Verify a writable-WASM write actually lands (reproducible TinyGo fixture + write-landing test)

[adnaan]

Verify a writable-WASM write actually lands (reproducible TinyGo fixture + write test)

Follow-up from #216 / #310 (M5 Phase 3). CLI parity for WASM sources landed: tinkerdown cli now constructs wasm sources, list works, and a read-only module correctly refuses a write. But the piece #216 is actually named for — a successful write through a module that exports write — has zero automated coverage in any transport (CLI or WebSocket).

Why it's not covered yet

• The only committed .wasm in the repo (examples/lvt-source-wasm-test/sources/quotes.wasm) is read-only — it exports fetch/get_result_len/free_result but no write, so WasmSource.IsReadonly() is correctly true.
• No TinyGo is available in the CI/dev environment used for M5, and the loader's fixed-offset //export ABI is incompatible with standard-Go wasip1 (which is why the wasm-source template mandates tinygo build -target=wasi).
• Committing a prebuilt writable .wasm that can't be rebuilt in-repo would reintroduce the committed-artifact provenance trap from make build regenerates the committed client bundle from stale node_modules, breaking checkbox e2e tests #295/Run a browser e2e smoke subset in CI so bundle regressions aren't purely human-detected #297 (a binary that can silently disagree with its source).

What to build (in a TinyGo-available environment)

• A write-exporting WASM fixture (a minimal TinyGo module exporting write alongside fetch), with its tinygo build wired into make so the .wasm is reproducible from source — never a committed mystery binary.
• A test that lands a write and observes the effect, over both transports: tinkerdown cli … add and the live WebSocket/serve path.
• Then close feat: writable WASM sources (Phase C2) #216 with the write path demonstrated end-to-end.

Verified today (so this issue is scoped to the gap, not the whole feature)

• WasmSource.WriteItem exists and enforces the readonly guard (internal/wasm/source.go).
• createCLISource constructs wasm; tinkerdown cli … list quotes returns rows; tinkerdown cli … add on the read-only module returns "source is read-only".

🤖 Generated with Claude Code

https://claude.ai/code/session_018M9pJSPmG6i1D8s6rpEV4h