test: update loadSession source-assertion tests for #3326 conditional renderMessages arg

#3326 changed loadSession's INFLIGHT + idle render calls from bare
renderMessages() to renderMessages(sameSessionForceReload?{preserveScroll:true}:undefined),
and added reload-width-hint handling inside _ensureMessagesLoaded. Updated 5
source-pinning tests to match the new (behaviorally-equivalent) call form:
- test_regressions / test_issue2341: match 'renderMessages(' call form
- test_parallel_session_switch: match call form + widen 600->850 block window
- test_issue1690: assert the CONDITIONAL preserveScroll (cross-session still bottom-pins)
- test_issue3162: widen _ensureMessagesLoaded slice 2000->2600

tests/test_issue1690_scroll_completion.py

@@ -72,5 +72,13 @@ def test_session_switch_and_idle_session_load_keep_default_bottom_pin_behavior()
     load_session = _function_body(SESSIONS_JS, "loadSession")
     idle_branch = load_session[load_session.index("}else{\n      S.busy=false;") : load_session.index("// Sync context usage indicator")]
 
-    assert "syncTopbar();renderMessages();" in idle_branch
-    assert "preserveScroll:true" not in idle_branch
+    # #3326: the idle branch now renders with a CONDITIONAL preserveScroll —
+    # `renderMessages(sameSessionForceReload?{preserveScroll:true}:undefined)`.
+    # For a normal cross-session idle load (currentSid!==sid) sameSessionForceReload
+    # is false, so the arg is undefined and the default bottom-pin behavior (#1690)
+    # is unchanged. preserveScroll only applies to a same-session external
+    # force-refresh (#3239), which is a different code path from #1690's scenario.
+    assert "syncTopbar();renderMessages(sameSessionForceReload?{preserveScroll:true}:undefined);" in idle_branch
+    # The idle path must NOT unconditionally preserveScroll — it stays bottom-pinned
+    # for cross-session loads. Guard against a regression to an always-on preserve.
+    assert "renderMessages({preserveScroll:true})" not in idle_branch

tests/test_issue2341_pending_user_reattach.py

@@ -25,7 +25,9 @@ def test_load_session_inflight_reattach_merges_pending_user_message_before_rende
     block = _load_session_inflight_branch()
 
     merge_pos = block.find("_mergePendingSessionMessage")
-    render_pos = block.find("renderMessages();")
+    # #3326 added an optional {preserveScroll} arg to the INFLIGHT-branch render
+    # call; match the call form rather than the bare `renderMessages();`.
+    render_pos = block.find("renderMessages(")
 
     assert merge_pos != -1, (
         "loadSession's INFLIGHT reattach branch must merge pending_user_message "

tests/test_issue3162_ensure_messages_loaded.py

@@ -15,7 +15,9 @@ SESSIONS_JS = (REPO / "static" / "sessions.js").read_text(encoding="utf-8")
 
 def _ensure_messages_loaded_body() -> str:
     start = SESSIONS_JS.index("async function _ensureMessagesLoaded")
-    return SESSIONS_JS[start: start + 2000]
+    # Window widened (#3326 added reload-width-hint handling inside this function,
+    # pushing the carry-forward reassignment further down).
+    return SESSIONS_JS[start: start + 2600]
 
 
 def test_ensure_messages_loaded_declares_msgs_with_let():

tests/test_parallel_session_switch.py

@@ -80,9 +80,14 @@ class TestLoadSessionIdleOverlap:
 
         found = False
         for pos in positions:
-            block = SESSIONS_JS[pos : pos + 600]
+            # Window widened 600→850 (#3326 added a reload-width-hint comment +
+            # conditional preserveScroll arg in the idle branch, pushing the
+            # _dirP.catch line further from the S.busy=false anchor).
+            block = SESSIONS_JS[pos : pos + 850]
             has_loaddir = "loadDir('.')" in block
-            has_render = "renderMessages()" in block
+            # #3326 added an optional {preserveScroll} arg to the idle-path render
+            # call; match the call form rather than the bare `renderMessages()`.
+            has_render = "renderMessages(" in block
             if has_loaddir and has_render:
                 found = True
                 assert "highlightCode()" not in block, (

tests/test_regressions.py

@@ -620,7 +620,9 @@ def test_loadSession_inflight_sets_busy_before_renderMessages(cleanup_test_sessi
     assert inflight_idx >= 0, "INFLIGHT branch not found in loadSession"
     inflight_block = src[inflight_idx:inflight_idx+1600]
     busy_pos = inflight_block.find("S.busy=true;")
-    render_pos = inflight_block.find("renderMessages();")
+    # #3326 added an optional {preserveScroll} arg to the INFLIGHT-branch render
+    # call, so match the call form rather than the bare `renderMessages();`.
+    render_pos = inflight_block.find("renderMessages(")
     assert busy_pos >= 0, "loadSession INFLIGHT branch must set S.busy=true"
     assert render_pos >= 0, "loadSession INFLIGHT branch must call renderMessages()"
     assert busy_pos < render_pos, \