refactor(#2455): split hive-agent-mcp into its own bin crate

hive-agent-mcp/src/paths.rs

@@ -0,0 +1,19 @@
+//! Per-agent path resolution for this MCP server. Self-contained (mirrors
+//! the sibling helper daemons' own `paths.rs`) so the bin does not link the
+//! harness lib just to resolve the agent's state dir. Only the one helper
+//! the MCP server needs lives here.
+
+use std::path::PathBuf;
+
+/// Durable state directory for the current agent. Reads `HYPERHIVE_STATE_DIR`
+/// first (always set by the meta flake to `/agents/{label}/state`); falls back
+/// to the same pattern derived from `HIVE_LABEL` for dev/test environments
+/// where the env var may not be set.
+#[must_use]
+pub fn state_dir() -> PathBuf {
+    if let Some(p) = std::env::var_os("HYPERHIVE_STATE_DIR") {
+        return PathBuf::from(p);
+    }
+    let label = std::env::var("HIVE_LABEL").unwrap_or_default();
+    PathBuf::from(format!("/agents/{label}/state"))
+}