jobq: make NodeGuid an actual guid

Third time the operator asked for a guid and got a substitute: first an
i64 index, then a {random job id, per-builder counter} pair. The pair was
defensible in isolation -- a foreign handle misses rather than colliding,
with no new dependency -- but "an equivalent that avoids a dep" is a
counter-proposal, not an implementation.

It is also simpler as a guid, which was the question asked: NodeGuid(Uuid)
drops the `job` field, the `next_seq` counter, `fresh_job_id()` and the
`Cell` import, and halves the type's doc. One random draw per node rather
than one per builder -- noise next to what a node does when it runs.

uuid 1.24 was already in Cargo.lock as a transitive dependency, so this
adds an edge rather than a package.

Cargo.lock

@@ -1758,6 +1758,7 @@ dependencies = [
  "serde",
  "serde_json",
  "thiserror 2.0.18",
+ "uuid",
 ]
 
 [[package]]

Cargo.toml

@@ -64,6 +64,7 @@ hive-sock-client = { path = "hive-sock-client" }
 hive-types = { path = "hive-types" }
 thiserror = "2"
 tower-http = { version = "0.7", features = ["fs"] }
+uuid = { version = "1", features = ["v4"] }
 rmcp = { version = "2", default-features = false, features = [
   "server",
   "macros",

hive-jobq/Cargo.toml

@@ -12,6 +12,7 @@ chrono = { workspace = true }
 enumflags2.workspace = true
 serde = { workspace = true }
 thiserror = { workspace = true }
+uuid = { workspace = true }
 
 [dev-dependencies]
 serde_json = { workspace = true }

hive-jobq/src/builder.rs

@@ -26,7 +26,7 @@
 //! silent reorder — a builder that sorted for you would quietly accept a shape
 //! the graph itself cannot express.
 
-use std::cell::{Cell, RefCell};
+use std::cell::RefCell;
 use std::collections::HashMap;
 
 use crate::{Dep, DepWhen, Graph, GraphError, NodeId, TerminalState};
@@ -38,32 +38,14 @@ use crate::{Dep, DepWhen, Graph, GraphError, NodeId, TerminalState};
 /// insert time and are meaningful system-wide, while this is a builder-local
 /// label that stops existing once the job is inserted.
 ///
-/// The `job` half is what makes it safe to compare. A [`NodeRef`] converts into
-/// a bare `NodeGuid`, dropping the borrow that ties it to its builder — so a
-/// handle *can* be carried to a different job (captured by an inner closure,
-/// say). Were the identity a plain per-builder counter, the two jobs' `0`s would
-/// be equal and that handle would silently resolve to an unrelated node. With a
-/// per-builder random half it simply isn't found, and the insert fails by name.
+/// It is a v4 uuid because it has to survive leaving its builder. A [`NodeRef`]
+/// converts into a bare `NodeGuid`, dropping the borrow that tied it to the
+/// builder — so a handle *can* be carried into a different job (captured by an
+/// inner closure, say). Under a per-builder counter the two jobs' `0`s would be
+/// equal and that handle would silently address an unrelated node; drawn at
+/// random per node it simply isn't found, and the insert fails by name.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct NodeGuid {
-    /// Identifies the builder that issued this handle. Random per builder, so
-    /// two jobs' handles never compare equal.
-    job: u64,
-    /// Position within that builder — the cheap half, since `job` already
-    /// separates one builder's handles from another's.
-    seq: u32,
-}
-
-/// A fresh identity for one builder.
-///
-/// `RandomState` is seeded from the process's random state and advances per
-/// instance, so each builder gets a distinct, unguessable value — enough to
-/// make a foreign handle a miss rather than a collision. No `rand` dependency
-/// for what is a collision-avoidance job, not a cryptographic one.
-fn fresh_job_id() -> u64 {
-    use std::hash::BuildHasher as _;
-    std::collections::hash_map::RandomState::new().hash_one(0_u8)
-}
+pub struct NodeGuid(uuid::Uuid);
 
 /// Why a job could not be inserted.
 #[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
@@ -117,10 +99,6 @@ struct Pending<N, R> {
 #[derive(Debug)]
 pub struct JobBuilder<N, R> {
     nodes: RefCell<Vec<Pending<N, R>>>,
-    /// Identifies this builder in every handle it issues.
-    job: u64,
-    /// Position within this builder — the `seq` half of a [`NodeGuid`].
-    next_seq: Cell<u32>,
 }
 
 // Hand-written rather than derived: `#[derive(Default)]` would demand
@@ -129,8 +107,6 @@ impl<N, R> Default for JobBuilder<N, R> {
     fn default() -> Self {
         Self {
             nodes: RefCell::new(Vec::new()),
-            job: fresh_job_id(),
-            next_seq: Cell::new(0),
         }
     }
 }
@@ -160,11 +136,7 @@ impl<N, R> JobBuilder<N, R> {
     /// The returned handle is where those are declared; it is [`Copy`], so it
     /// can be named as a dependency as many times as needed.
     pub fn node(&self, payload: N) -> NodeRef<'_, N, R> {
-        let guid = NodeGuid {
-            job: self.job,
-            seq: self.next_seq.get(),
-        };
-        self.next_seq.set(guid.seq + 1);
+        let guid = NodeGuid(uuid::Uuid::new_v4());
         self.nodes.borrow_mut().push(Pending {
             guid,
             payload,
@@ -558,9 +530,9 @@ mod tests {
     /// job — an inner closure capturing an outer handle, say — must not
     /// silently address whichever node happens to sit at the same position.
     ///
-    /// This is what the random half of a [`NodeGuid`] buys: with a plain
-    /// per-builder counter both jobs' first handles would be equal, and the
-    /// edge below would resolve, wrongly, to the second job's own node.
+    /// This is what a random [`NodeGuid`] buys: with a plain per-builder
+    /// counter both jobs' first handles would be equal, and the edge below
+    /// would resolve, wrongly, to the second job's own node.
     #[test]
     fn a_handle_from_another_job_is_not_silently_resolved() {
         let mut g = graph();