From 8128019680df9a16a5f2d1e2d95c4f41955f37bf Mon Sep 17 00:00:00 2001
From: cyrus <cyrus@tinyhumans.ai>
Date: Fri, 25 Sep 2026 16:08:54 +0530
Subject: [PATCH] fix(stream): hold a bare </>/< followed only by whitespace
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TinySweeper flagged a real streaming regression in the prior commit:
the complete-tag regex now accepts a space before the DSML/namespace
marker (`< | DSML | invoke`), but the streaming scrubber's hold-back
list only matched fixed literal opener prefixes ("<invoke ", "<|DSML",
...). None of those start with a space, so a fragment boundary landing
on "< " (bracket plus whitespace, marker not arrived yet) released it
as plain text — and once split from its bracket, the marker that
followed could never complete an opener, silently dropping the call.

Add `trailing_bare_angle_bracket`: hold a `<` or `</` at the very end
of the buffered tail when it is followed only by whitespace so far.
Self-correcting once more text arrives — it only re-fires while the
tail's end still looks like a bare bracket with nothing conclusive
after it, exactly mirroring how a lone `<` was already held before
this gap.

Test plan:
- New test `a_whitespace_prefixed_dsml_opener_split_before_the_marker_is_held`
  reproduces TinySweeper's exact scenario (feed "< ", then the rest) —
  fails without the fix, passes with it.
- `cargo test -p tinytools-agent`: 323 passed, including
  `plural_tool_calls_prose_is_not_held` (confirms ordinary `<` in
  prose is unaffected).
- `cargo fmt --all -- --check`: clean.
- `cargo clippy --all-targets --all-features -- -D warnings`: clean.
---
 crates/tinytools-agent/src/stream/mod.rs  | 22 ++++++++++++++++++++++
 crates/tinytools-agent/src/stream/test.rs | 20 ++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/crates/tinytools-agent/src/stream/mod.rs b/crates/tinytools-agent/src/stream/mod.rs
index 5ae526e..d5a86e9 100644
--- a/crates/tinytools-agent/src/stream/mod.rs
+++ b/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;
diff --git a/crates/tinytools-agent/src/stream/test.rs b/crates/tinytools-agent/src/stream/test.rs
index fa1dbb3..4775c29 100644
--- a/crates/tinytools-agent/src/stream/test.rs
+++ b/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!(