[bcorey]

Wrote some error reporting improvements with codex to help me and paul debug engine connection failures.

Before:

    thread 'docs::kcl_doc::test::kcl_test_examples_std_helix_2' (61059438) panicked at kcl-lib/src/docs/kcl_doc.rs:1866:21:
Error testing example std-helix-2 for std::helix in /Users/bc/repos/modeling-app/rust/kcl-lib/std/prelude.kcl:
could not send request to the engine: could not send json over websocket: Trying to work with closed connection       

What it tells us:

• engine connection closed

After:

    thread 'docs::kcl_doc::test::kcl_test_examples_std_helix_3' (61167552) panicked at kcl-lib/src/docs/kcl_doc.rs:1869:25:
Error testing example std-helix-3 for std::helix in /Users/bc/repos/modeling-app/rust/kcl-lib/std/prelude.kcl: could not send request to the engine: could not send json over websocket: Trying to work with closed connection; failed request:
modeling_cmd_batch_req : [EdgeLinesVisible, ObjectVisible, SetGridScale, ObjectVisible, SetDefaultSystemProperties];
last request written to WebSocket: modeling_cmd_req: SceneClearAll;
last modeling request written to WebSocket: modeling_cmd_req: SceneClearAll
(API call ID: unavailable: session data not received)   

What it tells us:

• we failed to send this batch [x, y, z] to the engine
• engine connection closed
• we previously sent SceneClearAll to the engine
• the engine never sent us session data

If the engine had sent us session data, we would have a handy ID to search logs with. since it hasn't, we can narrow down the kinds of issues we're facing.

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Project	Deployment	Actions	Updated
modeling-app	Ready	Preview	Sep 22, 2026 7:04pm UTC

[codspeed]

Merging this PR will not alter performance

✅ 159 untouched benchmarks
⏩ 129 skipped benchmarks¹

---

_{Comparing bcorey/improve-engine-connection-error-report (da66fba) with main (984a13a)²}

Footnotes

1. 129 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (dacd00a) during the generation of this report, so 984a13a was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[bcorey]

rebased onto main & tested errors. we now prioritize websocket closed messages when available as part of work done last week and do a better job of putting engine responses in the terminal output, so things look different.

Invalid pool

Error testing example std-appearance-hexString-2 for std::appearance::hexString in /Users/bc/repos/modeling-app/rust/kcl-lib/std/appearance.kcl:
WebSocket protocol error: Connection reset without closing handshake (Engine upgrade request ID: 8d86ff54-c63a-40f7-860c-41a627152eb6)   

EdgeLinesVisible on CPU

Error testing example std-array-concat-0 for std::array::concat in /Users/bc/repos/modeling-app/rust/kcl-lib/std/array.kcl:
command EdgeLinesVisible resulted in errors: 
Graphics have not been enabled for this geometry context (API call ID: 4ea5ba5f-20ec-4bd5-b672-1f9ad7a519b6)

PlaneSetColor on CPU

Error testing example std-appearance-hexString-3 for std::appearance::hexString in /Users/bc/repos/modeling-app/rust/kcl-lib/std/appearance.kcl:
command PlaneSetColor resulted in errors: 
Graphical views cannot be created when graphics are not enabled (API call ID: 9cdf0ae6-6e03-4772-aa8b-f47e7422f198) 

These are all the same as on main with the addition of the api call IDs on the modeling commands