t27c gen-c: local nested array declared as [16]u8 m[16] #7441

t27c gen-c emits a local nested-array declaration with the wrong C shape, whatever the initializer is.

fn f() void {
    var m: [16][16]u8 = ...;
}

comes out as

[16]u8 m[16] = ...;

which is not C. A global of the same type is lowered correctly; only function locals are affected.

Hit by the seven 16x16 locals in specs/depin/prove.t27.

Found by the gen-c defects lane while fixing #7353 (nested repeat initializers). Part of #5980 (the self-hosted core must match gen-c byte for byte, so it refuses local nested arrays until this is fixed).

Boundary

• specs/depin/prove.t27

User Scenarios

• Given a t27 function containing a local variable declared as var m: [16][16]u8 = ...;, When t27c gen-c compiles the function, Then the emitted C declaration must have the correct nested array shape uint8_t m[16][16] (or equivalent) and not the malformed [16]u8 m[16].

Requirements

FR-001: The C code generator MUST emit correct C array declarators for local nested array variables, mapping the t27 type [N][M]T to the C declarator T name[N][M].
FR-002: The fix MUST NOT change the already-correct lowering of global nested array declarations.
FR-003: The compiler MUST continue to pass all existing gen-c test cases.

Success Criteria

• t27c gen-c specs/depin/prove.t27 exits with exit 0 and the generated C file contains seven correct 16×16 local array declarations (e.g., uint8_t m[16][16];).
• The self-hosted core build (blocked by this defect) compiles without errors related to local nested arrays.