---
id: PLN-0072
ticket: rgba8888-framebuffer-and-pixel-format-direction
title: RGBA8888 Residue Removal and End to End Validation
status: open
created: 2026-05-23
ref_decisions: [DEC-0029]
tags: [gfx, framebuffer, rgb565, rgba8888, renderer, assets, host, backend]
---

## Briefing

Close the RGBA8888 migration by removing residual RGB565 contract text and code
paths, running end-to-end validation, and preparing the discussion thread for
post-execution lessons.

## Source Decisions

- DEC-0029 - RGBA8888 Runtime Pixel Format Contract.

## Dependencies

- PLN-0067 through PLN-0071 must be complete or merged into the execution branch.

## Target

The repository must no longer expose RGB565, `Gfx*565`, `u16` framebuffer/color
contracts, RGB565 palette payloads, or RGB565 host conversion as active runtime
contract.

## Scope

Included:

- Whole-repository residue audit.
- End-to-end build and test validation.
- Documentation consistency checks.
- Final migration notes needed for housekeeping and lessons.
- Any small missed cleanup in code, docs, tests, or fixtures that directly
  violates DEC-0029.

## Out of Scope

- New alpha-only commands.
- Performance optimization after broad alpha support.
- GPU backend, render thread, RGB565 backend, multi-format backend abstraction.
- New visual design work for the Hub.

## Execution Plan

1. Run repository-wide residue scans.
   - Search for `RGB565`, `rgb565`, `Gfx.*565`, `clear_565`, `u16` near color
     or framebuffer APIs, `GLYPH_BANK_PALETTE.*u16`, `size_of::<u16>()` near
     palette code, `draw_rgb565`, and `0xFFFF` near color validation.
   - Classify every remaining hit as removed, historical-only, unrelated, or a
     bug.

2. Remove active-contract residues.
   - Delete or rename any remaining active `Gfx*565` surface.
   - Remove RGB565 helpers from runtime and host normal paths.
   - Remove comments that still describe RGB565 as current behavior.
   - Remove tests that assert RGB565 output.

3. Verify docs and ABI consistency.
   - Ensure `docs/specs/runtime/04-gfx-peripheral.md`,
     `docs/specs/runtime/15-asset-management.md`, and
     `docs/specs/runtime/16-host-abi-and-syscalls.md` agree on RGBA8888.
   - Ensure public syscall declarations and docs use format-neutral names.
   - Ensure any historical RGB565 mention is clearly historical and not
     normative.

4. Run full test/build validation.
   - Run the repo's standard build command.
   - Run the relevant Rust test suites across HAL, drivers, system, VM, tools,
     and host.
   - Run any visual/snapshot validation available in the repository.

5. Record final evidence.
   - Capture the exact commands and outcomes in the plan or final PR notes.
   - List remaining historical RGB565 mentions and why they are acceptable.
   - Identify lesson candidates for `discussion-housekeep` after execution.

## Acceptance Criteria

- [ ] Repository scan finds no active RGB565 runtime contract.
- [ ] No public `Gfx*565` API, syscall, metadata, or ABI declaration remains.
- [ ] No normal renderer or host path performs RGB565 conversion.
- [ ] No asset decode path accepts RGB565 palettes as compatible runtime input.
- [ ] Specs, docs, ABI contracts, code, fixtures, and tests agree on RGBA8888.
- [ ] Full validation commands pass or any failure is documented as unrelated.
- [ ] The discussion thread has enough evidence for housekeeping and lessons.

## Tests / Validation

- Run the standard repository build command.
- Run affected crate tests: `prometeu-hal`, `prometeu-drivers`,
  `prometeu-system`, `prometeu-vm`, `prometeu-bytecode`,
  `prometeu-host-desktop-winit`, and `pbxgen-stress` where applicable.
- Run all available visual/snapshot tests.
- Run repository-wide `rg` residue scans described above.
- Run `discussion validate`.

## Risks

- Some remaining RGB565 references may be legitimate historical notes. They
  must be marked clearly enough that readers cannot mistake them for active
  contract.
- End-to-end visual validation may not exist yet. If so, record the gap and add
  minimal deterministic checks around RGBA channel order and alpha behavior.