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  <main>
    <span class="eyebrow">05 · Pattern</span>
    <h1>Result pattern with three issue kinds</h1>
    <p class="lede">
      Validation results carry more than errors. Some issues block, some require user
      acknowledgement, some are pure advisory. Three kinds. Names describe what the UI does, not
      how loud the author wants to scream.
    </p>

    <div class="callout">
      <strong>Note:</strong> the types on this page (<code>Result&lt;T&gt;</code>,
      <code>ValidationIssue</code>) are pedagogical — they describe the <em>principle</em>. For how
      this lands inside the existing <code>ErrorOr</code> + <code>ValidationProblemDetails</code> +
      <code>ApiController&lt;TTokenData&gt;</code> house style, see
      <a href="06-reconciliation.html">06 · Reconciliation</a>.
    </div>

    <h2>The wrong way</h2>
    <p>Logging-flavoured severity enums (<code>Info / Hint / Suggestion / Warning / Error</code>) leak into validation results and create distinctions that no one — devs, admins authoring rules, end users — can pick correctly. "Severity" is the wrong word; it imports baggage from logging where the question is <em>how loud to scream</em>. In validation the question is <em>what does the UI do</em>.</p>

    <h2>The right question</h2>
    <p>Two orthogonal questions describe every possible validation outcome:</p>
    <ol>
      <li><strong>Does it block submission?</strong></li>
      <li><strong>If it blocks, can the user override?</strong></li>
    </ol>
    <p>Three valid combinations. The fourth (doesn't block + overridable) is nonsense.</p>

    <h2>The enum</h2>
<pre><code class="language-csharp">public enum IssueKind
{
    Advisory,     // surface, never blocks
    Confirmable,  // blocks until user acknowledges
    Blocking      // hard fail, no override
}
</code></pre>
    <p>Names describe behavior. No numeric ranking, no severity word.</p>

    <h2>Mapping real cases</h2>
    <table>
      <thead><tr><th>Real-world example</th><th>Kind</th></tr></thead>
      <tbody>
        <tr><td>Customer flagged for compliance review</td><td>Advisory</td></tr>
        <tr><td>Auto-applied default term: 36 months</td><td>Advisory</td></tr>
        <tr><td>Amount exceeds typical limit, confirm to proceed</td><td>Confirmable</td></tr>
        <tr><td>Optional KYC field missing — can submit without</td><td>Confirmable</td></tr>
        <tr><td>Credit score below tenant minimum</td><td>Blocking</td></tr>
        <tr><td>Required field missing or out of range</td><td>Blocking</td></tr>
      </tbody>
    </table>

    <h2>The issue record</h2>
<pre><code class="language-csharp">public sealed record ValidationIssue(
    IssueKind Kind,
    string Code,        // stable, machine-readable, e.g. "Loan.AmountAboveTypical"
    string Message,     // human-readable, optionally localized server-side
    string? Field = null,    // null = form-level / cross-field
    string? Source = null);  // optional audit hint, e.g. "RuleEngine:rule-id-7c2..."
</code></pre>
    <p>Four required fields. <code>Field</code> and <code>Source</code> optional. Resist the urge to add <code>MessageKey</code>, <code>Args</code>, <code>Category</code> until something concrete needs them.</p>

    <h2>The result type</h2>
<pre><code class="language-csharp">public sealed class Result&lt;T&gt;
{
    public bool IsSuccess { get; init; }
    public T? Value { get; init; }
    public IReadOnlyList&lt;ValidationIssue&gt; Issues { get; init; } = Array.Empty&lt;ValidationIssue&gt;();

    public IEnumerable&lt;ValidationIssue&gt; Blocking    =&gt; Issues.Where(i =&gt; i.Kind == IssueKind.Blocking);
    public IEnumerable&lt;ValidationIssue&gt; Confirmable =&gt; Issues.Where(i =&gt; i.Kind == IssueKind.Confirmable);
    public IEnumerable&lt;ValidationIssue&gt; Advisory    =&gt; Issues.Where(i =&gt; i.Kind == IssueKind.Advisory);

    public bool HasBlocking      =&gt; Blocking.Any();
    public bool RequiresAck      =&gt; Confirmable.Any();

    public static Result&lt;T&gt; Ok(T value, params ValidationIssue[] advisories) =&gt;
        new() { IsSuccess = true, Value = value, Issues = advisories };

    public static Result&lt;T&gt; Fail(params ValidationIssue[] issues) =&gt;
        new() { IsSuccess = false, Issues = issues };
}
</code></pre>

