host: review fixes for cargo.build, the test runner, the console, and main; tests for every PROTOCOL.md rule

cargo.build and the runner (review T22R): builds use the network again;
core.unlock and core.notify in order under the runner; quiet test
output; manifest preparation keeps [workspace], target tables, renamed
and optional entries; cargo.rpc.discover; -32004 with data.output;
retention of 10 builds; light, empty test worlds with an in-memory
journal; only CARGO_/RUST_/SAUSAGE_ variables; stdin is null; the runner
through --config. A compile cache that cannot be created is not fatal.
Activation replaces plugin.wasm without a gap.

Console and main: init ships the workspace Cargo.lock and creates the
world atomically; each console command runs in its own task, so ps,
stop, and kill work during a slow call; SAUSAGE_HEADLESS; the terminal
mode is restored; signals during boot; chat text is not taken as a
command.

Tests: 20 more tests for PROTOCOL.md sections 2 to 10; the cargo tests
choose the libtest binary from cargo's JSON output and time out.

sdk/tests/plugins/probe/src/main.rs

@@ -123,6 +123,21 @@ impl Probe {
         });
         Ok("started".into())
     }
+    /// Leave an unfinished diagnostic before the SDK writes its framed response.
+    fn framed_output(&self) -> Result<String> {
+        print!("partial diagnostic");
+        Ok("intact".into())
+    }
+    /// Keep the process alive until the test releases its background task.
+    fn background_hold(&self) -> Result<String> {
+        sausage_plugin::background(async {
+            while !std::path::Path::new("/release-background").exists() {
+                wstd::task::sleep(wstd::time::Duration::from_millis(10)).await;
+            }
+            std::fs::write("/background-ended", "done").unwrap();
+        });
+        Ok(sausage_plugin::pid())
+    }
     /// Keep a pollable alive for one hour.
     fn sleepy(&self) -> Result<()> {
         sausage_plugin::background(async {