ATTinyCore >=1.5.0 declares ATTinyCore:micronucleus@2.5-azd1b as a tool
dependency, hosted at https://azduino.com/bin/micronucleus/. That host
has been unreachable (connection refused) for extended periods, causing
every ATtiny85 compile to fail at the core-install step with:
Download failed: performing HEAD request: ... dial tcp ...: connection refused
Failed to install required core: ATTinyCore:avr
micronucleus is only used for USB upload — never for compilation — but
arduino-cli refuses to install a core whose tool deps cannot fetch.
Pin to 1.4.1, the last release whose micronucleus binary is hosted on
github.com (digistump release, reachable). The FQBN clock options we
ship (clock=16pll on attinyx5, etc.) are unchanged across 1.4.x.
- backend/app/services/arduino_cli.py: new CORE_INSTALL_VERSIONS map
consulted by ensure_core_for_board so the runtime auto-install
passes "ATTinyCore:avr@1.4.1" instead of unversioned latest.
- backend/Dockerfile and docker/entrypoint.sh: same pin so a fresh
image bakes 1.4.1 in and never hits the runtime fallback path.
Existing regression tests in test/backend/unit/test_arduino_cli_attinycore.py
still pass (they assert presence, not version).
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