feat(taskbuffer): add sliding-window rate limiting and result-sharing to TaskConstraintGroup and integrate with TaskManager

changelog.md

@@ -1,5 +1,17 @@
 # Changelog
 
+## 2026-02-15 - 6.1.0 - feat(taskbuffer)
+add sliding-window rate limiting and result-sharing to TaskConstraintGroup and integrate with TaskManager
+
+- Added IRateLimitConfig and TResultSharingMode types and exported them from the public index
+- TaskConstraintGroup: added rateLimit and resultSharingMode options, internal completion timestamp tracking, and last-result storage
+- TaskConstraintGroup: new helpers - pruneCompletionTimestamps, getRateLimitDelay, getNextAvailableDelay, recordResult, getLastResult, hasResultSharing
+- TaskConstraintGroup: rate-limit logic enforces maxPerWindow (counts running + completions) and composes with cooldown/maxConcurrent
+- TaskManager: records successful task results to constraint groups and resolves queued entries immediately when a shared result exists
+- TaskManager: queue drain now considers unified next-available delay (cooldown + rate limit) when scheduling retries
+- Documentation updated: README and hints with usage examples for sliding-window rate limiting and result sharing
+- Comprehensive tests added for rate limiting, concurrency interaction, and result-sharing behavior
+
 ## 2026-02-15 - 6.0.1 - fix(taskbuffer)
 no changes to commit
 

readme.hints.md

@@ -12,14 +12,31 @@
 - Typed data bag accessible as `task.data`
 
 ### TaskConstraintGroup
-- `new TaskConstraintGroup<TData>({ name, constraintKeyForExecution, maxConcurrent?, cooldownMs?, shouldExecute? })`
+- `new TaskConstraintGroup<TData>({ name, constraintKeyForExecution, maxConcurrent?, cooldownMs?, shouldExecute?, rateLimit?, resultSharingMode? })`
 - `constraintKeyForExecution(task, input?)` returns a string key (constraint applies) or `null` (skip). Receives both task and runtime input.
 - `shouldExecute(task, input?)` — optional pre-execution check. Returns `false` to skip (deferred resolves `undefined`). Can be async.
 - `maxConcurrent` (default: `Infinity`) — max concurrent tasks per key
 - `cooldownMs` (default: `0`) — minimum ms gap between completions per key
-- Methods: `getConstraintKey(task, input?)`, `checkShouldExecute(task, input?)`, `canRun(key)`, `acquireSlot(key)`, `releaseSlot(key)`, `getCooldownRemaining(key)`, `getRunningCount(key)`, `reset()`
+- `rateLimit` (optional) — `{ maxPerWindow: number, windowMs: number }` sliding window rate limiter. Counts both running + completed tasks in window.
+- `resultSharingMode` (default: `'none'`) — `'none'` | `'share-latest'`. When `'share-latest'`, queued tasks for the same key resolve with the first task's result without executing.
+- Methods: `getConstraintKey(task, input?)`, `checkShouldExecute(task, input?)`, `canRun(key)`, `acquireSlot(key)`, `releaseSlot(key)`, `getCooldownRemaining(key)`, `getRateLimitDelay(key)`, `getNextAvailableDelay(key)`, `getRunningCount(key)`, `recordResult(key, result)`, `getLastResult(key)`, `hasResultSharing()`, `reset()`
 - `ITaskExecution<TData>` type exported from index — `{ task, input }` tuple
 
+### Rate Limiting (v6.1.0+)
+- Sliding window rate limiter: `rateLimit: { maxPerWindow: N, windowMs: ms }`
+- Counts running + completed tasks against the window cap
+- Per-key independence: saturating key A doesn't block key B
+- Composable with `maxConcurrent` and `cooldownMs`
+- `getNextAvailableDelay(key)` returns `Math.max(cooldownRemaining, rateLimitDelay)` — unified "how long until I can run" answer
+- Drain timer auto-schedules based on shortest delay across all constraints
+
+### Result Sharing (v6.1.0+)
+- `resultSharingMode: 'share-latest'` — queued tasks for the same key get the first task's result without executing
+- Only successful results are shared (errors from `catchErrors: true` or thrown errors are NOT shared)
+- `shouldExecute` is NOT called for shared results (the task's purpose was already fulfilled)
+- `lastResults` persists until `reset()` — for time-bounded sharing, use `shouldExecute` to control staleness
+- Composable with rate limiting: rate-limited waiters get shared result without waiting for the window
+
 ### TaskManager Constraint Integration
 - `manager.addConstraintGroup(group)` / `manager.removeConstraintGroup(name)`
 - `triggerTaskByName()`, `triggerTask()`, `addExecuteRemoveTask()`, cron callbacks all route through `triggerTaskConstrained()`
@@ -28,7 +45,7 @@
 
 ### Exported from index.ts
 - `TaskConstraintGroup` class
-- `ITaskConstraintGroupOptions` type
+- `ITaskConstraintGroupOptions`, `IRateLimitConfig`, `TResultSharingMode` types
 
 ## Error Handling (v3.6.0+)
 - `Task` now has `catchErrors` constructor option (default: `false`)

readme.md

@@ -13,7 +13,7 @@ For reporting bugs, issues, or security vulnerabilities, please visit [community
 ## 🌟 Features
 
