Summary

Targeted dead-code slice (part of the #969 warnings-baseline effort): annotate the
spec-complete HIR/FPGA grammar enums in bootstrap/src/compiler.rs with a per-enum
#[allow(dead_code)] so the build stops emitting "variants never constructed" warnings
for an intentionally-broad AST surface, and lower the recorded warnings baseline 655 -> 647.

Motivation

The "Hardware IR (HIR) -- Phase 0 FPGA foundation" section defines a deliberately
spec-complete set of grammar enums. Several of their variants are not yet constructed by
the current lowering path, which is expected at this phase -- the AST surface is intentionally
wider than today's consumers. These show up as 8 dead_code warnings that are pure noise:
they do not indicate a bug, and the variants are part of the documented spec, not accidental.

This is the same conservative, per-item pattern used in #1111 and #1122: we annotate the
specific enums (NOT the whole file, NOT a crate-level allow), with a comment explaining the
intent, so the suppression stays scoped and reviewable.

Scope (exactly 8 enums, HIR/FPGA section)

HwType, HwResetKind, HwResetPolarity, HwEdge, HirAlwaysStmtKind, HwMemKind,
HwCrossStrategy, HwFifoKind.

Each gets a #[allow(dead_code)] between its #[derive(...)] and pub enum (valid Rust;
keeps the diff minimal). The first enum is preceded by a short comment block explaining this
is an intentionally spec-complete AST surface, annotated per-enum rather than file-level.

Effect

• Build warnings: 655 -> 647 (8 variants never constructed warnings removed).
• scripts/warnings-baseline.sh baseline updated 655 -> 647 with a history note.
• No behavior change: #[allow(dead_code)] only suppresses the lint; no code is added,
  removed, or rewired. Full test suite unaffected.

Verification

• cargo build --bin t27c -> 647 warnings (was 655).
• make warnings-baseline -> OK (647 <= 647).
• Full suite green, 0 regressions.

L6 gf16 SSOT untouched; catalog stays 83; no gen/ edits; ASCII-only added lines; no quality
claim added.