test(firmware): verify virtual Linux GPIO through flat hardware modules

[nicksan222]

Summary

• Flatten firmware hardware modules by role: pins.rs for board descriptors, buttons.rs for events/polling, debounce.rs for timing, and linux_gpio.rs for Linux device access. Keep hardware::pins::* intact.
• Add a Linux GPIO reader for the board's active-low buttons (internal pull-ups by default), with an external-bias option for simulated inputs.
• Reuse the existing QEMU E2E guest with gpio-sim: drive one representative button through /dev/gpiochip* and assert typed press/release events reach the real firmware runtime. The existing scripted tests remain responsible for all 12 pin mappings, bounce, held inputs, and read failures.
• Sync the root and isolated Yocto Cargo locks and crate fetch metadata.

Verification

• just --justfile apps/firmware/justfile check (including the default Docker/QEMU E2E suite)
• just --justfile apps/firmware/justfile yocto-check
• just --justfile apps/firmware/justfile cross-build
• Guest probe also reached LINUX_VM_PASS under QEMU software emulation without KVM (before the module-only layout refactor).

The test exercises real guest-kernel GPIO, not Pi electrical hardware or a built Yocto image. The Linux reader is not yet attached to the production executable's startup.

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(requestId: serverGenReqId_86897a04-5cd2-4d8f-9888-0974ec97a9f8)

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-24T16:52:46.853357Z	11953bb	PR opened

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