 - **🎯 Type-Safe Task Management** — Full TypeScript support with generics and type inference
-- **🔒 Constraint-Based Concurrency** — Per-key mutual exclusion, group concurrency limits, and cooldown enforcement via `TaskConstraintGroup`
+- **🔒 Constraint-Based Concurrency** — Per-key mutual exclusion, group concurrency limits, cooldown enforcement, sliding-window rate limiting, and result sharing via `TaskConstraintGroup`
 - **📊 Real-Time Progress Tracking** — Step-based progress with percentage weights
 - **⚡ Smart Buffering** — Intelligent request debouncing and batching
 - **⏰ Cron Scheduling** — Schedule tasks with cron expressions
@@ -311,6 +311,105 @@ const [cert1, cert2, cert3] = await Promise.all([r1, r2, r3]);
 - Has closure access to external state modified by prior executions
 - If multiple constraint groups have `shouldExecute`, **all** must return `true`
 
+### Sliding Window Rate Limiting
+
+Enforce "N completions per time window" with burst capability. Unlike `cooldownMs` (which forces even spacing between executions), `rateLimit` allows bursts up to the cap, then blocks until the window slides:
+
+```typescript
+// Let's Encrypt style: 300 new orders per 3 hours
+const acmeRateLimit = new TaskConstraintGroup({
+  name: 'acme-rate',
+  constraintKeyForExecution: () => 'acme-account',
+  rateLimit: {
+    maxPerWindow: 300,
+    windowMs: 3 * 60 * 60 * 1000, // 3 hours
+  },
+});
+
+manager.addConstraintGroup(acmeRateLimit);
+
+// All 300 can burst immediately. The 301st waits until the oldest
+// completion falls out of the 3-hour window.
+for (const domain of domains) {
+  manager.triggerTaskConstrained(certTask, { domain });
+}
+```
+
+Compose multiple rate limits for layered protection:
+
+```typescript
+// Per-domain weekly cap AND global order rate
+const perDomainWeekly = new TaskConstraintGroup({
+  name: 'per-domain-weekly',
+  constraintKeyForExecution: (task, input) => input.registeredDomain,
+  rateLimit: { maxPerWindow: 50, windowMs: 7 * 24 * 60 * 60 * 1000 },
+});
+
+const globalOrderRate = new TaskConstraintGroup({
+  name: 'global-order-rate',
+  constraintKeyForExecution: () => 'global',
+  rateLimit: { maxPerWindow: 300, windowMs: 3 * 60 * 60 * 1000 },
+});
+
+manager.addConstraintGroup(perDomainWeekly);
+manager.addConstraintGroup(globalOrderRate);
+```
+
+Combine with `maxConcurrent` and `cooldownMs` for fine-grained control:
+
+```typescript
+const throttled = new TaskConstraintGroup({
+  name: 'acme-throttle',
+  constraintKeyForExecution: () => 'acme',
+  maxConcurrent: 5,          // max 5 concurrent requests
+  cooldownMs: 1000,           // 1s gap after each completion
+  rateLimit: {
+    maxPerWindow: 300,
+    windowMs: 3 * 60 * 60 * 1000,
+  },
+});
+```
+
+### Result Sharing — Deduplication for Concurrent Requests
+
+When multiple callers request the same resource concurrently, `resultSharingMode: 'share-latest'` ensures only one execution occurs. All queued waiters receive the same result:
+
+```typescript
+const certMutex = new TaskConstraintGroup({
+  name: 'cert-per-tld',
+  constraintKeyForExecution: (task, input) => extractTld(input.domain),
+  maxConcurrent: 1,
+  resultSharingMode: 'share-latest',
+});
+
+manager.addConstraintGroup(certMutex);
+
+const certTask = new Task({
+  name: 'obtain-cert',
+  taskFunction: async (input) => {
+    return await acmeClient.obtainWildcard(input.domain);
+  },
+});
+manager.addTask(certTask);
+
+// Three requests for *.example.com arrive simultaneously
+const [cert1, cert2, cert3] = await Promise.all([
+  manager.triggerTaskConstrained(certTask, { domain: 'api.example.com' }),
+  manager.triggerTaskConstrained(certTask, { domain: 'www.example.com' }),
+  manager.triggerTaskConstrained(certTask, { domain: 'mail.example.com' }),
+]);
+
+// Only ONE ACME request was made.
+// cert1 === cert2 === cert3 — all callers got the same cert object.
+```
+
+**Result sharing semantics:**
+
+- `shouldExecute` is NOT called for shared results (the task's purpose was already fulfilled)
+- Error results are NOT shared — queued tasks execute independently after a failure
+- `lastResults` persists until `reset()` — for time-bounded sharing, use `shouldExecute` to control staleness
+- Composable with rate limiting: rate-limited waiters get shared results without waiting for the window
+
 ### How It Works
 
