Clarify Security Harness fallback defaults

README.md

@@ -283,7 +283,7 @@ effort = ""   # the Model's variant, passed as #effort; default blank, for OpenC
 [security]
 fix = false   # Security runs may fix reproduced findings; default false
 review = false   # Runs review their change for Security findings; default false
-harness = ""   # the Harness a Security run uses unless its command names one; default blank, for harness.default or Claude Code
+harness = ""   # the Harness a Security run uses unless its command names one; default blank; blank or missing uses harness.default, or Claude Code if harness.default is missing
 ```
 
 Every key holds its real value, so a Run reading it does exactly what it does with no file. `email.to` has no default, so `setup` suggests one: the public email of your GitHub profile (from `gh api user`), else your global git `user.email`, unless that is a `@users.noreply.github.com` address, which can't receive mail. With neither, `email.to` is the only line written commented out, as above. `setup` never asks `gh` for more scopes, so a private GitHub email is not read, and a Run never looks the suggestion up: `--email` with no address and no `email.to` still stops the Run. From a terminal (stdin and stderr both terminals), `setup` first asks, on stderr:
@@ -762,7 +762,7 @@ A failed fix keeps its **Claim**, even if it pushed nothing, and stays open for
 
 `email`, optionally followed by an address, or `email.always` in the User config asks for one **Run notification** when the Security run ends, whether the audit succeeded, failed or was interrupted. `no-email` overrides the default. The notification says how the audit ended and lists each finding it recorded or matched to an existing private record: its severity when known, title and private link. It includes no finding write-up, trace or evidence, since it passes through Resend. Detailed failure causes stay in the local logs; the notification gives the audit's status and log paths. A recording failure still lists the records reached before it failed. When a run leaves a reproduced finding unfixed and neither the command nor the User config decided against fixing, its notification and stderr offer both `thirdshift secure security-fix` and `fix = true` under `[security]`. With `no-security-fix`, or the setting turned off, it offers nothing. A skipped Security run sends none. The usual address and Resend API key checks run before the skip checks or any work; a failed send is a warning and never changes the run's outcome.
 
-A Security run chooses its Harness from the command's `harness` word, then `[security] harness` in the User config, then `harness.default`, then Claude Code. A blank or missing Security setting keeps that default. Model and Effort come from the chosen Harness's own `[harness.<name>]` section, with command words taking precedence. For example, `harness claude` overrides `[security] harness = "codex"` and uses `[harness.claude]`.
+A Security run chooses its Harness from the command's `harness` word, then `[security] harness` in the User config, then `harness.default`, then Claude Code. When `security.harness` is blank or missing, it uses `harness.default`; when `harness.default` is also missing, it uses Claude Code. Model and Effort come from the chosen Harness's own `[harness.<name>]` section, with command words taking precedence. For example, `harness claude` overrides `[security] harness = "codex"` and uses `[harness.claude]`.
 
 Codex security sessions and their Resumes set `agents.max_concurrent_threads_per_session=8` and ask for fresh sub-agents with `fork_turns: "none"`, so the skill's verifiers stay independent.
 

src/config.rs

@@ -771,7 +771,7 @@ effort = ""   # the Model's variant, passed as #effort; default blank, for OpenC
 [security]
 fix = false   # Security runs may fix reproduced findings; default false
 review = false   # Runs review their change for Security findings; default false
-harness = ""   # the Harness a Security run uses unless its command names one; default blank, for harness.default or Claude Code
+harness = ""   # the Harness a Security run uses unless its command names one; default blank; blank or missing uses harness.default, or Claude Code if harness.default is missing
 "#;
 
 /// The line `DEFAULTS` holds for `email.to`, which has no default.

tests/security_run.rs

@@ -1897,14 +1897,15 @@ fn a_blank_or_missing_security_harness_preserves_the_default_harness_and_its_set
             args.windows(2)
                 .any(|pair| pair == [json!("-c"), json!("model_reasoning_effort=\"high\"")])
         );
+
+        let scenario = Scenario::new();
+        scenario.user_config_is(security);
+        scenario.agent_does(&audit_script("[]"));
+        let result = scenario.run(&["secure"]);
+        assert_eq!(result.code, Some(0), "{security}: {}", result.stderr);
+        assert_eq!(scenario.claude_calls().len(), 1, "{security}");
+        assert!(scenario.codex_calls().is_empty(), "{security}");
     }
-    let scenario = Scenario::new();
-    scenario.user_config_is("[security]\nharness = \"\"\n");
-    scenario.agent_does(&audit_script("[]"));
-    let result = scenario.run(&["secure"]);
-    assert_eq!(result.code, Some(0), "{}", result.stderr);
-    assert_eq!(scenario.claude_calls().len(), 1);
-    assert!(scenario.codex_calls().is_empty());
 }
 
 #[test]

tests/setup.rs

@@ -371,7 +371,12 @@ fn setup_asks_once_about_security_fixing_with_off_as_the_default_and_writes_yes(
     let config: toml::Table = text.parse().unwrap();
     assert_eq!(config["security"]["fix"].as_bool(), Some(true));
     assert_eq!(config["security"]["harness"].as_str(), Some(""));
-    assert!(text.contains("# the Harness a Security run uses unless its command names one"));
+    assert!(
+        text.contains(
+            "# the Harness a Security run uses unless its command names one; default blank; blank or missing uses harness.default, or Claude Code if harness.default is missing"
+        ),
+        "{text}"
+    );
 }
 
 #[test]