Stop losing a lease to an arrow character

Run 9's planner wrote a dead end as "tried X -> failed because Y". The content
was exactly what the protocol asks for. The parser split on "→" only, refused
the handoff, and a refused handoff fails the release rather than the turn, so
the lease expired with the work intact and unrecorded.

Accept either arrow. A separator is not the thing being validated.

The prefix stripping was also wrong on the right-hand side: it trimmed
"failed because " from an untrimmed string that started with a space, so every
parsed dead end kept the literal prefix in why_failed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CVbaKucEYBjMqVeUgJUsc1

internal/herdr/adapter_test.go

@@ -365,3 +365,31 @@ func TestLastObservedCommandSkipsOrchestrasOwnHandoffWrite(t *testing.T) {
 		}
 	}
 }
+
+// Run 9 lost a lease because the agent wrote "->" instead of "→". The content
+// was exactly right, the handoff was refused, and a refused handoff fails the
+// release rather than the turn.
+func TestDeadEndAcceptsEitherArrowAndStripsThePrefixes(t *testing.T) {
+	for _, arrow := range []string{"→", "->"} {
+		a, err := parseHandoffAnswer(`NEXT: inspect the failing integration test
+WHY: isolate the regression before changing production code
+REMAINING: fix the assertion after identifying the cause
+DEAD ENDS: tried finding ids "F1".."F8" ` + arrow + ` failed because the schema requires lowercase
+OPEN Q: whether the remote worker has the updated fixture
+LEARNED: the fixture requires a committed scratch branch
+`)
+		if err != nil {
+			t.Fatalf("arrow %q: %v", arrow, err)
+		}
+		if len(a.DeadEnds) != 1 {
+			t.Fatalf("arrow %q: parsed %d dead ends", arrow, len(a.DeadEnds))
+		}
+		d := a.DeadEnds[0]
+		if d.Tried != `finding ids "F1".."F8"` {
+			t.Errorf("arrow %q: tried = %q", arrow, d.Tried)
+		}
+		if d.WhyFailed != "the schema requires lowercase" {
+			t.Errorf("arrow %q: why_failed = %q", arrow, d.WhyFailed)
+		}
+	}
+}