 When you trigger a task through `TaskManager` (via `triggerTask`, `triggerTaskByName`, `addExecuteRemoveTask`, or cron), the manager:
@@ -319,8 +418,9 @@ When you trigger a task through `TaskManager` (via `triggerTask`, `triggerTaskBy
 2. If no constraints apply (all matchers return `null`) → checks `shouldExecute` → runs or skips
 3. If all applicable constraints have capacity → acquires slots → checks `shouldExecute` → runs or skips
 4. If any constraint blocks → enqueues the task; when a running task completes, the queue is drained
-5. Cooldown-blocked tasks auto-retry after the shortest remaining cooldown expires
+5. Cooldown/rate-limit-blocked tasks auto-retry after the shortest remaining delay expires
-6. Queued tasks re-check `shouldExecute` when their turn comes — stale work is automatically pruned
+6. Queued tasks check for shared results first (if any group has `resultSharingMode: 'share-latest'`)
+7. Queued tasks re-check `shouldExecute` when their turn comes — stale work is automatically pruned
 
 ## 🎯 Core Concepts
 
@@ -926,6 +1026,8 @@ const acmeTasks = manager.getTasksMetadataByLabel('tenantId', 'acme');
 | `maxConcurrent` | `number` | `Infinity` | Max concurrent tasks per key |
 | `cooldownMs` | `number` | `0` | Minimum ms between completions per key |
 | `shouldExecute` | `(task, input?) => boolean \| Promise<boolean>` | — | Pre-execution check. Return `false` to skip; deferred resolves `undefined`. |
+| `rateLimit` | `IRateLimitConfig` | — | Sliding window: `{ maxPerWindow, windowMs }`. Counts running + completed tasks. |
+| `resultSharingMode` | `TResultSharingMode` | `'none'` | `'none'` or `'share-latest'`. Queued tasks get first task's result without executing. |
 
 ### TaskConstraintGroup Methods
 
@@ -933,12 +1035,17 @@ const acmeTasks = manager.getTasksMetadataByLabel('tenantId', 'acme');
 | --- | --- | --- |
 | `getConstraintKey(task, input?)` | `string \| null` | Get the constraint key for a task + input |
 | `checkShouldExecute(task, input?)` | `Promise<boolean>` | Run the `shouldExecute` callback (defaults to `true`) |
-| `canRun(key)` | `boolean` | Check if a slot is available |
+| `canRun(key)` | `boolean` | Check if a slot is available (considers concurrency, cooldown, and rate limit) |
 | `acquireSlot(key)` | `void` | Claim a running slot |
-| `releaseSlot(key)` | `void` | Release a slot and record completion time |
+| `releaseSlot(key)` | `void` | Release a slot and record completion time + rate-limit timestamp |
 | `getCooldownRemaining(key)` | `number` | Milliseconds until cooldown expires |
+| `getRateLimitDelay(key)` | `number` | Milliseconds until a rate-limit slot opens |
+| `getNextAvailableDelay(key)` | `number` | Max of cooldown + rate-limit delay — unified "when can I run" |
 | `getRunningCount(key)` | `number` | Current running count for key |
-| `reset()` | `void` | Clear all state |
+| `recordResult(key, result)` | `void` | Store result for sharing (no-op if mode is `'none'`) |
+| `getLastResult(key)` | `{result, timestamp} \| undefined` | Get last shared result for key |
+| `hasResultSharing()` | `boolean` | Whether result sharing is enabled |
+| `reset()` | `void` | Clear all state (running counts, cooldowns, rate-limit timestamps, shared results) |
 
