refactor: extract global coordination into invariant-coordinator crate

Cargo.toml

@@ -1,8 +1,10 @@
 [workspace]
 resolver = "3"
 members = [
+    "crates/invariant-coordinator",
     "crates/invariant-engine",
     "crates/invariant-journal",
+    "crates/invariant-scheduler",
     "crates/invariant-types",
 ]
 

crates/invariant-coordinator/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "invariant-coordinator"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

crates/invariant-coordinator/src/domain/error.rs

@@ -0,0 +1,81 @@
+use std::fmt;
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum DomainError {
+    EmptyJobId,
+    EmptyTargetRef,
+    EmptyWorkerId,
+    EmptyLeaseToken,
+    ZeroLeaseDuration,
+    TimeOverflow,
+    LeaseEpochOverflow,
+    AttemptOverflow,
+    JobAlreadyLeased,
+    JobNotLeased,
+    JobTerminal,
+    LeaseHeldByDifferentWorker,
+    StaleLease,
+    LeaseExpired,
+}
+
+impl fmt::Display for DomainError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let message = match self {
+            Self::EmptyJobId => "job id cannot be empty",
+            Self::EmptyTargetRef => "target ref cannot be empty",
+            Self::EmptyWorkerId => "worker id cannot be empty",
+            Self::EmptyLeaseToken => "lease token cannot be empty",
+            Self::ZeroLeaseDuration => "lease duration must be greater than zero",
+            Self::TimeOverflow => "scheduler time overflow",
+            Self::LeaseEpochOverflow => "lease epoch overflow",
+            Self::AttemptOverflow => "attempt number overflow",
+            Self::JobAlreadyLeased => "job already has an active lease",
+            Self::JobNotLeased => "job is not leased",
+            Self::JobTerminal => "job is terminal",
+            Self::LeaseHeldByDifferentWorker => "lease is held by a different worker",
+            Self::StaleLease => "lease credential is stale",
+            Self::LeaseExpired => "lease has expired",
+        };
+        f.write_str(message)
+    }
+}
+
+impl std::error::Error for DomainError {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn display_should_render_stable_messages_for_all_domain_errors() {
+        let cases = [
+            (DomainError::EmptyJobId, "job id cannot be empty"),
+            (DomainError::EmptyTargetRef, "target ref cannot be empty"),
+            (DomainError::EmptyWorkerId, "worker id cannot be empty"),
+            (DomainError::EmptyLeaseToken, "lease token cannot be empty"),
+            (
+                DomainError::ZeroLeaseDuration,
+                "lease duration must be greater than zero",
+            ),
+            (DomainError::TimeOverflow, "scheduler time overflow"),
+            (DomainError::LeaseEpochOverflow, "lease epoch overflow"),
+            (DomainError::AttemptOverflow, "attempt number overflow"),
+            (
+                DomainError::JobAlreadyLeased,
+                "job already has an active lease",
+            ),
+            (DomainError::JobNotLeased, "job is not leased"),
+            (DomainError::JobTerminal, "job is terminal"),
+            (
+                DomainError::LeaseHeldByDifferentWorker,
+                "lease is held by a different worker",
+            ),
+            (DomainError::StaleLease, "lease credential is stale"),
+            (DomainError::LeaseExpired, "lease has expired"),
+        ];
+
+        for (error, expected) in cases {
+            assert_eq!(error.to_string(), expected);
+        }
+    }
+}