diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index cd6fbe50b7..ad2156422f 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -1098,6 +1098,13 @@ class _RequestClientRegistry:
 # timeout's run-budget cap is applied AFTER this floor (AIAgent._compute_non_stream_stale_timeout).
 HIGH_EFFORT_SILENCE_FLOOR_SECONDS = 300.0
 
+# First-progress budget for a lifecycle-only stream on an official-Codex large request: the
+# stream opened but no substantive model event has arrived. Measured from the physical-attempt
+# start (a reconnect restarts it; lifecycle frames do not), and applied regardless of reasoning
+# effort. Equal to the high-effort floor today, but a separate knob so tuning one cannot silently
+# retune the other.
+CODEX_FIRST_PROGRESS_TIMEOUT_SECONDS = 300.0
+
 
 def _high_effort_silence_floor(agent) -> float:
     """``HIGH_EFFORT_SILENCE_FLOOR_SECONDS`` when the wire reasoning config is enabled at ``high`` or any
@@ -1216,7 +1223,7 @@ def _resolve_nonstream_watchdogs(agent, api_kwargs: dict) -> _NonStreamWatchdogs
         idle_timeout=idle_timeout, idle_requires_progress=progress_gated,
         # A lifecycle frame proves transport liveness, not model progress. Bound that phase
         # from the physical-attempt start; events cannot restart the grace period.
-        progress_timeout=HIGH_EFFORT_SILENCE_FLOOR_SECONDS if progress_gated else 0.0)
+        progress_timeout=CODEX_FIRST_PROGRESS_TIMEOUT_SECONDS if progress_gated else 0.0)
 
 
 def _codex_silent_hang_hint(agent, api_kwargs: dict) -> Optional[str]:
diff --git a/tests/agent/test_codex_ttfb_watchdog.py b/tests/agent/test_codex_ttfb_watchdog.py
index 318db3ec3a..7947a13f2f 100644
--- a/tests/agent/test_codex_ttfb_watchdog.py
+++ b/tests/agent/test_codex_ttfb_watchdog.py
@@ -71,14 +71,18 @@ def _make_codex_agent(
     return agent
 
 
-def _shorten_implicit_idle_watchdog(monkeypatch, helpers, timeout=2.0):
-    """Keep the resolver on its implicit branch while scaling time for tests."""
+def _shorten_implicit_idle_watchdog(monkeypatch, helpers, timeout=2.0, **overrides):
+    """Keep the resolver on its implicit branch while scaling time for tests.
+
+    ``timeout`` shortens ``idle_timeout``; ``overrides`` set any other resolved field."""
     monkeypatch.delenv("HERMES_CODEX_EVENT_STALE_TIMEOUT_SECONDS", raising=False)
     original = helpers._resolve_nonstream_watchdogs
 
     def resolve(agent, api_kwargs):
         watchdogs = original(agent, api_kwargs)
         watchdogs.idle_timeout = timeout
+        for field, value in overrides.items():
+            setattr(watchdogs, field, value)
         return watchdogs
 
     monkeypatch.setattr(helpers, "_resolve_nonstream_watchdogs", resolve)
@@ -343,15 +347,7 @@ def test_large_codex_lifecycle_only_stream_hits_attempt_progress_budget(tmp_path
     from agent import chat_completion_helpers as h
 
     agent = _make_codex_agent(tmp_path, monkeypatch)
-    original = h._resolve_nonstream_watchdogs
-
-    def resolve(agent, kwargs):
-        wd = original(agent, kwargs)
-        wd.ttfb_timeout = 0.9
-        wd.progress_timeout = 0.9
-        return wd
-
-    monkeypatch.setattr(h, "_resolve_nonstream_watchdogs", resolve)
+    _shorten_implicit_idle_watchdog(monkeypatch, h, ttfb_timeout=0.9, progress_timeout=0.9)
     closes = []
 
     def stream_attempt():