State the handoff length limit on every field it bounds

The prompt gave "at most 200 characters" for NEXT, WHY and REMAINING. The
validator applies it to OPEN Q and LEARNED as well, and run 10 lost a lease to
a 219-character OPEN Q against a limit nobody had stated for that field.

Third instance of one shape: a constraint the code enforces and no brief
mentions. The other two were the research finding id and the dead-end
separator.

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

internal/herdr/adapter_test.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -408,3 +409,22 @@ LEARNED: e
 		t.Error("a dead end with no separator was accepted")
 	}
 }
+
+// Every field the validator bounds must say so. Run 10 lost a lease to a
+// 219-character OPEN Q against a limit the prompt stated for NEXT, WHY and
+// REMAINING only.
+func TestHandoffPromptStatesTheLimitOnEveryBoundedField(t *testing.T) {
+	for _, field := range []string{"NEXT", "WHY", "REMAINING", "OPEN Q", "LEARNED"} {
+		i := strings.Index(handoffPrompt, field+":")
+		if i < 0 {
+			t.Fatalf("the prompt never names %s", field)
+		}
+		line := handoffPrompt[i:]
+		if j := strings.Index(line, "\n"); j >= 0 {
+			line = line[:j]
+		}
+		if !strings.Contains(line, "200 characters") {
+			t.Errorf("%s is bounded at 200 but the prompt never says so: %q", field, line)
+		}
+	}
+}