diff --git a/internal/agent/agent.go b/internal/agent/agent.go
index 3870747e..80064d7b 100644
--- a/internal/agent/agent.go
+++ b/internal/agent/agent.go
@@ -156,3 +156,32 @@ func ids(as []*Agent) []string {
 	sort.Strings(s)
 	return s
 }
+
+// Spell puts a value typed for field key the way this agent spells it: a
+// catalog model is "copilot/gpt-6" in some agents and "magpie/copilot/gpt-6"
+// in others, and either is taken in both. A value the picker offers as is
+// stays, and so does one it doesn't know (a model the agent reaches on its
+// own that isn't listed); a "magpie/…" value the catalog doesn't have is an
+// error rather than a model the agent would ask its own vendor for.
+func (a *Agent) Spell(key, v string) (string, error) {
+	f := a.Field(key)
+	if f == nil || f.Options == nil || v == "" {
+		return v, nil
+	}
+	opts := f.Options(a.Values())
+	for _, o := range opts {
+		if o.Value == v {
+			return v, nil
+		}
+	}
+	ref, prefixed := strings.CutPrefix(v, magpieID+"/")
+	for _, o := range opts {
+		if o.Ref != "" && o.Ref == ref {
+			return o.Value, nil
+		}
+	}
+	if prefixed {
+		return "", fmt.Errorf("%s isn't a model in magpie's catalog (magpie models lists them)", ref)
+	}
+	return v, nil
+}
diff --git a/internal/agent/spell_test.go b/internal/agent/spell_test.go
new file mode 100644
index 00000000..ec7fa864
--- /dev/null
+++ b/internal/agent/spell_test.go
@@ -0,0 +1,37 @@
+package agent
+
+import "testing"
+
+func TestSpell(t *testing.T) {
+	opts := func(prefix string) func(map[string]string) []Option {
+		return func(map[string]string) []Option {
+			return []Option{
+				{Value: "gpt-6"},
+				{Value: prefix + "copilot/gpt-6-sol", Ref: "copilot/gpt-6-sol"},
+			}
+		}
+	}
+	get := func() string { return "" }
+	bare := &Agent{Fields: []Field{{Key: "model", Get: get, Options: opts("")}}}
+	prefixed := &Agent{Fields: []Field{{Key: "model", Get: get, Options: opts("magpie/")}}}
+	for _, c := range []struct {
+		a       *Agent
+		in, out string
+		err     bool
+	}{
+		{bare, "copilot/gpt-6-sol", "copilot/gpt-6-sol", false},
+		{bare, "magpie/copilot/gpt-6-sol", "copilot/gpt-6-sol", false},
+		{prefixed, "copilot/gpt-6-sol", "magpie/copilot/gpt-6-sol", false},
+		{prefixed, "magpie/copilot/gpt-6-sol", "magpie/copilot/gpt-6-sol", false},
+		{bare, "gpt-6", "gpt-6", false},
+		{bare, "some-unlisted-model", "some-unlisted-model", false},
+		{bare, "", "", false},
+		{bare, "magpie/copilot/nope", "", true},
+		{prefixed, "magpie/copilot/nope", "", true},
+	} {
+		got, err := c.a.Spell("model", c.in)
+		if got != c.out || (err != nil) != c.err {
+			t.Errorf("%q: got %q, %v; want %q, err %v", c.in, got, err, c.out, c.err)
+		}
+	}
+}
diff --git a/main.go b/main.go
index d7e2d2e1..43a164d2 100644
--- a/main.go
+++ b/main.go
@@ -192,6 +192,10 @@ func set(a *agent.Agent, key, value string) error {
 		}
 		return fmt.Errorf("%s has no field %q (fields: %s)", a.Name, key, strings.Join(keys, ", "))
 	}
+	value, err := a.Spell(f.Key, value)
+	if err != nil {
+		return err
+	}
 	if err := f.Set(value); err != nil {
 		return err
 	}