fix(nestsclient): skip Active announce when AnnouncePlease prefix doesn't match — moq-lite Lite-03 announce.rs

Per moq-lite Lite-03 (kixelated/moq `rs/moq-lite/src/lite/announce.rs`),
a publisher MUST only emit `Announce(Active)` for broadcasts whose path
starts with the requested AnnouncePlease prefix. Pre-fix, when
`MoqLitePath.stripPrefix(please.prefix, ourSuffix)` returned `null`, we
fell through to `?: announcePublisher.suffix` and emitted Active under
our full suffix anyway, falsely advertising the broadcast under a
prefix the subscriber didn't request.

Production never bit because the relay always opens its announce bidi
to us with `prefix=""` (which always matches), but a future peer-to-
peer or namespace-scoped subscriber would have observed a ghost
broadcast under whatever prefix they asked about.

The fix: if `stripPrefix` returns `null`, FIN the bidi cleanly without
writing any Announce body. The subscriber sees an empty announce
stream and moves on.

Regression test:
`MoqLiteSessionTest.publisher_skips_announce_when_announce_please_prefix_does_not_match`.

Audit doc: nestsClient/plans/2026-05-09-moq-lite-rfc-compliance.md (M4).

https://claude.ai/code/session_012TGfo99Ugz7fcCPv85a8Tq

nestsClient/src/commonMain/kotlin/com/vitorpamplona/nestsclient/moq/lite/MoqLiteSession.kt

@@ -838,8 +838,27 @@ class MoqLiteSession internal constructor(
                         MoqLiteControlType.Announce -> {
                             val pleasePayload = buffer.readSizePrefixed() ?: return@collect
                             val please = MoqLiteCodec.decodeAnnouncePlease(pleasePayload)
-                            val emittedSuffix =
+                            // Per moq-lite Lite-03 (`rs/moq-lite/src/lite/announce.rs`),
-                                MoqLitePath.stripPrefix(please.prefix, announcePublisher.suffix) ?: announcePublisher.suffix
+                            // a publisher MUST only emit Active for broadcasts whose
+                            // path starts with the requested prefix. If our suffix
+                            // doesn't match, FIN cleanly without writing any
+                            // Announce — the relay/peer sees an empty announce
+                            // stream and moves on. Pre-fix we'd fall through the
+                            // `null` branch of stripPrefix and falsely emit
+                            // `Active(suffix=ourFullSuffix)`, advertising under a
+                            // prefix the subscriber didn't ask for. Production
+                            // never bit because the relay always asks for
+                            // `prefix=""`, but a future peer-to-peer or
+                            // namespace-scoped subscriber would see a ghost.
+                            val emittedSuffix = MoqLitePath.stripPrefix(please.prefix, announcePublisher.suffix)
+                            if (emittedSuffix == null) {
+                                Log.w("NestTx") {
+                                    "ANNOUNCE inbound prefix='${please.prefix}' does not match publisher.suffix='${announcePublisher.suffix}' — FIN without Active"
+                                }
+                                runCatching { bidi.finish() }
+                                dispatched = true
+                                return@collect
+                            }
                             bidi.write(
                                 MoqLiteCodec.encodeAnnounce(
                                     MoqLiteAnnounce(

nestsClient/src/commonTest/kotlin/com/vitorpamplona/nestsclient/moq/lite/MoqLiteSessionTest.kt

@@ -533,6 +533,43 @@ class MoqLiteSessionTest {
             session.close()
         }
 
+    @Test
+    fun publisher_skips_announce_when_announce_please_prefix_does_not_match() =
+        runBlocking {
+            // Lite-03 audit M4: when the relay opens an Announce bidi
+            // with a non-empty prefix that doesn't match our broadcast
+            // suffix, the publisher MUST NOT emit Active under the
+            // requested prefix (or under our own suffix) — kixelated's
+            // `rs/moq-lite/src/lite/announce.rs::Producer` only emits
+            // for matching prefixes. Pre-fix we'd fall through the
+            // `null` branch of `MoqLitePath.stripPrefix` and announce
+            // ourselves anyway. Verified here by FINing the bidi
+            // cleanly without writing any Announce body.
+            val (clientSide, serverSide) = FakeWebTransport.pair()
+            val session = MoqLiteSession.client(clientSide, pumpScope)
+
+            val publisher = session.publish(broadcastSuffix = "speakerPubkey", track = "audio/data")
+
+            // Relay opens Announce bidi with a non-matching prefix.
+            val relayBidi = serverSide.openBidiStream()
+            relayBidi.write(Varint.encode(MoqLiteControlType.Announce.code))
+            relayBidi.write(
+                MoqLiteCodec.encodeAnnouncePlease(
+                    MoqLiteAnnouncePlease(prefix = "differentRoom"),
+                ),
+            )
+
+            // The bidi MUST end with no body (peer FIN), and
+            // `relayBidi.incoming().toList()` therefore returns empty.
+            // Use a generous timeout so a slow fake doesn't false-pass
+            // by hanging instead of FINing.
+            val chunks = withTimeout(2_000) { relayBidi.incoming().toList() }
+            assertEquals(emptyList(), chunks, "non-matching prefix must FIN without writing any Announce body")
+
+            publisher.close()
+            session.close()
+        }
+
     @Test
     fun publisher_replies_subscribeDrop_when_track_is_not_published() =
         runBlocking {