 ### TaskManager Methods
 
@@ -986,6 +1093,8 @@ import type {
   ITaskStep,
   ITaskFunction,
   ITaskConstraintGroupOptions,
+  IRateLimitConfig,
+  TResultSharingMode,
   StepNames,
 } from '@push.rocks/taskbuffer';
 ```

test/test.13.constraints.ts

@@ -870,4 +870,566 @@ tap.test('should use both task.data and input in constraint key', async () => {
   await manager.stop();
 });
 
+// =============================================================================
+// Rate Limiting Tests
+// =============================================================================
+
+// Test 24: Basic N-per-window rate limiting
+tap.test('should enforce N-per-window rate limit', async () => {
+  const manager = new taskbuffer.TaskManager();
+  const execTimestamps: number[] = [];
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'rate-limit-basic',
+    maxConcurrent: Infinity,
+    constraintKeyForExecution: () => 'shared',
+    rateLimit: {
+      maxPerWindow: 3,
+      windowMs: 1000,
+    },
+  });
+  manager.addConstraintGroup(constraint);
+
+  const makeTask = (id: number) =>
+    new taskbuffer.Task({
+      name: `rl-${id}`,
+      taskFunction: async () => {
+        execTimestamps.push(Date.now());
+        return `done-${id}`;
+      },
+    });
+
+  const tasks = [makeTask(1), makeTask(2), makeTask(3), makeTask(4), makeTask(5)];
+  for (const t of tasks) manager.addTask(t);
+
+  const results = await Promise.all(tasks.map((t) => manager.triggerTaskConstrained(t)));
+
+  // All 5 should eventually complete
+  expect(results).toEqual(['done-1', 'done-2', 'done-3', 'done-4', 'done-5']);
+
+  // First 3 should execute nearly simultaneously
+  const firstBatchSpread = execTimestamps[2] - execTimestamps[0];
+  expect(firstBatchSpread).toBeLessThan(100);
+
+  // 4th and 5th should wait for the window to slide (at least ~900ms after first)
+  const fourthDelay = execTimestamps[3] - execTimestamps[0];
+  expect(fourthDelay).toBeGreaterThanOrEqual(900);
+
+  await manager.stop();
+});
+
+// Test 25: Rate limit + maxConcurrent interaction
+tap.test('should enforce both rate limit and maxConcurrent independently', async () => {
+  const manager = new taskbuffer.TaskManager();
+  let running = 0;
+  let maxRunning = 0;
+  const execTimestamps: number[] = [];
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'rate-concurrent',
+    maxConcurrent: 2,
+    constraintKeyForExecution: () => 'shared',
+    rateLimit: {
+      maxPerWindow: 3,
+      windowMs: 2000,
+    },
+  });
+  manager.addConstraintGroup(constraint);
+
+  const makeTask = (id: number) =>
+    new taskbuffer.Task({
+      name: `rc-${id}`,
+      taskFunction: async () => {
+        running++;
+        maxRunning = Math.max(maxRunning, running);
+        execTimestamps.push(Date.now());
+        await smartdelay.delayFor(50);
+        running--;
+      },
+    });
+
+  const tasks = [makeTask(1), makeTask(2), makeTask(3), makeTask(4)];
+  for (const t of tasks) manager.addTask(t);
+
+  await Promise.all(tasks.map((t) => manager.triggerTaskConstrained(t)));
+
+  // Concurrency limit should be enforced
+  expect(maxRunning).toBeLessThanOrEqual(2);
+
+  // 4th task should wait for rate limit window (only 3 allowed per 2s)
+  const fourthDelay = execTimestamps[3] - execTimestamps[0];
+  expect(fourthDelay).toBeGreaterThanOrEqual(1900);
+
+  await manager.stop();
+});
+
+// Test 26: Rate limit + cooldownMs interaction
+tap.test('should enforce both rate limit and cooldown together', async () => {
+  const manager = new taskbuffer.TaskManager();
+  const execTimestamps: number[] = [];
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'rate-cooldown',
+    maxConcurrent: 1,
+    cooldownMs: 200,
+    constraintKeyForExecution: () => 'shared',
+    rateLimit: {
+      maxPerWindow: 2,
+      windowMs: 2000,
+    },
+  });
+  manager.addConstraintGroup(constraint);
+
+  const makeTask = (id: number) =>
+    new taskbuffer.Task({
+      name: `rcd-${id}`,
+      taskFunction: async () => {
+        execTimestamps.push(Date.now());
+      },
+    });
+
+  const tasks = [makeTask(1), makeTask(2), makeTask(3)];
+  for (const t of tasks) manager.addTask(t);
+
+  await Promise.all(tasks.map((t) => manager.triggerTaskConstrained(t)));
+
+  // Cooldown between first and second: at least 200ms
+  const gap12 = execTimestamps[1] - execTimestamps[0];
+  expect(gap12).toBeGreaterThanOrEqual(150);
+
+  // Third task blocked by rate limit (only 2 per 2000ms window) AND cooldown
+  const gap13 = execTimestamps[2] - execTimestamps[0];
+  expect(gap13).toBeGreaterThanOrEqual(1900);
+
+  await manager.stop();
+});
+
+// Test 27: Per-key rate limit independence
+tap.test('should apply rate limit per key independently', async () => {
+  const manager = new taskbuffer.TaskManager();
+  const execLog: string[] = [];
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'rate-per-key',
+    constraintKeyForExecution: (_task, input?: string) => input,
+    rateLimit: {
+      maxPerWindow: 1,
+      windowMs: 2000,
+    },
+  });
+  manager.addConstraintGroup(constraint);
+
+  const task = new taskbuffer.Task({
+    name: 'rate-key-task',
+    taskFunction: async (input: string) => {
+      execLog.push(input);
+    },
+  });
