Function build_persistent_spawn_env 

pub(crate) async fn build_persistent_spawn_env(
    mstore: Arc<Store>,
    id_store: Arc<Store>,
    identity_store: Arc<Store>,
    broker: Option<Arc<Broker>>,
    block_meta: &HashMap<String, Value>,
    block_id: &str,
    auth_key: &str,
    base_env_vars: HashMap<String, String>,
) -> Result<HashMap<String, String>, SpawnGateError>

Builds the full spawn environment for a persistent-controller CLI process: cmd:env base → Layer 3 identity/credential gate → the two RESERVED wrapper variables (unconditionally overwritten — AGENTMUX_AUTH_KEY/AGENTMUX_BLOCKID) → the two agent-identity variables and per-agent git identity (all user-overridable via cmd:env) → bundled/user tools PATH → the reserved guards (gh_guard, account_login_guard: no agent gets a human’s gh login or the account’s cloud login).

Shared by every real spawn of a persistent-controller CLI — this function’s own logic used to live inline in run_agent_turn below, and only there. PersistentSubprocessController::start()’s eager-resume path (SPEC_PERSISTENT_CONTROLLER_EAGER_RESUME_ON_RECONNECT_2026_09_20.md) built its own second, independent copy of a SUBSET of this — codex P1 on PR #3513 found it had already drifted from this one: missing PATH and (then) MuxBus-token injection entirely, and using entry().or_insert() instead of an unconditional overwrite for the two reserved wrapper variables (meaning a stale persisted cmd:env value for either would silently survive across an eager resume, unlike a live message send). One function, not two copies kept in sync by hand.

Err(SpawnGateError) means the caller must NOT spawn — same contract as inject_identity_env_async itself, which this wraps.