chore: import upstream snapshot with attribution

Server/tests/test_stdio_instance_resolution.py

@@ -0,0 +1,100 @@
+"""Stdio instance-resolution guard tests.
+
+Regression coverage for #1023: the stdio connection pool used to silently
+route an unbound session (no unity_instance, no default) to the most-recently
+heartbeated editor, letting one project's session retarget another. The pool
+now refuses to guess when 2+ instances are connected, mirroring the HTTP
+"multiple connected, no active set" guard.
+"""
+
+from datetime import datetime, timedelta
+
+import pytest
+
+from models.models import UnityInstanceInfo
+from transport.legacy.unity_connection import UnityConnectionPool
+
+
+def _instance(name: str, port: int, heartbeat: datetime | None) -> UnityInstanceInfo:
+    return UnityInstanceInfo(
+        id=f"{name}@{name.lower()}hash",
+        name=name,
+        path=f"/path/{name}",
+        hash=f"{name.lower()}hash",
+        port=port,
+        status="running",
+        last_heartbeat=heartbeat,
+    )
+
+
+def test_resolve_none_with_single_instance_selects_it():
+    """Sole connected instance is unambiguous and selected without a hint."""
+    pool = UnityConnectionPool()
+    only = _instance("Solo", 6400, datetime.now())
+
+    resolved = pool._resolve_instance_id(None, [only])
+
+    assert resolved.id == only.id
+
+
+def test_resolve_none_with_multiple_instances_raises():
+    """2+ instances and nothing pinned must error instead of guessing (#1023)."""
+    pool = UnityConnectionPool()
+    now = datetime.now()
+    newer = _instance("Newer", 6400, now)
+    older = _instance("Older", 6401, now - timedelta(seconds=30))
+
+    with pytest.raises(ConnectionError, match="Multiple Unity instances"):
+        pool._resolve_instance_id(None, [newer, older])
+
+
+def test_resolve_none_does_not_fall_back_to_most_recent_heartbeat():
+    """The guard must not leak the most-recently-heartbeated id into the error.
+
+    Proves we no longer auto-pick sorted_instances[0]; both ids are offered as
+    explicit choices rather than one being silently returned.
+    """
+    pool = UnityConnectionPool()
+    now = datetime.now()
+    newer = _instance("Newer", 6400, now)
+    older = _instance("Older", 6401, now - timedelta(seconds=30))
+
+    with pytest.raises(ConnectionError) as exc_info:
+        pool._resolve_instance_id(None, [newer, older])
+
+    message = str(exc_info.value)
+    assert newer.id in message
+    assert older.id in message
+
+
+def test_resolve_none_with_default_instance_still_works():
+    """An explicit default short-circuits the multi-instance guard."""
+    pool = UnityConnectionPool()
+    pool._default_instance_id = "Newer@newerhash"
+    now = datetime.now()
+    newer = _instance("Newer", 6400, now)
+    older = _instance("Older", 6401, now - timedelta(seconds=30))
+
+    resolved = pool._resolve_instance_id(None, [newer, older])
+
+    assert resolved.id == "Newer@newerhash"
+
+
+def test_resolve_explicit_identifier_unaffected_by_guard():
+    """Explicit selection still resolves even with multiple instances."""
+    pool = UnityConnectionPool()
+    now = datetime.now()
+    newer = _instance("Newer", 6400, now)
+    older = _instance("Older", 6401, now - timedelta(seconds=30))
+
+    resolved = pool._resolve_instance_id("Older@olderhash", [newer, older])
+
+    assert resolved.id == "Older@olderhash"
+
+
+def test_resolve_no_instances_raises_distinct_error():
+    """No instances at all still raises the "none found" error, not the guard."""
+    pool = UnityConnectionPool()
+
+    with pytest.raises(ConnectionError, match="No Unity Editor instances found"):
+        pool._resolve_instance_id(None, [])