core: sausage-vfs per process (/, /proc, /self, /run), activation, graph, watcher, upgrades

- /proc is a core layer: core/ (PROTOCOL.md, graph.json, graph.dot,
  locks.json, plugins/<name>/discover.json and client.rs) and one folder
  per process (info.json, log, and its /self files).
- Locks are released only after the task ended, the store dropped, and
  in-flight file operations returned.
- core.activate and core.revert with copies, discovery, compatibility
  checks of imports and consumers, groups, force. An admission gate
  makes the snapshot of old processes complete.
- Graph of discover documents by hash, refreshed by a file watcher.
- Upgrades: grace periods (x-sausage-grace), stop, service restarts,
  rpc.retired.
- SDK plugins in the real core (cli/tests/sdk.rs).

cli/src/execution.rs

@@ -1,7 +1,7 @@
 //! Execution of native futures and WASI processes, including transport drainage.
 use crate::{
     Host, NativeContext, NativePlugin,
-    process::{ProcessGuard, ProcessInfo},
+    process::ProcessInfo,
     runtime::{Instance, InstanceConfig},
 };
 use serde_json::{Value, json};
@@ -17,11 +17,7 @@ impl Host {
         native: Option<NativePlugin>,
         incoming: mpsc::UnboundedReceiver<Value>,
         has_id: bool,
-    ) {
-        let _guard = ProcessGuard {
-            host: self.clone(),
-            pid: pid.clone(),
-        };
+    ) -> String {
         if let Some(native) = native {
             let context = NativeContext {
                 host: self.clone(),
@@ -29,13 +25,12 @@ impl Host {
             };
             let result = native(context, info.method, info.params).await;
             self.answer(&pid, result);
-            self.finish(&pid, "exit 0");
-            return;
+            return "exit 0".into();
         }
         let result = self
             .run_guest(&pid, &info, &component.unwrap(), incoming, has_id)
             .await;
-        self.finish(&pid, &result.unwrap_or_else(|error| error.to_string()));
+        result.unwrap_or_else(|error| error.to_string())
     }
 
     /// Drain stdout before deciding whether the guest returned an answer.
@@ -47,8 +42,14 @@ impl Host {
         mut incoming: mpsc::UnboundedReceiver<Value>,
         has_id: bool,
     ) -> anyhow::Result<String> {
+        let (memory, tracker, store_ended) = {
+            let state = self.0.state.lock().unwrap();
+            let p = state.processes.get(pid).unwrap();
+            (p.memory.clone(), p.files.clone(), p.store_ended.clone())
+        };
         let config = InstanceConfig {
-            world: self.0.world.root.clone(),
+            filesystem: self.mounts(Some(pid.into()), memory, tracker).await?,
+            store_ended,
             network: true,
             env: vec![
                 ("SAUSAGE_PID".into(), pid.into()),