proto, memoryd: no line of an entry may start with §, and headers are exact

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/proto/src/memory.rs

@@ -144,7 +144,8 @@ impl ConsolidateEntry {
 }
 
 /// Why an entry's text is not a well-formed entry: empty once trimmed, too long, or holding a line
-/// that is only the separator. `None` when it is fine.
+/// that starts with the separator, spaces aside. In `notes.md` such a line would read as a header,
+/// and a header says where an entry came from. `None` when it is fine.
 pub fn entry_problem(text: &str, max: usize) -> Option<String> {
     if text.trim().is_empty() {
         return Some("an entry cannot be empty".to_string());
@@ -156,9 +157,9 @@ pub fn entry_problem(text: &str, max: usize) -> Option<String> {
         ));
     }
     for line in text.lines() {
-        if line.trim() == SEPARATOR {
+        if line.trim_start().starts_with(SEPARATOR) {
             return Some(format!(
-                "an entry cannot hold a line that is only {SEPARATOR}"
+                "an entry cannot hold a line that starts with {SEPARATOR}"
             ));
         }
     }