This independent workspace answers one narrow question: can the GPUI version currently used by Zed expose the minimum semantic tree Lumbridge needs for a workspace and terminal pane, while accepting real platform IME input?

Reproducibility

Upstream: https://github.com/zed-industries/zed
Commit: ce48461eaadd16c65c31f835511ab96bd3b6e746
GPUI license at this commit: Apache-2.0
Rust: 1.97.1, matching the upstream rust-toolchain.toml

Both gpui and gpui_platform are pinned to the full commit. This directory is an independent Cargo workspace, so its toolchain and dependency graph do not change Lumbridge's root MSRV or release graph.

Semantics under test

The rendered tree contains:

an application named Lumbridge accessibility probe;
a stable, externally identifiable Region named Lumbridge workspace;
a stable, focusable Pane named Local terminal pane;
selected = true on the pane;
real GPUI keyboard focus tracked on the pane;
the description Needs input: choose whether to run the proposed command;
a Terminal child named Terminal output for the pane's content.

Current GPUI exposes these through its AccessKit integration using role, accessibility_id, aria_label, aria_description, aria_selected, focusable, and track_focus. The deterministic unit test checks the exact AccessKit role and properties. The binary compile-checks GPUI's element wiring; a platform screen reader remains necessary for end-to-end AT-SPI/VoiceOver validation.

Input and IME proof

The focused pane also installs a real ElementInputHandler<ImeTextReceiver> during element paint. ImeTextReceiver implements GPUI's EntityInputHandler, including text queries, UTF-16 selection, marked-text composition, replacement, unmarking, selection updates, editable length, and IME candidate bounds. This is the code path GPUI's platform adapters call for composed operating-system text input.

The backing buffer stores UTF-8 only at valid scalar boundaries and translates the platform's UTF-16 ranges before mutation. Deterministic tests cover:

replacing a selected decomposed e plus combining acute accent with é;
a marked decomposed-accent IME composition and commit;
inserting, selecting, and replacing the multi-codepoint grapheme 👩🏽‍💻;
collapsed selection placement after every replacement.

These tests prove range conversion and composed-text preservation without splitting UTF-8. An actual keyboard IME on X11/Wayland and macOS remains an end-to-end platform test, not a unit-test claim.

Commands

cargo check --locked
cargo test --locked
cargo clippy --locked --all-targets -- -D warnings

The first command installs the pinned Rust toolchain if rustup does not already have it and downloads Zed's GPUI dependency closure.

On Ubuntu hosts that have only the runtime libraries, checks work with RUST_FONTCONFIG_DLOPEN=1. Linking a test or binary additionally needs the unversioned linker names normally installed by libxcb1-dev, libxkbcommon-dev, and libxkbcommon-x11-dev. The amd-server validation used temporary symlinks under the ignored target/native-libs directory and set LIBRARY_PATH to that directory; no system packages or root files changed.

Observed local cost

On amd-server, the first successful check required roughly 90 seconds after installing/fetching, with some Cargo-cache contention from concurrent work. The lockfile contains 691 packages. After check, test, Clippy, and a debug build, the isolated target directory was 4.4 GiB and the debug binary was 535 MiB. The minimal Rust 1.97.1 toolchain occupies 624 MiB. These are development costs, not optimized release measurements.