RP2040: USB CDC output drops characters with `-scheduler=cores` on TinyGo 0.41.1

## Summary On Raspberry Pi Pico / RP2040, USB CDC output appears to drop characters when using `-scheduler=cores`. The same program prints correctly with TinyGo 0.40.1, but the output becomes corrupted with TinyGo 0.41.1. ## Environment - Board: Raspberry Pi Pico / RP2040 - Host OS: Windows 11 - CPU: AMD Ryzen 5 5600G - Shell: Git Bash / MINGW64 - Install method: Scoop - USB connection: onboard USB CDC - Serial monitor: `tinygo flash -monitor` - TinyGo 0.40.1: - `tinygo version 0.40.1 windows/amd64 (using go version go1.24.13 and LLVM version 20.1.1)` - TinyGo 0.41.1: - `tinygo version 0.41.1 windows/amd64 (using go version go1.24.13 and LLVM version 20.1.1)` ## Reproducer ```go package main import "time" func main() { time.Sleep(2 * time.Second) println("start usb only") for i := 0; i < 100; i++ { if i == 0 || i%10 == 0 { println("rounds ok:", i, "/ 100") } time.Sleep(10 * time.Millisecond) } println("test finished") } ``` ## Commands TinyGo 0.40.1: ```bash scoop reset tinygo@0.40.1 C:/Users/user/scoop/shims/tinygo.exe flash -target=pico -scheduler=cores -monitor main_usb_only.go ``` TinyGo 0.41.1: ```bash scoop reset tinygo@0.41.1 C:/Users/user/scoop/shims/tinygo.exe flash -target=pico -scheduler=cores -monitor main_usb_only.go ``` I also checked `-scheduler=tasks` with TinyGo 0.41.1: ```bash C:/Users/user/scoop/shims/tinygo.exe flash -target=pico -scheduler=tasks -monitor main_usb_only.go ``` ## Observed behavior With TinyGo 0.40.1 and `-scheduler=cores`, the output appears correct: ```text Connected to COM3. Press Ctrl-C to exit. start usb only rounds ok: 0 / 100 rounds ok: 10 / 100 rounds ok: 20 / 100 rounds ok: 30 / 100 rounds ok: 40 / 100 rounds ok: 50 / 100 rounds ok: 60 / 100 rounds ok: 70 / 100 rounds ok: 80 / 100 rounds ok: 90 / 100 test finished ``` With TinyGo 0.41.1 and `-scheduler=cores`, the output drops characters: ```text Connected to COM3. Press Ctrl-C to exit. ds ok: 100y rounds ok: 10 / 100 rounds ok: 20 / 100 rounds ok: 30 / 100 rk: 40 / 100 rou 100 rnds ok: 60 rounds ok: 70 / 100 rounds ok: 80 / 100 r100 test finished ``` With TinyGo 0.41.1 and `-scheduler=tasks`, the same program prints correctly: ```text Connected to COM3. Press Ctrl-C to exit. start usb only rounds ok: 0 / 100 rounds ok: 10 / 100 rounds ok: 20 / 100 rounds ok: 30 / 100 rounds ok: 40 / 100 rounds ok: 50 / 100 rounds ok: 60 / 100 rounds ok: 70 / 100 rounds ok: 80 / 100 rounds ok: 90 / 100 test finished ``` ## Expected behavior USB CDC output should not drop characters when using `-scheduler=cores`. The output should be consistent with the behavior of TinyGo 0.40.1 and with `-scheduler=tasks`.