+  manager.addTask(task);
+
+  // Trigger 2 for key-A and 1 for key-B
+  const [r1, r2, r3] = await Promise.all([
+    manager.triggerTaskConstrained(task, 'key-A'),
+    manager.triggerTaskConstrained(task, 'key-B'),
+    manager.triggerTaskConstrained(task, 'key-A'), // should wait for window
+  ]);
+
+  // key-A and key-B first calls should both execute immediately
+  expect(execLog[0]).toEqual('key-A');
+  expect(execLog[1]).toEqual('key-B');
+  // key-A second call eventually executes
+  expect(execLog).toContain('key-A');
+  expect(execLog.length).toEqual(3);
+
+  await manager.stop();
+});
+
+// Test 28: getNextAvailableDelay returns correct value
+tap.test('should return correct getNextAvailableDelay and canRun after waiting', async () => {
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'delay-check',
+    constraintKeyForExecution: () => 'key',
+    rateLimit: {
+      maxPerWindow: 1,
+      windowMs: 500,
+    },
+  });
+
+  // Initially: can run, no delay
+  expect(constraint.canRun('key')).toBeTrue();
+  expect(constraint.getNextAvailableDelay('key')).toEqual(0);
+
+  // Acquire and release to record a completion
+  constraint.acquireSlot('key');
+  constraint.releaseSlot('key');
+
+  // Now: rate limit saturated
+  expect(constraint.canRun('key')).toBeFalse();
+  const delay = constraint.getNextAvailableDelay('key');
+  expect(delay).toBeGreaterThan(0);
+  expect(delay).toBeLessThanOrEqual(500);
+
+  // Wait for window to slide
+  await smartdelay.delayFor(delay + 50);
+
+  expect(constraint.canRun('key')).toBeTrue();
+  expect(constraint.getNextAvailableDelay('key')).toEqual(0);
+});
+
+// Test 29: reset() clears rate-limit timestamps
+tap.test('should clear rate limit timestamps on reset', async () => {
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'reset-rate',
+    constraintKeyForExecution: () => 'key',
+    rateLimit: {
+      maxPerWindow: 1,
+      windowMs: 60000,
+    },
+  });
+
+  constraint.acquireSlot('key');
+  constraint.releaseSlot('key');
+  expect(constraint.canRun('key')).toBeFalse();
+
+  constraint.reset();
+  expect(constraint.canRun('key')).toBeTrue();
+  expect(constraint.getRateLimitDelay('key')).toEqual(0);
+});
+
+// =============================================================================
+// Result Sharing Tests
+// =============================================================================
+
+// Test 30: Basic result sharing — multiple waiters get first task's result
+tap.test('should share result with queued tasks (share-latest mode)', async () => {
+  const manager = new taskbuffer.TaskManager();
+  let execCount = 0;
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'share-basic',
+    maxConcurrent: 1,
+    constraintKeyForExecution: () => 'shared',
+    resultSharingMode: 'share-latest',
+  });
+  manager.addConstraintGroup(constraint);
+
+  const makeTask = (id: number) =>
+    new taskbuffer.Task({
+      name: `share-${id}`,
+      taskFunction: async () => {
+        execCount++;
+        await smartdelay.delayFor(100);
+        return 'shared-result';
+      },
+    });
+
+  const t1 = makeTask(1);
+  const t2 = makeTask(2);
+  const t3 = makeTask(3);
+
+  manager.addTask(t1);
+  manager.addTask(t2);
+  manager.addTask(t3);
+
+  const [r1, r2, r3] = await Promise.all([
+    manager.triggerTaskConstrained(t1),
+    manager.triggerTaskConstrained(t2),
+    manager.triggerTaskConstrained(t3),
+  ]);
+
+  // Only 1 execution, all get same result
+  expect(execCount).toEqual(1);
+  expect(r1).toEqual('shared-result');
+  expect(r2).toEqual('shared-result');
+  expect(r3).toEqual('shared-result');
+
+  await manager.stop();
+});
+
+// Test 31: Different keys get independent results
+tap.test('should share results independently per key', async () => {
+  const manager = new taskbuffer.TaskManager();
+  let execCount = 0;
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'share-per-key',
+    maxConcurrent: 1,
+    constraintKeyForExecution: (_task, input?: string) => input,
+    resultSharingMode: 'share-latest',
+  });
+  manager.addConstraintGroup(constraint);
+
+  const task = new taskbuffer.Task({
+    name: 'keyed-share',
+    taskFunction: async (input: string) => {
+      execCount++;
+      await smartdelay.delayFor(50);
+      return `result-for-${input}`;
+    },
+  });
+  manager.addTask(task);
+
+  const [r1, r2] = await Promise.all([
+    manager.triggerTaskConstrained(task, 'key-A'),
+    manager.triggerTaskConstrained(task, 'key-B'),
+  ]);
+
+  // Different keys → both execute independently
+  expect(execCount).toEqual(2);
+  expect(r1).toEqual('result-for-key-A');
+  expect(r2).toEqual('result-for-key-B');
+
+  await manager.stop();
+});
+
+// Test 32: Default mode ('none') — no sharing
+tap.test('should not share results when mode is none (default)', async () => {
+  const manager = new taskbuffer.TaskManager();
+  let execCount = 0;
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'no-share',
+    maxConcurrent: 1,
+    constraintKeyForExecution: () => 'shared',
+    // resultSharingMode defaults to 'none'
+  });
+  manager.addConstraintGroup(constraint);
+
+  const makeTask = (id: number) =>
+    new taskbuffer.Task({
+      name: `noshare-${id}`,
