Add cross-platform testing docs and D110 zwasm allocator injection decision

- CLAUDE.md: cross-platform testing section, --seed 0 note, reference links
- .dev/references/setup-orbstack.md: shared VM setup (with zwasm)
- .dev/references/ubuntu-testing-guide.md: test commands, known differences
- D110: future plan for zwasm allocator injection to eliminate dual-GC

Author: chaploud

.claude/CLAUDE.md

@@ -232,6 +232,15 @@ Wasm history: `bench/wasm_history.yaml` — CW vs wasmtime wasm benchmark progre
 **Baseline accuracy**: Sequential full-suite runs cause thermal throttling.
 For accurate baselines, measure each benchmark individually with 10+ runs.
 
+## Cross-Platform Testing (Ubuntu x86_64)
+
+Test on Ubuntu x86_64 via OrbStack before releases. See:
+- Setup: `.dev/references/setup-orbstack.md` (shared VM with zwasm)
+- Commands: `.dev/references/ubuntu-testing-guide.md`
+
+**Critical**: `zig build test --seed 0` required on Rosetta (crashes without it).
+3 float-format test failures are known/accepted platform differences.
+
 ## Notice
 
 **Shell escaping**: For `swap!`, `nil?` etc., write a temp .clj file instead of `-e`.
@@ -302,3 +311,5 @@ Check `.claude/references/zig-tips.md` first, then Zig stdlib at
 | Known issues      | `.dev/known-issues.md`               | Bug/workaround/debt tracking (P0-P3)       |
 | Baselines         | `.dev/baselines.md`                  | Non-functional regression thresholds       |
 | Bytecode debug    | `./zig-out/bin/cljw --dump-bytecode` | When VM tests fail or bytecode looks wrong |
+| Ubuntu testing    | `.dev/references/ubuntu-testing-guide.md` | OrbStack VM test commands + --seed 0 |
+| OrbStack setup    | `.dev/references/setup-orbstack.md`  | VM creation (shared with zwasm)            |

.dev/decisions.md

@@ -912,3 +912,29 @@ refactoring tractable.
 **Rules**: `.claude/rules/zone-deps.md` (auto-loads on src/ edits).
 
 **Result targets**: 0 upward imports, bootstrap.zig < 200 LOC, main.zig < 200 LOC.
+
+## D110: zwasm Allocator Injection — Eliminate Dual-GC
+
+**Date**: 2026-03-08
+**Status**: Future (depends on zwasm D128)
+**Decision**: When zwasm implements allocator injection (D128), CW will pass its
+own GC-managed allocator to zwasm instead of letting zwasm use an internal Arena.
+This eliminates the dual-GC lifecycle mismatch.
+
+**Current problem**: CW GC (Mark-Sweep) manages wasm Value objects (wasm_module,
+wasm_fn, wasm_instance). When CW GC sweeps these, it frees the CW-side wrapper,
+but zwasm's internal Arena retains the underlying memory. The Arena only frees
+on full deinit (process exit), so long-running CW processes that load/unload
+Wasm modules will leak zwasm-side memory.
+
+**Target state**: CW passes its allocator to `zwasm.Engine.init(cw_allocator)`.
+zwasm allocations become CW GC-visible. When CW GC sweeps a wasm Value, the
+underlying zwasm memory is also reclaimable.
+
+**Scope**: Only zwasm's internal bookkeeping (module metadata, function tables,
+instance state). Wasm linear memory remains separately managed per spec.
+
+**Migration**: Minimal CW changes — update `wasm_types.zig` to pass allocator
+at Engine construction. Requires zwasm D128 to be implemented first.
+
+Related: zwasm D128, cw-new D13.

