fix: store and load every value type at its own width

[arcjet-rei]

Gravity reads and writes guest memory for record fields, list elements, a host import's result and an export's indirect parameters. Several value types were handled at the wrong width or type there:

• F32Store and F64Store called WriteUint64Le. Since fix: Handle Wasm ValueTypes returned by imports #141 made import-side floats plain float32/float64, a host import returning a record with a float field generated Go that did not compile. On the export side, F32Store wrote 8 bytes for a 4-byte value and overwrote the memory after it, and F32Load read 8 bytes.
• I32Store8 accepted only 0 and 1, so storing a u8, s8, enum or option<u8> payload above 1 panicked.
• I32Store16, I64Store, I32Load8S, I32Load16U and I32Load16S were todo!(), so u16, s16, u64, s64 and s8 values in memory crashed gravity.

Each store now writes exactly its width with an explicit conversion, and the missing loads are implemented. The integer lifts use Go conversions, so they accept both the uint64 that api.Function.Call returns and the narrower values a load produces. Floats use wazero's WriteFloat32Le/ReadFloat32Le and their f64 counterparts for imports, and the IEEE bits for exports.

The new memory example sends a record of every scalar type (17 flattened values, so it always travels through memory) into and out of an export and a host import. It also round-trips a 68-byte record whose trailing f32 sits directly before a string allocation.

Regenerating existing bindings rewrites some lines: stores gain explicit conversions such as WriteByte(p, uint8(0)), and bool stores lose their 0/1 switch. The bytes written are unchanged for every value those stores receive.

🤖 Generated with Claude Code

[arcjet-review]

Arcjet Review — 🟡 Medium Risk

Decision: Checked

Rationale: This PR makes meaningful changes to core code generation for Wasm canonical ABI memory loads/stores, so the risk is Medium rather than Low. The changes appear well-scoped and consistent: byte/16/32/64-bit integer stores now explicitly write the correct width, missing 8/16/64-bit memory operations are implemented, and f32/f64 handling now distinguishes host import float values from export-side raw IEEE bits returned by wazero. The new memory example and tests exercise round-trips through both exports and host imports across boundary integer values, strings, chars, bools, options, enums, and floats. Security review found no hardcoded secrets, auth changes, injection paths, or new unsafe command/query construction. The dependency change is limited to a new example crate using exact pinned versions, and does not introduce an apparent application runtime dependency.

Summary of Changes

Fixes Gravity's generated Go bindings so scalar values are loaded from and stored to guest memory at their canonical ABI widths, including f32/f64, i8/u8, i16/u16, and i64/u64 paths. Adds a new memory example and generated stdout fixtures to test indirect record parameters/results and host import memory interactions.

Escalation Triggers

• Dependency Changes: Adds examples/memory/Cargo.toml with pinned wit-bindgen and wit-component dependencies for the new example crate.

Review Focus Areas

• Confirm the newly added example dependencies are already acceptable for the workspace and are covered by the repository's lockfile/update process.
  Dependency changes can affect supply-chain risk even when versions are pinned and used only for examples.
• When reviewing manually, verify the Direction::Import versus Direction::Export float handling matches the generated call paths for both direct and indirect parameters/results.
  The correctness of f32/f64 handling depends on whether the generated Go code receives native float values or raw wazero IEEE-bit return values.
• Run the new memory example tests together with the generated fixture tests.
  The changed code is code generation; exercising the generated bindings is the best way to catch type-width regressions or compile-time mismatches.

Notes

The diff exceeds the 500-line automated-review threshold, largely because it includes generated stdout fixtures. Automated review still found the implementation coherent, but humans should skim the generated outputs and run the relevant tests before merge.

Path filtering: 1 file excluded by ignore paths. 14 of 15 files included in review.

The AI assessed this PR as approvable, but the trust level (1) does not allow auto-approval. A human reviewer must approve this PR.

_{Review: 3b69e21a | Model: openai/gpt-5.5 | Powered by Arcjet Review}