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    <header>
      <div class="tag">announcement &nbsp;·&nbsp; v2.0.2 &nbsp;·&nbsp; <a href="https://github.com/cassian-gate/cassian-gate/releases/tag/v2.0.2">release notes</a></div>
      <h1>Cassian Gate v2 — a deterministic validation gate for network changes</h1>
      <p><strong>Update:</strong> Use <strong>v2.0.2 or later</strong>. Versions v2.0.0 and v2.0.1 were published before the Apache 2.0 repository license file and package license metadata were added. v2.0.2 is the correctly licensed public release.</p>
      <p class="lede">
        The hardest network failures are not the ones you missed in config review. They are the ones config review could not have caught.
      </p>
    </header>

    <section>
      <p>A configuration can be internally consistent and still be operationally wrong. A failover path can look fine on paper and still converge incorrectly. A route policy can appear correct and still leak or suppress something under real protocol interaction. By the time monitoring tells you there is a problem, you are already in production.</p>

      <p>That is the gap Cassian Gate is built to close.</p>

      <p>Cassian Gate v2 is the first public release line. It is a deterministic, execution-backed validation gate for network changes. It sits between <em>change proposed</em> and <em>change deployed</em>. You declare a topology and the tests and scenarios you care about. Cassian Gate runs them in a controlled environment and returns a binary PASS or FAIL verdict with authoritative artifacts.</p>

      <p class="muted">It is not a static config analysis tool. It is not a monitoring system. It is not an AI system deciding whether your change is safe. It is an execution-backed proof gate.</p>
    </section>

    <section>
      <h2>The problem</h2>
      <p>Network change review still depends heavily on some combination of config review, intent review, peer experience, maintenance-window caution, and post-change monitoring. All of these matter. None of them are the same as proving actual behavior before production.</p>
      <p>Cassian Gate is built for the question those methods cannot fully answer:</p>
      <p class="emphasis">Should this change proceed?</p>
    </section>

    <section>
      <h2>What Cassian Gate does</h2>
      <p>You give Cassian Gate a topology, the tests you want to run, and the scenarios you want to exercise (failovers, link outages, grey failures, policy changes). Cassian Gate then:</p>
      <ul class="plain">
        <li><strong>Builds the declared environment</strong> using containerlab.</li>
        <li><strong>Provisions it deterministically</strong> — interfaces, addressing, routing, convergence.</li>
        <li><strong>Runs the tests and scenarios</strong> you declared.</li>
        <li><strong>Records expected, observed, verdict, and evidence</strong> for each assertion.</li>
        <li><strong>Writes authoritative artifacts</strong> — <code>results.json</code>, <code>topology.resolved.yaml</code>, <code>results.summary.txt</code>.</li>
        <li><strong>Exits cleanly for CI</strong> with a binary PASS or FAIL.</li>
      </ul>
      <p>The goal is not interesting simulation. It is explicit pre-deployment proof.</p>
    </section>

    <section>
      <h2>Example run</h2>
      <div class="output"><span class="dim">$ cassian test topologies/first-run-proof-minimal.yaml</span>

<span class="label">[lifecycle]</span> resolve     <span class="pass">ok</span>
<span class="label">[lifecycle]</span> generate    <span class="pass">ok</span>
<span class="label">[lifecycle]</span> deploy      <span class="pass">ok</span>   (containerlab, 4 nodes)
<span class="label">[lifecycle]</span> provision   <span class="pass">ok</span>   (interfaces, addressing, BGP, convergence)

<span class="label">[tests]</span>
  ping  h1 -> h2                             <span class="pass">PASS</span>
  tcp   h1 -> h2:8080                        <span class="pass">PASS</span>
  invariant  bgp_session_up r1<->r2          <span class="pass">PASS</span>
  invariant  route_present 10.0.2.0/24 on r1 <span class="pass">PASS</span>

<span class="label">[scenarios]</span>
  primary-path-failover                      <span class="pass">PASS</span>
    link_down r1<->r2
    wait_for  bgp_session_up r1<->r3         <span class="pass">converged</span>
    ping      h1 -> h2                       <span class="pass">PASS</span>
    link_up   r1<->r2

<span class="pass">RESULT: PASS</span>  (4 tests, 1 scenario, 0 failures)
<span class="dim">exit 0</span></div>
      <p class="caption">That output is a UI for humans. The authoritative artifact is <code>results.json</code> — machine-consumable, schema-versioned, and the only thing a CI job should trust for its verdict.</p>
    </section>