    <h2>Acknowledgement protocol</h2>
    <p>The client submits with an optional set of acknowledged issue codes. The strategy treats a confirmable issue as blocking unless its code appears in the set.</p>
<pre><code class="language-csharp">public sealed class SubmitLoanApplicationRequest
{
    public Guid CustomerId { get; init; }
    public decimal Amount { get; init; }
    public int TermMonths { get; init; }
    public string Purpose { get; init; } = "";
    public Dictionary&lt;string, object?&gt; ExtendedFields { get; init; } = new();
    public IReadOnlySet&lt;string&gt;? AcknowledgedIssueCodes { get; init; }
}
</code></pre>
<pre><code class="language-csharp">public async Task&lt;Result&lt;Guid&gt;&gt; ExecuteAsync(
    SubmitLoanApplicationRequest input, CancellationToken ct)
{
    var binding = bindings.Get(FeatureKey)!;
    var issues = (await rules.EvaluateAsync(binding.FlowVersionId, "Submit", input, ct)).Issues;

    var ack = input.AcknowledgedIssueCodes ?? new HashSet&lt;string&gt;();
    var unacknowledged = issues.Where(i =&gt;
        i.Kind == IssueKind.Confirmable &amp;&amp; !ack.Contains(i.Code)).ToList();
    var blocking = issues.Where(i =&gt; i.Kind == IssueKind.Blocking).ToList();

    if (blocking.Count &gt; 0 || unacknowledged.Count &gt; 0)
        return Result&lt;Guid&gt;.Fail([..blocking, ..unacknowledged]);

    var advisories = issues.Where(i =&gt; i.Kind == IssueKind.Advisory).ToArray();
    var application = LoanApplication.Create(/* ... */);
    await repo.AddAsync(application, ct);

    return Result&lt;Guid&gt;.Ok(application.Id, advisories);
}
</code></pre>

    <div class="callout">
      <strong>Critical:</strong> never trust the acknowledgement set to <em>skip</em> evaluation.
      Server always re-runs all rules. The ack list only changes whether a confirmable issue counts
      as blocking. If a stale client sends an ack for a code the server no longer produces, the ack
      is ignored.
    </div>

    <h2>HTTP mapping</h2>
    <table>
      <thead><tr><th>Case</th><th>Status</th><th>Body</th></tr></thead>
      <tbody>
        <tr><td>Shape validation fail (FluentValidation)</td><td>400</td><td>RFC 7807 problem details</td></tr>
        <tr><td>Success, no issues</td><td>200 / 201</td><td><code>{ data, issues: [] }</code></td></tr>
        <tr><td>Success with advisories</td><td>200 / 201</td><td><code>{ data, issues: [advisories] }</code></td></tr>
        <tr><td>Confirmable issues, unacknowledged</td><td>409 Conflict</td><td><code>{ issues, requiresAcknowledgement: true }</code></td></tr>
        <tr><td>Blocking issues</td><td>422 Unprocessable Entity</td><td><code>{ issues }</code></td></tr>
      </tbody>
    </table>
    <p>409 is chosen so clients can reliably branch: <em>"open acknowledgement modal, resubmit with ack codes"</em>. 422 means "fix the data". 200 means "we're done; here are some things to note".</p>

