core: review fixes, init builds the agent, console without a terminal

Activation path (review T6R): a broken plugin or a stray file in
/plugins blocks no activation; candidates replace their own entries;
discovery has a 10 s deadline and its process is stopped after the
answer; an unchanged hash keeps plugin.prev.wasm; activations run in
their own task; the watcher is not recursive; no duplicate services;
rpc.retired waits for live processes of its version; reads and hashes
on blocking threads.

Guest I/O and per-call paths: a stdin write error is EOF, stdout and
stderr are drained before the status; stderr is lossy UTF-8 and goes
to the journal from its own reader; compiled components are freed;
shutdown starts no new processes; lock queues drop stopping processes;
compile before the admission gate; CommandPre per component;
core.unlock in order; null errors are successes; the journal thread
survives SQLite errors.

sausage init builds the agent with cargo.build; sausage without a
command creates ./world. The console reads plain lines without a
terminal. PROTOCOL.md and DECISIONS.md describe the decided rules. The
flake tests the whole workspace and checks the packaged cargo.build.

DECISIONS.md

@@ -69,3 +69,12 @@ a plugin, or a change that the agent makes to itself.
   core.
 - **The SDK is not published.** `cargo` points `sausage-plugin = "0.1"` at
   its own copy, which it also shows in `/plugins/cargo/sdk/`.
+- **Discovery has a deadline of 10 seconds.** It is an internal call of the
+  core, not a limit on plugins. Without it, one plugin that does not answer
+  would block every activation.
+- **A broken plugin blocks nobody.** A plugin without a document is already
+  broken, so the check cannot protect it. The graph shows it as
+  "unavailable", and `core.revert` and `force` always work.
+- **`rpc.retired` is best effort.** It does not run if the host stops first.
+  A persistent queue of retirements would be more core for a rare case, so a
+  new version checks its own migration marker instead.