according to @jimmo mpremote should be able to resume a repl session on a connected mcu without a reboot by using the following command pattern:

mpremote connect exec "start_something()"
mpremote connect resume exec "continue_here()"

where the resume is the important part.
see Discord discussion

however when I try this :

1. I see that any variables set in the the first mpremote commands are lost
2. I see that the esp32 performs a soft reset after exiting the raw REPL
   (observed through logic analyzer)

So even though the 2nd mpremote command does not force a reset, by that time a soft reboot has already occurred.
I also see a soft reset after:

• exiting the repl
• eval "42"
• exec "print(42)"

Actual result on windows :

C:\develop\usb>mpremote exec "foo=bar=42;print(foo)"
42

C:\develop\usb>mpremote resume exec "print(bar)"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'bar' isn't defined

Expected

the MCU not to reset between two mpremote commands similar to the behavour on linux

$ mpr exec "foo=bar=42; print(foo)"
42
$ mpr exec "print(bar)"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'bar' isn't defined
$ mpr exec "foo=bar=42; print(foo)"
42
$ mpr resume exec "print(bar)"
42

results as seen by a logic analyzer hooked up to the RX/TX pins of the esp32

\x01\x03
>>> 
>>> 
>>> 
>>> 
raw REPL; CTRL-B to exit
\x02OKx05A\x01foo=bar=43;print(foo)\x04
MPY: soft reboot
raw REPL; CTRL-B to exit
>R\x01\x80\0\x01\x0443
\x04\x04>ets Jun  8 2016 00:22:57

rst:0x1 (POWERON_RESET),boot:0x17 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:4540
ho 0 tail 12 room 4
load:0x40078000,len:12448
load:0x40080400,len:4124
entry 0x40080680
MicroPython v1.19.1 on 2022-06-18; 4MB/OTA module with ESP32
Type "help()" for more information.
>>> 
>>> 
>>> 
>>> 
>>> 
raw REPL; CTRL-B to exit
\x02R\x01\x80\0\x01\x04\x04Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'foo' isn't defined
\x04>ets Jun  8 2016 00:22:57

rst:0x1 (POWERON_RESET),boot:0x17 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:4540
ho 0 tail 12 room 4
load:0x40078000,len:12448
load:0x40080400,len:4124
entry 0x40080680
MicroPython v1.19.1 on 2022-06-18; 4MB/OTA module with ESP32
Type "help()" for more information.
>>> 

other observations

• same behavior is observed with multiple firmware versions, and on different boards
• esp8266 devices do NOT soft-reset in the same way ( note: all my esp8266 devices use a different serialport driver)

Versions

• mpremote : 0.4.0
• pyserial: 3.5
• Python 3.9.13
• Version: 1.72.2 (user setup)
• OS: Windows_NT x64 10.0.22621
• Micropython - v1.19.1
• MCU - all esp32
• serial port driver esp32 : Silicon Laboratories Inc. 11.1.0.53
• serial port driver esp8266 : wch.cn - No version or other details

> mpremote devs
COM9 01665F52 10c4:ea60 Silicon Labs None # esp32
COM11 0001 10c4:ea60 Silicon Labs None # esp32 
COM20 00000000A 0403:6001 FTDI None # UART debug 
COM21  1a86:7523 wch.cn None # ESP8266

firmwares

• mpremote connect com9 get-info
  {'ver': 'v1.19.1', 'build': '', 'platform': 'esp32', 'port': 'esp32', 'machine': 'ESP32 module (spiram) with ESP32', 'release': '1.19.1', 'nodename': 'esp32', 'name': 'micropython', 'family': 'micropython', 'sysname': 'esp32', 'version': '1.19.1'}
• mpremote connect com11 get-info
  {'ver': 'v1.19.1', 'build': '', 'platform': 'esp32', 'port': 'esp32', 'machine': '4MB/OTA module with ESP32', 'release': '1.19.1', 'nodename': 'esp32', 'name': 'micropython', 'family': 'micropython', 'sysname': 'esp32', 'version': '1.19.1'}
• mpremote connect com21 get-info
  {'ver': 'v1.19.1', 'build': '', 'platform': 'esp8266', 'port': 'esp8266', 'machine': 'ESP module (1M) with ESP8266', 'release': '1.19.1', 'nodename': 'esp8266', 'name': 'micropython', 'family': 'micropython', 'sysname': 'esp8266', 'version': '1.19.1'}

oldest firmware tested with same behavior:

• mpremote connect com9 get-info
  {'ver': 'v1.10', 'build': '', 'platform': 'esp32', 'port': 'esp32', 'machine': 'ESP32 module with ESP32', 'release': '1.10.0', 'nodename': 'esp32', 'name': 'micropython', 'family': 'micropython', 'sysname': 'esp32', 'version': '1.10.0'}