ww: hare-feature batch (_, const, [_]T, ..., size/offset, assert, for-else)

selfhost/CLAUDE.md

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+selfhost — ww reimplementation of the toolchain (wcc, w6c, w6a, w6l, ww, wwdump). Compiled by the C bootstrap (`../cmd/`); the goal is to eventually compile itself.
+
+Identifiers: Plan 9 style. lowercase, words run together (`newbuf`, `tcpsock`, `parsefile`). No snake_case.
+
+Syntax and idioms: Hare-shaped. Trailing `;`, `=` after fn/type signatures, `export` for visibility, `match`/`?`/`!` for tagged-union errors. Consult `ref/hare/` for canonical signatures and error-handling patterns before inventing your own.
+
+The C bootstrap's cgen ("wwstage") has four known silent-miscompilation traps. They produce wrong runtime behavior, not compile errors. When porting C → ww here, default to the workarounds:
+
+1. **Two-level field write through pointer field doesn't stick.**
+   `r.sym.isdyn = 1` where `r.sym: *T` drops the write. Bind the inner pointer to a local first:
+   ```
+   let sym: *lsym = r.sym;
+   sym.isdyn = 1;
+   ```
+
+2. **Tuple return `(scalar, str)` corrupts the str half.** Both ptr and len come back garbage. Split into two functions — one returns the scalar, another returns the str. Plain `str` returns are fine.
+
+3. **`def NAME: str = "...";` is broken.** The `.len` picks up an unrelated accumulator. Wrap the literal in a nullary fn instead:
+   ```
+   fn namestr() str = { return "..."; };
+   ```
+
+4. **`amalloc(n)` with n < struct size silently corrupts neighbours.** No error — the bump arena hands out n bytes and field writes overflow into the next record. When introducing or growing a struct, audit every `amalloc(_, n)` call site and over-size (we routinely pass 48 for a 40-byte struct). Symptom: linked-list prepends lose all but the most recent entry.
+
+If a port "should work" but the binary is wrong, suspect these first.