refactor(io): address audit findings (dedup, dead-code, comment hygiene)

[BANANASJIM]

Addresses a batch of LOW audit findings across src/io/. All changes are behavior-identical simplifications/dead-code removal/comment hygiene; existing tests cover the touched paths.

• uhid.zig: drop unreachable if (n < 4) return null in pollOutputReport (a short read already returns error.IncompleteUhidEvent).
• uhid.zig: remove redundant @min/copy_len pad-copy in uhidCreate, uhidInput, and sendCreate; both event structs are smaller than UHID_EVENT_SIZE, so a direct @memcpy(buf[0..bytes.len], bytes) guarded by a comptime size assert preserves the invariant without the dead runtime branch.
• uhid_descriptor.zig: trim the already-implemented "forward-compat with FFB output reports" rationale on INPUT_REPORT_ID; drop the TODO marker from the skipped buildForPid golden-fixture test and rename it.
• usbraw.zig: extract a private libusbOpenAndClaim helper for the duplicated libusb init/open/detach/claim sequence shared by UsbrawDevice.open and UsbrawSuppress.openSuppress.
• netlink.zig: collapse the duplicate WouldBlock/else recv error arms (both return) into catch return.

Skipped (recorded, not changed): pub uhidCreate/uhidInput are imported by test files so moving them test-only is out of scope; ArrayListUnmanaged rename is churn-only (empty-init std.ArrayList(u8){} is already the unmanaged form in 0.15); uinput.create two-pass axis loop cannot merge without changing the existing >16-axis behavior; the suggested errdefer uhidDestroy test is non-falsifiable without root.

Test plan: ./scripts/padctl-docker test → EXIT=0; zig fmt --check (0.15.2) clean on changed files.

refs: codebase audit

Summary by CodeRabbit

• Refactor

  • Simplified I/O driver error handling and event validation logic.
  • Consolidated USB device initialization code to reduce duplication and improve consistency.

• Tests

  • Updated test naming in the descriptor module.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 6709eb79-d53b-4fcd-b046-ff2ec177e35d

📥 Commits

Reviewing files that changed from the base of the PR and between 9aea692 and 93fca95.

📒 Files selected for processing (4)

• src/io/netlink.zig
• src/io/uhid.zig
• src/io/uhid_descriptor.zig
• src/io/usbraw.zig

📝 Walkthrough

Walkthrough

The PR improves robustness across the I/O subsystem: netlink receive errors are handled uniformly, UHID event buffers are validated at compile time to eliminate truncation, and libusb device initialization logic is extracted into a reusable helper with proper resource cleanup on failure.

Changes

I/O subsystem robustness improvements

Layer / File(s)	Summary
Netlink error handling simplification src/io/netlink.zig	drainNetlink's receive loop unifies error handling for posix.recv with a single catch return, removing special-case handling of error.WouldBlock.
UHID buffer safety and framing src/io/uhid.zig, src/io/uhid_descriptor.zig	uhidCreate, uhidInput, and UhidDevice.sendCreate add compile-time assertions that extern event structs fit within UHID_EVENT_SIZE and copy exact serialized sizes instead of runtime truncation. pollOutputReport removes redundant short-read guard. Descriptor doc comment and test naming are clarified.
USB raw device initialization refactoring src/io/usbraw.zig	New libusbOpenAndClaim helper encapsulates libusb init, device open, kernel driver detach, interface claim, and failure rollback. UsbrawDevice.open and UsbrawSuppress.openSuppress use the helper to eliminate duplication and simplify error cleanup with non-optional context pointers.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• BANANASJIM/padctl#357: Both PRs modify src/io/usbraw.zig libusb open/claim flow and the UsbrawSuppress mechanism for suppress-interface claiming.
• BANANASJIM/padctl#369: Both PRs modify error paths in UsbrawDevice.open and UsbrawSuppress.openSuppress around libusb_claim_interface cleanup and rollback.
• BANANASJIM/padctl#140: Both PRs change src/io/uhid.zig UHID event buffer construction and payload framing in uhidCreate, uhidInput, and event header parsing.

Poem

🐰 A rabbit hops through the I/O burrow,
Compile-time buffers, no truncation to borrow,
Libusb helpers cleaned and reused with care,
Netlink simplicity flowing through the air!
Robust and swift through the kernel-space square. 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main changes: refactoring in the io module to address audit findings including deduplication, dead-code removal, and comment improvements, which directly match the changeset across netlink.zig, uhid.zig, uhid_descriptor.zig, and usbraw.zig.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/audit-io

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