+      taskFunction: async () => {
+        execCount++;
+        await smartdelay.delayFor(50);
+        return `result-${execCount}`;
+      },
+    });
+
+  const t1 = makeTask(1);
+  const t2 = makeTask(2);
+
+  manager.addTask(t1);
+  manager.addTask(t2);
+
+  const [r1, r2] = await Promise.all([
+    manager.triggerTaskConstrained(t1),
+    manager.triggerTaskConstrained(t2),
+  ]);
+
+  // Both should execute independently
+  expect(execCount).toEqual(2);
+  expect(r1).toEqual('result-1');
+  expect(r2).toEqual('result-2');
+
+  await manager.stop();
+});
+
+// Test 33: Sharing takes priority over shouldExecute for queued tasks
+tap.test('should not call shouldExecute for shared results', async () => {
+  const manager = new taskbuffer.TaskManager();
+  let shouldExecuteCalls = 0;
+  let execCount = 0;
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'share-vs-should',
+    maxConcurrent: 1,
+    constraintKeyForExecution: () => 'shared',
+    resultSharingMode: 'share-latest',
+    shouldExecute: () => {
+      shouldExecuteCalls++;
+      return true;
+    },
+  });
+  manager.addConstraintGroup(constraint);
+
+  const makeTask = (id: number) =>
+    new taskbuffer.Task({
+      name: `svs-${id}`,
+      taskFunction: async () => {
+        execCount++;
+        await smartdelay.delayFor(100);
+        return 'shared-value';
+      },
+    });
+
+  const t1 = makeTask(1);
+  const t2 = makeTask(2);
+  const t3 = makeTask(3);
+
+  manager.addTask(t1);
+  manager.addTask(t2);
+  manager.addTask(t3);
+
+  const initialShouldExecuteCalls = shouldExecuteCalls;
+
+  await Promise.all([
+    manager.triggerTaskConstrained(t1),
+    manager.triggerTaskConstrained(t2),
+    manager.triggerTaskConstrained(t3),
+  ]);
+
+  // Only 1 execution
+  expect(execCount).toEqual(1);
+
+  // shouldExecute called once for the first task, but not for shared results
+  // (t2 and t3 get shared result without going through executeWithConstraintTracking)
+  const totalShouldExecuteCalls = shouldExecuteCalls - initialShouldExecuteCalls;
+  expect(totalShouldExecuteCalls).toEqual(1);
+
+  await manager.stop();
+});
+
+// Test 34: Error results NOT shared — queued task executes after failure
+tap.test('should not share error results with queued tasks', async () => {
+  const manager = new taskbuffer.TaskManager();
+  let execCount = 0;
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'share-error',
+    maxConcurrent: 1,
+    constraintKeyForExecution: () => 'shared',
+    resultSharingMode: 'share-latest',
+  });
+  manager.addConstraintGroup(constraint);
+
+  const failTask = new taskbuffer.Task({
+    name: 'fail-share',
+    catchErrors: true,
+    taskFunction: async () => {
+      execCount++;
+      await smartdelay.delayFor(50);
+      throw new Error('fail');
+    },
+  });
+
+  const successTask = new taskbuffer.Task({
+    name: 'success-share',
+    taskFunction: async () => {
+      execCount++;
+      await smartdelay.delayFor(50);
+      return 'success-result';
+    },
+  });
+
+  manager.addTask(failTask);
+  manager.addTask(successTask);
+
+  const [r1, r2] = await Promise.all([
+    manager.triggerTaskConstrained(failTask),
+    manager.triggerTaskConstrained(successTask),
+  ]);
+
+  // Both should have executed (error result not shared)
+  expect(execCount).toEqual(2);
+  expect(r2).toEqual('success-result');
+
+  await manager.stop();
+});
+
+// Test 35: Multiple constraint groups — sharing from one group applies
+tap.test('should share result when any applicable group has sharing enabled', async () => {
+  const manager = new taskbuffer.TaskManager();
+  let execCount = 0;
+
+  const sharingGroup = new taskbuffer.TaskConstraintGroup({
+    name: 'sharing-group',
+    maxConcurrent: 1,
+    constraintKeyForExecution: () => 'shared',
+    resultSharingMode: 'share-latest',
+  });
+
+  const nonSharingGroup = new taskbuffer.TaskConstraintGroup({
+    name: 'non-sharing-group',
+    maxConcurrent: 5,
+    constraintKeyForExecution: () => 'all',
+    // resultSharingMode defaults to 'none'
+  });
+
+  manager.addConstraintGroup(sharingGroup);
+  manager.addConstraintGroup(nonSharingGroup);
+
+  const makeTask = (id: number) =>
+    new taskbuffer.Task({
+      name: `multi-share-${id}`,
+      taskFunction: async () => {
+        execCount++;
+        await smartdelay.delayFor(100);
+        return 'multi-group-result';
+      },
+    });
+
+  const t1 = makeTask(1);
+  const t2 = makeTask(2);
+
+  manager.addTask(t1);
+  manager.addTask(t2);
+
+  const [r1, r2] = await Promise.all([
+    manager.triggerTaskConstrained(t1),
+    manager.triggerTaskConstrained(t2),
+  ]);
+
+  // Only 1 execution due to sharing from the sharing group
+  expect(execCount).toEqual(1);
+  expect(r1).toEqual('multi-group-result');
+  expect(r2).toEqual('multi-group-result');
+
+  await manager.stop();
+});
+
+// Test 36: Result sharing + rate limit combo
+tap.test('should resolve rate-limited waiters with shared result', async () => {
+  const manager = new taskbuffer.TaskManager();
+  let execCount = 0;
+
+  const constraint = new taskbuffer.TaskConstraintGroup({
+    name: 'share-rate',
+    maxConcurrent: 1,
+    constraintKeyForExecution: () => 'shared',
