Don't leak RUST_LOG into supervisor

[jmcphers]

This change removes the RUST_LOG environment variable from the kernel supervisor's environment. It is (now) unnecessary since we already use a command-line argument to set the log level, and because kernels inherit the supervisor's environment, it can affect the log level of Rust-based programs invoked from the kernels (such as uv).

Addresses #8538.

Release Notes

New Features

• N/A

Bug Fixes

• Remove superfluous RUST_LOG environment variable from R and Python sessions

QA Notes

• It should still be possible to specify RUST_LOG manually via e.g. the Environment Variables feature
• The R extension sets a value for RUST_LOG as well, so you'll see that value in R sessions
• The main thing to verify here, in addition to RUST_LOG no longer being overridden, is that the kernel's log level setting still works

[github-actions]

E2E Tests 🚀
This PR will run tests tagged with: @:critical

^{readme  valid tags}

[sharon-wang]

Python

>>> import os
>>> os.getenv("RUST_LOG")
# nothing returned ✅ 

R

> Sys.getenv("RUST_LOG")
[1] "warn,ark=warn"

• this looks to be in line with

  positron/extensions/positron-r/src/kernel-spec.ts

  Lines 36 to 47 in 9026016

  	// Check the R kernel log level setting
  	const config = vscode.workspace.getConfiguration('positron.r');
  	const logLevel = config.get<string>('kernel.logLevel') ?? 'warn';
  	const logLevelForeign = config.get<string>('kernel.logLevelExternal') ?? 'warn';
  	const userEnv = config.get<object>('kernel.env') ?? {};
  	const profile = config.get<string>('kernel.profile');
  	/* eslint-disable */
  	const env = <Record<string, string>>{
  	'RUST_BACKTRACE': '1',
  	'RUST_LOG': logLevelForeign + ',ark=' + logLevel,

Kernel Supervisor

"kernelSupervisor.logLevel": "error"

2025-07-15 18:10:27.111 [info] Positron Kernel Supervisor activated
2025-07-15 18:10:27.111 [info] 01:10:27 [Positron] Generated connection file path: /var/folders/07/9qwx1rk15rjd0mly1bjwycgc0000gp/T/kallichore-51c34b02-89346.json
2025-07-15 18:10:27.111 [info] 01:10:27 [Positron] Using native IPC transport: unix sockets
2025-07-15 18:10:27.111 [info] 01:10:27 [Positron] Starting Kallichore server /Users/sashimi/dev/positron-dev/extensions/positron-supervisor/resources/kallichore/kcserver with connection file /var/folders/07/9qwx1rk15rjd0mly1bjwycgc0000gp/T/kallichore-51c34b02-89346.json
01:10:30 [Positron] Read domain socket connection information from /var/folders/07/9qwx1rk15rjd0mly1bjwycgc0000gp/T/kallichore-51c34b02-89346.json: /var/folders/07/9qwx1rk15rjd0mly1bjwycgc0000gp/T/kc-89411.sock, constructed base path: http://unix:/var/folders/07/9qwx1rk15rjd0mly1bjwycgc0000gp/T/kc-89411.sock:
01:10:30 [Positron] Kallichore 0.1.51 server online with 0 sessions
01:10:30 [Positron] Running as pid 89411 (terminal pid 89357)
01:10:30 [Positron] Kallichore server started in 2953ms
01:10:30 [Positron] Streaming Kallichore server logs from /var/folders/07/9qwx1rk15rjd0mly1bjwycgc0000gp/T/kallichore-51c34b02-89346.log (log level: error)
01:10:30 [Positron] Creating session: {"sessionId":"r-31d848ad","sessionMode":"console","createdTimestamp":1752628227673,"startReason":"Affiliated R runtime for workspace"}

"kernelSupervisor.logLevel": "info"

...
01:12:21 [INFO] Server set to shut down after 1 hours of inactivity
01:12:22 [INFO] new_session("r-8b94a031") - X-Span-ID: "9e505a79-a5fb-43f3-bc2b-3d1990e7aef6"
01:12:22 [INFO] start_session("r-8b94a031") - X-Span-ID: "fc6b5ec8-5649-4532-827d-872b2a57d1b1"
01:12:22 [INFO] [session r-8b94a031] Kernel supports JEP 66 (protocol version 5.5) - creating registration socket for handshake
01:12:22 [INFO] [session r-8b94a031] Waiting for JEP 66 handshake
...

"kernelSupervisor.logLevel": "trace"

...
01:13:48 [INFO] [session r-ca992a61] Waiting for JEP 66 handshake
01:13:48 [DEBUG] (8) kcserver::kernel_session: End of output stream (kind: Stdout)
01:13:48 [DEBUG] (8) kcserver::kernel_session: End of output stream (kind: Stderr)
01:13:48 [INFO] Received handshake request from kernel
01:13:48 [INFO] [session r-ca992a61] Sending successful handshake reply to kernel
01:13:48 [INFO] [session r-ca992a61] Handshake completed successfully
01:13:48 [INFO] [session r-ca992a61] JEP 66 handshake completed successfully
01:13:48 [TRACE] (8) kcserver::kernel_session: [crates/kcserver/src/kernel_session.rs:715] [session r-ca992a61] Waiting for kernel sockets to connect
...

[sharon-wang]

Pulling in main should resolve the unit test failure!