From 7e90e4d081bee9c380ff0ab0a476bcf48edfbef8 Mon Sep 17 00:00:00 2001
From: roboomp <omp@can.ac>
Date: Thu, 25 Jun 2026 12:14:45 +0000
Subject: [PATCH] fix(agent): released ollama-cloud semaphore slot when waiter
 aborts

Semaphore.acquire now accepts an AbortSignal so a queued waiter that is cancelled (parent task abort, wall-clock budget elapsing) removes itself from the wait queue instead of being resolved by the next release. The provider semaphore in runSubprocess passes the run's abortSignal through, preventing aborted ollama-cloud subagents from permanently draining the provider concurrency budget.

Fixes #3464
---
 packages/coding-agent/src/task/executor.ts    |  3 +-
 packages/coding-agent/src/task/parallel.ts    | 36 +++++++++++++++++--
 ...sue-3464-ollama-cloud-task-backoff.test.ts | 25 +++++++++++++
 3 files changed, 59 insertions(+), 5 deletions(-)

diff --git a/packages/coding-agent/src/task/executor.ts b/packages/coding-agent/src/task/executor.ts
index 41cc0a2e4..de686e6b4 100644
--- a/packages/coding-agent/src/task/executor.ts
+++ b/packages/coding-agent/src/task/executor.ts
@@ -1991,9 +1991,8 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 			if (model) {
 				providerSemaphore = getProviderSemaphore(settings, model.provider);
 				if (providerSemaphore) {
-					await awaitAbortable(providerSemaphore.acquire());
+					await providerSemaphore.acquire(abortSignal);
 					providerSemaphoreAcquired = true;
-					checkAbort();
 				}
 			}
 
diff --git a/packages/coding-agent/src/task/parallel.ts b/packages/coding-agent/src/task/parallel.ts
index 34f082a1c..a07dd38c0 100644
--- a/packages/coding-agent/src/task/parallel.ts
+++ b/packages/coding-agent/src/task/parallel.ts
@@ -100,13 +100,37 @@ export class Semaphore {
 		this.#max = normalizedMax > 0 ? normalizedMax : Number.POSITIVE_INFINITY;
 	}
 
-	async acquire(): Promise<void> {
+	/**
+	 * Resolves when a slot is available. Pass an `AbortSignal` so callers that
+	 * stop waiting (parent task cancelled, wall-clock budget elapsed) also stop
+	 * occupying a queue slot — otherwise a later `release()` would resolve the
+	 * abandoned waiter, permanently shrinking effective concurrency for the
+	 * remaining lifetime of the process (issue #3464 review feedback).
+	 */
+	async acquire(signal?: AbortSignal): Promise<void> {
+		if (signal?.aborted) {
+			throw semaphoreAbortReason(signal);
+		}
 		if (this.#current < this.#max) {
 			this.#current++;
 			return;
 		}
-		const { promise, resolve } = Promise.withResolvers<void>();
-		this.#queue.push(resolve);
+		const { promise, resolve, reject } = Promise.withResolvers<void>();
+		const queue = this.#queue;
+		let waiter: () => void = resolve;
+		if (signal) {
+			const onAbort = () => {
+				const index = queue.indexOf(waiter);
+				if (index >= 0) queue.splice(index, 1);
+				reject(semaphoreAbortReason(signal));
+			};
+			waiter = () => {
+				signal.removeEventListener("abort", onAbort);
+				resolve();
+			};
+			signal.addEventListener("abort", onAbort, { once: true });
+		}
+		queue.push(waiter);
 		return promise;
 	}
 
@@ -119,3 +143,9 @@ export class Semaphore {
 		}
 	}
 }
+
+function semaphoreAbortReason(signal: AbortSignal): unknown {
+	const reason = signal.reason;
+	if (reason !== undefined) return reason;
+	return new Error("Semaphore acquire aborted");
+}
diff --git a/packages/coding-agent/test/issue-3464-ollama-cloud-task-backoff.test.ts b/packages/coding-agent/test/issue-3464-ollama-cloud-task-backoff.test.ts
index 06e27adf2..0c923fd13 100644
--- a/packages/coding-agent/test/issue-3464-ollama-cloud-task-backoff.test.ts
+++ b/packages/coding-agent/test/issue-3464-ollama-cloud-task-backoff.test.ts
@@ -17,6 +17,7 @@ import {
 import { AuthStorage } from "@oh-my-pi/pi-coding-agent/session/auth-storage";
 import { SessionManager } from "@oh-my-pi/pi-coding-agent/session/session-manager";
 import { runSubprocess } from "@oh-my-pi/pi-coding-agent/task/executor";
+import { Semaphore } from "@oh-my-pi/pi-coding-agent/task/parallel";
 import type { AgentDefinition } from "@oh-my-pi/pi-coding-agent/task/types";
 import { EventBus } from "@oh-my-pi/pi-coding-agent/utils/event-bus";
 import { TempDir } from "@oh-my-pi/pi-utils";
@@ -217,4 +218,28 @@ describe("issue #3464: ollama-cloud task backoff", () => {
 		gates.get("CloudTwo")?.resolve();
 		await second;
 	});
+
+	it("frees a queued slot when its acquire waiter is aborted", async () => {
+		const semaphore = new Semaphore(1);
+		await semaphore.acquire();
+		const controller = new AbortController();
+		const aborted = semaphore.acquire(controller.signal);
+		controller.abort();
+		await aborted.then(
+			() => {
+				throw new Error("Aborted semaphore.acquire should reject");
+			},
+			() => {},
+		);
+
+		const nextStarted = deferred();
+		const next = (async () => {
+			await semaphore.acquire();
+			nextStarted.resolve();
+		})();
+		semaphore.release();
+		await nextStarted.promise;
+		semaphore.release();
+		await next;
+	});
 });