library: the harness keeps the subscribers, and an id belongs to whoever opened it

Three services had each written the same thing and got it three different
ways: input polled the process list to notice a dead subscriber, and only
when someone else subscribed; the power service never noticed at all; the
device manager noticed drivers but not subscribers. The harness owns the
table now, driven by the events a protocol declares — it registers on the
reserved verb, frames each event once, posts to everyone interested without
waiting on any of them, and reclaims a slot when the kernel says its owner
died. Interest masks moved to the envelope, so a subscriber that wants only
mice asks the same way everywhere.

Two consequences the plan had not foreseen. The device manager now hears a
supervised child's death twice, once as its supervisor and once as a
subscriber, so restart backoff counted every crash twice and gave up after
half as many; it retires the id before counting. And the kernel's published
exit table had eight slots for what is now six subscriptions in a plain
boot, so it holds sixteen.

The other half is a hole the design named early and left standing: a
backend handed out a small integer and then honoured it from anyone. A
process that guessed a file's node id read another client's file; a display
layer had no owner at all, so any client could reconfigure or destroy any
layer; a USB device token was never checked against the client that opened
it. Each is now bound to the task that opened it, and a wrong owner gets
exactly what an unknown id gets — the refusal must not become the oracle
the identical answers elsewhere were designed to remove. Closing a file
changed with it: it used to succeed unconditionally, which would have told
a caller which ids existed.

Suite 111/111, with a new case in which one process holds a file and a
layer, hands both ids to a second process, and finds them untouched after
that process has tried everything with them.

system/configuration/protocol.csv

@@ -148,6 +148,16 @@
 /test/system/services/input-source,          kernel,                          open,       input
 /test/system/services/input-test,            kernel,                          open,       input
 
+# The guessable-id probe (test/system/services/badge-scope-test) runs as two
+# processes of one binary: the owner, which the scenario spawns, and the intruder,
+# which the owner spawns with the ids it holds. Both reach the compositor — the
+# owner to create the layer, the intruder to be refused it — so the binary is
+# named twice, once per supervisor. The second row needs no 'supervise'
+# delegation: the owner was spawned by the KERNEL, which is a chain init can
+# vouch for on its own.
+/test/system/services/badge-scope-test,      kernel,                          open,       display
+/test/system/services/badge-scope-test,      /test/*,                         open,       display
+
 # The conformance probe (test/system/services/protocol-conformance-test) asks
 # every provider its boot bound for the envelope's reserved verbs. It reaches
 # ONLY the two contracts its own scenario boots a provider for, named one at a