fix(2): mattermost functional tests share a deterministic admin bootstrap (_mm.bootstrap_admin) — only ONE unauthenticated first-user creation is allowed, so the multi-user test no longer collides with create_message

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/mattermost-lts/functional/_mm.py

@@ -0,0 +1,47 @@
+"""Shared mattermost-lts test helpers.
+
+mattermost lets the FIRST user be created unauthenticated (and makes them system admin); after that,
+open signups are disabled (`api.user.create_user.no_open_server`). Several functional tests share one
+per-run deployment (the custom tier), so they cannot each create "the first user." Instead they all
+bootstrap ONE deterministic admin: whichever test runs first creates it (201, as the first user); the
+rest log in as the same admin. Subsequent (non-first) users are created via the admin token, which
+works regardless of the open-signup setting.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "..", "runner"))
+from harness import http as harness_http  # noqa: E402
+
+ADMIN_EMAIL = "ccci-admin@ccci.example.com"
+ADMIN_USERNAME = "ccciadmin"
+ADMIN_PW = "Ccci-Test-Pw-2026!"
+
+
+def bearer(token: str) -> dict[str, str]:
+    return {"Authorization": f"Bearer {token}"}
+
+
+def bootstrap_admin(base: str) -> str:
+    """Return a system-admin session token for the shared deployment.
+
+    Create the deterministic admin as the first user if the server is fresh (201); otherwise it
+    already exists (400/403) — log in as it. Either way we end with a valid admin token. RAISES if
+    neither create nor login yields a usable session (a genuinely broken auth path)."""
+    # Try to create the first user (unauthenticated; only succeeds on a fresh server).
+    harness_http.http_post(
+        f"{base}/users",
+        data={"email": ADMIN_EMAIL, "username": ADMIN_USERNAME, "password": ADMIN_PW},
+        timeout=30,
+    )
+    # Whether or not creation succeeded (it 4xxs if the admin already exists / signups closed), log in.
+    status, _, hdrs = harness_http.post_with_headers(
+        f"{base}/users/login", data={"login_id": ADMIN_EMAIL, "password": ADMIN_PW}, timeout=30
+    )
+    assert status == 200, f"admin login failed: HTTP {status}"
+    token = hdrs.get("Token") or hdrs.get("token")
+    assert token, f"admin login returned no Token header; headers={list(hdrs.keys())}"
+    return token