fix(gateway): slash commands never interrupt a running agent (#12334)

Any recognized slash command now bypasses the Level-1 active-session
guard instead of queueing + interrupting. A mid-run /model (or
/reasoning, /voice, /insights, /title, /resume, /retry, /undo,
/compress, /usage, /provider, /reload-mcp, /sethome, /reset) used to
interrupt the agent AND get silently discarded by the slash-command
safety net — zero-char response, dropped tool calls.

Root cause:
- Discord registers 41 native slash commands via tree.command().
- Only 14 were in ACTIVE_SESSION_BYPASS_COMMANDS.
- The other ~15 user-facing ones fell through base.py:handle_message
  to the busy-session handler, which calls running_agent.interrupt()
  AND queues the text.
- After the aborted run, gateway/run.py:9912 correctly identifies the
  queued text as a slash command and discards it — but the damage
  (interrupt + zero-char response) already happened.

Fix:
- should_bypass_active_session() now returns True for any resolvable
  slash command. ACTIVE_SESSION_BYPASS_COMMANDS stays as the subset
  with dedicated Level-2 handlers (documentation + tests).
- gateway/run.py adds a catch-all after the dedicated handlers that
  returns a user-visible "agent busy — wait or /stop first" response
  for any other resolvable command.
- Unknown text / file-path-like messages are unchanged — they still
  queue.

Also:
- gateway/platforms/discord.py logs the invoker identity on every
  slash command (user id + name + channel + guild) so future
  ghost-command reports can be triaged without guessing.

Tests:
- 15 new parametrized cases in test_command_bypass_active_session.py
  cover every previously-broken Discord slash command.
- Existing tests for /stop, /new, /approve, /deny, /help, /status,
  /agents, /background, /steer, /update, /queue still pass.
- test_steer.py's ACTIVE_SESSION_BYPASS_COMMANDS check still passes.

Fixes #5057. Related: #6252, #10370, #4665.

tests/gateway/test_command_bypass_active_session.py

@@ -268,6 +268,82 @@ class TestCommandBypassActiveSession:
         )
 
 
+# ---------------------------------------------------------------------------
+# Tests: non-bypass-set commands (no dedicated Level-2 handler) also bypass
+# instead of interrupting + being discarded.  Regression for the Discord
+# ghost-slash-command bug where /model, /reasoning, /voice, /insights, /title,
+# /resume, /retry, /undo, /compress, /usage, /provider, /reload-mcp,
+# /sethome, /reset silently interrupted the running agent.
+# ---------------------------------------------------------------------------
+
+
+class TestAllResolvableCommandsBypassGuard:
+    """Every recognized slash command must bypass the Level-1 active-session
+    guard. Without this, commands the user fires mid-run interrupt the agent
+    AND get silently discarded by the slash-command safety net (zero-char
+    response)."""
+
+    @pytest.mark.parametrize(
+        "command_text,canonical",
+        [
+            ("/model claude-sonnet-4", "model"),
+            ("/model", "model"),
+            ("/reasoning high", "reasoning"),
+            ("/personality default", "personality"),
+            ("/voice on", "voice"),
+            ("/insights 7", "insights"),
+            ("/title my session", "title"),
+            ("/resume yesterday", "resume"),
+            ("/retry", "retry"),
+            ("/undo", "undo"),
+            ("/compress", "compress"),
+            ("/usage", "usage"),
+            ("/provider", "provider"),
+            ("/reload-mcp", "reload-mcp"),
+            ("/sethome", "sethome"),
+        ],
+    )
+    @pytest.mark.asyncio
+    async def test_command_bypasses_guard(self, command_text, canonical):
+        """Any resolvable slash command bypasses instead of being queued."""
+        adapter = _make_adapter()
+        sk = _session_key()
+        adapter._active_sessions[sk] = asyncio.Event()
+
+        await adapter.handle_message(_make_event(command_text))
+
+        assert sk not in adapter._pending_messages, (
+            f"{command_text} was queued as pending — it should bypass the guard"
+        )
+        assert len(adapter.sent_responses) > 0, (
+            f"{command_text} produced no response — it should be dispatched, "
+            "not silently discarded"
+        )
+
+    def test_should_bypass_returns_true_for_every_registered_command(self):
+        """Spot-check: the commands previously-broken on Discord all bypass."""
+        from hermes_cli.commands import should_bypass_active_session
+
+        for cmd in (
+            "model", "reasoning", "personality", "voice", "insights", "title",
+            "resume", "retry", "undo", "compress", "usage", "provider",
+            "reload-mcp", "sethome", "reset",
+        ):
+            assert should_bypass_active_session(cmd) is True, (
+                f"/{cmd} must bypass the active-session guard"
+            )
+
+    def test_should_bypass_returns_false_for_unknown(self):
+        """Unknown words don't bypass — they get queued as user text."""
+        from hermes_cli.commands import should_bypass_active_session
+
+        assert should_bypass_active_session("foobar") is False
+        assert should_bypass_active_session(None) is False
+        assert should_bypass_active_session("") is False
+        # A file path split on whitespace: '/path/to/file.py' -> 'path/to/file.py'
+        assert should_bypass_active_session("path/to/file.py") is False
+
+
 # ---------------------------------------------------------------------------
 # Tests: non-bypass messages still get queued
 # ---------------------------------------------------------------------------