    <section>
      <h2>What it is</h2>
      <ul class="plain">
        <li><strong>Execution-backed.</strong> Cassian Gate validates behavior by running the declared environment and checking what actually happens. Not config text analysis. Not intent graph reasoning.</li>
        <li><strong>Deterministic.</strong> Same topology, same commit, same verdict. The gate is reproducible from its own artifacts via <code>cassian replay</code>.</li>
        <li><strong>CI-safe.</strong> Clean-state execution, clean exit codes, authoritative artifacts. Drops into GitHub Actions or GitLab CI as a single job.</li>
        <li><strong>Narrow.</strong> Cassian Gate v2 validates FRR-based topologies. That means FRR as the routing NOS, plus host and firewall (nftables) nodes. SONiC support is in progress. Arista cEOS support is planned next.</li>
      </ul>
    </section>

    <section>
      <h2>What it is not</h2>
      <div class="scope">
        <p>Cassian Gate does not give you a confidence score, a heuristic safety estimate, or an AI-generated guess. The gate either passes or it does not.</p>
        <p>Cassian Gate does not auto-remediate, does not replace monitoring, does not run against live infrastructure, and does not claim feature-parity NOS simulation.</p>
        <p>AI is advisory only — it can explain results or summarize evidence, but AI does not decide pass/fail, alter artifacts, or change execution meaning. That separation is not negotiable.</p>
      </div>
      <p class="muted">The narrowness is deliberate. Trust comes from explicit scope and deterministic behavior, not from overclaiming.</p>
    </section>

    <section>
      <h2>How to try it</h2>
      <p>Install:</p>
      <pre>pipx install cassian-gate</pre>
      <p>Run the proof kit:</p>
      <pre>git clone https://github.com/cassian-gate/cassian-gate.git
cd cassian-gate
cassian doctor
cassian test topologies/first-run-proof-minimal.yaml</pre>
      <p class="muted">First run pulls container images (about 500 MB) and may take several minutes. Subsequent runs complete in under a minute on the proof topologies.</p>
      <p>To see the gate catch a real failure — a change that looks fine but breaks behavior:</p>
      <pre>cassian test topologies/first-run-proof-fail-catching.yaml</pre>
      <p class="muted">That topology is designed to reach a FAIL verdict and produce a clear artifact showing what was caught and why.</p>
    </section>

    <section>
      <h2>What's next</h2>
      <p>v2 is the foundation. The next work is visible and committed:</p>
      <ul class="plain">
        <li><strong>SONiC support</strong> — second NOS. In progress.</li>
        <li><strong>Arista cEOS support</strong> — planned next, with paid commercial delivery.</li>
        <li><strong>Deepening the FRR surface</strong> — additional invariants (OSPF, interface state, BGP policy), richer state capture, user-defined invariants.</li>
        <li><strong>Proof surface improvements</strong> — better invariant failure output, test tags, topology composition.</li>
      </ul>
      <p class="muted">The expansion path is deliberate and documented. What the community shapes is the edges — which invariants matter most, where onboarding breaks, what proof recipes convert.</p>
    </section>

    <section>
      <h2>Try it and tell us what happened</h2>
      <p>If you try Cassian Gate, the most valuable thing you can do is tell us what happened — especially if something confused you, broke, or was missing.</p>
      <ul class="discussion">
        <li><a href="https://cassiangate.dev">→ cassiangate.dev</a></li>
        <li><a href="https://github.com/cassian-gate/cassian-gate">→ github.com/cassian-gate/cassian-gate</a></li>
        <li><a href="https://github.com/cassian-gate/cassian-gate/releases/tag/v2.0.2">→ v2.0.2 release notes</a></li>
        <li><a href="https://github.com/cassian-gate/cassian-gate/discussions">→ discussions</a></li>
        <li><a href="https://github.com/cassian-gate/cassian-gate/blob/main/topologies/first-run-proof-minimal.yaml">→ proof kit (passing)</a></li>
        <li><a href="https://github.com/cassian-gate/cassian-gate/blob/main/topologies/first-run-proof-fail-catching.yaml">→ proof kit (fail-catching)</a></li>
      </ul>
      <p class="muted">Friction reports, missing invariants, topology authoring pain, and "the docs did not explain X" are all valuable. If you run Cassian Gate in CI against a real change and it catches something, that is the kind of signal that shapes what gets built next.</p>
    </section>

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