fix(sandbox): strict profile no longer lets a child rewrite ~/.kigi

Port of upstream grok-build 1.0.14 ("--sandbox strict now restricts
writes to ~/.grok/sessions only"), shaped for Kigi.

The strict profile granted the whole ~/.kigi read-write, so a sandboxed
command could plant a global SessionStart hook or flip
`[sandbox].profile` in config.toml for the next launch. Landlock cannot
carve a child out of a write grant, so the home is now read-only
except an explicit allowlist of state subtrees (run, sessions,
worktrees, worktree_pool, tasks, memory, logs, debug, crash, memtrace,
trace-exports); config.toml, auth.json, sandbox.toml, hooks/, bin/ and
vendor/ stay read-only. A symlinked state dir under the home is
followed only to the default ~/.kigi/sessions.

What the process itself writes there after enforcement moves or is
minted first:
- kigi-shell `apply_sandbox` mints the device id, extracts the bundled
  rg and the bundled skills BEFORE enforcement for every profile that
  restricts home writes (`restricts_home_writes`, custom profiles
  extending strict included).
- The sandbox audit log lives at ~/.kigi/sessions/sandbox-events.jsonl.
- Leader lock/socket default to ~/.kigi/run/, the leader stderr log to
  ~/.kigi/logs/leader.log; discovery scans run/ and the legacy root,
  and the default target prefers the current socket.
Root-level caches (version.json, agent_id, slash-mru.json, pager.toml,
claude_import_state.json) degrade best-effort under strict; documented.

Claude-Session: https://claude.ai/code/session_01RUqV8HVGXcAETyYbZ2tPQ4

crates/codegen/kigi-shell/src/leader/lock.rs

@@ -52,10 +52,16 @@ pub fn default_lock_path_in(root: &Path) -> PathBuf {
     root.join("leader.lock")
 }
 
+/// Runtime files live under `~/.kigi/run`: the one home subtree a strict
+/// sandbox leaves writable for them.
+pub(super) fn runtime_root() -> PathBuf {
+    kigi_home().join("run")
+}
+
 /// Effective leader lock path: the [`LEADER_SOCKET_ENV`] override's sibling
-/// `.lock` when set, else the default under kigi home.
+/// `.lock` when set, else the default under `~/.kigi/run`.
 pub fn default_lock_path() -> PathBuf {
-    resolve_lock_path(leader_socket_override(), &kigi_home())
+    resolve_lock_path(leader_socket_override(), &runtime_root())
 }
 
 pub fn default_socket_path_in(root: &Path) -> PathBuf {
@@ -63,9 +69,9 @@ pub fn default_socket_path_in(root: &Path) -> PathBuf {
 }
 
 /// Effective leader socket path: the [`LEADER_SOCKET_ENV`] override when set,
-/// else the default under kigi home.
+/// else the default under `~/.kigi/run`.
 pub fn default_socket_path() -> PathBuf {
-    resolve_socket_path(leader_socket_override(), &kigi_home())
+    resolve_socket_path(leader_socket_override(), &runtime_root())
 }
 
 /// The instance suffix encoded in a lock/socket file-name pair
@@ -145,6 +151,9 @@ impl LeaderLock {
     }
 
     fn open_lock_file(&self) -> Result<File, LockError> {
+        if let Some(parent) = self.lock_path.parent() {
+            std::fs::create_dir_all(parent)?;
+        }
         Ok(OpenOptions::new()
             .read(true)
             .write(true)