ci: make CI genuinely green — rust-ci toolchain pin + canonical Julia ABI-FFI gate (#42)

## Summary

Make CI genuinely green. The shared rust-ci pin on `main` predates
standards#439, so the SHA-pinned `dtolnay/rust-toolchain` step errors
out before the job runs. This bumps the pin so rust-ci actually runs and
replaces the estate-banned Python ABI-FFI gate with the canonical Julia
gate (matches `verisimiser`). The Rust sources are already fmt +
clippy(`-D warnings`) clean.

## Changes

- **rust-ci:** bump `rust-ci-reusable.yml` pin `d135b05` → `8dc2bf0`
(current `standards` HEAD; includes #439 toolchain fix + #441/#442).
- **ABI-FFI gate:** remove `scripts/abi-ffi-gate.py` (Python banned
estate-wide); add `scripts/abi-ffi-gate.jl` (behaviour-identical Julia
port); workflow installs Julia 1.11.5. Matches `verisimiser`'s canonical
gate.

## RSR Quality Checklist

### Required
- [x] Tests pass (`cargo test --locked --all-targets`)
- [x] Code is formatted (`cargo fmt --all -- --check`)
- [x] Linter is clean (`cargo clippy --locked --all-targets -- -D
warnings`)
- [x] No banned language patterns (removes the last Python file from CI)
- [x] SPDX license headers present on new/modified files
- [x] No secrets, credentials, or `.env` files included

### As Applicable
- [x] ABI/FFI changes validated (gate logic preserved; conformance OK)

## Testing

Verified locally with the toolchain CI uses (cargo 1.94.1, rustfmt
1.8.0): `cargo fmt --check`, `clippy -D warnings`, `cargo check
--locked`, `cargo test --locked` all pass.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---
_Generated by [Claude
Code](https://claude.ai/code/session_01A6PSzJWpRxtzGDjUCEh7Mx)_

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/abi-ffi-gate.yml

@@ -21,8 +21,15 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+      - name: Install Julia 1.11.5
+        run: |
+          curl -fsSL https://julialang-s3.julialang.org/bin/linux/x64/1.11/julia-1.11.5-linux-x86_64.tar.gz -o /tmp/julia.tar.gz
+          tar -xf /tmp/julia.tar.gz -C /tmp
+          echo "/tmp/julia-1.11.5/bin" >> "$GITHUB_PATH"
       - name: Run ABI-FFI gate
-        run: python3 scripts/abi-ffi-gate.py
+        run: |
+          julia --version   # confirms the pinned 1.11.5 is on PATH, not the runner default
+          julia scripts/abi-ffi-gate.jl
 
   zig-build:
     name: Zig FFI builds + tests (Zig 0.14.0)

.github/workflows/rust-ci.yml

@@ -14,4 +14,4 @@ permissions:
 
 jobs:
   rust-ci:
-    uses: hyperpolymath/standards/.github/workflows/rust-ci-reusable.yml@d135b05bfc647d0c0fbfedc7e80f37ea50f49236
+    uses: hyperpolymath/standards/.github/workflows/rust-ci-reusable.yml@8dc2bf039d1ff0372d650895c46bea7fbaec68ff

