t27c gen-zig: a fn parameter typed []const []const u8 is split into two parameters #9397

Re-filed from #6669. An attempt claimed that issue on 2026-10-07 and left an empty branch, and a dispatch row that has spent its retry ceiling keeps its issue for good - so no bee could take it again, however much the brief improved. The work below is carried over unchanged.

Observed

A parameter whose type is a slice of slices does not survive gen-zig. Source (from a draft of specs/tri/utils/template.t27, PR #5084):

fn lookup(name: []const u8, names: []const []const u8, values: []const []const u8) -> []const u8 {

Emitted Zig (lab t27c built at c813a19, tri lab-exec):

fn lookup(name: []const u8, names: []const, @"u8": , values: []const, @"u8": ) []const u8 {

and zig refuses it: expected type expression, found ','.

Expected

names: []const []const u8 in the emitted Zig, as [N][]const u8 locals already are.

Notes

• Workaround used in the spec: a slice of structs ([]const Entry with name/value fields).
• Struct fields declared as the string "[]const []const u8" (specs/tri/io/fs.t27, specs/tri/pipeline/workflow.t27) may hit the same path; not checked.

Refs #5083

Boundary

• specs/tri/io/fs.t27
• specs/tri/pipeline/workflow.t27
• specs/tri/utils/template.t27

User Scenarios

• Given a .t27 spec containing a function parameter typed []const []const u8, when the spec is compiled with t27c gen-zig, then the emitted Zig parameter retains the slice-of-slices type []const []const u8 as a single parameter.

Requirements

FR-001: The Zig code generator MUST emit a single parameter for a slice-of-slices type ([]const []const u8) instead of splitting it into multiple parameters.
FR-002: The generated Zig code MUST compile without syntax errors when a function parameter has type []const []const u8.

Success Criteria

• t27c gen-zig specs/tri/utils/template.t27 exits with exit 0 and the emitted lookup function signature contains names: []const []const u8 as a single parameter.
• t27c gen-zig specs/tri/io/fs.t27 exits with exit 0 and any struct fields typed []const []const u8 are emitted correctly in Zig.
• t27c gen-zig specs/tri/pipeline/workflow.t27 exits with exit 0 and any struct fields typed []const []const u8 are emitted correctly in Zig.

The instruments

Every one of these reads and prints; none of them writes. Run them from the repository root, with <spec> replaced by the file in ## Boundary:

.t27 is not Rust and not Zig, and a bee fluent in either writes one by
accident. Measured 2026-09-20: a bee filled eight bodies in
specs/file/watcher.t27 with return Ok(());, Err(FileError::WatcherNotFound)
and for i in 0..watchers.length. The parse ratchet refused the whole file --
Unexpected token in expression: RParen, line 123 -- and a spec that does not
parse generates nothing, so every test it already carried stopped running.

At the top level the parser accepts exactly these eight forms, with an optional
pub, and no others:

const   var   fn   enum   struct   test   invariant   bench

There is no trait, no impl, no type X = ..., no generics, no macro. What
a bee reaches for from another language, and what happens:

• Rust's result sugar (Ok(()), Err(E::V), ?) is not a construct here.
• Rust macros (println!, format!, vec!) are not constructs here.
• A range loop (for i in 0..n) is Rust and Zig, not this language.
• Zig builtins (catch unreachable, @intCast, @constCast) are not constructs here.
• Cross-module reuse (use other::fn;) parses and then generates a comment and an unqualified call, so the Zig fails with use of undeclared identifier (use a::b; generates no import, so no spec can reuse a function from another spec #4298). It does not work yet.

t27c parse <spec> answers in one line whether what you wrote is the language.
Run it before you report, every time.

• t27c spec-status <spec> - the compiler's one-word verdict: IMPLEMENTED, PARTIAL, UNWRITTEN, NOPARSE, NOFN. Exit code is 0 whatever it says, so read the word.
• t27c symbols <spec> - every name the file declares, with its kind. Answers "does this already exist here?" before you add it.
• t27c outline <spec> - per function: its locals, what it calls, what it returns. The contract you are implementing against.
• t27c coverage <spec> - which functions have a test and which do not. The issue asks for tests; this is how you check you wrote them.
• t27c lint <spec> - style and shape warnings. It OVER-REPORTS has no test or invariant: measured 2026-09-20 over 60 specs it printed 677 of those where coverage found 190 untested functions, disagreeing on 59 of the 60 - it warns about bit_to_trit_pair in specs/base/ternary_encoding.t27, which test bit_to_trit_pair_zero calls on line 249. Read it as a hint; coverage is the answer.
• t27c typecheck <spec> - types, before generation. Prints Typecheck OK (0 errors, 0 warnings) or the errors.
• t27c test-report <spec> - builds this spec and runs its own tests, which is what the oracle does. BLOCKED means the generated Zig does not compile, with the error beside it.
• python3 tools/dupe_scan.py --name <function> - where that function already lives, if it does. 576 of 4021 bodies here are byte-identical copies.

The rest of the toolbelt is in docs/BEE_TOOLBELT.md.