    <h2>Two-phase validation (recommended)</h2>
    <div class="mermaid">
graph LR
    A[Client edits form] --&gt; B[POST /api/.../validate]
    B --&gt; C[Server runs full pipeline]
    C --&gt; D[Returns issues, no persist]
    D --&gt; E{Any blocking?}
    E --&gt;|yes| F[Show errors inline]
    E --&gt;|no, has confirmable| G[Show confirm modal]
    E --&gt;|no, advisory only| H[Show banner notes]
    G --&gt;|user confirms| I[POST /api/... with ack codes]
    F --&gt;|user fixes| A
    H --&gt; I
    I --&gt; J[Server persists]
    </div>
    <ul>
      <li><code>POST /api/&lt;feature&gt;/validate</code> — full pipeline, never persists, returns <code>Result&lt;T&gt;</code> with <code>Value</code> null.</li>
      <li><code>POST /api/&lt;feature&gt;</code> — persists if <code>!HasBlocking</code> and all confirmable codes are acknowledged.</li>
    </ul>

    <h2>Controller mapping helper</h2>
<pre><code class="language-csharp">public static class ResultExtensions
{
    public static IActionResult ToActionResult&lt;T&gt;(
        this Result&lt;T&gt; result,
        ControllerBase controller,
        Func&lt;T, IActionResult&gt; onSuccess)
    {
        if (result.IsSuccess)
            return onSuccess(result.Value!);

        if (result.HasBlocking)
            return controller.UnprocessableEntity(new
            {
                issues = result.Issues.Select(Format)
            });

        // Only confirmable issues outstanding
        return controller.Conflict(new
        {
            requiresAcknowledgement = true,
            issues = result.Issues.Select(Format)
        });
    }

    private static object Format(ValidationIssue i) =&gt; new
    {
        kind = i.Kind.ToString(),
        code = i.Code,
        message = i.Message,
        field = i.Field
    };
}
</code></pre>

    <h2>Rule engine wiring</h2>
    <p>The <code>RULE</code> table drops the integer <code>Severity</code> column in favour of a <code>Kind</code> column storing <code>"Advisory"</code>, <code>"Confirmable"</code>, or <code>"Blocking"</code>.</p>
<pre><code class="language-json">{
  "id": "amount-above-typical",
  "field": "Amount",
  "operator": "lte",
  "value": 1000000,
  "kind": "Confirmable",
  "code": "Loan.AmountAboveTypical",
  "message": "Amount exceeds typical range — please confirm"
}
</code></pre>
    <p>Admin UI rule editor exposes a <em>Kind</em> dropdown with three options. No numeric severity, no separate "bypassable" checkbox.</p>

    <h2>Per-tenant kind overrides</h2>
    <p>Same rule, Tenant A treats as <code>Confirmable</code>, Tenant B treats as <code>Blocking</code>. Two options:</p>
    <ol>
      <li>Duplicate the rule under Tenant B's flow version with a different <code>Kind</code>. Costs storage; trivially auditable.</li>
      <li>Add a <code>RULE_KIND_OVERRIDE</code> table keyed by <code>(FlowVersionId, RuleId) → Kind</code>. Saves duplication; one more join.</li>
    </ol>
    <p>Prefer (1) until duplication actually hurts. Flow versions are already the unit of variation — leaning on them keeps the model simple.</p>

    <h2>Audit</h2>
    <p>Every persisted submission stores the acknowledged issue codes at the moment of submission. If a confirmable rule's wording changes later, the audit trail still shows what the user agreed to.</p>

    <h2>What we deliberately left out</h2>
    <table>
      <thead><tr><th>Field</th><th>Why omitted</th></tr></thead>
      <tbody>
        <tr><td><code>MessageKey</code> / <code>Args</code> for i18n</td><td>Localize server-side or with an i18n catalog keyed on <code>Code</code>. Don't pollute the wire format until a real i18n requirement lands.</td></tr>
        <tr><td><code>Category</code></td><td><code>Code</code>'s prefix already groups (<code>Loan.X</code>, <code>Compliance.Y</code>). Don't add a second taxonomy.</td></tr>
        <tr><td>Priority / display order</td><td>UI sorts by <code>Kind</code> then <code>Field</code> then declaration order. Sufficient.</td></tr>
        <tr><td><code>Importance</code> orthogonal axis</td><td>Speculative. Add only when a real screen needs it.</td></tr>
      </tbody>
    </table>

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