fix(discord): widen expired-defer handling to /thread slash command

Same 10062 degrade-gracefully pattern as _run_simple_slash: create the
thread anyway, skip the ephemeral followups that need a live
interaction token. Non-expiry defer errors still raise.

plugins/platforms/discord/adapter.py

@@ -4600,7 +4600,17 @@ class DiscordAdapter(BasePlatformAdapter):
         """Create a Discord thread from a slash command and start a session in it."""
         if not await self._check_slash_authorization(interaction, "/thread"):
             return
-        await interaction.response.defer(ephemeral=True)
+        deferred_response = False
+        try:
+            await interaction.response.defer(ephemeral=True)
+            deferred_response = True
+        except Exception as e:
+            if not self._is_discord_unknown_interaction(e):
+                raise
+            logger.warning(
+                "[Discord] /thread: interaction expired before defer. "
+                "Creating the thread anyway, skipping interaction followups.",
+            )
         result = await self._create_thread(
             interaction,
             name=name,
@@ -4610,7 +4620,8 @@ class DiscordAdapter(BasePlatformAdapter):
 
         if not result.get("success"):
             error = result.get("error", "unknown error")
-            await interaction.followup.send(f"Failed to create thread: {error}", ephemeral=True)
+            if deferred_response:
+                await interaction.followup.send(f"Failed to create thread: {error}", ephemeral=True)
             return
 
         thread_id = result.get("thread_id")
@@ -4618,7 +4629,8 @@ class DiscordAdapter(BasePlatformAdapter):
 
         # Tell the user where the thread is
         link = f"<#{thread_id}>" if thread_id else f"**{thread_name}**"
-        await interaction.followup.send(f"Created thread {link}", ephemeral=True)
+        if deferred_response:
+            await interaction.followup.send(f"Created thread {link}", ephemeral=True)
 
         # Track thread participation so follow-ups don't require @mention
         if thread_id:

tests/gateway/test_discord_thread_slash_expired_defer.py

@@ -0,0 +1,72 @@
+"""Sibling coverage for expired slash defer handling: /thread creation must
+still run when the interaction token has expired (Discord error 10062), just
+skipping the ephemeral followups."""
+
+from types import SimpleNamespace
+from unittest.mock import AsyncMock
+
+import pytest
+
+from gateway.config import PlatformConfig
+from plugins.platforms.discord.adapter import DiscordAdapter
+
+
+class _UnknownInteraction(Exception):
+    status = 404
+    code = 10062
+
+
+def _adapter():
+    a = DiscordAdapter(PlatformConfig(enabled=True, token="***"))
+    a._check_slash_authorization = AsyncMock(return_value=True)
+    return a
+
+
+@pytest.mark.asyncio
+async def test_thread_create_slash_survives_expired_defer():
+    adapter = _adapter()
+    interaction = SimpleNamespace(
+        response=SimpleNamespace(defer=AsyncMock(side_effect=_UnknownInteraction("Unknown interaction"))),
+        followup=SimpleNamespace(send=AsyncMock()),
+    )
+    adapter._create_thread = AsyncMock(
+        return_value={"success": True, "thread_id": "999", "thread_name": "t"}
+    )
+    adapter._threads = SimpleNamespace(mark=lambda _tid: None)
+
+    await adapter._handle_thread_create_slash(interaction, name="t")
+
+    adapter._create_thread.assert_awaited_once()
+    interaction.followup.send.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_thread_create_slash_normal_defer_still_follows_up():
+    adapter = _adapter()
+    interaction = SimpleNamespace(
+        response=SimpleNamespace(defer=AsyncMock()),
+        followup=SimpleNamespace(send=AsyncMock()),
+    )
+    adapter._create_thread = AsyncMock(
+        return_value={"success": True, "thread_id": "999", "thread_name": "t"}
+    )
+    adapter._threads = SimpleNamespace(mark=lambda _tid: None)
+
+    await adapter._handle_thread_create_slash(interaction, name="t")
+
+    interaction.followup.send.assert_awaited()
+
+
+@pytest.mark.asyncio
+async def test_thread_create_slash_reraises_non_expiry_errors():
+    adapter = _adapter()
+    interaction = SimpleNamespace(
+        response=SimpleNamespace(defer=AsyncMock(side_effect=RuntimeError("boom"))),
+        followup=SimpleNamespace(send=AsyncMock()),
+    )
+    adapter._create_thread = AsyncMock()
+
+    with pytest.raises(RuntimeError):
+        await adapter._handle_thread_create_slash(interaction, name="t")
+
+    adapter._create_thread.assert_not_awaited()