Python API client example crashes the headless simulation

Hi,

Running the [api client](https://github.com/a-b-street/abstreet/blob/main/headless/examples/python_client.py) example crashes the simulation. I saw in [the other issue](https://github.com/a-b-street/abstreet/issues/996) that traffic sim is not maintained anymore. Does the error seem like something that happens because of the map (everything's default in my case). If so, is there a way to "fix" the map to not cause the crash, or does this look like a deeper issue?

```
branch: main
commit 0964f29315820c91b171b585eb51e300164e9197 (HEAD -> main, origin/main, origin/HEAD)
Author: pdobacz <5735525+pdobacz@users.noreply.github.com>
Date: Wed Sep 10 08:24:40 2025 +0200
```
```bash
git:(main) rustc --version
rustc 1.91.1 (ed61e7d7e 2025-11-07) (Homebrew)
git:(main) cargo --version
cargo 1.91.1 (Homebrew)
git:(main) sw_vers
ProductName: macOS
ProductVersion: 15.7.2
BuildVersion: 24G325
git:(main) rustc -vV
rustc 1.91.1 (ed61e7d7e 2025-11-07) (Homebrew)
binary: rustc
commit-hash: ed61e7d7e242494fb7057f2657300d9e77bb4fcb
commit-date: 2025-11-07
host: aarch64-apple-darwin
release: 1.91.1
LLVM version: 21.1.5
git:(main) uname -m
arm64
```

```bash
python python_client.py
Did you just start the simulation? Time is currently 00:00:00.0
Reset the simulation: sim reloaded

Simulating before any edits
Traceback (most recent call last):
File "/opt/homebrew/lib/python3.11/site-packages/urllib3/connectionpool.py", line 793, in urlopen
response = self._make_request(
^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/urllib3/connectionpool.py", line 537, in _make_request
response = conn.getresponse()
^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/urllib3/connection.py", line 466, in getresponse
httplib_response = super().getresponse()
^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/Cellar/python@3.11/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/http/client.py", line 1395, in getresponse
response.begin()
File "/opt/homebrew/Cellar/python@3.11/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/http/client.py", line 325, in begin
version, status, reason = self._read_status()
^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/Cellar/python@3.11/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/http/client.py", line 294, in _read_status
raise RemoteDisconnected("Remote end closed connection without"
http.client.RemoteDisconnected: Remote end closed connection without response

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/opt/homebrew/lib/python3.11/site-packages/requests/adapters.py", line 667, in send
resp = conn.urlopen(
^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/urllib3/connectionpool.py", line 847, in urlopen
retries = retries.increment(
^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/urllib3/util/retry.py", line 470, in increment
raise reraise(type(error), error, _stacktrace)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/urllib3/util/util.py", line 38, in reraise
raise value.with_traceback(tb)
File "/opt/homebrew/lib/python3.11/site-packages/urllib3/connectionpool.py", line 793, in urlopen
response = self._make_request(
^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/urllib3/connectionpool.py", line 537, in _make_request
response = conn.getresponse()
^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/urllib3/connection.py", line 466, in getresponse
httplib_response = super().getresponse()
^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/Cellar/python@3.11/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/http/client.py", line 1395, in getresponse
response.begin()
File "/opt/homebrew/Cellar/python@3.11/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/http/client.py", line 325, in begin
version, status, reason = self._read_status()
^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/Cellar/python@3.11/3.11.11/Frameworks/Python.framework/Versions/3.11/lib/python3.11/http/client.py", line 294, in _read_status
raise RemoteDisconnected("Remote end closed connection without"
urllib3.exceptions.ProtocolError: ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response'))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/Users/i/projects/inv-game/mapy/build/headless/examples/python_client.py", line 148, in
main()
File "/Users/i/projects/inv-game/mapy/build/headless/examples/python_client.py", line 25, in main
trips1, delays1, thruput1 = run_experiment()
^^^^^^^^^^^^^^^^
File "/Users/i/projects/inv-game/mapy/build/headless/examples/python_client.py", line 105, in run_experiment
print(requests.get(api + '/sim/goto-time',
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/requests/api.py", line 73, in get
return request("get", url, params=params, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/requests/api.py", line 59, in request
return session.request(method=method, url=url, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/requests/sessions.py", line 589, in request
resp = self.send(prep, **send_kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/requests/sessions.py", line 703, in send
r = adapter.send(request, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/opt/homebrew/lib/python3.11/site-packages/requests/adapters.py", line 682, in send
raise ConnectionError(err, request=request)
requests.exceptions.ConnectionError: ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response'))
```

```bash
RUST_BACKTRACE=1 cargo run --release --bin headless -- --port=1234
warning: hiding a lifetime that's elided elsewhere is confusing
--> map_model/src/pathfind/engine.rs:102:27
|
102 | pub fn reuse_ordering(&self) -> CreateEngine {
| ^^^^^ ^^^^^^^^^^^^ the same lifetime is hidden here
| |
| the lifetime is elided here
|
= help: the same lifetime is referred to in inconsistent ways, making the signature confusing
= note: `#[warn(mismatched_lifetime_syntaxes)]` on by default
help: use `'_` for type paths
|
102 | pub fn reuse_ordering(&self) -> CreateEngine<'_> {
| ++++

warning: `map_model` (lib) generated 1 warning (run `cargo fix --lib -p map_model` to apply 1 suggestion)
Finished `release` profile [optimized] target(s) in 0.72s
Running `target/release/headless --port=1234`
setup headless...
