Add server-initiated-multi-server-arbitration scenario (#62)

README.md

@@ -16,6 +16,7 @@ Current scenarios:
 - `server-initiated-request-format` (Client requests a mid-stream codec switch): start the server first, then the client. The server begins streaming in Opus; the client is instructed to emit `stream/request-format` with FLAC at a fixed timestamp and the server responds with a fresh `stream/start`. No SDK currently emits `stream/request-format`, so every case currently fails fast on the `stream-request-format-emit` capability
 - `server-initiated-pcm-24bit` (Server initiates connection and client wants 24-bit PCM): start the server first, then the client. The server re-packs the fixture as 24-bit PCM (3-byte packed, little-endian, two's complement). No SDK in the matrix declares the `pcm-24bit-decode` capability yet, so every case currently fails fast and the matrix surfaces the gap (notably the `sendspin-go` SDK has no 24-bit code path per the audit)
 - `server-initiated-external-source` (Client enters and leaves `external_source` mid-stream): start the server first, then the client. The client transitions to `external_source` and back; the harness verifies the server emits the right `group/update` and `stream/end` and that the previous group is restored. Per the audit only SendspinKit exposes a client-side API; no client in the matrix declares the `external-source-client-api` capability yet, so every case fails fast
+- `server-initiated-multi-server-arbitration` (Client arbitrates between two connected servers): two servers connect to one client with different `connection_reason` values; the harness verifies the client sends `client/goodbye` with `'another_server'` on the right socket and ends up speaking to the right server per the spec's decision table. Per the audit only sendspin-cpp and sendspin-cli implement these rules; no client in the matrix declares the `multi-server-arbitration` capability yet, so every case fails fast
 
 ## Current coverage
 

src/conformance/implementations.py

@@ -67,6 +67,7 @@
                 "stream-request-format-emit",
                 "pcm-24bit-decode",
                 "external-source-client-api",
+                "multi-server-arbitration",
             ),
         ),
     ),

src/conformance/scenarios.py

@@ -196,6 +196,27 @@
 )
 
 
+SERVER_INITIATED_MULTI_SERVER_ARBITRATION = ScenarioSpec(
+    id="server-initiated-multi-server-arbitration",
+    display_name="Client arbitrates between two connected servers",
+    description=(
+        "Two servers connect to one client (one with "
+        "`connection_reason: 'discovery'`, one with `'playback'`). The harness "
+        "asserts the client sends `client/goodbye` with the right reason "
+        "(`'another_server'`) on the right socket and ends up speaking to the "
+        "right server per the spec's decision table. Per the audit, only "
+        "sendspin-cpp and sendspin-cli (via aiosendspin) implement these rules; "
+        "every other client SDK collapses to \"whichever connection happened "
+        "first\" and defaults to the wrong goodbye reason on switch."
+    ),
+    initiator_role="server",
+    preferred_codec="pcm",
+    required_role_families=("player",),
+    verification_mode="capability-only",
+    required_capability="multi-server-arbitration",
+)
+
+
 SERVER_INITIATED_EXTERNAL_SOURCE = ScenarioSpec(
     id="server-initiated-external-source",
     display_name="Client enters and leaves `external_source` mid-stream",
@@ -247,6 +268,7 @@
     SERVER_INITIATED_REQUEST_FORMAT,
     SERVER_INITIATED_PCM_24BIT,
     SERVER_INITIATED_EXTERNAL_SOURCE,
+    SERVER_INITIATED_MULTI_SERVER_ARBITRATION,
 )
 
 SCENARIOS: dict[str, ScenarioSpec] = {scenario.id: scenario for scenario in SCENARIO_LIST}