harden(server): explicit verify-commit success gate + non-member/genesis hook tests

- verify_org_signer now rejects on a non-zero git verify-commit exit instead of
  relying on the stderr fingerprint regex alone (PM hardening note 1).
- org_hook_signed: add commit_signed_by_non_member_is_rejected (exercises the
  signature rejection path) and genesis_bootstrap_with_sole_owner_is_accepted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/relicario-server/tests/org_hook_signed.rs

@@ -150,3 +150,80 @@ fn owner_promoting_an_admin_is_accepted() {
         .assert()
         .success();
 }
+
+#[test]
+fn commit_signed_by_non_member_is_rejected() {
+    // A commit signed by a key that is NOT in members.json must be rejected:
+    // verify_org_signer rebuilds allowed_signers from the current members only,
+    // so a non-member signature fails `git verify-commit`.
+    let (tmp, _owner_priv, _admin_priv, allowed) = bootstrap();
+    let repo = tmp.path();
+
+    // A stranger key, never registered as a member.
+    let (stranger_priv, _stranger_pub) = write_keypair(repo, "stranger");
+
+    // Stranger signs a commit touching an UNRESTRICTED file (members.json stays
+    // owner+admin, so allowed_signers excludes the stranger).
+    fs::write(repo.join("manifest.enc"), b"\x02ciphertext").unwrap();
+    git(repo, &["add", "manifest.enc"]);
+    let status = Command::new("git")
+        .current_dir(repo)
+        .args([
+            "-c", "gpg.format=ssh",
+            "-c", &format!("user.signingkey={}", stranger_priv.display()),
+            "-c", &format!("gpg.ssh.allowedSignersFile={}", allowed.display()),
+            "commit", "-S", "-q", "-m", "stranger-write",
+        ])
+        .status()
+        .unwrap();
+    assert!(status.success());
+    let out = Command::new("git")
+        .current_dir(repo)
+        .args(["rev-parse", "HEAD"])
+        .output()
+        .unwrap();
+    let sha = String::from_utf8(out.stdout).unwrap().trim().to_string();
+
+    AssertCommand::cargo_bin("relicario-server")
+        .unwrap()
+        .current_dir(repo)
+        .args(["verify-org-commit", &sha])
+        .assert()
+        .failure()
+        .stderr(predicate::str::contains("REJECT"));
+}
+
+#[test]
+fn genesis_bootstrap_with_sole_owner_is_accepted() {
+    // A root (parent-less) commit registering the sole owner, signed by that
+    // owner, is the genesis bootstrap and must be accepted.
+    let tmp = TempDir::new().unwrap();
+    let repo = tmp.path();
+    git(repo, &["init", "-q", "-b", "main"]);
+    git(repo, &["config", "user.email", "t@t"]);
+    git(repo, &["config", "user.name", "t"]);
+
+    let (owner_priv, owner_pub) = write_keypair(repo, "owner");
+    let allowed = repo.join("allowed_signers");
+    fs::write(&allowed, format!("relicario {}\n", owner_pub.trim())).unwrap();
+
+    let sole_owner = format!(
+        r#"{{
+  "schema_version": 1,
+  "members": [
+    {{ "member_id": "1111111111111111", "display_name": "Owner", "role": "owner",
+       "ed25519_pubkey": "{}", "collections": [], "added_at": 0, "added_by": "1111111111111111" }}
+  ]
+}}"#,
+        owner_pub.trim()
+    );
+    // First commit in a fresh repo → root (is_root == true).
+    let sha = signed_members_commit(repo, &owner_priv, &allowed, "org-init", &sole_owner);
+
+    AssertCommand::cargo_bin("relicario-server")
+        .unwrap()
+        .current_dir(repo)
+        .args(["verify-org-commit", &sha])
+        .assert()
+        .success();
+}