fix(note): stop trimming Unicode whitespace off the last frontmatter field

to_markdown() removed serde_yaml's trailing newline with trim_end(), which
trims any Unicode whitespace. A note whose last serialized field ended in
U+00A0 (or U+2007, U+3000, ...) lost that character on every write, so the
value read back off disk differed from the one stored. Strip newlines only.

Found by the note round-trip proptest; its failing seed is checked in, plus
an explicit regression test over three Unicode space characters.

Author: fakebizprez

crates/memory-core/proptest-regressions/note.txt

@@ -0,0 +1,7 @@
+# Seeds for failure cases proptest has generated in the past. It is
+# automatically read and these particular cases re-run before any
+# novel cases are generated.
+#
+# It is recommended to check this file in to source control so that
+# everyone who runs the test benefits from these saved cases.
+cc f41cf5be61fda18330784477bb1c1fa0867b4589e96f1d5dc65d07957072d4d6 # shrinks to note = Note { frontmatter: NoteFrontmatter { title: "0", aliases: ["¡", "!"], tags: [], note_type: Fact, created: 2000-01-01, updated: 2000-01-01, expires: None, source: Some("é\u{a0}") }, body: "" }

crates/memory-core/src/note.rs

@@ -150,8 +150,10 @@ impl Note {
     pub fn to_markdown(&self) -> Result<String> {
         self.frontmatter.validate()?;
         let yaml = serde_yaml::to_string(&self.frontmatter)?;
-        // serde_yaml adds a trailing newline; keep a single blank line after ---
-        let yaml = yaml.trim_end();
+        // serde_yaml adds a trailing newline; strip newlines only. `trim_end` would
+        // also eat Unicode whitespace belonging to the last field's value (U+00A0
+        // and friends), silently corrupting it on the way to disk.
+        let yaml = yaml.trim_end_matches('\n');
         let mut out = String::with_capacity(yaml.len() + self.body.len() + 16);
         out.push_str("---\n");
         out.push_str(yaml);
@@ -382,6 +384,39 @@ Related: [[docker-registry-auth]]
         }
     }
 
+    /// Regression: `to_markdown` used to `trim_end()` serde_yaml's trailing
+    /// newline. That trims *Unicode* whitespace, so a last field ending in
+    /// U+00A0 (or U+2007, U+3000, …) lost that character on every write.
+    #[test]
+    fn trailing_unicode_whitespace_in_the_last_field_survives_a_round_trip() {
+        for suffix in ['\u{a0}', '\u{2007}', '\u{3000}'] {
+            let source = format!("session{suffix}");
+            let note = Note {
+                frontmatter: NoteFrontmatter {
+                    title: "Trailing whitespace".into(),
+                    aliases: vec!["nbsp".into(), "unicode space".into()],
+                    tags: vec![],
+                    note_type: NoteType::Fact,
+                    created: date(2026, 8, 15),
+                    updated: date(2026, 8, 15),
+                    expires: None,
+                    source: Some(source.clone()),
+                },
+                body: String::new(),
+            };
+
+            let markdown = note.to_markdown().unwrap();
+            let parsed = Note::parse(&markdown).unwrap();
+            assert_eq!(
+                parsed.frontmatter.source.as_deref(),
+                Some(source.as_str()),
+                "U+{:04X} was stripped from the last frontmatter field",
+                suffix as u32
+            );
+            assert_eq!(parsed, note);
+        }
+    }
+
     #[test]
     fn parse_spec_example_round_trip() {
         let note = Note::parse(SPEC_EXAMPLE).unwrap();