Transpiler: support multi-byte static fields (int/ushort)

[Copilot]

PreAllocateStaticFields allocated 1 byte per static field regardless of type, so int/ushort fields overlapped adjacent fields in zero-page memory.

Changes

• Transpiler.cs — BuildStaticFieldSizes() reads field types from metadata signatures via DecodeFieldSize(). PreAllocateStaticFields() now allocates 2 bytes for ushort/short/int/uint fields and returns a WordStaticFields set alongside addresses. LocalCount initialized from total byte count instead of field count.
• LocalVariableManager.cs — WordStaticFields HashSet (paralleling WordLocals). StaticFieldAddresses setter uses per-field size when computing LocalCount.
• IL2NESWriter.StructFields.cs — HandleLdsfld emits LDA+LDX for word fields, sets _ushortInAX. HandleStsfld emits STA+STX from A:X, or zero-extends byte values into the high byte.
• IL2NESWriter.cs — WordStaticFields forwarding property.

Example

static class G
{
    public static ushort word_val;  // now gets 2 bytes at $0328-$0329
    public static byte byte_val;   // 1 byte at $0325
    public static int int_val;     // 2 bytes at $0326-$0327 (capped to 16-bit)
}

G.word_val = 300;        // → LDA #$2C, STA $0328, STX $0329 (hi=$01)
G.int_val = G.byte_val;  // → LDA $0325, STA $0326, LDA #$00, STA $0327

Test

Added wordfield sample with ushort and int static fields validating correct allocation, 16-bit load/store, and zero-extension.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Transpiler: support multi-byte static fields (int/ushort)</issue_title>
<issue_description>Follow-up from PR #211 (crypto.c sample port) review.

PreAllocateStaticFields in Transpiler.cs allocates exactly 1 byte per static field regardless of type. When a sample uses int or ushort static fields:

static class G
{
    public static int int_temp0;  // needs 2-4 bytes, only gets 1
}

The field overlaps with adjacent fields in zero-page memory, causing corruption.

Use case

The crypto sample needs int for screen coordinate math where byte would overflow:

G.int_temp0 = G.enemies_x[G.i];
G.int_temp0 <<= 1;
G.int_temp0 -= G.scr_x;
if (G.int_temp0 < 0 || G.int_temp0 > 255) { G.i++; continue; }
G.temp0 = (byte)G.int_temp0;

Current workaround

Use pairs of byte fields and manual hi/lo splitting, or restructure math to stay within byte range.

Implementation

1. PreAllocateStaticFields needs to detect field types from metadata (similar to DetectWordLocals for local variables)
2. Allocate 2 bytes for ushort/short/int fields (NES is 8-bit, so 16-bit is sufficient)
3. HandleLdsfld/HandleStsfld need to emit 16-bit load/store sequences for word-sized fields
4. LocalVariableManager.GetOrAllocateStaticField needs a size parameter

Context

Blocking the crypto sample (PR #211). See review: #211 (review)</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Transpiler: support multi-byte static fields (int/ushort) #236

---

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[jonathanpeppers]

🤖 Reviewed and verified — this looks great.

What I checked:

• Field size detection: BuildStaticFieldSizes() correctly reads field signatures via DecodeFieldSize() and caps at 2 bytes. Skips non-static and RVA fields.
• Address allocation: PreAllocateStaticFields allocates sequential addresses with per-field sizes. The tuple return (addresses, wordFields, totalBytes) keeps all three pieces synchronized.
• 16-bit emission: HandleLdsfld emits LDA addr / LDX addr+1 and sets _ushortInAX. HandleStsfld handles all four state combinations correctly (_ushortInAX, _runtimeValueInA, _immediateInA, fallback).
• Zero-extension: Storing a byte into a word field correctly zeros the high byte.
• LocalCount: Main writer uses explicit staticFieldBytes; method writers get correct offsets via methodFrameOffsets (which starts from mainLocalCount).
• ROM disassembly: Verified the wordfield ROM — ldc_i4 300 → LDX #$01, LDA #$2C, STA $0328, STX $0329 ✓, byte→word zero-extend STA $0326, LDA #$00, STA $0327 ✓, conv_u1 correctly discards X ✓.
• All 509 tests pass locally.

[jonathanpeppers]

🤖 CI is green. Ready for human review.

[Copilot]

Pull request overview

Adds proper 16-bit (word) support for user-defined static fields in the dotnes transpiler so ushort/short/int/uint statics don’t overlap adjacent RAM allocations and can be loaded/stored as 16-bit values.

Changes:

• Allocate static fields by byte-size derived from metadata signatures (with int/uint capped to 16-bit for NES use).
• Track which static fields are word-sized and emit 16-bit ldsfld/stsfld sequences (A:low, X:high) including zero-extension when storing byte→word.
• Add a wordfield test sample (debug+release inputs) and snapshot to validate correct behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/dotnes.tasks/Utilities/Transpiler.cs	Computes per-static-field sizes from metadata and pre-allocates shared addresses + WordStaticFields set.
src/dotnes.tasks/Utilities/LocalVariableManager.cs	Adds WordStaticFields tracking and uses it when advancing LocalCount for preallocated statics.
src/dotnes.tasks/Utilities/IL2NESWriter.StructFields.cs	Emits 16-bit load/store for word static fields and handles byte→word zero-extension on stores.
src/dotnes.tasks/Utilities/IL2NESWriter.cs	Forwards WordStaticFields through the writer API.
src/dotnes.tests/TranspilerTests.cs	Adds wordfield to snapshot test matrix (debug + release).
src/dotnes.tests/TranspilerTests.Write.wordfield.verified.bin	New ROM snapshot for the wordfield sample.
src/dotnes.tests/Data/wordfield.debug.dll	New debug input DLL for wordfield transpilation test.
src/dotnes.tests/Data/wordfield.release.dll	New release input DLL for wordfield transpilation test.