feat(injects,conversations): configurable inject header, urgent inject marks the turn it cut

tests/test_conversations.py

@@ -274,10 +274,25 @@ async def test_urgent_interrupts_and_goes_first(world: World) -> None:
     ]
     assert client.prompts[0] == "first"
     assert client.prompts[1].startswith("[инжект: крон")
+    assert "прервал предыдущий тёрн" in client.prompts[1]
     assert client.prompts[1].endswith("ALERT")
     assert client.prompts[2] == "second"
 
 
+async def test_inject_header_is_configurable(world: World) -> None:
+    from beaver_gateway.core.conversations import ConversationTexts
+
+    world.conversations._texts = ConversationTexts(  # noqa: SLF001
+        inject_header=lambda ctx: (
+            f"[от {ctx.origin}, {ctx.priority}, cut={ctx.interrupted_turn}]"
+        )
+    )
+    conv = await world.conversations.create(kind="master", agent="a", origin="test")
+    await world.conversations.inject(conv, "hi", urgency="urgent", origin="panel")
+    await world.settle(conv, 1)
+    assert ScriptedClient.instances[0].prompts[0] == "[от panel, urgent, cut=False]\nhi"
+
+
 async def test_normal_injects_ride_with_the_next_user_message(world: World) -> None:
     conv = await world.conversations.create(kind="master", agent="a", origin="test")
     await world.conversations.inject(