+    resultSharingMode: 'share-latest',
+    rateLimit: {
+      maxPerWindow: 1,
+      windowMs: 5000,
+    },
+  });
+  manager.addConstraintGroup(constraint);
+
+  const makeTask = (id: number) =>
+    new taskbuffer.Task({
+      name: `sr-${id}`,
+      taskFunction: async () => {
+        execCount++;
+        await smartdelay.delayFor(50);
+        return 'rate-shared-result';
+      },
+    });
+
+  const t1 = makeTask(1);
+  const t2 = makeTask(2);
+  const t3 = makeTask(3);
+
+  manager.addTask(t1);
+  manager.addTask(t2);
+  manager.addTask(t3);
+
+  const startTime = Date.now();
+  const [r1, r2, r3] = await Promise.all([
+    manager.triggerTaskConstrained(t1),
+    manager.triggerTaskConstrained(t2),
+    manager.triggerTaskConstrained(t3),
+  ]);
+  const elapsed = Date.now() - startTime;
+
+  // Only 1 execution; waiters get shared result without waiting for rate limit window
+  expect(execCount).toEqual(1);
+  expect(r1).toEqual('rate-shared-result');
+  expect(r2).toEqual('rate-shared-result');
+  expect(r3).toEqual('rate-shared-result');
+
+  // Should complete quickly (not waiting 5s for rate limit window)
+  expect(elapsed).toBeLessThan(1000);
+
+  await manager.stop();
+});
+
 export default tap.start();

ts/00_commitinfo_data.ts

@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@push.rocks/taskbuffer',
-  version: '6.0.1',
+  version: '6.1.0',
   description: 'A flexible task management library supporting TypeScript, allowing for task buffering, scheduling, and execution with dependency management.'
 }

ts/index.ts

@@ -12,7 +12,7 @@ export { TaskStep } from './taskbuffer.classes.taskstep.js';
 export type { ITaskStep } from './taskbuffer.classes.taskstep.js';
 
 // Metadata interfaces
-export type { ITaskMetadata, ITaskExecutionReport, IScheduledTaskInfo, ITaskEvent, TTaskEventType, ITaskConstraintGroupOptions, ITaskExecution } from './taskbuffer.interfaces.js';
+export type { ITaskMetadata, ITaskExecutionReport, IScheduledTaskInfo, ITaskEvent, TTaskEventType, ITaskConstraintGroupOptions, ITaskExecution, IRateLimitConfig, TResultSharingMode } from './taskbuffer.interfaces.js';
 
 import * as distributedCoordination from './taskbuffer.classes.distributedcoordinator.js';
 export { distributedCoordination };

ts/taskbuffer.classes.taskconstraintgroup.ts

@@ -1,15 +1,19 @@
 import type { Task } from './taskbuffer.classes.task.js';
-import type { ITaskConstraintGroupOptions } from './taskbuffer.interfaces.js';
+import type { ITaskConstraintGroupOptions, IRateLimitConfig, TResultSharingMode } from './taskbuffer.interfaces.js';
 
 export class TaskConstraintGroup<TData extends Record<string, unknown> = Record<string, unknown>> {
   public name: string;
   public maxConcurrent: number;
   public cooldownMs: number;
+  public rateLimit: IRateLimitConfig | null;
+  public resultSharingMode: TResultSharingMode;
   private constraintKeyForExecution: (task: Task<any, any, TData>, input?: any) => string | null | undefined;
   private shouldExecuteFn?: (task: Task<any, any, TData>, input?: any) => boolean | Promise<boolean>;
 
   private runningCounts = new Map<string, number>();
   private lastCompletionTimes = new Map<string, number>();
+  private completionTimestamps = new Map<string, number[]>();
+  private lastResults = new Map<string, { result: any; timestamp: number }>();
 
   constructor(options: ITaskConstraintGroupOptions<TData>) {
     this.name = options.name;
@@ -17,6 +21,8 @@ export class TaskConstraintGroup<TData extends Record<string, unknown> = Record<
     this.maxConcurrent = options.maxConcurrent ?? Infinity;
     this.cooldownMs = options.cooldownMs ?? 0;
     this.shouldExecuteFn = options.shouldExecute;
+    this.rateLimit = options.rateLimit ?? null;
+    this.resultSharingMode = options.resultSharingMode ?? 'none';
   }
 
   public getConstraintKey(task: Task<any, any, TData>, input?: any): string | null {
@@ -47,6 +53,16 @@ export class TaskConstraintGroup<TData extends Record<string, unknown> = Record<
       }
     }
 
+    if (this.rateLimit) {
+      this.pruneCompletionTimestamps(subGroupKey);
+      const timestamps = this.completionTimestamps.get(subGroupKey);
+      const completedInWindow = timestamps ? timestamps.length : 0;
+      const running = this.runningCounts.get(subGroupKey) ?? 0;
+      if (completedInWindow + running >= this.rateLimit.maxPerWindow) {
+        return false;
+      }
+    }
+
     return true;
   }
 
@@ -64,6 +80,12 @@ export class TaskConstraintGroup<TData extends Record<string, unknown> = Record<
       this.runningCounts.set(subGroupKey, next);
     }
     this.lastCompletionTimes.set(subGroupKey, Date.now());
+
+    if (this.rateLimit) {
+      const timestamps = this.completionTimestamps.get(subGroupKey) ?? [];
+      timestamps.push(Date.now());
+      this.completionTimestamps.set(subGroupKey, timestamps);
+    }
   }
 
   public getCooldownRemaining(subGroupKey: string): number {
@@ -82,8 +104,61 @@ export class TaskConstraintGroup<TData extends Record<string, unknown> = Record<
     return this.runningCounts.get(subGroupKey) ?? 0;
   }
 
+  // Rate limit helpers
+  private pruneCompletionTimestamps(subGroupKey: string): void {
+    const timestamps = this.completionTimestamps.get(subGroupKey);
