fix(relay): compare every filter in FiltersChanged, not just the first

`needsToResendRequest(List, List)` used a non-local `return` inside
`forEachIndexed`, so the loop always returned on iteration 0 and only
`filters[0]` was ever compared. A subscription whose first filter happened
to be unchanged reported "no resend needed" however much the rest had
changed, leaving the relay serving a stale filter set and the app silently
missing events. Only the size check offered any protection, so the bug was
invisible whenever the filter count stayed constant.

Replaces the loop with an indexed scan over all filters, which also drops
the lambda allocation and matches the hot-path style in this package.

Adds FiltersChangedTest. 3 of its 9 cases fail on the unfixed code — all of
them changes beyond index 0 — while the other 6 pass both before and after,
pinning the blast radius to exactly the buggy behaviour. Coverage includes
the deliberate `since`-moves-forward exemption, which must not trigger a
resend on any index.

Note for reviewers: PoolRequests.kt:490 and :528 use this inverted as a
"same as last" refusal check, so those become stricter — filter sets that
differ only beyond index 0 were previously treated as identical and will
now correctly be treated as changed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip01Core/relay/client/pool/FiltersChanged.kt

@@ -29,10 +29,14 @@ object FiltersChanged {
     ): Boolean {
         if (oldFilters.size != newFilters.size) return true
 
-        oldFilters.forEachIndexed { index, oldFilter ->
-            val newFilter = newFilters.getOrNull(index) ?: return true
-
-            return needsToResendRequest(oldFilter, newFilter)
+        // Every filter must be compared. This used to be a forEachIndexed whose body
+        // `return`ed on the first iteration — a non-local return from this function — so
+        // only filters[0] was ever checked and a subscription whose first filter happened
+        // to be unchanged reported "no resend needed" however much the rest had changed,
+        // leaving the relay serving a stale filter set.
+        // Indexing is safe: the sizes were just proven equal.
+        for (i in oldFilters.indices) {
+            if (needsToResendRequest(oldFilters[i], newFilters[i])) return true
         }
         return false
     }

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip01Core/relay/client/pool/FiltersChangedTest.kt

@@ -0,0 +1,93 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.nip01Core.relay.client.pool
+
+import com.vitorpamplona.quartz.nip01Core.relay.filters.Filter
+import kotlin.test.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class FiltersChangedTest {
+    private fun authors(vararg a: String) = Filter(authors = a.toList())
+
+    @Test
+    fun emptyListsAreUnchanged() {
+        assertFalse(FiltersChanged.needsToResendRequest(emptyList(), emptyList()))
+    }
+
+    @Test
+    fun differentSizesNeedResend() {
+        assertTrue(FiltersChanged.needsToResendRequest(listOf(authors("a")), listOf(authors("a"), authors("b"))))
+    }
+
+    @Test
+    fun identicalSingleFilterDoesNotNeedResend() {
+        assertFalse(FiltersChanged.needsToResendRequest(listOf(authors("a")), listOf(authors("a"))))
+    }
+
+    @Test
+    fun changedFirstFilterNeedsResend() {
+        assertTrue(FiltersChanged.needsToResendRequest(listOf(authors("a")), listOf(authors("b"))))
+    }
+
+    /**
+     * Regression: the loop used a non-local `return` on the first iteration, so only
+     * filters[0] was ever compared. A subscription whose first filter was unchanged
+     * reported "no resend needed" no matter what happened to the rest, and silently
+     * went stale — the relay kept serving the old filter set.
+     */
+    @Test
+    fun changedSecondFilterNeedsResend() {
+        val old = listOf(authors("a"), authors("b"))
+        val new = listOf(authors("a"), authors("CHANGED"))
+        assertTrue(FiltersChanged.needsToResendRequest(old, new))
+    }
+
+    @Test
+    fun changedLastOfManyNeedsResend() {
+        val old = listOf(authors("a"), authors("b"), authors("c"), authors("d"))
+        val new = listOf(authors("a"), authors("b"), authors("c"), authors("CHANGED"))
+        assertTrue(FiltersChanged.needsToResendRequest(old, new))
+    }
+
+    @Test
+    fun allIdenticalOfManyDoesNotNeedResend() {
+        val old = listOf(authors("a"), authors("b"), authors("c"))
+        val new = listOf(authors("a"), authors("b"), authors("c"))
+        assertFalse(FiltersChanged.needsToResendRequest(old, new))
+    }
+
+    /** `since` moving forward is deliberately NOT a resend trigger, on any index. */
+    @Test
+    fun sinceMovingForwardOnLaterFilterDoesNotNeedResend() {
+        val old = listOf(Filter(authors = listOf("a"), since = 100), Filter(authors = listOf("b"), since = 100))
+        val new = listOf(Filter(authors = listOf("a"), since = 100), Filter(authors = listOf("b"), since = 200))
+        assertFalse(FiltersChanged.needsToResendRequest(old, new))
+    }
+
+    /** ...but moving backwards in time is, including on a later filter. */
+    @Test
+    fun sinceMovingBackwardsOnLaterFilterNeedsResend() {
+        val old = listOf(Filter(authors = listOf("a"), since = 100), Filter(authors = listOf("b"), since = 200))
+        val new = listOf(Filter(authors = listOf("a"), since = 100), Filter(authors = listOf("b"), since = 100))
+        assertTrue(FiltersChanged.needsToResendRequest(old, new))
+    }
+}