diff --git a/hive-claude/Cargo.toml b/hive-claude/Cargo.toml
index 63e6f608..f9cd1756 100644
--- a/hive-claude/Cargo.toml
+++ b/hive-claude/Cargo.toml
@@ -11,3 +11,6 @@ serde = { workspace = true }
 serde_json.workspace = true
 thiserror.workspace = true
 tokio.workspace = true
+
+[dev-dependencies]
+tempfile = "3"
diff --git a/hive-claude/src/store.rs b/hive-claude/src/store.rs
index 064aa924..11e80545 100644
--- a/hive-claude/src/store.rs
+++ b/hive-claude/src/store.rs
@@ -50,7 +50,6 @@ impl SessionStore {
     /// (including anything already archived to `*.jsonl.archived`) are skipped.
     #[must_use]
     pub fn find_by_title(&self, title: &str) -> Option<PathBuf> {
-        let marker = format!("\"customTitle\":\"{title}\"");
         for entry in std::fs::read_dir(self.project_dir()).ok()?.flatten() {
             let path = entry.path();
             if path.extension().and_then(|e| e.to_str()) != Some("jsonl") {
@@ -62,7 +61,7 @@ impl SessionStore {
             if std::io::BufReader::new(file)
                 .lines()
                 .map_while(std::result::Result::ok)
-                .any(|line| line.contains(&marker))
+                .any(|line| line_sets_title(&line, title))
             {
                 return Some(path);
             }
@@ -93,3 +92,81 @@ impl SessionStore {
         Ok(Some(target))
     }
 }
+
+/// True if `line` is the session's `custom-title` event whose **top-level**
+/// `customTitle` field equals `title`.
+///
+/// Parsing the line (rather than substring-matching the whole transcript) is
+/// what makes this robust: a message that merely *quotes* the marker in its
+/// content has no top-level `customTitle` key, so it can't cause a false match
+/// on the wrong session file; the compact-vs-spaced JSON form is irrelevant;
+/// and titles containing `"` / `\` are handled by the parser. Verified shape
+/// (claude 2.1.x): `{"type":"custom-title","customTitle":"<title>",…}`.
+///
+/// The `contains` pre-check keeps the common case cheap — only the rare line
+/// mentioning `customTitle` is parsed as JSON, not every transcript line.
+fn line_sets_title(line: &str, title: &str) -> bool {
+    if !line.contains("customTitle") {
+        return false;
+    }
+    let Ok(value) = serde_json::from_str::<serde_json::Value>(line) else {
+        return false;
+    };
+    value.get("customTitle").and_then(|t| t.as_str()) == Some(title)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn write(dir: &std::path::Path, name: &str, lines: &[&str]) {
+        std::fs::write(dir.join(name), lines.join("\n")).unwrap();
+    }
+
+    #[test]
+    fn find_by_title_matches_only_the_custom_title_event() {
+        let home = tempfile::tempdir().unwrap();
+        let cwd = std::path::Path::new("/agents/iris/state");
+        let store = SessionStore::new(home.path(), cwd);
+        let proj = store.project_dir();
+        std::fs::create_dir_all(&proj).unwrap();
+
+        // The real titled session.
+        write(
+            &proj,
+            "real.jsonl",
+            &[
+                r#"{"type":"summary","summary":"x"}"#,
+                r#"{"type":"custom-title","customTitle":"iris","sessionId":"real"}"#,
+            ],
+        );
+        // A DIFFERENT session whose transcript merely quotes the marker string
+        // in message content — must NOT match.
+        write(
+            &proj,
+            "other.jsonl",
+            &[
+                r#"{"type":"custom-title","customTitle":"someone-else","sessionId":"other"}"#,
+                r#"{"type":"assistant","message":{"content":[{"type":"text","text":"the file had \"customTitle\":\"iris\" in it"}]}}"#,
+            ],
+        );
+
+        assert_eq!(store.find_by_title("iris"), Some(proj.join("real.jsonl")));
+        assert_eq!(store.find_by_title("nobody"), None);
+    }
+
+    #[test]
+    fn find_by_title_tolerates_spaced_json_and_escapes() {
+        let home = tempfile::tempdir().unwrap();
+        let store = SessionStore::new(home.path(), std::path::Path::new("/x"));
+        let proj = store.project_dir();
+        std::fs::create_dir_all(&proj).unwrap();
+        // Spaced JSON form + a title needing JSON escaping.
+        write(
+            &proj,
+            "s.jsonl",
+            &[r#"{ "type": "custom-title", "customTitle": "a\"b" }"#],
+        );
+        assert_eq!(store.find_by_title("a\"b"), Some(proj.join("s.jsonl")));
+    }
+}