Add process management: enumerate, supervisor-gated kill, exit notifications

process_enumerate snapshots the task table (the device_enumerate shape, so
ps is a user program); system_spawn returns the child id, records the caller
as supervisor, and takes an exit endpoint; process_kill is allowed only for
the supervisor. Every death — exit, fault, or kill — posts a child-exit badge
to that endpoint (the IRQ-as-IPC pattern as SIGCHLD). A target caught off-CPU
is reaped in place; a running one is condemned and finished at its next
system call or tick, guarded so teardown never lands mid-kernel-operation.
Tested by process-list, process-kill, and supervision (a ring-3 supervisor
exercising the whole surface); design notes in docs/process-management.md.

test/qemu_test.py

@@ -222,6 +222,24 @@ CASES = [
      "smp":    4,
      "expect": r"DANOS-TEST-RESULT: PASS",
      "fail":   r"DANOS-TEST-RESULT: FAIL"},
+    # process_enumerate: a task-table snapshot lists spawned processes by name and
+    # id alongside the kernel tasks, and a too-small buffer still reports the total.
+    {"name": "process-list",
+     "expect": r"DANOS-TEST-RESULT: PASS",
+     "fail":   r"DANOS-TEST-RESULT: FAIL"},
+    # process_kill + the exit notification: only the supervisor may kill; a blocked
+    # victim is reaped in place and a spinning one dies by the deferred (tick) path;
+    # each death posts one exit badge to the endpoint given at spawn.
+    {"name": "process-kill",
+     "smp":    4,
+     "expect": r"DANOS-TEST-RESULT: PASS",
+     "fail":   r"DANOS-TEST-RESULT: FAIL"},
+    # The user-side whole: process-test supervises two children from ring 3 —
+    # spawn with an exit endpoint, enumerate, kill, notification, gone.
+    {"name": "supervision",
+     "smp":    4,
+     "expect": r"DANOS-TEST-RESULT: PASS",
+     "fail":   r"DANOS-TEST-RESULT: FAIL"},
     # The initial_ramdisk: the loader ferries a bundle of user binaries; the kernel parses
     # it and spawns each as a ring-3 process (here the VFS-server stub heartbeats).
     {"name": "initial-ramdisk",