.dev/references/setup-orbstack.md

@@ -0,0 +1,38 @@
+# OrbStack Ubuntu x86_64 VM Setup
+
+One-time setup for local Ubuntu x86_64 testing via OrbStack on Apple Silicon.
+This VM is shared with zwasm — if already created, skip to verification.
+
+## VM Creation
+
+```bash
+orb create --arch amd64 ubuntu my-ubuntu-amd64
+```
+
+## Tool Installation
+
+See `zwasm/.dev/references/setup-orbstack.md` for full installation commands.
+The same VM and tools are used for both projects:
+
+| Tool       | Version  | Path                     |
+| ---------- | -------- | ------------------------ |
+| Zig        | 0.15.2   | /opt/zig/zig             |
+| wasmtime   | 42.0.1   | ~/.wasmtime/bin/wasmtime |
+| wasm-tools | 1.245.1  | /usr/local/bin/wasm-tools|
+| WASI SDK   | 25       | /opt/wasi-sdk            |
+| Rust       | stable   | ~/.cargo/bin/rustc       |
+| hyperfine  | system   | /usr/bin/hyperfine       |
+
+## Verification
+
+```bash
+orb run -m my-ubuntu-amd64 bash -lc "zig version && wasmtime --version"
+# Expected: 0.15.2, wasmtime-cli 42.0.1
+```
+
+## Notes
+
+- VM name: `my-ubuntu-amd64` (shared between zwasm and ClojureWasm)
+- Mac filesystem accessible inside VM at original paths (e.g., `/Users/shota.508/...`)
+  but building directly from Mac FS is slow — rsync to VM-local storage instead
+- OrbStack uses Rosetta for x86_64 emulation on Apple Silicon

.dev/references/ubuntu-testing-guide.md

@@ -0,0 +1,80 @@
+# Ubuntu x86_64 Testing Guide (OrbStack)
+
+How to run ClojureWasm tests on the local OrbStack Ubuntu x86_64 VM.
+
+## Connection
+
+```bash
+# Interactive shell
+orb shell my-ubuntu-amd64
+
+# One-shot command (used by Claude Code)
+orb run -m my-ubuntu-amd64 bash -lc "COMMAND"
+```
+
+Claude Code uses stateless one-shot execution — each `orb run` starts a fresh shell.
+Always use `bash -lc` to load `.bashrc` (PATH for zig, wasmtime, etc.).
+
+## Sync Project
+
+Rsync from Mac filesystem to VM-local storage for build performance:
+
+```bash
+orb run -m my-ubuntu-amd64 bash -lc "
+  rsync -a --delete \
+    --exclude='.zig-cache' --exclude='zig-out' \
+    '/Users/shota.508/ClojureWasm/' ~/ClojureWasm/
+"
+```
+
+Run sync before each test session to pick up latest changes.
+
+## Test Commands
+
+All commands run inside the VM at `~/ClojureWasm/`:
+
+```bash
+# Unit tests (IMPORTANT: --seed 0 required on Rosetta)
+orb run -m my-ubuntu-amd64 bash -lc "cd ~/ClojureWasm && zig build test --seed 0"
+
+# Full test suite
+orb run -m my-ubuntu-amd64 bash -lc "cd ~/ClojureWasm && zig build test --seed 0 && \
+  zig build -Doptimize=ReleaseSafe && \
+  ./zig-out/bin/cljw test"
+
+# E2E tests
+orb run -m my-ubuntu-amd64 bash -lc "cd ~/ClojureWasm && bash test/e2e/run_e2e.sh"
+
+# Benchmarks
+orb run -m my-ubuntu-amd64 bash -lc "cd ~/ClojureWasm && bash bench/run_bench.sh --quick"
+```
+
+## Critical: --seed 0 Workaround
+
+**`zig build test` crashes without `--seed 0` on Rosetta x86_64 emulation.**
+
+Root cause: Zig 0.15.2 build runner's `shuffleWithIndex` (Random.zig:375) produces
+an index out of bounds under Rosetta's Random implementation. The `--seed 0` flag
+disables test shuffling, avoiding the crash entirely.
+
+This is 100% reproducible without the flag and 100% fixed with it.
+
+## Known Platform Differences
+
+3 float-format tests fail on x86_64 due to platform-specific formatting differences
+(e.g., `-0.0` vs `0.0`, exponential notation). These are cosmetic, not bugs:
+
+- `test.core-print: print double -0.0`
+- `test.core-print: print MIN_VALUE`
+- `test.core-print: print MAX_VALUE`
+
+These are tracked and accepted — not regressions.
+
+## Expected Results
+
+| Suite      | Expectation                          |
+| ---------- | ------------------------------------ |
+| Unit tests | 1338+ pass (3 known float failures)  |
+| cljw test  | 83 namespaces, no crashes            |
+| E2E        | all pass                             |
+| Benchmarks | no regression vs Mac baseline        |