diff --git a/gateway/run.py b/gateway/run.py
index 9e6b2e745cb43..a00af86cf6b82 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -18974,6 +18974,21 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
             else getattr(source, "auto_thread_initial_name", None)
         )
         thread_name = self._sanitize_discord_thread_title(title)
+        # Relay lane only: the connector's egress guard resolves the owning
+        # tenant from the outbound metadata's scope_id (guild) / user_id
+        # (author). Those discriminator caches are keyed by the PARENT channel
+        # chat_id (learned at inbound), NOT the thread id. rename_thread
+        # defaults chat_id to the thread id when no parent is given, so the
+        # scope/author lookup misses and the connector declines the op
+        # ("target not routed to an onboarded tenant" — the live failure on
+        # staging 2026-08-01). Pass the parent channel id (the relay source's
+        # chat_id IS the parent channel; the thread came from send-result
+        # feedback) so the discriminators resolve. Native lane needs nothing:
+        # its source IS the thread and it renames via the direct Discord API,
+        # not the relay egress guard.
+        parent_chat_id = (
+            str(source.chat_id) if use_connector_guard and source.chat_id else None
+        )
         logger.info(
             "discord auto-thread rename: thread=%s lane=%s new_title=%r",
             target_thread_id,
@@ -18986,6 +19001,7 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
                 thread_name,
                 prefer_connector_created=use_connector_guard,
                 only_if_current_name=guard_name,
+                parent_chat_id=parent_chat_id,
             )
             logger.info(
                 "discord auto-thread rename result: thread=%s applied=%s",
diff --git a/tests/gateway/relay/test_relay_threads.py b/tests/gateway/relay/test_relay_threads.py
index c4aae3e495f9b..a0f5fe1522464 100644
--- a/tests/gateway/relay/test_relay_threads.py
+++ b/tests/gateway/relay/test_relay_threads.py
@@ -150,6 +150,40 @@ async def test_rename_thread_connector_guard_takes_precedence_over_string():
     assert "only_if_current_name" not in action
 
 
+@pytest.mark.asyncio
+async def test_rename_thread_resolves_scope_from_parent_chat_not_thread():
+    """The connector's egress guard resolves the owning tenant from the
+    outbound metadata's scope_id / user_id, and the adapter's discriminator
+    caches are keyed by the PARENT channel chat_id (learned at inbound), never
+    the thread id. A rename that passes parent_chat_id must carry that
+    discriminator; a rename keyed only on the thread id must not — reproducing
+    the live decline ("target not routed to an onboarded tenant") and its fix.
+    """
+    adapter, stub = _adapter()
+    # Simulate the inbound-learned scope for the PARENT channel only.
+    adapter._scope_by_chat["chan-parent"] = "guild-123"
+
+    # Fix: pass the parent chat id -> scope_id resolves.
+    await adapter.rename_thread(
+        "th-9",
+        "Real Title",
+        prefer_connector_created=True,
+        parent_chat_id="chan-parent",
+    )
+    fixed = stub.sent[-1]
+    assert fixed["metadata"].get("scope_id") == "guild-123"
+
+    # Regression shape: keyed on the thread id alone (no parent) -> no scope_id,
+    # which is exactly what made the connector decline the op.
+    await adapter.rename_thread(
+        "th-9",
+        "Real Title",
+        prefer_connector_created=True,
+    )
+    unscoped = stub.sent[-1]
+    assert "scope_id" not in unscoped["metadata"]
+
+
 # ── the relay semantic-rename lane (marker parity) ───────────────────────
 
 
@@ -331,7 +365,7 @@ async def test_title_rename_polls_feedback_that_arrives_late():
         prefer_connector_created=False,
         parent_chat_id=None,
     ):
-        renames.append((thread_id, name, prefer_connector_created))
+        renames.append((thread_id, name, prefer_connector_created, parent_chat_id))
         return True
 
     adapter.rename_thread = rename_thread  # type: ignore[method-assign]
@@ -348,8 +382,14 @@ async def test_title_rename_polls_feedback_that_arrives_late():
     )
     await task
     # Relay lane uses the connector-owned guard (prefer_connector_created=True),
-    # not the fragile cross-repo initial-name string.
-    assert renames == [("th-9", "Debugging the flux capacitor", True)]
+    # not the fragile cross-repo initial-name string. It MUST pass the PARENT
+    # channel chat_id so the connector's egress guard can resolve the tenant
+    # (the discriminator caches are keyed by the parent channel, not the thread;
+    # omitting it made the connector decline "target not routed to an onboarded
+    # tenant" — the live failure on staging 2026-08-01).
+    assert renames == [
+        ("th-9", "Debugging the flux capacitor", True, "chan-parent")
+    ]
 
 
 @pytest.mark.asyncio