diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index f7100b579a..33a8614eb0 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -5,6 +5,7 @@
 - Added privacy-safe pseudonymous product analytics for onboarding, command use, execution modes, run outcomes, TTFT, latency, usage, tools, retries, and compactions, with disclosure and opt-out controls ([ENG-4682](https://linear.app/primeintellect/issue/ENG-4682/add-privacy-safe-posthog-analytics-to-prime-agent)).
 - Changed sent agent messages in the IPython cell UI to show only the message text with a `╰─` gutter when expanded, matching received messages, and hid the raw `agent_message.send` receipt dictionary.
 - Fixed Homebrew installs attempting to self-update their versioned Cellar keg instead of directing users to `brew upgrade prime-agent` ([#844](https://github.com/PrimeIntellect-ai/prime-agent/issues/844))
+- Fixed macOS timezone changes invalidating the running daemon's process identity ([#879](https://github.com/PrimeIntellect-ai/prime-agent/issues/879)).
 
 ## [0.7.1] - 2026-08-07
 
diff --git a/packages/coding-agent/src/core/session-lease.ts b/packages/coding-agent/src/core/session-lease.ts
index 6c4e2975cf..2b23832fa2 100644
--- a/packages/coding-agent/src/core/session-lease.ts
+++ b/packages/coding-agent/src/core/session-lease.ts
@@ -110,12 +110,17 @@ function isProcessAlive(pid: number): boolean {
 	}
 }
 
-type ProcessQuery = (command: string, args: string[]) => string;
+interface ProcessQueryOptions {
+	env?: NodeJS.ProcessEnv;
+}
+
+type ProcessQuery = (command: string, args: string[], options?: ProcessQueryOptions) => string;
 
-function runProcessQuery(command: string, args: string[]): string {
+function runProcessQuery(command: string, args: string[], options?: ProcessQueryOptions): string {
 	return execFileSync(command, args, {
 		encoding: "utf8",
 		stdio: ["ignore", "pipe", "ignore"],
+		env: options?.env,
 	});
 }
 
@@ -137,6 +142,20 @@ export function getWindowsProcessStartId(pid: number, query: ProcessQuery = runP
 	}
 }
 
+export function getPsProcessStartId(pid: number, query: ProcessQuery = runProcessQuery): string | undefined {
+	if (!Number.isInteger(pid) || pid <= 0) {
+		return undefined;
+	}
+	try {
+		const startTime = query("ps", ["-p", String(pid), "-o", "lstart="], {
+			env: { ...process.env, TZ: "UTC", LC_ALL: "C" },
+		}).trim();
+		return startTime ? `ps:${startTime}` : undefined;
+	} catch {
+		return undefined;
+	}
+}
+
 export function getProcessStartId(pid: number): string | undefined {
 	if (!Number.isInteger(pid) || pid <= 0) {
 		return undefined;
@@ -155,12 +174,7 @@ export function getProcessStartId(pid: number): string | undefined {
 	} catch {
 		// Fall through to the portable process listing used on macOS and BSD.
 	}
-	try {
-		const startTime = runProcessQuery("ps", ["-p", String(pid), "-o", "lstart="]).trim();
-		return startTime ? `ps:${startTime}` : undefined;
-	} catch {
-		return undefined;
-	}
+	return getPsProcessStartId(pid);
 }
 
 let currentProcessStartId: string | undefined;
diff --git a/packages/coding-agent/test/daemon-ps.test.ts b/packages/coding-agent/test/daemon-ps.test.ts
index 6233a9353e..96cd524ada 100644
--- a/packages/coding-agent/test/daemon-ps.test.ts
+++ b/packages/coding-agent/test/daemon-ps.test.ts
@@ -15,7 +15,7 @@ import {
 	sortDaemons,
 	verifyHelloSupervisorPid,
 } from "../src/cli/daemon-ps.js";
-import { getProcessStartId } from "../src/core/session-lease.js";
+import { getProcessStartId, getPsProcessStartId } from "../src/core/session-lease.js";
 import { defaultDaemonSocketDir } from "../src/modes/daemon/daemon-socket.js";
 
 describe("worker socket classification", () => {
@@ -116,6 +116,38 @@ describe("verifyHelloSupervisorPid", () => {
 	});
 });
 
+describe("getPsProcessStartId", () => {
+	it("uses a stable timezone and locale for the portable process identity", () => {
+		let queryEnvironment: NodeJS.ProcessEnv | undefined;
+		const result = getPsProcessStartId(1234, (_command, _args, options) => {
+			queryEnvironment = options?.env;
+			return "Sat Aug  8 06:00:00 2026\n";
+		});
+
+		expect(result).toBe("ps:Sat Aug  8 06:00:00 2026");
+		expect(queryEnvironment).toMatchObject({ TZ: "UTC", LC_ALL: "C" });
+	});
+
+	it("preserves the surrounding environment", () => {
+		let queryEnvironment: NodeJS.ProcessEnv | undefined;
+		const previous = process.env.PRIME_AGENT_PROCESS_START_TEST;
+		process.env.PRIME_AGENT_PROCESS_START_TEST = "preserved";
+		try {
+			getPsProcessStartId(1234, (_command, _args, options) => {
+				queryEnvironment = options?.env;
+				return "Sat Aug  8 06:00:00 2026\n";
+			});
+			expect(queryEnvironment?.PRIME_AGENT_PROCESS_START_TEST).toBe("preserved");
+		} finally {
+			if (previous === undefined) {
+				delete process.env.PRIME_AGENT_PROCESS_START_TEST;
+			} else {
+				process.env.PRIME_AGENT_PROCESS_START_TEST = previous;
+			}
+		}
+	});
+});
+
 describe("parsePsEtimes", () => {
 	it("maps pid to elapsed seconds", () => {
 		const uptimes = parsePsEtimes("  1234  86400\n  5678      42\n");