Honor fanout follower schema minimum

Fanout validation now relies on the scenario schema's followers minimum
instead of imposing an extra five-follower floor. This keeps runner preflight
consistent with accepted suite configuration.

#802 (comment)

Assisted-by: Codex:gpt-5.5

Author: dahlia

packages/cli/src/bench/scenarios/fanout.test.ts

@@ -65,18 +65,18 @@ test("fanoutRunner - triggers benchmark hook and reports drain", async () => {
   assert.strictEqual(triggerRecipients, 5);
 });
 
-test("fanoutRunner.validate - requires enough followers for fanout queue", () => {
+test("fanoutRunner.validate - accepts schema-minimum follower count", () => {
   const scenario = normalizeSuite({
     version: 1,
     target: "http://target.test/",
     scenarios: [{
       name: "fanout",
       type: "fanout",
       sender: "alice",
-      followers: 4,
+      followers: 1,
     }],
   }).scenarios[0];
-  assert.throws(() => fanoutRunner.validate?.(scenario), /at least 5/);
+  assert.doesNotThrow(() => fanoutRunner.validate?.(scenario));
 });
 
 test("fanoutRunner.validate - rejects invalid sinkBase URLs", () => {

packages/cli/src/bench/scenarios/fanout.ts

@@ -38,12 +38,6 @@ export const fanoutRunner: ScenarioRunner = {
           `trigger.kind: "benchmark-hook".`,
       );
     }
-    if ((scenario.followers ?? DEFAULT_FOLLOWERS) < 5) {
-      throw new Error(
-        `Scenario "${scenario.name}": fanout needs at least 5 followers to ` +
-          "exercise Fedify's fanout queue.",
-      );
-    }
     resolveSinkBase(scenario.name, scenario.raw.sinkBase);
   },