Seed the checkpoint scope-key hasher for deterministic restore

workflow/internal/checkpoint/checkpoint_json.go

@@ -16,8 +16,16 @@ type scopeKeyHasherImpl struct{}
 
 var scopeKeyHasherInstance hashmap.Hasher[workflow.ScopeKey] = scopeKeyHasherImpl{}
 
+// scopeKeyHashSeed is a fixed process-wide seed. maphash.Hash's zero value
+// picks a new random seed on first use, so without SetSeed the same key would
+// hash differently on every call — breaking Load/Delete and shared-scope key
+// collapse on a map restored from JSON. state.go seeds its ScopeKey hasher the
+// same way.
+var scopeKeyHashSeed = maphash.MakeSeed()
+
 func (scopeKeyHasherImpl) Hash(s workflow.ScopeKey) uint64 {
 	var h maphash.Hash
+	h.SetSeed(scopeKeyHashSeed)
 	s.Hash(&h)
 	return h.Sum64()
 }

workflow/internal/checkpoint/json_test.go

@@ -4,6 +4,7 @@ package checkpoint_test
 
 import (
 	"encoding/json"
+	"fmt"
 	"reflect"
 	"testing"
 
@@ -115,3 +116,28 @@ func TestRunnerStateData_JsonRoundtrip(t *testing.T) {
 		t.Fatalf("ResponsePortOwners = %+v, want %+v", got.ResponsePortOwners, state.ResponsePortOwners)
 	}
 }
+
+// A Checkpoint's StateData map is rebuilt from JSON on Unmarshal. Its scope-key
+// hasher must use a fixed seed: a zero-value maphash.Hash picks a new random
+// seed on every call, so Load on a restored map would miss the key it just
+// stored (and shared-scope keys would not collapse).
+func TestCheckpoint_JsonRoundtrip_StateDataRemainsLoadable(t *testing.T) {
+	key := workflow.ScopeKey{ID: workflow.ScopeID{ExecutorID: "exec1"}, Key: "k"}
+	keyJSON, err := json.Marshal(key)
+	if err != nil {
+		t.Fatalf("marshal key: %v", err)
+	}
+	valJSON, err := json.Marshal(workflow.AnyPortableValue("v"))
+	if err != nil {
+		t.Fatalf("marshal value: %v", err)
+	}
+	data := []byte(fmt.Sprintf(`{"StateData":[{"Key":%s,"Value":%s}]}`, keyJSON, valJSON))
+
+	var cp checkpoint.Checkpoint
+	if err := json.Unmarshal(data, &cp); err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+	if _, ok := cp.StateData.Load(key); !ok {
+		t.Fatal("restored StateData.Load(key) = false: the scope-key hasher is not deterministic across calls")
+	}
+}