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Proof Requirements

Current State (2026-06-21 — verified with Idris2 0.7.0 + Zig 0.15.2)

The ABI package typechecks end-to-end (all modules %default total, no postulate / believe_me / assert_total), and the hand-written Idris layout constants are now cross-checked against the real C layout the Zig compiler emits (see Cross-language ABI below):

cd src/interface/abi && idris2 --typecheck gsa-abi.ipkg
# 1/3: Building Types (Types.idr)
# 2/3: Building Layout (Layout.idr)
# 3/3: Building Foreign (Foreign.idr)

Toolchain: Idris2 0.7.0, Chez backend (.tool-versions pins idris2 0.7.0).

What is proven (machine-checked)

Memory layout (Layout.idr)

For every one of the 8 ABI structs — ServerHandle, ProbeResult, ConfigField, A2MLConfig, GameProfile, ServerOctad, Fingerprint, DriftReport — all four layout properties are proven:

Property Meaning

NoOverlap

no two fields’ [offset, offset+size) ranges overlap

AllFieldsAligned

every field offset is a multiple of its alignment

SizeAligned

total struct size is a multiple of the struct alignment

SizeCoversFields

total size ≥ sum of field sizes (padding accounted)

Discharged by decision procedures (decNoOverlap, decAllAligned, decSizeAligned, decSizeCovers) extracted via getYes; each proof typechecks only because its Dec reduces to Yes for that concrete layout — i.e. a malformed layout would fail to compile.

Also still proven: the per-type size/alignment Refl proofs, the SizeOf↔layout agreement (LayoutMatchesSizeOf), and cross-platform x86_64 ≡ aarch64 equivalence.

Alignment (Layout.idr)

  • alignUpCeil offset a = ceilDiv offset a * a (via an in-module total ceilDiv).

  • alignUpCeilIsMultiple — constructive Refl proof that the result is k * a.

Correction to the prior version of this file: the earlier alignUpCeilIsMultiple did not typecheck (the case form left the goal stuck). It was rewritten via ceilDiv so the witness is a direct Refl. There is no remaining alignUpEquiv postulate — the proven path uses alignUpCeil/ceilDiv directly, so that obligation is moot.

Domain validators (Types.idr)

Decidable portInRange, nonEmptyId, configFieldCountPositive, allPortsValid, the Valid* smart constructors, and the linear ServerHandle with its erased non-null witness.

Cross-language ABI (abi_layout.zig / abi_serde.zig)

The Idris proofs above show the model is internally consistent; the Zig side now checks that model against reality and makes it a live runtime contract.

  • Layout cross-check (was the open HIGH item). Each of the 8 structs is declared as a Zig extern struct (abi_layout.zig). A comptime block asserts @offsetOf / @sizeOf / @alignOf of every field equals the proven Idris constant — lifted verbatim from Layout.idr into abi_layout_expected.zig by scripts/gen_abi_expected.zig. Any divergence is a compile error, so the library cannot build against a layout the proofs do not describe. A negative test (perturbing one offset) confirms the guard bites; the check also runs under zig build test.

  • Live offset contract. The previously-unimplemented FFI readers that GSA.ABI.Foreign binds are now real (abi_serde.zig): read_int / read_double / read_ptr decode fields at a byte offset; read_string, array_len, array_get_string, is_null, free handle strings/arrays; apply_config / close_handle round out the surface. Emitters (serializeDriftReport / serializeFingerprint / serializeStringArray) write the wire structs, and gossamer_gsa_drift_struct exports one. Round-trip tests read each field back at its proven Layout.idr offset, standing in for the Idris reader — so agreement is an end-to-end cross-language guarantee.

  • Idris consumer. Foreign.getDrift now decodes a DriftReport at offsets taken from offsetOf … driftReportLayout (not the previous, wrong hand-tuned 0/4/12/20/28), via prim__driftStruct + prim__readPtr/readInt/readDouble.

Regenerate the expected table whenever Layout.idr changes: zig run scripts/gen_abi_expected.zig (then the Zig cross-check re-validates).

What still needs proving

  • Server probe safety (MEDIUM). Prove probes cause no side effects on targets. Needs a specification first.

  • Configuration drift-detection completeness (LOW). Needs a richer spec.

  • Access control for admin panels (LOW). Needs a specification.

Notes

  • Foreign.idr’s linear ServerHandle wrappers now typecheck: each handle is consumed by a pattern match and rebuilt for the borrow-return, so linearity is respected (previously they used the handle twice and did not compile).