+    if (!timestamps || !this.rateLimit) return;
+    const cutoff = Date.now() - this.rateLimit.windowMs;
+    let i = 0;
+    while (i < timestamps.length && timestamps[i] <= cutoff) {
+      i++;
+    }
+    if (i > 0) {
+      timestamps.splice(0, i);
+    }
+  }
+
+  public getRateLimitDelay(subGroupKey: string): number {
+    if (!this.rateLimit) return 0;
+    this.pruneCompletionTimestamps(subGroupKey);
+    const timestamps = this.completionTimestamps.get(subGroupKey);
+    const completedInWindow = timestamps ? timestamps.length : 0;
+    const running = this.runningCounts.get(subGroupKey) ?? 0;
+    if (completedInWindow + running < this.rateLimit.maxPerWindow) {
+      return 0;
+    }
+    // If only running tasks fill the window (no completions yet), we can't compute a delay
+    if (!timestamps || timestamps.length === 0) {
+      return 1; // minimal delay; drain will re-check after running tasks complete
+    }
+    // The oldest timestamp in the window determines when a slot opens
+    const oldestInWindow = timestamps[0];
+    const expiry = oldestInWindow + this.rateLimit.windowMs;
+    return Math.max(0, expiry - Date.now());
+  }
+
+  public getNextAvailableDelay(subGroupKey: string): number {
+    return Math.max(this.getCooldownRemaining(subGroupKey), this.getRateLimitDelay(subGroupKey));
+  }
+
+  // Result sharing helpers
+  public recordResult(subGroupKey: string, result: any): void {
+    if (this.resultSharingMode === 'none') return;
+    this.lastResults.set(subGroupKey, { result, timestamp: Date.now() });
+  }
+
+  public getLastResult(subGroupKey: string): { result: any; timestamp: number } | undefined {
+    return this.lastResults.get(subGroupKey);
+  }
+
+  public hasResultSharing(): boolean {
+    return this.resultSharingMode !== 'none';
+  }
+
   public reset(): void {
     this.runningCounts.clear();
     this.lastCompletionTimes.clear();
+    this.completionTimestamps.clear();
+    this.lastResults.clear();
   }
 }

ts/taskbuffer.classes.taskmanager.ts

@@ -143,7 +143,14 @@ export class TaskManager {
     }
 
     try {
-      return await task.trigger(input);
+      const result = await task.trigger(input);
+      // Record result for groups with result sharing (only on true success, not caught errors)
+      if (!task.lastError) {
+        for (const { group, key } of groups) {
+          group.recordResult(key, result);
+        }
+      }
+      return result;
     } finally {
       // Release slots
       for (const { group, key } of groups) {
@@ -181,6 +188,18 @@ export class TaskManager {
         continue;
       }
 
+      // Check result sharing — if any applicable group has a shared result, resolve immediately
+      const sharingGroups = applicableGroups.filter(({ group }) => group.hasResultSharing());
+      if (sharingGroups.length > 0) {
+        const groupWithResult = sharingGroups.find(({ group, key }) =>
+          group.getLastResult(key) !== undefined
+        );
+        if (groupWithResult) {
+          entry.deferred.resolve(groupWithResult.group.getLastResult(groupWithResult.key)!.result);
+          continue;
+        }
+      }
+
       const allCanRun = applicableGroups.every(({ group, key }) => group.canRun(key));
       if (allCanRun) {
         // executeWithConstraintTracking handles shouldExecute check internally
@@ -190,9 +209,9 @@ export class TaskManager {
         );
       } else {
         stillQueued.push(entry);
-        // Track shortest cooldown for timer scheduling
+        // Track shortest delay for timer scheduling (cooldown + rate limit)
         for (const { group, key } of applicableGroups) {
-          const remaining = group.getCooldownRemaining(key);
+          const remaining = group.getNextAvailableDelay(key);
           if (remaining > 0 && remaining < shortestCooldown) {
             shortestCooldown = remaining;
           }

ts/taskbuffer.interfaces.ts

@@ -1,12 +1,21 @@
 import type { ITaskStep } from './taskbuffer.classes.taskstep.js';
 import type { Task } from './taskbuffer.classes.task.js';
 
+export interface IRateLimitConfig {
+  maxPerWindow: number;  // max completions allowed within the sliding window
+  windowMs: number;      // sliding window duration in ms
+}
+
+export type TResultSharingMode = 'none' | 'share-latest';
+
 export interface ITaskConstraintGroupOptions<TData extends Record<string, unknown> = Record<string, unknown>> {
   name: string;
   constraintKeyForExecution: (task: Task<any, any, TData>, input?: any) => string | null | undefined;
   maxConcurrent?: number;  // default: Infinity
   cooldownMs?: number;     // default: 0
   shouldExecute?: (task: Task<any, any, TData>, input?: any) => boolean | Promise<boolean>;
+  rateLimit?: IRateLimitConfig;
+  resultSharingMode?: TResultSharingMode;  // default: 'none'
 }
 
 export interface ITaskExecution<TData extends Record<string, unknown> = Record<string, unknown>> {

ts_web/00_commitinfo_data.ts

@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@push.rocks/taskbuffer',
-  version: '6.0.1',
+  version: '6.1.0',
   description: 'A flexible task management library supporting TypeScript, allowing for task buffering, scheduling, and execution with dependency management.'
 }