips (the operator /32) + @ssh_port (the claimed port).