alktype/docs/architecture/open-questions.md

status, last_updated

status	last_updated
draft	2026-07-22

Open Questions

Each open question lives in its own file under questions/, named NNN-slug.md (mirroring the ADR convention). This file is the index: theme-grouped tables for scannability, plus a cross-theme Deferred / Blocked section that surfaces the safe-exit deferrals with their blocking conditions inline — so "what's currently parked and why" is answerable at a glance.

Status values:

• open — Needs to be resolved now. Has a clear path to resolution.
• resolved — Decided. The resolution is stated cleanly, without caveats about how it could be changed later.
• deferred(scope) — Cannot be resolved yet. The information is genuinely missing — a crate spec, POC result, or use case that doesn't exist yet. Has a concrete blocking condition. Not a failure — scope management.
• deferred(unclear) — Cannot be resolved yet. The pieces exist (decided in other ADRs, existing types, existing patterns) but the composition — how they fit together — isn't clear yet. Resolution requires investigation (work through examples, maybe POC), not waiting. Has a concrete investigation target and an impacts field. Not a failure — honest uncertainty in a poorly-defined problem space.
• partially resolved — Some aspects decided, others deferred or open.
• dissolved — The question was reframed out of existence (e.g., superseded by an ADR that retires the premise). Kept for reference.

Impacts field: Every unresolved OQ (open, deferred(scope), deferred(unclear), partially resolved) should have an Impacts field stating what it blocks downstream. Be specific: "blocks the first hub deployment because the hub dials workers" not "blocks the hub crate." This is the triage signal that makes the deferral's urgency visible.

Door type classifications follow ADR-009 — they describe reversal cost (how expensive it is to undo), not urgency:

• One-way door: Reversal requires rewriting significant code or permanently closes a capability. Getting it wrong is expensive — requires ADR before implementation.
• Two-way door: Reversal is cheap or additive. Getting it wrong is recoverable — decide, implement, revert if needed.

Door type is separate from whether a decision is made. A two-way door is a decision you make now and can revert later, not a decision to defer.

By Theme

Layout Engine

OQ	Title	Status	Door	Pri
OQ-069	Arrays of Variable-Length-Element Structs	deferred(scope)	two	low

Platform Support

OQ	Title	Status	Door	Pri
OQ-070	no_std + alloc Support	deferred(scope)	two	low

Schema Construction

OQ	Title	Status	Door	Pri
OQ-071	Builder API for Schema Construction	deferred(scope)	two	med

Deferred / Blocked

The safe-exit visibility surface. These questions are parked because the information needed to resolve them does not exist yet — each has a concrete blocking condition. They are not failures; they are scope management. This section exists so "what's currently blocking the architect" is answerable at a glance, not by filtering the tables above.

OQ-069: Arrays of Variable-Length-Element Structs

• Blocked on: A concrete consumer that needs arrays of structs with variable-length fields, where the elements are interleaved ([fixed_0][str_0][fixed_1][str_1]...) and the engine must walk sequentially rather than use a fixed stride. The SFTP Name packet has Vec<File> where File contains strings, but SFTP serializes this as a sequence of length-prefixed strings (the serde SeqAccess pattern), not as an array of fixed-stride structs. Arrays of fixed-size structs are fully supported.
• Priority: low
• Full file: OQ-069

OQ-070: no_std + alloc Support

• Blocked on: An embedded use case that requires no_std + alloc (e.g., a microcontroller running Rust without std). The WASM target has std available via wasm-bindgen. The engine's core (offset computation, read/write) is already allocation-free; the jsonschema dependency is the only alloc consumer.
• Priority: low
• Full file: OQ-070

OQ-071: Builder API for Schema Construction

• Blocked on: A concrete need for programmatic schema construction in Rust. The current consumers (SFTP, metatensor, binary call frames, TTY negotiation) all have schemas that can be hand-written or generated from TypeBox. A builder API would be a fluent Rust API that produces the same JSON Schema structure — it would sit on top of the engine, not inside it.
• Priority: medium
• Full file: OQ-071