Document VM debugging tools and island authoring rules in CLAUDE.md

Tools: vm-trace, bytecode-inspect, deps-check, prim-check,
test_boot.sh, sx-build-all.sh — with usage examples.

Island rules: (do ...) for multi-expression bodies, nested let for
cross-references, (deref (computed ...)) for reactive derived text,
effects in inner let for OCaml SSR compatibility.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -226,3 +226,70 @@ Dev bind mounts in `docker-compose.dev.yml` must mirror the Docker image's COPY
 
 - Use Context7 MCP for up-to-date library documentation
 - Playwright MCP is available for browser automation/testing
+
+### VM / Bytecode Debugging Tools
+
+These are OCaml server commands sent via the epoch protocol (`printf '(epoch N)\n(command args)\n' | sx_server.exe`). They're available in any context where the OCaml kernel is running (dev server, CLI, tests).
+
+```bash
+# Full build pipeline — OCaml + JS browser + JS test + run tests
+./scripts/sx-build-all.sh
+
+# WASM boot test — verify sx_browser.bc.js loads in Node.js without a browser
+bash hosts/ocaml/browser/test_boot.sh
+```
+
+#### `(vm-trace "<sx-source>")`
+Step through bytecode execution. Returns a list of trace entries, each with:
+- `:opcode` — instruction name (CONST, CALL, JUMP_IF_FALSE, etc.)
+- `:stack` — top 5 values on the stack at that point
+- `:depth` — frame nesting depth
+
+Requires the compiler to be loaded (`lib/compiler.sx`). Use this to debug unexpected VM behavior — it shows exactly what the bytecode does step by step.
+
+```bash
+printf '(epoch 1)\n(load "lib/compiler.sx")\n(epoch 2)\n(vm-trace "(+ 1 2)")\n' | sx_server.exe
+```
+
+#### `(bytecode-inspect "<function-name>")`
+Disassemble a compiled function's bytecode. Returns a dict with:
+- `:arity` — number of parameters
+- `:num_locals` — stack frame size
+- `:constants` — constant pool (strings, numbers, symbols)
+- `:bytecode` — list of instructions, each with `:offset`, `:opcode`, `:operands`
+
+Only works on functions that have been JIT-compiled (have a `vm_closure`). Use this to verify the compiler emits correct bytecode.
+
+```bash
+printf '(epoch 1)\n(bytecode-inspect "my-function")\n' | sx_server.exe
+```
+
+#### `(deps-check "<sx-source>")`
+Strict symbol resolution checker. Parses the source, walks the AST, and checks every symbol reference against:
+- Environment bindings (defines, let bindings)
+- Primitive functions table
+- Special form names (if, when, cond, let, define, etc.)
+
+Returns `{:resolved (...) :unresolved (...)}`. Run this on `.sx` files before compilation to catch typos and missing imports (e.g., `extract-verb-info` vs `get-verb-info`).
+
+```bash
+printf '(epoch 1)\n(deps-check "(defcomp ~my-comp () (div (frobnicate x)))")\n' | sx_server.exe
+# => {:resolved ("defcomp" "div") :unresolved ("frobnicate" "x")}
+```
+
+#### `(prim-check "<function-name>")`
+Scan compiled bytecode for `CALL_PRIM` instructions and verify each primitive name exists in the runtime. Returns `{:valid (...) :invalid (...)}`. Catches mismatches like `length` vs `len` that would crash at runtime.
+
+```bash
+printf '(epoch 1)\n(prim-check "my-compiled-fn")\n' | sx_server.exe
+# => {:valid ("+" "len" "first") :invalid ("length")}
+```
+
+### SX Island Authoring Rules
+
+Key patterns discovered from the reactive runtime demos (see `sx/sx/reactive-runtime.sx`):
+
+1. **Multi-expression bodies need `(do ...)`** — `fn`, `let`, and `when` bodies evaluate only the last expression. Wrap multiples in `(do expr1 expr2 expr3)`.
+2. **`let` is parallel, not sequential** — bindings in the same `let` can't reference each other. Use nested `let` blocks when functions need to reference signals defined earlier.
+3. **Reactive text needs `(deref (computed ...))`** — bare `(len (deref items))` is NOT reactive. Wrap in `(deref (computed (fn () (len (deref items)))))`.
+4. **Effects go in inner `let`** — signals in outer `let`, functions and effects in inner `let`. The OCaml SSR evaluator can't resolve outer `let` bindings from same-`let` lambdas.