fix(background): drop delivery exception detail from chat replies

/background show became reachable from a chat transport in this branch,
and a chat gateway message is an external surface under the CWE-209 rule
while the local terminal is not. The notify row rendered the persisted
result verbatim, so a "failed: <reason>" outcome carried exception text
to a surface that must not see it.

Collapses that form to "failed" on the headless path only. The REPL table
is untouched, and the curated "missing <channel> integration: ..." hints
stay whole because they are the actionable half.

Author: SawhneySatvik

gateway/tests/runtime/test_slash_routing.py

@@ -276,6 +276,25 @@ def test_gateway_background_show_returns_the_rca_as_plain_text() -> None:
     assert not _BOX_DRAWING & set(sink.finalized), sink.finalized
 
 
+def test_gateway_background_show_does_not_leak_delivery_exception_detail() -> None:
+    task_id = _seed_record(
+        task_id="bg-chat-redact",
+        notification_results={
+            "email": "failed: SMTPRecipientsRefused",
+            "telegram": "sent",
+            "buzz": "missing buzz integration: Buzz is not configured.",
+        },
+    )
+
+    sink = _run_gateway_slash(f"/background show {task_id}")
+
+    assert sink.finalized is not None
+    assert "email:failed" in sink.finalized
+    assert "SMTPRecipientsRefused" not in sink.finalized
+    assert "telegram:sent" in sink.finalized
+    assert "missing buzz integration: Buzz is not configured." in sink.finalized
+
+
 def test_gateway_background_list_is_plain_and_bounded() -> None:
     """One line per record, and the root cause is trimmed. An unbounded list of
     twenty folded RCAs overruns the 4096-character message cap, and the transports

surfaces/interactive_shell/command_registry/background_cmds.py

@@ -172,6 +172,10 @@ def _plain_list(records: dict[str, BackgroundInvestigationRecord]) -> str:
     return "\n".join(lines)
 
 
+def _chat_safe_outcome(outcome: str) -> str:
+    return "failed" if outcome.startswith("failed:") else outcome
+
+
 def _plain_show(task_id: str, record: BackgroundInvestigationRecord) -> str:
     """The same bounded sections the chat notification adapters already send."""
     from platform.notifications.rca_summary import summary_sections
@@ -190,7 +194,9 @@ def _plain_show(task_id: str, record: BackgroundInvestigationRecord) -> str:
     if next_steps:
         lines += ["", "What to do next:"] + [f"  - {item}" for item in next_steps]
     if record.notification_results:
-        delivered = ", ".join(f"{k}:{v}" for k, v in record.notification_results.items())
+        delivered = ", ".join(
+            f"{k}:{_chat_safe_outcome(v)}" for k, v in record.notification_results.items()
+        )
         lines += ["", f"Notified: {delivered}"]
     return "\n".join(lines)