fix(sessions): scope #4354 unstick to skip the active mid-send session (#2689 Opus gate)

Gate-found (Opus SHIP-WITH-FIXES; Codex SAFE — split resolved by reading the
contract: no dropped-turn, but a real transient start-race flicker). #4424
removed the _sendInProgress guards entirely; that re-opened the #2689 start-race
SYMPTOM for the one session mid-send (a /api/sessions poll landing during the
/api/chat/start round-trip would blank the just-sent bubble + queue a spurious
force-reload). Re-add the guard SCOPED to sid===_sendInProgressSid only, in both
_reconcileActiveSessionIdleStateFromList and _purgeStaleInflightEntries — a
long-hung session has _sendInProgress===false so it still gets unstuck (#4354),
only the in-flight start window is protected. Also fixes Opus's test-masking
finding: test_inflight_send_start_race now strips JS comments before asserting +
requires a real , so a comment can't green-light the #2689 guard, and
adds coverage for the reconcile path.

Co-authored-by: bergeouss <bergeouss@users.noreply.github.com>

tests/test_inflight_send_start_race.py

@@ -39,9 +39,19 @@ def test_send_preserves_optimistic_messages_across_chat_start_await():
     )
 
 
+def _strip_js_comments(src: str) -> str:
+    """Remove // line comments and /* */ block comments so source-grep assertions
+    match real statements, not comment text (a comment must not satisfy a guard
+    regression check). Good enough for these structural checks — not a full JS parser."""
+    import re
+    src = re.sub(r"/\*.*?\*/", "", src, flags=re.DOTALL)
+    src = re.sub(r"(?m)//.*$", "", src)
+    return src
+
+
 def test_stale_inflight_purge_preserves_current_send_before_stream_id_exists():
     """Sidebar cleanup must not delete the active send before /api/chat/start responds."""
-    body = _function_body(SESSIONS_JS, "_purgeStaleInflightEntries")
+    body = _strip_js_comments(_function_body(SESSIONS_JS, "_purgeStaleInflightEntries"))
 
     assert "_sendInProgress" in body and "_sendInProgressSid" in body, (
         "_purgeStaleInflightEntries() should skip the current send while start is in progress"
@@ -49,6 +59,27 @@ def test_stale_inflight_purge_preserves_current_send_before_stream_id_exists():
     skip_idx = body.index("_sendInProgress")
     delete_idx = body.index("delete INFLIGHT[sid];")
     assert skip_idx < delete_idx, "the current-send skip must run before any purge deletion"
+    # The skip must be a real guarded `continue`, not just a token in a comment (#4354/#2689).
+    assert "continue;" in body[skip_idx:delete_idx], (
+        "the current-send skip must be an actual `continue` before the purge deletion"
+    )
+
+
+def test_idle_reconcile_preserves_current_send_before_stream_id_exists():
+    """The list-poll idle reconciler must not clear the session that is mid-send.
+
+    #4354 removed the _sendInProgress guard here to unstick a hung indicator;
+    #2689's start-race protection must still cover the ONE session actively
+    mid-send (server row is briefly idle during /api/chat/start). Verified
+    against comment-stripped source so a comment can't satisfy the check.
+    """
+    body = _strip_js_comments(_function_body(SESSIONS_JS, "_reconcileActiveSessionIdleStateFromList"))
+    assert "_sendInProgress" in body and "_sendInProgressSid" in body, (
+        "_reconcileActiveSessionIdleStateFromList() must skip the active mid-send session"
+    )
+    guard_idx = body.index("_sendInProgress")
+    clear_idx = body.index("S.busy=false")
+    assert guard_idx < clear_idx, "the mid-send skip must run before the idle clear"
 
 
 def test_send_clears_stale_busy_state_before_queue_branch():