fix(openai): keep referenced tool call when deduping websocket input IDs

The input item ID dedupe added in #3620 keeps only the last occurrence of
each item id. When an upstream reuses the same item id across a re-sent or
repaired tool call (so two function_call items share an id but carry
different call_ids), the last-wins rule can drop the function_call whose
call_id still has a matching function_call_output. The upstream then rejects
the request with HTTP 400 "No tool call found for function call output with
call_id ...", breaking every subsequent turn over the Codex WebSocket path.

Make the dedupe orphan-aware: when several input items share an id, never
replace an item whose call_id is still referenced by a tool-call output with
one that is not. This keeps a single item per id (preserving the original
intent) while ensuring retained tool calls stay paired with their outputs.

Adds a regression test covering two function_call items that share an id
where only the earlier call_id has a surviving output.

sdk/api/handlers/openai/openai_responses_websocket.go

@@ -728,14 +728,50 @@ func dedupeInputItemsByID(rawArray string) (string, error) {
 		return "", errUnmarshal
 	}
 
-	lastIndexByID := make(map[string]int, len(items))
+	// Collect the call_ids that are still referenced by tool-call output
+	// items. When several input items share the same id, the one we keep must
+	// preserve any call_id that has a matching output; otherwise the upstream
+	// rejects the request with "No tool call found for function call output".
+	referencedCallIDs := make(map[string]struct{}, len(items))
+	for _, item := range items {
+		if len(item) == 0 {
+			continue
+		}
+		switch strings.TrimSpace(gjson.GetBytes(item, "type").String()) {
+		case "function_call_output", "custom_tool_call_output":
+			callID := strings.TrimSpace(gjson.GetBytes(item, "call_id").String())
+			if callID != "" {
+				referencedCallIDs[callID] = struct{}{}
+			}
+		}
+	}
+
+	// For each id, choose the index to keep. The default is the last
+	// occurrence (matching the original dedupe behavior), but we never replace
+	// an item whose call_id still has a matching output with one that does not.
+	// This keeps a single item per id while ensuring retained tool calls stay
+	// paired with their outputs.
+	keepIndexByID := make(map[string]int, len(items))
+	keepReferencedByID := make(map[string]bool, len(items))
 	for i, item := range items {
 		if len(item) == 0 {
 			continue
 		}
 		itemID := strings.TrimSpace(gjson.GetBytes(item, "id").String())
-		if itemID != "" {
-			lastIndexByID[itemID] = i
+		if itemID == "" {
+			continue
+		}
+		callID := strings.TrimSpace(gjson.GetBytes(item, "call_id").String())
+		_, referenced := referencedCallIDs[callID]
+		referenced = referenced && callID != ""
+		if _, seen := keepIndexByID[itemID]; !seen {
+			keepIndexByID[itemID] = i
+			keepReferencedByID[itemID] = referenced
+			continue
+		}
+		if referenced || !keepReferencedByID[itemID] {
+			keepIndexByID[itemID] = i
+			keepReferencedByID[itemID] = referenced
 		}
 	}
 
@@ -746,7 +782,7 @@ func dedupeInputItemsByID(rawArray string) (string, error) {
 		}
 		itemID := strings.TrimSpace(gjson.GetBytes(item, "id").String())
 		if itemID != "" {
-			if lastIndexByID[itemID] != i {
+			if keepIndexByID[itemID] != i {
 				continue
 			}
 		}

sdk/api/handlers/openai/openai_responses_websocket_test.go

@@ -1845,6 +1845,29 @@ func TestDedupeResponsesWebsocketInputItemsByIDAfterRepair(t *testing.T) {
 	}
 }
 
+func TestDedupeResponsesWebsocketInputItemsByIDKeepsReferencedToolCall(t *testing.T) {
+	// Two function_call items share the same id but carry different call_ids
+	// (e.g. the upstream reused the item id across a re-sent/repaired call).
+	// Only the first call_id has a matching function_call_output. Deduping by
+	// id must keep the referenced call so the output is not orphaned, which
+	// previously triggered an upstream 400 "No tool call found for function
+	// call output with call_id ...".
+	payload := []byte(`{"input":[{"type":"function_call","id":"fc-1","call_id":"call-1","name":"exec_command"},{"type":"function_call","id":"fc-1","call_id":"call-2","name":"exec_command"},{"type":"function_call_output","id":"fco-1","call_id":"call-1"}]}`)
+
+	deduped := dedupeResponsesWebsocketInputItemsByID(payload)
+
+	items := gjson.GetBytes(deduped, "input").Array()
+	if len(items) != 2 {
+		t.Fatalf("deduped input len = %d, want 2: %s", len(items), deduped)
+	}
+	if items[0].Get("id").String() != "fc-1" ||
+		items[0].Get("call_id").String() != "call-1" ||
+		items[1].Get("id").String() != "fco-1" ||
+		items[1].Get("call_id").String() != "call-1" {
+		t.Fatalf("unexpected deduped input: %s", deduped)
+	}
+}
+
 func TestResponsesWebsocketCompactionResetsTurnStateOnCustomToolTranscriptReplacement(t *testing.T) {
 	gin.SetMode(gin.TestMode)