move hive-sh4re's harness_dir() into hive-agent-sock, drop the dev-fallback derivation

hive-agent-sock/src/lib.rs

@@ -18,6 +18,8 @@ use serde::{Deserialize, Serialize};
 
 use hive_sh4re::LooseEnd;
 
+pub mod paths;
+
 /// In-container path of the harness-served in-agent socket. The harness
 /// binds it on boot; the in-container producers dial it for todo ops.
 /// (Placeholder default — the harness + producers resolve the real path

hive-agent-sock/src/paths.rs

@@ -0,0 +1,30 @@
+//! In-container harness-directory resolution, shared by the harness
+//! itself and every producer daemon that dials the in-agent socket
+//! (`hive-bash-mcp`, and any future producer that writes artifacts
+//! alongside the harness's own state).
+
+use std::path::PathBuf;
+
+/// Base harness directory for the current agent. Reads
+/// `HYPERHIVE_HARNESS_DIR`, always injected by the meta flake's
+/// `systemd.globalEnvironment` for every in-container service
+/// (`nix/host-modules` — see `hive-c0re/src/meta.rs`'s per-agent
+/// environment block). Every process this crate's wire types serve
+/// (the harness, `hive-bash-daemon`, ...) runs under that same
+/// environment, so there is no legitimate runtime path where it's
+/// unset — a missing var means the container is misconfigured, not
+/// that a fallback derivation should paper over it.
+///
+/// # Panics
+///
+/// Panics if `HYPERHIVE_HARNESS_DIR` is not set. Deliberate: a wrong
+/// silently-derived path here means task files, sqlite stores, and the
+/// in-agent socket itself could resolve to the wrong directory — a
+/// loud crash at startup beats a quiet cross-agent path collision.
+#[must_use]
+pub fn harness_dir() -> PathBuf {
+    PathBuf::from(
+        std::env::var_os("HYPERHIVE_HARNESS_DIR")
+            .expect("HYPERHIVE_HARNESS_DIR must be set — the meta flake injects it for every in-container service; a missing value means the container's environment is misconfigured"),
+    )
+}