scripts/abi-ffi-gate.jl

@@ -0,0 +1,116 @@
+#!/usr/bin/env julia
+# SPDX-License-Identifier: MPL-2.0
+# Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+#
+# abi-ffi-gate.jl — fail (exit 1) if the Zig FFI does not conform to the Idris2
+# ABI. The Idris2 ABI is the source of truth. Checks, with no compile toolchain
+# needed (pure base-Julia text analysis):
+#
+#   1. the Zig FFI carries no unrendered `{{...}}` template tokens;
+#   2. every `%foreign "C:<name>"` symbol declared anywhere in the ABI .idr
+#      sources is exported by the Zig FFI (`export fn <name>`);
+#   3. the Zig `Result = enum(c_int)` and the Idris `resultToInt` agree on BOTH
+#      names and integer values (the `Error`/`err` spelling is treated as one).
+#
+# Usage: julia scripts/abi-ffi-gate.jl [repo_root]   (defaults to cwd)
+#
+# Julia port of the former scripts/abi-ffi-gate.py (Python is banned estate-wide,
+# RSR-H4); behaviour is identical.
+
+"camelCase / PascalCase → snake_case (insert `_` before each non-initial capital)."
+camel_to_snake(s) = lowercase(replace(s, r"(?<!^)(?=[A-Z])" => "_"))
+
+"Canonical result-code key: lowercased, with `err`/`error` unified to `error`."
+function canon_rc(name)
+    n = lowercase(name)
+    (n == "err" || n == "error") ? "error" : n
+end
+
+"Return {variant => value} for the C-ABI `Result` enum (the `enum(c_int)` block whose `ok = 0`), or empty."
+function find_result_enum(zig::AbstractString)
+    best = Dict{String,Int}()
+    for m in eachmatch(r"enum\s*\(\s*c_int\s*\)\s*\{(.*?)\}"s, zig)
+        body = m.captures[1]
+        variants = Dict{String,Int}()
+        for vm in eachmatch(r"@?\"?([A-Za-z_][A-Za-z0-9_]*)\"?\s*=\s*(\d+)", body)
+            variants[canon_rc(vm.captures[1])] = parse(Int, vm.captures[2])
+        end
+        # The Result enum is the one starting at ok = 0.
+        if get(variants, "ok", nothing) == 0 && length(variants) > length(best)
+            best = variants
+        end
+    end
+    return best
+end
+
+"Collect every `*.idr` under `abi_dir`, skipping any `build/` output directory."
+function idr_sources(abi_dir::AbstractString)
+    files = String[]
+    isdir(abi_dir) || return files
+    for (root, _dirs, fs) in walkdir(abi_dir)
+        occursin("/build/", root * "/") && continue
+        for f in fs
+            endswith(f, ".idr") && push!(files, joinpath(root, f))
+        end
+    end
+    return files
+end
+
+function main(root::AbstractString)::Int
+    name = basename(rstrip(abspath(root), '/'))
+    abi_dir = joinpath(root, "src/interface/abi")
+    zig_path = joinpath(root, "src/interface/ffi/src/main.zig")
+    errs = String[]
+
+    idr_files = idr_sources(abi_dir)
+    if isempty(idr_files)
+        println("ABI-FFI GATE: SKIP ($name) — no Idris2 ABI .idr files under $abi_dir")
+        return 0
+    end
+    if !isfile(zig_path)
+        println("ABI-FFI GATE: FAIL ($name) — no Zig FFI at $zig_path")
+        return 1
+    end
+
+    idr = join((read(p, String) for p in idr_files), "\n")
+    zig = read(zig_path, String)
+
+    # 1. unrendered template tokens
+    toks = sort(unique(String(m.match) for m in eachmatch(r"\{\{[A-Za-z0-9_]+\}\}", zig)))
+    isempty(toks) || push!(errs, "Zig FFI has unrendered template tokens: $(toks)")
+
+    # 2. foreign C symbols must be exported
+    csyms = sort(unique(String(m.captures[1]) for m in eachmatch(r"C:([A-Za-z0-9_]+)", idr)))
+    exports = Set(String(m.captures[1]) for m in eachmatch(r"export fn ([A-Za-z0-9_]+)", zig))
+    missing_syms = [s for s in csyms if !(s in exports)]
+    isempty(missing_syms) ||
+        push!(errs, "$(length(missing_syms)) ABI function(s) not exported by the Zig FFI: $(missing_syms)")
+
+    # 3. result-code map (names + values) must agree
+    idr_rc = Dict{String,Int}()
+    for m in eachmatch(r"resultToInt\s+([A-Za-z0-9]+)\s*=\s*(\d+)", idr)
+        idr_rc[canon_rc(camel_to_snake(m.captures[1]))] = parse(Int, m.captures[2])
+    end
+    zig_rc = find_result_enum(zig)
+    if !isempty(idr_rc) && isempty(zig_rc)
+        push!(errs, "no Zig `enum(c_int)` Result block (with `ok = 0`) found to compare result codes")
+    elseif !isempty(idr_rc) && !isempty(zig_rc) && idr_rc != zig_rc
+        push!(errs, "Result-code map differs (name or value):\n" *
+                    "      Idris resultToInt: $(sort(collect(idr_rc)))\n" *
+                    "      Zig   Result enum: $(sort(collect(zig_rc)))")
+    end
+
+    if !isempty(errs)
+        println("ABI-FFI GATE: FAIL ($name)")
+        for e in errs
+            println("  - " * e)
+        end
+        return 1
+    end
+    println("ABI-FFI GATE: OK ($name) — $(length(csyms)) ABI functions exported, " *
+            "$(length(idr_rc)) result codes match")
+    return 0
+end
+
+root = length(ARGS) >= 1 ? ARGS[1] : "."
+exit(main(root))