fix(query-core): clear timers when timer ID is 0 (TanStack#10401)

* fix(query-core): use explicit undefined check for timer IDs

  Custom TimeoutProvider implementations may return 0 as a valid timer
  ID (e.g. a counter-based provider), but the existing truthy checks
  treated 0 as "no timer" and skipped clearTimeout/clearInterval. This
  left stale timers running, causing unexpected refetches and GC leaks.

  Compare against undefined instead, matching the optional `?:
  ManagedTimerId` field types.

  Fixes TanStack#10395

* chore: add changeset for TanStack#10395

---------

Co-authored-by: Dominik Dorfmeister 🔮 <office@dorfmeister.cc>

Author: semimikoh

.changeset/fix-timer-id-zero-falsy-check.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/query-core': patch
+---
+
+fix(query-core): use explicit `undefined` check for timer IDs so that custom `TimeoutProvider`s returning `0` as a valid timer ID are properly cleared

packages/query-core/src/queryObserver.ts

@@ -417,14 +417,14 @@ export class QueryObserver<
   }
 
   #clearStaleTimeout(): void {
-    if (this.#staleTimeoutId) {
+    if (this.#staleTimeoutId !== undefined) {
       timeoutManager.clearTimeout(this.#staleTimeoutId)
       this.#staleTimeoutId = undefined
     }
   }
 
   #clearRefetchInterval(): void {
-    if (this.#refetchIntervalId) {
+    if (this.#refetchIntervalId !== undefined) {
       timeoutManager.clearInterval(this.#refetchIntervalId)
       this.#refetchIntervalId = undefined
     }

packages/query-core/src/removable.ts

@@ -30,7 +30,7 @@ export abstract class Removable {
   }
 
   protected clearGcTimeout() {
-    if (this.#gcTimeout) {
+    if (this.#gcTimeout !== undefined) {
       timeoutManager.clearTimeout(this.#gcTimeout)
       this.#gcTimeout = undefined
     }