Stage 397: PR #2689 — fix(chat): preserve inflight send state during start race

Co-authored-by: ai-ag2026 <ai-ag2026@users.noreply.github.com>

static/messages.js

@@ -415,7 +415,8 @@ async function send(){
   if(typeof upsertActiveSessionForLocalTurn==='function'){
     upsertActiveSessionForLocalTurn({title:displayText.slice(0,64),messageCount:S.messages.length,timestampMs:Date.now()});
   }
-  INFLIGHT[activeSid]={messages:[...S.messages],uploaded:uploadedNames,toolCalls:[]};
+  const optimisticMessages=[...S.messages];
+  INFLIGHT[activeSid]={messages:optimisticMessages,uploaded:uploadedNames,toolCalls:[]};
   if(typeof saveInflightState==='function'){
     saveInflightState(activeSid,{streamId:null,messages:INFLIGHT[activeSid].messages,uploaded:uploadedNames,toolCalls:[]});
   }
@@ -486,9 +487,13 @@ async function send(){
       // against real active-stream metadata before the background refresh lands.
       upsertActiveSessionForLocalTurn({title:S.session&&S.session.title||displayText.slice(0,64),messageCount:S.messages.length,timestampMs:Date.now()});
     }
+    if(!INFLIGHT[activeSid]){
+      INFLIGHT[activeSid]={messages:optimisticMessages,uploaded:uploadedNames,toolCalls:[]};
+    }
+    const currentInflight=INFLIGHT[activeSid];
     markInflight(activeSid, streamId);
     if(typeof saveInflightState==='function'){
-      saveInflightState(activeSid,{streamId,messages:INFLIGHT[activeSid].messages,uploaded:uploadedNames,toolCalls:INFLIGHT[activeSid].toolCalls||[]});
+      saveInflightState(activeSid,{streamId,messages:currentInflight.messages||optimisticMessages,uploaded:uploadedNames,toolCalls:currentInflight.toolCalls||[]});
     }
     // Refresh session list so background streaming indicators appear immediately for the
     // session that was just started and any others that may already be running.

static/sessions.js

@@ -310,6 +310,9 @@ function _purgeStaleInflightEntries() {
     }
   }
   for (const sid of Object.keys(INFLIGHT)) {
+    if (typeof _sendInProgress !== 'undefined' && _sendInProgress && sid === _sendInProgressSid) {
+      continue;
+    }
     if (!sessionsById.has(sid)) {
       // Session is absent from _allSessions — it was deleted / archived /
       // filtered and can never stream again, so drop the entry.

tests/test_inflight_send_start_race.py

@@ -0,0 +1,51 @@
+"""Regression coverage for send/start optimistic INFLIGHT races."""
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+MESSAGES_JS = (REPO_ROOT / "static" / "messages.js").read_text(encoding="utf-8")
+SESSIONS_JS = (REPO_ROOT / "static" / "sessions.js").read_text(encoding="utf-8")
+
+
+def _function_body(src: str, name: str) -> str:
+    marker = f"function {name}"
+    start = src.index(marker)
+    brace = src.index("{", start)
+    depth = 1
+    i = brace + 1
+    while depth and i < len(src):
+        if src[i] == "{":
+            depth += 1
+        elif src[i] == "}":
+            depth -= 1
+        i += 1
+    return src[brace + 1 : i - 1]
+
+
+def test_send_preserves_optimistic_messages_across_chat_start_await():
+    """send() must not dereference INFLIGHT[activeSid] after await without a fallback."""
+    body = _function_body(MESSAGES_JS, "send")
+    setup_idx = body.index("const optimisticMessages=[...S.messages];")
+    inflight_idx = body.index("INFLIGHT[activeSid]={messages:optimisticMessages")
+    await_idx = body.index("const startData=await api('/api/chat/start'")
+    save_idx = body.index("saveInflightState(activeSid,{streamId", await_idx)
+
+    assert setup_idx < inflight_idx < await_idx < save_idx
+    post_await = body[await_idx:save_idx]
+    assert "if(!INFLIGHT[activeSid])" in post_await, (
+        "send() should recreate the INFLIGHT entry if a session-list refresh pruned it"
+    )
+    assert "messages:INFLIGHT[activeSid].messages" not in body[save_idx : save_idx + 220], (
+        "saveInflightState() should use a guarded local/current inflight object, not a blind nested read"
+    )
+
+
+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")
+
+    assert "_sendInProgress" in body and "_sendInProgressSid" in body, (
+        "_purgeStaleInflightEntries() should skip the current send while start is in progress"
+    )
+    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"