From c9eb91f38b833ab628b113486f765135c3b58961 Mon Sep 17 00:00:00 2001
From: Noah Treuhaft <noah.treuhaft@gmail.com>
Date: Tue, 2 Jun 2026 14:39:50 -0400
Subject: [PATCH] vam: handle error(fusion(...)) in defuse()

---
 runtime/vam/expr/function/defuse.go      | 12 ++++++++++++
 runtime/ztests/expr/function/defuse.yaml | 10 ++++++++++
 2 files changed, 22 insertions(+)

diff --git a/runtime/vam/expr/function/defuse.go b/runtime/vam/expr/function/defuse.go
index 16f3cd258..e453b0c73 100644
--- a/runtime/vam/expr/function/defuse.go
+++ b/runtime/vam/expr/function/defuse.go
@@ -52,6 +52,8 @@ func (d *defuse) eval(in vector.Any) vector.Any {
 			vecs = append(vecs, d.eval(vec))
 		}
 		return vector.NewDynamic(dynamic.Tags, vecs)
+	case vector.KindError:
+		return d.defuseError(in)
 	case vector.KindFusion:
 		fusion := vector.PushView(in).(*vector.Fusion)
 		return d.downcast.call(fusion.Values, fusion.Subtypes.Types())
@@ -157,3 +159,13 @@ func (d *defuse) defuseMap(in vector.Any) vector.Any {
 	}
 	return vector.NewDynamic(tags, vecs)
 }
+
+func (d *defuse) defuseError(in vector.Any) vector.Any {
+	errVec := vector.PushView(in).(*vector.Error)
+	valsVec := d.eval(errVec.Vals)
+	return vector.Apply(vector.ApplyNone, func(vecs ...vector.Any) vector.Any {
+		vec := vecs[0]
+		typ := d.sctx.LookupTypeError(vec.Type())
+		return vector.NewError(typ, vec)
+	}, valsVec)
+}
diff --git a/runtime/ztests/expr/function/defuse.yaml b/runtime/ztests/expr/function/defuse.yaml
index e82c3fe2d..b278f71a0 100644
--- a/runtime/ztests/expr/function/defuse.yaml
+++ b/runtime/ztests/expr/function/defuse.yaml
@@ -202,6 +202,16 @@ output: *input
 
 spq: fuse | defuse(this)
 
+input: &input |
+  error("a")
+  error(0)::(null|error(int64))
+
+output: *input
+
+---
+
+spq: fuse | defuse(this)
+
 input: &input |
   1::(int64|null)