fix: ESP native deploy hangs while writing partitions

[zackees]

Context
FastLED ESP32-S3 AutoResearch validation is now using fbuild exclusively. While validating LCD_CLOCKLESS on an attached ESP32-S3 (COM22), fbuild successfully built the staged AutoResearch firmware but consistently hung during native ESP flash deploy.

This blocks fbuild-only hardware validation for FastLED LCD/clockless changes even when the firmware build itself succeeds.

Reproduction
From FastLED/FastLED worktree fix/2690-2693-autoresearch-lcd:

bash autoresearch esp32s3 --lcd --upload-port COM22 --lanes 1 --strip-sizes 400 --skip-lint --skip-schema --project-dir .build/pio/esp32s3 --timeout 180 --verbose

The wrapper invokes:

.\.venv\Scripts\fbuild.exe C:\Users\niteris\dev\fastled\.claude\worktrees\fix-2690-2693-autoresearch-lcd\.build\pio\esp32s3 deploy -e esp32s3 -p COM22 -v

fbuild completes the build and produces:

• .build/pio/esp32s3/.fbuild/build/esp32s3/release/firmware.elf
• .build/pio/esp32s3/.fbuild/build/esp32s3/release/firmware.bin
• bootloader.bin, partitions.bin, and boot_app0.bin

Daemon log excerpt:

build completed in 371.3s
verifying ... firmware.bin on COM22 via espflash (esp32s3)
verify-flash: device image differs; proceeding with full flash
flashing ... firmware.bin to COM22 via espflash (esp32s3)
native write: writing region port=COM22 region=Bootloader offset=0x0 size=18736
native write: progress port=COM22 region=bootloader pct=100 current=1 total=1
native write: region complete port=COM22 region=bootloader skipped=false
Binary successfully written to flash!
native write: writing region port=COM22 region=Partitions offset=0x8000 size=3072

After the partitions line, no further progress is logged and the fbuild client/daemon stay alive indefinitely.

I also retried the cached artifact with a conservative upload baud:

.\.venv\Scripts\fbuild.exe C:\Users\niteris\dev\fastled\.claude\worktrees\fix-2690-2693-autoresearch-lcd\.build\pio\esp32s3 deploy -e esp32s3 -p COM22 --skip-build -b 115200 --monitor --timeout 180 --halt-on-success TEST_COMPLETED_EXIT_(OK|ERROR) --halt-on-error panic|abort\(|TEST_FAILED|ERROR

That reproduced the same hang at the partitions region:

verifying ... firmware.bin on COM22 via espflash (esp32s3)
verify-flash: device image differs; proceeding with full flash
flashing ... firmware.bin to COM22 via espflash (esp32s3)
native write: writing region port=COM22 region=Bootloader offset=0x0 size=18736
native write: progress port=COM22 region=bootloader pct=100 current=1 total=1
native write: region complete port=COM22 region=bootloader skipped=false
Binary successfully written to flash!
native write: writing region port=COM22 region=Partitions offset=0x8000 size=3072

Historical daemon logs show the same pattern for ESP32-C6 on COM9: bootloader write completes, then the deploy stops after region=Partitions offset=0x8000.

Expected behavior

• fbuild should finish flashing partitions and app firmware, then return success or enter monitor mode.
• If native espflash stalls, fbuild should time out and fall back to esptool or return an actionable deploy error.
• The fbuild client should not hang indefinitely after a successful bootloader write.

Acceptance criteria

• ESP32 native deploy completes past the partitions region for ESP32-S3 and ESP32-C6.
• A failed native write has a bounded timeout and reports the region/offset that failed.
• FastLED AutoResearch can use fbuild-only deploy+monitor without PlatformIO fallback.