diff --git a/gateway/run.py b/gateway/run.py
index c907ba4187..40215b808c 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -953,7 +953,7 @@ def _warm_turn_machinery_sync() -> int:
     """Synchronously initialize first-turn prerequisites (executor thread); returns the schema count.
 
     Covers the lazy init seen in skeleton turns: ``run_agent`` import graph, tool schemas (+ ``check_fn``
-    TTL cache), context files."""
+    TTL cache), context files, the local Python toolchain probe (#106064)."""
     import run_agent  # noqa: F401  # heavy import graph, cached in sys.modules
     import model_tools
 
@@ -964,6 +964,15 @@ def _warm_turn_machinery_sync() -> int:
         build_context_files_prompt()
     except Exception:
         logger.debug("context-file warm-up failed (non-fatal)", exc_info=True)
+    from hermes_cli.config import load_config_readonly
+
+    agent_cfg = load_config_readonly().get("agent")
+    if not isinstance(agent_cfg, dict) or agent_cfg.get("environment_probe", True):
+        # The resolver owns remote-backend omission, the single worker, its cache and the bounded
+        # wait; calling it here is what the first prompt build would otherwise do on the hot path.
+        from tools.env_probe import get_environment_probe_line
+
+        get_environment_probe_line()
     return len(tool_defs)
 
 
diff --git a/tests/gateway/test_startup_environment_probe.py b/tests/gateway/test_startup_environment_probe.py
new file mode 100644
index 0000000000..4c0b18b9e5
--- /dev/null
+++ b/tests/gateway/test_startup_environment_probe.py
@@ -0,0 +1,47 @@
+"""The gateway boot warm-up primes the local toolchain probe the first prompt build reads (#106064)."""
+
+import pytest
+
+import model_tools
+from gateway import run as gateway_run
+from tools import env_probe
+from tools.terminal_scope import reset_terminal_scope, set_terminal_scope
+
+
+@pytest.fixture(autouse=True)
+def _probe_cache(monkeypatch):
+    monkeypatch.setattr(model_tools, "get_tool_definitions", lambda **_: [])
+    env_probe._reset_cache_for_tests()
+    yield
+    env_probe._reset_cache_for_tests()
+
+
+def _warm(tmp_path, monkeypatch, agent_section: dict, backend: str) -> None:
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+    (tmp_path / "config.yaml").write_text(f"agent: {agent_section!r}\n", encoding="utf-8")
+    token = set_terminal_scope({"TERMINAL_ENV": backend})
+    try:
+        gateway_run._warm_turn_machinery_sync()
+    finally:
+        reset_terminal_scope(token)
+
+
+def test_warmup_leaves_probe_cached_for_first_prompt(tmp_path, monkeypatch):
+    calls = []
+    monkeypatch.setattr(env_probe, "_build_probe_line", lambda: calls.append(1) or "Python toolchain: fixture.")
+
+    _warm(tmp_path, monkeypatch, {}, "local")
+
+    assert env_probe._PROBE_DONE.is_set()
+    assert env_probe.get_environment_probe_line() == "Python toolchain: fixture."
+    assert calls == [1]  # single worker; the first turn reuses the cache
+
+
+@pytest.mark.parametrize("agent_section,backend", [({"environment_probe": False}, "local"), ({}, "ssh")])
+def test_warmup_skips_probe_when_disabled_or_remote(tmp_path, monkeypatch, agent_section, backend):
+    monkeypatch.setattr(env_probe, "_build_probe_line", lambda: pytest.fail("host inspected"))
+
+    _warm(tmp_path, monkeypatch, agent_section, backend)
+
+    assert not env_probe._PROBE_DONE.is_set()
+    assert env_probe._PROBE_THREAD is None