add /shared mount: new shared directory accessible to all agents

hive-c0re/src/lifecycle.rs

@@ -31,6 +31,11 @@ pub const CONTAINER_CLAUDE_MOUNT: &str = "/root/.claude";
 /// state here; persists across destroy/recreate.
 pub const CONTAINER_NOTES_MOUNT: &str = "/state";
 
+/// Mount point of the shared directory accessible to all agents.
+/// All agents can read/write here; agents should only put things they're
+/// willing to lose (other agents may delete them).
+pub const CONTAINER_SHARED_MOUNT: &str = "/shared";
+
 const GIT_NAME: &str = "c0re";
 const GIT_EMAIL: &str = "c0re@hyperhive";
 
@@ -722,19 +727,27 @@ const HOST_APPLIED_ROOT: &str = "/var/lib/hyperhive/applied";
 /// `meta::meta_dir()` but duplicated here so lifecycle stays a leaf.
 const HOST_META_ROOT: &str = "/var/lib/hyperhive/meta";
 
+/// Shared directory accessible to all agents. All agents bind-mount this RW.
+const HOST_SHARED_ROOT: &str = "/var/lib/hyperhive/shared";
+
 fn set_nspawn_flags(
     container: &str,
     runtime_dir: &Path,
     claude_dir: &Path,
     notes_dir: &Path,
 ) -> Result<()> {
+    // Ensure /shared directory exists before binding. systemd-nspawn requires the bind source to exist.
+    std::fs::create_dir_all(HOST_SHARED_ROOT)
+        .with_context(|| format!("create {HOST_SHARED_ROOT}"))?;
+
     let path = format!("/etc/nixos-containers/{container}.conf");
     let original = std::fs::read_to_string(&path).with_context(|| format!("read {path}"))?;
     let mut binds = format!(
-        "--bind={runtime}:{CONTAINER_RUNTIME_MOUNT} --bind={claude}:{CONTAINER_CLAUDE_MOUNT} --bind={notes}:{CONTAINER_NOTES_MOUNT}",
+        "--bind={runtime}:{CONTAINER_RUNTIME_MOUNT} --bind={claude}:{CONTAINER_CLAUDE_MOUNT} --bind={notes}:{CONTAINER_NOTES_MOUNT} --bind={shared}:{CONTAINER_SHARED_MOUNT}",
         runtime = runtime_dir.display(),
         claude = claude_dir.display(),
         notes = notes_dir.display(),
+        shared = HOST_SHARED_ROOT,
     );
     if container == MANAGER_NAME {
         use std::fmt::Write as _;