diff --git a/src/autoresearch/role_runner.py b/src/autoresearch/role_runner.py
index 32d37a0c..e6748310 100644
--- a/src/autoresearch/role_runner.py
+++ b/src/autoresearch/role_runner.py
@@ -115,8 +115,9 @@ def build_harness(
     the ephemeral boundary (CI). The tokenless split keeps credentials out of
     the session either way."""
     if backend == "codex":
-        # the web: codex's native web_search tool, on when the spec grants it
-        web = ("--search",) if "WebSearch" in spec.tools else ()
+        # the web, when the spec grants it: the config override, because
+        # `codex exec` does not accept `--search`
+        web = ("-c", "tools.web_search=true") if "WebSearch" in spec.tools else ()
         return CodexHarness(
             api_key=api_key,
             binary=binary or "codex",
diff --git a/tests/test_attempt.py b/tests/test_attempt.py
index abb6fa50..7df5302b 100644
--- a/tests/test_attempt.py
+++ b/tests/test_attempt.py
@@ -1529,7 +1529,12 @@ def test_editor_harness_codex_backend_is_contained() -> None:
     assert harness.model == "gpt-5.6-terra"
     assert harness.timeout_s == 300
     # host codex config, then the web (the author spec grants WebSearch)
-    assert harness.extra_args == ("-c", "use_legacy_landlock=true", "--search")
+    assert harness.extra_args == (
+        "-c",
+        "use_legacy_landlock=true",
+        "-c",
+        "tools.web_search=true",
+    )
     assert harness.supports_resume is True  # codex exec resume, validated on 0.130.0
     with pytest.raises(ValueError, match="unknown backend"):
         build_harness("sk-o", spec, backend="bogus", container_image="img.sif")
diff --git a/tests/test_role_runner.py b/tests/test_role_runner.py
index 35ec7d1a..3546cae1 100644
--- a/tests/test_role_runner.py
+++ b/tests/test_role_runner.py
@@ -201,7 +201,10 @@ def test_build_harness_codex_is_uniform_for_all_roles() -> None:
     assert isinstance(judge, CodexHarness) and isinstance(editor, CodexHarness)
     assert judge.sandbox == editor.sandbox == "danger-full-access"
     assert judge.container_image == "" and editor.container_image == "img.sif"
-    assert "--search" in judge.extra_args and "--search" in editor.extra_args  # the web
+    # the web: the exec-compatible config override, never `--search` (which
+    # `codex exec` rejects — it killed every fleet attempt on 2026-08-29)
+    for h in (judge, editor):
+        assert "tools.web_search=true" in h.extra_args and "--search" not in h.extra_args
 
 
 def test_build_harness_hermes_toolsets_follow_the_spec(tmp_path: Path) -> None: