fix(lease-broker): no lease held is a no-op success, not a denied transition

revoke-lease.py read MOSAIC_LEASE_BROKER_SOCKET and MOSAIC_LEASE_SESSION_ID
with direct dict access inside the try block. A session that never held a
lease raised KeyError, fell into the fail-closed handler, and returned rc=2
on every lifecycle transition -- including compaction. Denying compaction to
a session that holds no lease protects nothing; it converts a recoverable
context limit into a lost session. That is D29.

Absence must be TOTAL to qualify for the no-op. If exactly one variable is
present the session is half-provisioned, which is real misconfiguration, and
it still takes the fail-closed path. An exported-but-empty variable counts as
absent.

Five unit tests cover the contract: no-op success, vacuous no-op (the broker
must not be contacted), both half-provisioned mirrors still rc=2, and empty
string as absent. Red control: 2 of the 5 fail without the guard.

The test is enumerated in test:framework-shell. Every other
src/lease-broker/*_unittest.py is enumerated there, and the #1017 membership
guard's population is *test*.sh under framework/tools/, so it does not see
python suites -- an unenumerated python test is silently never run.

Still open, not fixed here: why seat panes carry no MOSAIC_LEASE_* variables
at all.

packages/mosaic/framework/tools/lease-broker/revoke-lease.py

@@ -54,6 +54,22 @@ def main(
     arguments = parser.parse_args(argv)
     source_environment = os.environ if environ is None else environ
 
+    # D29: a session that never held a lease has nothing to revoke, and that is a
+    # SUCCESS, not a failed revocation. The block below is deliberately fail-closed
+    # for a broker that is unreachable, which is right — but it cannot distinguish
+    # "the broker is down" from "there was never a lease", so a bare-launched
+    # session was denied every lifecycle transition, including compaction. Denying
+    # compaction protects nothing there; it converts a recoverable context limit
+    # into a lost session.
+    #
+    # Absence must be TOTAL to qualify. If exactly one variable is present the
+    # session is half-provisioned, which is real misconfiguration, and it still
+    # takes the fail-closed path below.
+    lease_variables = ("MOSAIC_LEASE_BROKER_SOCKET", "MOSAIC_LEASE_SESSION_ID")
+    present = [name for name in lease_variables if source_environment.get(name)]
+    if not present:
+        return 0
+
     try:
         if not arguments.reason or len(arguments.reason) > 128:
             raise ValueError("invalid revoke reason")