diff --git a/gateway/relay/adapter.py b/gateway/relay/adapter.py
index 703cea0470..10cec8775d 100644
--- a/gateway/relay/adapter.py
+++ b/gateway/relay/adapter.py
@@ -780,9 +780,31 @@ class RelayAdapter(BasePlatformAdapter):
         channel_id = str(payload.get("channel_id") or "")
         guild_id = payload.get("guild_id")  # real Discord interaction wire field
         source = SessionSource(
-            platform=Platform.RELAY,
+            # The LOGICAL platform, not Platform.RELAY. This lane parses a
+            # Discord interaction wire payload, so the underlying platform is
+            # known statically — and it must be stamped for three consumers:
+            #   1. Session keys: the connector binds the interaction's
+            #      follow-up capability under buildSessionKey with
+            #      platform="discord" (interactionSessionSource); the relay
+            #      TEXT lane (ws_transport._event_from_wire) also maps to the
+            #      logical platform. RELAY here forked interaction sessions
+            #      away from both.
+            #   2. /sethome: with platform=RELAY the handler filed the home
+            #      channel under platforms.relay.home_channel (invisible to
+            #      cron delivery, which looks up the logical platform) and
+            #      mirrored it into the dead RELAY_HOME_CHANNEL env var.
+            #   3. Egress: _capture_scope records _platform_by_chat from this
+            #      value and deliberately skips the generic "relay".
+            platform=Platform.DISCORD,
             chat_id=channel_id,
-            chat_type="channel" if guild_id else "dm",
+            # "group", not "channel": the session key embeds chat_type, and
+            # BOTH the connector's capability binding (interactionSessionSource
+            # → buildSessionKey, chat_type "group") and the native Discord
+            # adapter's channel events key guild channels as "group". A
+            # "channel" slot here forked the interaction session from the
+            # chat's message session AND from the vault key the connector
+            # bound the follow-up capability under.
+            chat_type="group" if guild_id else "dm",
             user_id=str(user.get("id"))
             if isinstance(user, dict) and user.get("id")
             else None,
@@ -793,6 +815,15 @@ class RelayAdapter(BasePlatformAdapter):
             if guild_id
             else None,  # Discord guild → generic scope slot
             message_id=str(payload.get("id")) if payload.get("id") else None,
+            # Same upstream-trust marker the relay text lane stamps
+            # (ws_transport._event_from_wire): this interaction arrived over
+            # the per-instance-authenticated relay WS after the connector
+            # verified Discord's edge signature and resolved the tenant.
+            # Without it, authz treated the event as unauthenticated relay
+            # traffic — and /sethome's via_relay guard never engaged, which is
+            # how platform=RELAY home channels slipped through in the first
+            # place. Set locally, never read off the wire.
+            delivered_via_upstream_relay=True,
         )
         event = MessageEvent(text=text, message_type=message_type, source=source)
         if itype == 3:
diff --git a/tests/gateway/relay/test_relay_passthrough.py b/tests/gateway/relay/test_relay_passthrough.py
index 53e5424426..2150e9bf0b 100644
--- a/tests/gateway/relay/test_relay_passthrough.py
+++ b/tests/gateway/relay/test_relay_passthrough.py
@@ -17,7 +17,7 @@ import json
 
 import pytest
 
-from gateway.config import PlatformConfig
+from gateway.config import Platform, PlatformConfig
 from gateway.relay.adapter import RelayAdapter
 from gateway.relay.descriptor import CONTRACT_VERSION, CapabilityDescriptor
 from gateway.relay.ws_transport import PassthroughForward, _passthrough_from_wire
@@ -120,9 +120,21 @@ async def test_discord_interaction_routes_through_handle_message(adapter, monkey
     assert ev.source.chat_id == "chan-9"
     assert ev.source.scope_id == "guild-7"
     assert ev.source.user_id == "user-3"
-    assert ev.source.chat_type == "channel"
+    # LOGICAL platform + native-parity chat_type: the session key must match
+    # the connector's capability-vault binding (interactionSessionSource →
+    # buildSessionKey: platform "discord", chat_type "group") and the relay
+    # text lane. Platform.RELAY / "channel" here forked the session and made
+    # /sethome file the home channel under platforms.relay (invisible to cron).
+    assert ev.source.platform == Platform.DISCORD
+    assert ev.source.chat_type == "group"
+    # Authenticated upstream-trust marker, parity with the relay text lane
+    # (ws_transport._event_from_wire) — /sethome's via_relay guard keys on it.
+    assert ev.source.delivered_via_upstream_relay is True
     # Scope captured so the agent's reply re-asserts scope_id for egress.
     assert adapter._scope_by_chat.get("chan-9") == "guild-7"
+    # The logical platform is now recorded for egress sender selection too
+    # (_capture_scope skips only the generic "relay").
+    assert adapter._platform_by_chat.get("chan-9") == "discord"
 
 
 @pytest.mark.asyncio
@@ -166,3 +178,35 @@ async def test_application_command_subcommand_nesting_renders_names_then_values(
     assert ev.get_command_args() == "run deploy"
 
 
+@pytest.mark.asyncio
+async def test_dm_interaction_keys_as_discord_dm(adapter, monkeypatch):
+    """A guild-less (DM) interaction keys as a Discord DM: logical platform,
+    chat_type 'dm', and the authenticated relay marker — the /sethome-in-DM
+    shape must file under platforms.discord, never platforms.relay."""
+    await adapter.connect()
+    stub = adapter._transport
+    seen = []
+
+    async def fake_handle(event):
+        seen.append(event)
+
+    monkeypatch.setattr(adapter, "handle_message", fake_handle)
+    fwd = _interaction_forward(
+        {
+            "id": "i-dm",
+            "type": 2,
+            "channel_id": "dm-chan-1",
+            "data": {"name": "sethome"},
+            "user": {"id": "u9", "username": "ben"},
+        }
+    )
+    await stub.push_passthrough(fwd)
+    assert len(seen) == 1
+    ev = seen[0]
+    assert ev.source.platform == Platform.DISCORD
+    assert ev.source.chat_type == "dm"
+    assert ev.source.scope_id is None
+    assert ev.source.user_id == "u9"
+    assert ev.source.delivered_via_upstream_relay is True
+
+