alktype/AGENTS.md

AGENTS.md

Operating instructions for opencode agents working in this repo. opencode auto-loads this file as instructions, overriding the built-in defaults for this project. Custom agents in .opencode/agents/ inherit these rules unless their own prompts say otherwise.

Git Workflow

Commit and push when reasonable. When a change is complete and verified (build + lint + tests pass), commit and push to origin/main without asking. This overrides the built-in default of "only commit when explicitly asked."

The workflow:

1. Make the change
2. Verify: cargo test --release, cargo clippy --all-targets -- -D warnings, cargo doc --no-deps if docs changed, cargo build --target wasm32-unknown-unknown --release if layout/wasm-relevant code changed
3. Inspect git status and git diff before staging — stage only the intended files, never secrets
4. Write a concise commit message matching the repo style (see git log --oneline -10). For multi-point changes, use a summary line plus a body with bullet points and a verification block.
5. git push origin main
6. Report the commit hash and the verification summary

Exceptions — do not commit or push without asking:

• The change is exploratory / speculative (you're not sure the user wants it kept)
• The user is actively reviewing the diff and may ask for changes
• The change touches semver-relevant public API (this repo is on crates.io; the public surface is the 0.1.0 contract — AlkTypeEngine, Schema/Definitions/Discriminator builder types, FieldValue, AlkTypeKind, Endian, VariableEncoding, DiscriminatorKind, LayoutMode, OffsetMap/ByteRange, LayoutBuilder/PackedLayout/ FieldPosition, SequentialReader, UnionDispatch, AlkTypeError variants, and the data_access/schema/tunion/materialize/ validation public function signatures). Additive, non-breaking changes (new methods, new error variants, new builder setters) are fine to commit; renames, removals, signature changes, or behavioral shifts on existing public items are not.
• You'd be force-pushing, amending a published commit, creating an empty commit, or skipping hooks

Never commit secrets, keys, or credentials. If a commit fails or hooks reject it, fix the issue and create a new commit — do not amend the failed one.

Git identity is preconfigured (glm-5.2 <glm-5.2@alk.dev>). Do not change git config, skip hooks, or use git commit -i.

Project Conventions (Rust / binary struct engine)

This is a binary struct engine crate. The conventions below apply to all work in src/ and tests/. They mirror .opencode/agents/ implementation-specialist.md §Project Conventions and are repeated here so they apply to every session, not just spawned implementation agents.

1. No comments in code unless the user explicitly asks. This is a project-wide convention. Doc comments (///, //!) are fine and expected on public API. Inline // comments only when the user asks or when a non-obvious safety/correctness constraint would otherwise be missed (e.g., "the u32 at offset 1 is unaligned — correct for protocol wire formats, which pack fields tightly").

2. Error handling — AlkTypeError (the hand-rolled enum in src/error.rs) is the library error type. No anyhow or thiserror — this is a library crate with a single error enum covering the three engine phases (schema, offset, access) plus validation. Never panic in library code. No unwrap() or expect() outside tests — if you reach for unwrap, the error path wasn't specified, stop and decide what should actually happen.

3. Schemas are untrusted input — every engine path that walks a schema must return Err on a malformed schema, never panic!/ unreachable!. The downstream alkcall consumer accepts schemas from arbitrary internet peers in its hub/spoke topology, so a malicious or unsupported schema definition must produce a handleable error, not a crash. If you add a new AlkTypeKind variant, the k if k.is_fixed_size() guard pattern in offset_map and layout_builder will catch it at runtime via the _ => Err(...) arm; listing all fixed-size kinds explicitly to restore compile-time exhaustiveness is a separate cleanup, not a blocker (review #002, L2).

4. Overflow safety — use checked_add/try_from for any offset arithmetic or cast that can overflow on adversarial input. The data_access::write_bytes u32 truncation guard (review #002, M2) is the canonical pattern: validate the cast, return AlkTypeError::Access on failure. Do not regress to bare as u32 or + in production paths.

5. No async — the engine is fully synchronous. No tokio, no async/.await, no async-sync primitives. Schema compilation, layout walks, read/write, and validation are all blocking, CPU-bound operations.

6. No feature flags — the crate has no feature flags and no optional dependencies. default = [] in Cargo.toml. If a future need surfaces (e.g. no_std per OQ-002, or an optional strict RFC 3339 validator), raise it as an OQ/ADR before adding one.

7. WASM-clean — the only dependencies are jsonschema (with default-features = false) and serde_json (with preserve_order). No platform deps, no std::time, no filesystem, no threads. Must compile to wasm32-unknown-unknown. If you reach for a new dependency, first verify it's wasm-compatible and confirm it's worth the dependency cost.

8. serde_json's preserve_order is load-bearing — field order in the schema JSON determines byte order in packed mode, and the OffsetMap/PackedLayout iteration order in both modes. Do not disable the preserve_order feature, and do not sort schema object keys anywhere in the engine.

9. Naming — Rust standard: snake_case for functions/variables/ modules, PascalCase for types/traits, SCREAMING_SNAKE_CASE for constants.

10. Module structure — one module per file under src/, re-exported from src/lib.rs. Public API surface is the lib.rs re-exports; if a new public type or function needs to be visible to consumers, add it to the pub use block in lib.rs.

11. No unsafe — the crate has zero unsafe blocks and zero unsafe extern declarations. Bounds-checked slice access via data_access::check_bounds and get(..) with ok_or_else is the pattern. Do not introduce unsafe for performance; the bounds-check-eliding optimization belongs in the jsonschema/serde layer, not here.

Verification Commands

Run these before committing. All must pass.

cargo test --release                                  # full suite (~396 tests: 310 crate + 86 integration)
cargo clippy --all-targets -- -D warnings
cargo doc --no-deps                                   # if docs changed
cargo build --target wasm32-unknown-unknown --release # if layout/wasm-relevant code changed
cargo publish --dry-run --allow-dirty                 # before a release

Architecture Context

• docs/architecture/ — the authoritative spec. Read it before non-trivial changes. ADRs are numbered; OQs (open questions) track resolved/deferred decisions.
• ADR-001 — purpose, scope, "schema is the format" principle, jsonschema as the validation engine
• ADR-002 — two layout modes (packed sequential vs aligned static); the most important architectural decision
• ADR-003 — schema annotations (endianness, alignment, encoding, TUnion discriminators)
• ADR-004 — error handling and validation strategy; the AlkTypeError enum, load-time build, access-time check
• ADR-005 — Int64/Uint64 as first-class kinds; JSON precision caveat
• ADR-006 — reject non-final inline length-prefixed variable fields in aligned mode (prevents silent data corruption)
• ADR-007 — packed-mode read factory; engine.sequential_reader() returns an owned fresh reader (the reader has mutable cursor state)
• ADR-008 — reject TUnion in aligned mode for v1 (broken semantics)
• ADR-009 — builder API producing serde_json::Value; resolves OQ-003
• ADR-010 — validate_bytes on AlkTypeEngine; materialize Value from bytes, then validate
• If a TODO references a design direction that an ADR has since decided against, the TODO is stale — remove it and align with the ADR. Do not implement the rejected design.
• OQ-001 (deferred): arrays of variable-length-element structs — blocked on a concrete consumer that needs interleaved variable-stride arrays.
• OQ-002 (deferred): no_std + alloc support — blocked on an embedded use case; the core engine is already allocation-free, jsonschema is the only alloc consumer.