fix(stream): hold a bare </>/< followed only by whitespace

crates/tinytools-agent/src/stream/mod.rs

@@ -151,8 +151,30 @@ fn hold_from(tail: &str) -> usize {
             }
         }
     }
+    if let Some(idx) = trailing_bare_angle_bracket(tail) {
+        best = best.min(idx);
+    }
     best
 }
 
+/// Byte index of a trailing `<` or `</` in `tail` that is followed only by
+/// whitespace to the end of the string, if any (`<\s*$` / `</\s*$`).
+///
+/// The invoke-XML grammar's DSML/namespace prefix tolerates whitespace
+/// between the bracket and the marker (`< | DSML | invoke`), which the
+/// fixed-literal scan above cannot express — a gap of unknown width is not
+/// a literal to prefix-match against. Without this, a fragment boundary
+/// landing on the bracket and its whitespace (`"< "`) is released as plain
+/// text before the marker arrives, and the opener is unrecoverable once
+/// split from its `<`.
+fn trailing_bare_angle_bracket(tail: &str) -> Option<usize> {
+    let trimmed = tail.trim_end_matches(char::is_whitespace);
+    if let Some(stripped) = trimmed.strip_suffix("</") {
+        Some(stripped.len())
+    } else {
+        trimmed.strip_suffix('<').map(str::len)
+    }
+}
+
 #[cfg(test)]
 mod test;

crates/tinytools-agent/src/stream/test.rs

@@ -99,6 +99,26 @@ fn dsml_split_across_fragments_is_scrubbed() {
     assert_eq!(calls, 1);
 }
 
+#[test]
+fn a_whitespace_prefixed_dsml_opener_split_before_the_marker_is_held() {
+    // The complete-tag regex tolerates a space before the marker
+    // (`< | DSML | invoke`), but that must not regress streaming: a
+    // fragment boundary landing right after `<` and before the marker has
+    // arrived must still be held, or the opener is lost the moment the
+    // held-back fragment is flushed as narrative.
+    let mut s = StreamScrubber::new();
+    let first = s.feed("< ");
+    assert_eq!(
+        first.text, "",
+        "a possible whitespace-prefixed DSML opener must be held"
+    );
+    assert!(first.calls.is_empty());
+
+    let second = s.feed("| DSML | invoke name=\"read\">{\"path\":\"a\"}</| DSML | invoke>");
+    assert_eq!(second.calls.len(), 1);
+    assert_eq!(second.calls[0].name, "read");
+}
+
 #[test]
 fn plural_tool_calls_prose_is_not_held() {
     assert_eq!(