fix: follow-ups for salvaged PR #72425

- codex app-server sibling path: surface a WARNING (was silent debug) when
  the projected-message flush fails — same bug class as the main fix, but
  codex output has already streamed so fail-closed and agent_persisted=False
  are both wrong here (#860/#42039 duplicate-write hazard); loud durability
  gap logging instead.
- map session_persistence_failed in _format_turn_completion_explanation so
  the user sees an actionable reason instead of 'The request failed:
  unknown error' + explainer test.
- contributors/emails mapping for elco@thedaoist.gg (attribution CI).

agent/codex_runtime.py

@@ -778,12 +778,27 @@ def run_codex_app_server_turn(
         # the already-flushed user turn). See gateway/run.py agent_persisted.
         if getattr(agent, "_session_db", None) is not None:
             try:
-                agent._flush_messages_to_session_db(messages)
+                _codex_flush_ok = agent._flush_messages_to_session_db(messages)
             except Exception:
-                logger.debug(
+                _codex_flush_ok = False
+                logger.warning(
                     "codex app-server projected-message flush failed",
                     exc_info=True,
                 )
+            if _codex_flush_ok is False:
+                # Unlike the chat-completions loop (which fails closed BEFORE
+                # projection — see conversation_loop session_persistence_failed),
+                # codex output has already streamed to the user by the time this
+                # flush runs, so there is nothing left to withhold. We cannot
+                # flip agent_persisted=False either: the gateway fallback write
+                # would re-INSERT the already-flushed user turn (#860/#42039).
+                # Surface the durability gap loudly instead of a silent debug.
+                logger.warning(
+                    "codex app-server turn was delivered but could NOT be "
+                    "persisted to the session DB (session=%s) — this turn "
+                    "will be missing after restart/resume",
+                    getattr(agent, "session_id", None),
+                )
 
 
     # Counter ticks for the agent-improvement loop.