Harden streaming scroll unpin behavior (#1360) (#1377)

tests/test_issue1360_streaming_scroll_hardening.py

@@ -0,0 +1,62 @@
+"""Regression tests for #1360: streaming must not re-pin user scroll."""
+
+from pathlib import Path
+
+REPO = Path(__file__).parent.parent
+UI_JS = (REPO / "static" / "ui.js").read_text(encoding="utf-8")
+STYLE_CSS = (REPO / "static" / "style.css").read_text(encoding="utf-8")
+
+
+def _extract_function(src: str, name: str) -> str:
+    marker = f"function {name}("
+    idx = src.find(marker)
+    assert idx != -1, f"{name} not found"
+    depth = 0
+    for i, ch in enumerate(src[idx:], idx):
+        if ch == "{":
+            depth += 1
+        elif ch == "}":
+            depth -= 1
+            if depth == 0:
+                return src[idx:i + 1]
+    raise AssertionError(f"Could not extract {name}")
+
+
+def test_messages_scroller_disables_browser_scroll_anchoring():
+    assert "overflow-anchor:none" in STYLE_CSS, (
+        "#messages must disable browser scroll anchoring so tool/card inserts "
+        "cannot yank the transcript while the user reads earlier content."
+    )
+
+
+def test_scroll_repin_dead_zone_is_wider_for_mac_app_windows():
+    assert "clientHeight<250" in UI_JS, (
+        "The near-bottom re-pin threshold should be at least 250px so small "
+        "macOS app windows and trackpad momentum do not re-pin too eagerly."
+    )
+
+
+def test_queue_card_measurement_does_not_force_repin_during_streaming():
+    fn = _extract_function(UI_JS, "_renderQueueChips")
+    measurement_idx = fn.find("setTimeout(()=>")
+    assert measurement_idx != -1, "queue card measurement timeout not found"
+    measurement_block = fn[measurement_idx:measurement_idx + 500]
+
+    assert "S.activeStreamId" in measurement_block
+    assert "scrollIfPinned()" in measurement_block
+    assert "!S.activeStreamId" in measurement_block
+    assert "scrollToBottom()" in measurement_block
+    assert measurement_block.find("scrollIfPinned()") < measurement_block.find("scrollToBottom()")
+
+
+def test_queue_pill_click_does_not_force_repin_during_streaming():
+    fn = _extract_function(UI_JS, "_updateQueuePill")
+    click_idx = fn.find("pill.onclick=()=>")
+    assert click_idx != -1, "queue pill click handler not found"
+    click_block = fn[click_idx:click_idx + 700]
+
+    assert "S.activeStreamId" in click_block
+    assert "scrollIfPinned()" in click_block
+    assert "!S.activeStreamId" in click_block
+    assert "scrollToBottom()" in click_block
+    assert click_block.find("scrollIfPinned()") < click_block.find("scrollToBottom()")