fix(discord): narrow rate-limit catch and move sync state under gateway/

Two follow-ups on top of helix4u's slash-command sync hardening:

- Only suppress exceptions that are actually Discord 429 rate limits
  (discord.RateLimited, HTTPException with status 429, or a clearly
  rate-limit-named duck type). Arbitrary failures that happen to expose
  a retry_after attribute now re-raise to the outer handler instead of
  silently swallowing a cooldown.
- Move the sync-state JSON under $HERMES_HOME/gateway/ so the home root
  stops collecting ad-hoc runtime files.

Added a test verifying unrelated exceptions don't get misclassified as
rate limits.

tests/gateway/test_discord_connect.py

@@ -612,12 +612,59 @@ async def test_post_connect_initialization_respects_discord_retry_after(tmp_path
     await adapter._run_post_connect_initialization()
 
     sync.assert_awaited_once()
-    state = json.loads((tmp_path / discord_platform._DISCORD_COMMAND_SYNC_STATE_FILE).read_text())
+    state_path = (
+        tmp_path
+        / discord_platform._DISCORD_COMMAND_SYNC_STATE_SUBDIR
+        / discord_platform._DISCORD_COMMAND_SYNC_STATE_FILENAME
+    )
+    state = json.loads(state_path.read_text())
     entry = state["999"]
     assert entry["retry_after"] == 123.0
     assert entry["retry_after_until"] > entry["last_attempt_at"]
 
 
+@pytest.mark.asyncio
+async def test_post_connect_initialization_reraises_non_rate_limit_exceptions(tmp_path, monkeypatch):
+    """Arbitrary failures during sync must surface, not be swallowed as rate-limits."""
+    adapter = DiscordAdapter(PlatformConfig(enabled=True, token="test-token"))
+    monkeypatch.setattr("hermes_constants.get_hermes_home", lambda: tmp_path)
+
+    class _DesiredCommand:
+        def to_dict(self, tree):
+            return {"name": "status", "description": "Show Hermes status", "type": 1, "options": []}
+
+    adapter._client = SimpleNamespace(
+        tree=SimpleNamespace(get_commands=lambda: [_DesiredCommand()]),
+        application_id=4242,
+        user=SimpleNamespace(id=4242),
+    )
+
+    # Unrelated failure that happens to expose retry_after. Must NOT be
+    # caught by the rate-limit handler — it has nothing to do with 429s.
+    class _UnrelatedError(RuntimeError):
+        retry_after = 999.0
+
+    sync = AsyncMock(side_effect=_UnrelatedError("database is down"))
+    monkeypatch.setattr(adapter, "_safe_sync_slash_commands", sync)
+
+    # The outer _run_post_connect_initialization has a broad except Exception
+    # that logs defensively — so we assert on state NOT being written.
+    await adapter._run_post_connect_initialization()
+
+    sync.assert_awaited_once()
+    state_path = (
+        tmp_path
+        / discord_platform._DISCORD_COMMAND_SYNC_STATE_SUBDIR
+        / discord_platform._DISCORD_COMMAND_SYNC_STATE_FILENAME
+    )
+    state = json.loads(state_path.read_text()) if state_path.exists() else {}
+    entry = state.get("4242", {})
+    # Attempt was recorded before the sync call, but no rate-limit cooldown
+    # should have been persisted from the unrelated exception.
+    assert "retry_after_until" not in entry
+    assert "retry_after" not in entry
+
+
 @pytest.mark.asyncio
 async def test_safe_sync_slash_commands_paces_mutation_writes(monkeypatch):
     adapter = DiscordAdapter(PlatformConfig(enabled=True, token="test-token"))