Read data/system/us/seattle/scenarios/montlake/weekday.bin (1)... 0.0324s
Read data/system/us/seattle/maps/montlake.bin (3)... 0.0406s
generate movements (754)... 0.0013s
create blank sim...
setup offstreet parking (3,102)... 0.0021s
create blank sim... plus 0.0018s
create blank sim took 0.0039s
[2025-11-22T16:47:01Z INFO abstutil::time] - create blank sim took 0.0039s
[2025-11-22T16:47:01Z INFO abstutil::time] - setup offstreet parking (3,102)... 0.0021s
[2025-11-22T16:47:01Z INFO abstutil::time] - ... plus 0.0018s
Instantiating weekday...
trips for People (13,484)... 0.0044s
[2025-11-22T16:47:01Z WARN sim::sim::scenario] Not enough room to seed parked cars. Only found spots for 5,000 of 5,064
seed parked cars (5,064)... 0.0693s
spawn trips (36,614)... 0.0203s
Instantiating weekday... plus 0.0017s
Instantiating weekday took 0.0956s
setup headless... plus 0.0055s
setup headless took 0.1755s
[2025-11-22T16:47:01Z INFO abstutil::time] - setup headless took 0.1755s
[2025-11-22T16:47:01Z INFO abstutil::time] - Read data/system/us/seattle/scenarios/montlake/weekday.bin (1)... 0.0324s
[2025-11-22T16:47:01Z INFO abstutil::time] - Read data/system/us/seattle/maps/montlake.bin (3)... 0.0406s
[2025-11-22T16:47:01Z INFO abstutil::time] - generate movements (754)... 0.0013s
[2025-11-22T16:47:01Z INFO abstutil::time] - Instantiating weekday took 0.0956s
[2025-11-22T16:47:01Z INFO abstutil::time] - trips for People (13,484)... 0.0044s
[2025-11-22T16:47:01Z INFO abstutil::time] - seed parked cars (5,064)... 0.0693s
[2025-11-22T16:47:01Z INFO abstutil::time] - spawn trips (36,614)... 0.0203s
[2025-11-22T16:47:01Z INFO abstutil::time] - ... plus 0.0017s
[2025-11-22T16:47:01Z INFO abstutil::time] - ... plus 0.0055s
create blank sim...
create blank sim took 0.0001s
[2025-11-22T16:47:01Z INFO abstutil::time] - create blank sim took 0.0001s
[2025-11-22T16:47:01Z INFO headless] Listening on http://127.0.0.1:1234
[2025-11-22T16:47:07Z INFO headless] Handling /sim/get-time
[2025-11-22T16:47:07Z INFO headless] Handling /sim/reset
reset sim...
Read data/system/us/seattle/scenarios/montlake/weekday.bin (1)... 0.0134s
Read data/system/us/seattle/maps/montlake.bin (3)... 0.0268s
generate movements (754)... 0.0013s
create blank sim...
setup offstreet parking (3,102)... 0.0021s
create blank sim... plus 0.0017s
create blank sim took 0.0038s
[2025-11-22T16:47:07Z INFO abstutil::time] - create blank sim took 0.0038s
[2025-11-22T16:47:07Z INFO abstutil::time] - setup offstreet parking (3,102)... 0.0021s
[2025-11-22T16:47:07Z INFO abstutil::time] - ... plus 0.0017s
Instantiating weekday...
