test(dispatcher): cover defensive while-loop in mint path

Add a test that exercises the while-loop body in
DirectDispatcher._dispatch_request which skips past in-flight IDs
when minting. CI was failing with 99.99% coverage (fail-under=100%)
because line 264 was unreachable through normal API usage — the
max() advancement on caller-supplied IDs prevents natural collisions.
The test injects synthetic in-flight keys to prove the guard works.

Author: elang2

tests/shared/test_dispatcher.py

@@ -482,6 +482,38 @@ async def parked() -> None:
             assert [request_id for request_id in seen_ids if request_id != "3"] == [4, 5, 6]
 
 
+@pytest.mark.anyio
+async def test_minted_id_skips_injected_consecutive_in_flight_ids():
+    """Defensive guard: if _in_flight_ids contains the next sequential
+    candidates, the while-loop advances past all of them."""
+
+    async def noop(
+        ctx: DispatchContext[TransportContext], method: str, params: Mapping[str, Any] | None
+    ) -> dict[str, Any]:
+        return {}
+
+    client, server, close = direct_pair()
+    try:
+        async with anyio.create_task_group() as tg:
+            await tg.start(client.run, noop, noop)
+            await tg.start(server.run, noop, noop)
+            # send_raw_request on client dispatches on the server's peer
+            # (_dispatch_request runs on server). Inject synthetic in-flight
+            # keys into the SERVER so the mint loop must skip them.
+            # _next_id is 0, so mint increments to 1, finds it occupied,
+            # increments to 2, finds it occupied, increments to 3, finds it
+            # occupied, and finally lands on 4.
+            server._in_flight_ids.update({1, 2, 3})
+            result = await client.send_raw_request("ping", None)
+            assert result == {}
+            # After completion the id is discarded from in_flight, but the
+            # counter must have advanced to 4 (skipping 1, 2, 3).
+            assert server._next_id == 4
+            tg.cancel_scope.cancel()
+    finally:
+        close()
+
+
 @pytest.mark.anyio
 async def test_supplied_numeric_string_id_collides_with_its_int_twin(pair_factory: PairFactory):
     """ "7" and 7 are one id in the collision domain on BOTH dispatchers, so the