Pace candidate funnel to send capacity

tests/main-loop.test.ts

@@ -1,5 +1,9 @@
 import { describe, expect, it, vi } from 'vitest';
-import { currentHourlySendCount, startNonOverlappingSchedule } from '../src/main-loop.js';
+import {
+  calculateCandidateFunnelTarget,
+  currentHourlySendCount,
+  startNonOverlappingSchedule,
+} from '../src/main-loop.js';
 
 describe('startNonOverlappingSchedule', () => {
   it('does not begin a second response check until the prior check settles', async () => {
@@ -43,3 +47,29 @@ describe('currentHourlySendCount', () => {
     expect(currentHourlySendCount({ getStats: () => ({ messagesThisHour: 1 }) })).toBe(1);
   });
 });
+
+describe('calculateCandidateFunnelTarget', () => {
+  it('tracks remaining outbound capacity instead of growing to a fixed backlog', () => {
+    expect(calculateCandidateFunnelTarget(
+      [{ messagesRemaining: 3 }, { messagesRemaining: 5 }],
+      { maxReadyCandidates: 25, recentWindowMinutes: 60, minDelayBetweenMessagesMs: 300_000 },
+    )).toBe(8);
+  });
+
+  it('retains the configured ceiling and caps capacity by the freshness window', () => {
+    expect(calculateCandidateFunnelTarget(
+      [{ messagesRemaining: 100 }, { messagesRemaining: 100 }],
+      { maxReadyCandidates: 25, recentWindowMinutes: 30, minDelayBetweenMessagesMs: 300_000 },
+    )).toBe(12);
+  });
+
+  it('stops growing inventory when no running account can send', () => {
+    const options = {
+      maxReadyCandidates: 25,
+      recentWindowMinutes: 60,
+      minDelayBetweenMessagesMs: 300_000,
+    };
+    expect(calculateCandidateFunnelTarget([], options)).toBe(0);
+    expect(calculateCandidateFunnelTarget([{ messagesRemaining: 0 }], options)).toBe(0);
+  });
+});