fix(analytics): drop chunk-load errors from PostHog error tracking

docs/analytics.md

@@ -182,6 +182,10 @@ exception carries `route_name` too.
   `:code` in every property of every event, nested ones included
   (`$current_url`, `$pathname`, `$referrer`, `$initial_*`, exceptions,
   session replay snapshots).
+- Chunk-load errors are not sent: `before_send`
+  (`dropChunkLoadErrors`) drops an exception whose entries are all
+  chunk-load errors. `chunkReload` handles them, but a programmatic
+  `router.push()` still rejects and posthog-js would report it as unhandled.
 
 ## Person properties
 

src/lib/analytics/usePostHog.ts

@@ -5,6 +5,7 @@ import { useAnalyticsConsent } from "@/lib/analytics/useAnalyticsConsent";
 
 // Util
 import { redact } from "@/util/data";
+import { isChunkLoadError } from "@/lib/chunkReload";
 
 // Types & Interfaces
 import type { BeforeSendFn, PostHog, Properties } from "posthog-js";
@@ -50,6 +51,19 @@ export const maskUrlCodes: BeforeSendFn = (event) => {
 	};
 };
 
+/**
+ * before_send: drops exceptions that are only chunk-load errors. chunkReload
+ * already handles those (reload or message), but vue-router still rejects
+ * the router.push() that hit them, and posthog-js reports that rejection as
+ * unhandled after every deploy.
+ */
+export const dropChunkLoadErrors: BeforeSendFn = (event) => {
+	if (event?.event !== "$exception") return event;
+	const list = event.properties.$exception_list;
+	if (!Array.isArray(list) || !list.length) return event;
+	return list.every((entry) => isChunkLoadError(entry?.value)) ? null : event;
+};
+
 // storage keys PostHog writes: its own, the opt-out flag and survey state
 const POSTHOG_STORAGE_KEY =
 	/^((__)?ph_|seenSurvey_|inProgressSurvey_|lastSeenSurveyDate$)/;
@@ -169,7 +183,7 @@ async function startAnalytics(): Promise<void> {
 			// no cookie
 			persistence: "localStorage",
 			respect_dnt: true,
-			before_send: maskUrlCodes,
+			before_send: [maskUrlCodes, dropChunkLoadErrors],
 		});
 
 		// register global versions

src/tests/lib/analytics/usePostHog.test.ts

@@ -502,12 +502,16 @@ describe("usePostHog", () => {
 		) => ({ uuid: "u", event: name, properties, ...extra });
 
 		it("is passed to posthog.init as before_send", async () => {
-			const { maskUrlCodes } = await load({ consent: "granted" });
+			const { maskUrlCodes, dropChunkLoadErrors } = await load({
+				consent: "granted",
+			});
 			await settle();
 
 			expect(posthog.init).toHaveBeenCalledWith(
 				"phc_test",
-				expect.objectContaining({ before_send: maskUrlCodes })
+				expect.objectContaining({
+					before_send: [maskUrlCodes, dropChunkLoadErrors],
+				})
 			);
 		});
 
@@ -609,6 +613,51 @@ describe("usePostHog", () => {
 		});
 	});
 
+	describe("dropChunkLoadErrors", () => {
+		const CHUNK =
+			"Failed to fetch dynamically imported module: https://prunplanner.org/assets/chunks/HomepageView.abc123.js";
+		const exception = (...values: string[]) => ({
+			uuid: "u",
+			event: "$exception",
+			properties: {
+				$exception_list: values.map((value) => ({
+					type: "TypeError",
+					value,
+					mechanism: { handled: false },
+				})),
+			},
+		});
+
+		it("drops an exception that is only a chunk-load error", async () => {
+			const { dropChunkLoadErrors } = await load();
+
+			expect(dropChunkLoadErrors(exception(CHUNK))).toBeNull();
+		});
+
+		it("keeps other exceptions, mixed ones included", async () => {
+			const { dropChunkLoadErrors } = await load();
+			const other = exception("Cannot read properties of undefined");
+			const mixed = exception(CHUNK, "Cannot read properties of undefined");
+
+			expect(dropChunkLoadErrors(other)).toBe(other);
+			expect(dropChunkLoadErrors(mixed)).toBe(mixed);
+		});
+
+		it("keeps other events and exceptions without a list", async () => {
+			const { dropChunkLoadErrors } = await load();
+			const pageview = {
+				uuid: "u",
+				event: "$pageview",
+				properties: { message: CHUNK },
+			};
+			const empty = { uuid: "u", event: "$exception", properties: {} };
+
+			expect(dropChunkLoadErrors(null)).toBeNull();
+			expect(dropChunkLoadErrors(pageview)).toBe(pageview);
+			expect(dropChunkLoadErrors(empty)).toBe(empty);
+		});
+	});
+
 	// deny relies on posthog-js dropping requests while `__loaded` is false
 	describe("real posthog-js", () => {
 		async function captureWithRealPostHog() {