trips for People (13,484)... 0.0038s
[2025-11-22T16:47:07Z WARN sim::sim::scenario] Not enough room to seed parked cars. Only found spots for 5,000 of 5,064
seed parked cars (5,064)... 0.0676s
spawn trips (36,614)... 0.0204s
Instantiating weekday... plus 0.0013s
Instantiating weekday took 0.0931s
reset sim... plus 0.0048s
reset sim took 0.1394s
[2025-11-22T16:47:07Z INFO abstutil::time] - reset sim took 0.1394s
[2025-11-22T16:47:07Z INFO abstutil::time] - Read data/system/us/seattle/scenarios/montlake/weekday.bin (1)... 0.0134s
[2025-11-22T16:47:07Z INFO abstutil::time] - Read data/system/us/seattle/maps/montlake.bin (3)... 0.0268s
[2025-11-22T16:47:07Z INFO abstutil::time] - generate movements (754)... 0.0013s
[2025-11-22T16:47:07Z INFO abstutil::time] - Instantiating weekday took 0.0931s
[2025-11-22T16:47:07Z INFO abstutil::time] - trips for People (13,484)... 0.0038s
[2025-11-22T16:47:07Z INFO abstutil::time] - seed parked cars (5,064)... 0.0676s
[2025-11-22T16:47:07Z INFO abstutil::time] - spawn trips (36,614)... 0.0204s
[2025-11-22T16:47:07Z INFO abstutil::time] - ... plus 0.0013s
[2025-11-22T16:47:07Z INFO abstutil::time] - ... plus 0.0048s
[2025-11-22T16:47:07Z INFO headless] Handling /sim/goto-time
goto-time...
Advance sim to 12:00:00.0...
Alert at 00:18:02.4 (Person(PersonID(5792))): Car #5114 can't find parking on Lane #2370 or anywhere reachable from it. Possibly we're just totally out of parking space!
Alert at 00:19:27.0 (Person(PersonID(7729))): Car #6790 can't find parking on Lane #21698 or anywhere reachable from it. Possibly we're just totally out of parking space!
Alert at 00:20:43.4 (Person(PersonID(8844))): Car #7726 can't find parking on Lane #21698 or anywhere reachable from it. Possibly we're just totally out of parking space!
Alert at 00:20:59.9 (Person(PersonID(4241))): Car #3683 can't find parking on Lane #21698 or anywhere reachable from it. Possibly we're just totally out of parking space!

(....)

Alert at 10:36:14.1 (Intersection(IntersectionID(53))): AgentID(Car #9988) waking up AgentID(Car #10944), who's blocking it as part of a cycle
Alert at 10:36:14.1 (Intersection(IntersectionID(366))): AgentID(Car #10944) found turn conflict cycle involving {CarID { id: 10944, vehicle_type: Car }, CarID { id: 9988, vehicle_type: Car }}
Alert at 10:36:14.1 (Intersection(IntersectionID(366))): AgentID(Car #10944) waking up AgentID(Car #9988), who's blocking it as part of a cycle
Alert at 10:37:00.0 (Person(PersonID(5660))): Person 5660 had a trip cancelled, and their car was warped to Onstreet(LaneID { road: RoadID(78), offset: 1 }, 1)

thread 'tokio-runtime-worker' (4766406) panicked at sim/src/mechanics/intersection.rs:1039:45:
called `Option::unwrap()` on a `None` value
stack backtrace:
0: __rustc::rust_begin_unwind
1: core::panicking::panic_fmt
2: core::panicking::panic
3: core::option::unwrap_failed
4: sim::mechanics::intersection::IntersectionSimState::handle_accepted_conflicts
5: sim::mechanics::intersection::IntersectionSimState::maybe_start_turn
6: sim::mechanics::driving::DrivingSimState::update_car
7: sim::sim::Sim::minimal_step
8: sim::sim::Sim::timed_step
9: headless::handle_command
10: hyper::proto::h1::dispatch::Dispatcher::poll_loop
11: hyper::proto::h1::dispatch::Dispatcher::poll_catch
12: as core::future::future::Future>::poll
13: as core::future::future::Future>::poll
14: tokio::runtime::task::core::Core::poll
15: tokio::runtime::task::harness::Harness::poll
16: tokio::runtime::scheduler::multi_thread::worker::Context::run_task
17: tokio::runtime::scheduler::multi_thread::worker::Context::run
18: tokio::runtime::context::scoped::Scoped::set
19: tokio::runtime::context::runtime::enter_runtime
20: tokio::runtime::scheduler::multi_thread::worker::run
21: tokio::runtime::task::core::Core::poll
22: tokio::runtime::task::harness::Harness::poll
23: tokio::runtime::blocking::pool::Inner::run
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
```