Add computeTrustTier pure function with full test coverage

Tier 1 = default, Tier 2 = 5+ successes (0 malicious),
Tier 3 = 20+ successes (0 malicious). Any malicious forces Tier 1,
banned identities stay Tier 1. Failed resolutions are neutral.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

src/reputation.ts

@@ -1,5 +1,23 @@
-import type { IdentityStats } from "./types";
+import type { IdentityStats, ResolveOutcome } from "./types";
 
 export function scoreIdentity(stats: IdentityStats): number {
   return stats.locks * 2 + stats.actions * 3 + stats.successes * 10 - stats.failures * 5 - stats.malicious * 20;
 }
+
+export type TrustTier = 1 | 2 | 3;
+
+export function computeTrustTier(
+  history: ResolveOutcome[],
+  banned: boolean = false,
+): TrustTier {
+  if (banned) return 1;
+
+  const hasMalicious = history.some((h) => h === "malicious");
+  if (hasMalicious) return 1;
+
+  const successes = history.filter((h) => h === "success").length;
+
+  if (successes >= 20) return 3;
+  if (successes >= 5) return 2;
+  return 1;
+}

test/reputation.test.ts

@@ -0,0 +1,41 @@
+import { describe, it, expect } from "vitest";
+import { computeTrustTier } from "../src/reputation";
+import type { ResolveOutcome } from "../src/types";
+
+function makeHistory(successes: number, failed: number = 0, malicious: number = 0): ResolveOutcome[] {
+  return [
+    ...Array<ResolveOutcome>(successes).fill("success"),
+    ...Array<ResolveOutcome>(failed).fill("failed"),
+    ...Array<ResolveOutcome>(malicious).fill("malicious"),
+  ];
+}
+
+describe("computeTrustTier", () => {
+  it("new identity (empty history) returns Tier 1", () => {
+    expect(computeTrustTier([])).toBe(1);
+  });
+
+  it("identity with 0 successes returns Tier 1", () => {
+    expect(computeTrustTier(makeHistory(0, 3))).toBe(1);
+  });
+
+  it("identity with 4 successes returns Tier 1 (just under threshold)", () => {
+    expect(computeTrustTier(makeHistory(4))).toBe(1);
+  });
+
+  it("identity with 5 successes returns Tier 2", () => {
+    expect(computeTrustTier(makeHistory(5))).toBe(2);
+  });
+
+  it("identity with 20 successes returns Tier 3", () => {
+    expect(computeTrustTier(makeHistory(20))).toBe(3);
+  });
+
+  it("identity with 25 successes and 1 malicious returns Tier 1", () => {
+    expect(computeTrustTier(makeHistory(25, 0, 1))).toBe(1);
+  });
+
+  it("banned identity stays Tier 1 regardless of successes", () => {
+    expect(computeTrustTier(makeHistory(30), true)).toBe(1);
+  });
+});