fix(db): preserve explicit gcTime of 0 on live query collections

.changeset/live-query-gctime-zero.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/db': patch
+---
+
+Preserve an explicit `gcTime: 0` on live query collections. The live query config builder used `this.config.gcTime || 5000`, so a `gcTime` of `0` (which disables garbage collection) was treated as unset and silently replaced by the 5s default, causing the collection to be garbage collected instead of kept alive. Use `??` so only `undefined` falls back to the default.

packages/db/src/query/live/collection-config-builder.ts

@@ -248,7 +248,7 @@ export class CollectionConfigBuilder<
       sync: this.getSyncConfig(),
       compare: this.compare,
       defaultStringCollation: this.compareOptions,
-      gcTime: this.config.gcTime || 5000, // 5 seconds by default for live queries
+      gcTime: this.config.gcTime ?? 5000, // 5 seconds by default for live queries
       schema: this.config.schema,
       onInsert: this.config.onInsert,
       onUpdate: this.config.onUpdate,

packages/db/tests/query/live-query-collection.test.ts

@@ -449,6 +449,21 @@ describe(`createLiveQueryCollection`, () => {
     })
   })
 
+  it(`should forward an explicit gcTime of 0 (disable GC) instead of coercing it to the default`, () => {
+    const options = liveQueryCollectionOptions({
+      query: (q) =>
+        q
+          .from({ user: usersCollection })
+          .where(({ user }) => eq(user.active, true)),
+      gcTime: 0,
+    })
+
+    // gcTime: 0 disables garbage collection. A `|| 5000` fallback treats the
+    // explicit 0 as unset and silently replaces it with the 5s default, so the
+    // collection is garbage collected instead of being kept alive.
+    expect(options.gcTime).toBe(0)
+  })
+
   it(`should not reuse finalized graph after GC cleanup (resubscribe is safe)`, async () => {
     const liveQuery = createLiveQueryCollection({
       query: (q) =>