fix(mcu): honor AVR framework registry package pins #1494

Context

The AVR resolver accepts a registry-version platform_packages entry but builds with the family default. A focused repro uses the existing tests/platform/atmega8 board fixture:

[env:atmega8]
platform = atmelavr
board = ATmega8
framework = arduino
platform_packages = framework-arduino-avr-minicore@3.1.0

The ATmega8 board metadata selects core = MiniCore (crates/fbuild-config/assets/boards/json/ATmega8.json). The PlatformIO platform-atmelavr manifest maps the MiniCore framework to package framework-arduino-avr-minicore with version ~3.1.0. fbuild’s registry-version warning recognizes the pin, but avr_packages only resolves URL overrides for framework-arduino-avr and framework-arduino-avr-attiny; avr_framework_package routes those overrides only for core keys arduino, tiny, and tinymodern. MiniCore falls through to AvrFramework::for_core, whose embedded registry resolves MCUdude/MiniCore 2.2.2 (crates/fbuild-library/assets/avr_frameworks.json). Thus an explicit registry framework pin can be accepted while fbuild selects its distinct 2.2.2 default.

This is separate from the completed URL-override wiring in #667 and #669: those cover the standard Arduino AVR and ATTiny canonical keys, not registry semver resolution for other AVR package names.

Proposal

Resolve valid AVR platform = name@version and platform_packages = package@version aliases against PlatformIO platform/package metadata, including core-specific framework mappings, and build with the requested packages. Fail before compilation only for unavailable versions or genuinely unsupported inputs. Keep standard AVR and ATTiny URL/archive override behavior intact.

PlatformIO alias requirement

Resolve PlatformIO-hosted platform and framework package aliases to exact archive URLs/checksums. The AVR core-to-package map must select the requested registry package, including MiniCore, rather than applying a generic AVR default; preserve explicit URL overrides.

Acceptance criteria

• RED: add a focused resolution test or isolated build with the ini above and show the requested MiniCore package 3.1.0 is currently replaced with fbuild’s 2.2.2 default; cover that the warning does not make the pin effective.
• GREEN: valid published AVR platform and framework package aliases resolve their requested versions plus compatible dependencies and build with them; the MiniCore 3.1.0 repro no longer selects the 2.2.2 default. Unavailable or unsupported aliases fail before compilation; rejecting a valid supported alias is not completion.
• Cover core-specific package mappings, including MiniCore and the already-wired standard AVR / ATTiny packages; preserve URL/archive overrides.
• Make requested and resolved framework/toolchain versions visible in output or machine-readable build metadata.
• Unit tests: table-drive AtmelAvr and AtmelMegaAvr registry/manifest fixtures through the shared fbuild-core resolver, including MiniCore 3.1.0, Arduino AVR, and ATTiny package names; assert board-core mapping, exact payload URL/checksum, override precedence, and no fallback to the embedded 2.2.2 MiniCore default.

Decisions

• Group AVR and megaAVR resolver work under this family because the AVR framework JSON and orchestrator are shared; this report uses the concrete atmelavr MiniCore mismatch.
• Treat an explicit framework registry pin substituted by a family default as a correctness and reproducibility defect, even when fbuild emits the A pinned platform version is silently ignored — in platform and in platform_packages #1407 warning.
• Use ATmega8 as the minimal repro because its checked-in board metadata selects MiniCore, making the actual default package unambiguous.

Related issues

• A pinned platform version is silently ignored — in platform and in platform_packages #1407 added warning visibility for ignored pins but does not resolve them.
• audit: avr / framework-arduino-avr — does platform_packages override work? (parent #664) #667 and audit: attiny — does platform_packages override work? (parent #664) #669 cover AVR/ATTiny URL-based platform_packages override paths, not registry-version pins.

Core and AVR testing gate

• RED → GREEN: add failing exact-payload assertions for AVR and megaAVR to the shared offline fbuild-core generic-path suite before changing their adapters. Include MiniCore 3.1.0, standard Arduino AVR, and ATTiny; generic short, owner-qualified, and typed paths must resolve independently of the native platform enum.
• Assert exact platform/framework/toolchain payload version, host URL/SHA-256, stable cache identity, manifest dependencies, board-core mapping, and explicit platform_packages precedence. The MiniCore fixture must never resolve to fbuild's embedded 2.2.2 default.
• Separate AVR/megaAVR adapter/build tests must consume those core results, preserve URL/archive overrides, and report requested versus resolved identities. The shared core suite runs offline in CI without PlatformIO or compiler downloads.