USB-HID keyboard: Write can drop/corrupt HID reports, leaving keys stuck

[rdon-key]

machine/usb/hid/keyboard.Write can produce corrupted host-visible output even when called from a single goroutine.

In one run, the host started repeating 7, which looks like a stuck key state.

Environment

tinygo version 0.41.1 windows/amd64 (using go version go1.26.4 and LLVM version 20.1.1)
target: pico
scheduler: tasks
host: Windows

Reproducer

package main

import (
	"machine/usb/hid/keyboard"
	"time"
)

var kb = keyboard.Port()

func append3(b []byte, n int) []byte {
	b = append(b, byte('0'+(n/100)%10))
	b = append(b, byte('0'+(n/10)%10))
	b = append(b, byte('0'+n%10))
	return b
}

func main() {
	time.Sleep(3 * time.Second)

	kb.Write([]byte("\nBEGIN 100 WRITES\n"))

	var line [16]byte

	for i := 0; i < 100; i++ {
		b := line[:0]
		b = append3(b, i)
		b = append(b, ':', ' ')
		b = append(b, 'a', 'b', '\n')

		// Single goroutine, 100 writes only.
		kb.Write(b)
	}

	kb.Write([]byte("END 100 WRITES\n"))

	for {
		time.Sleep(time.Second)
	}
}

Run:

tinygo flash -target=pico -scheduler=tasks main.go

Expected output

The host should receive the lines in order:

BEGIN 100 WRITES
000: ab
001: ab
002: ab
003: ab
004: ab
005: ab
...
099: ab
END 100 WRITES

Actual output

One run produced:

BEGIN 100 WRITES
000: ab
001: ab
002: ab
003: ab
004: ab
005: ab0a77777777777777777777777777777

After that, the host appeared to keep repeating 7, as if the key was still pressed.

[rdon-key]

I also reproduced this with a current dev build on Raspberry Pi Pico / RP2040.
Environment:

tinygo version 0.42.0-dev-6605b6e4 windows/amd64 (using go version go1.26.1 and LLVM version 20.1.1)
target: pico
board: Raspberry Pi Pico / RP2040
scheduler: tasks
host: Windows

So this does not appear to be limited to TinyGo 0.41.1.