docs(corpus): meld-fused fixture prerequisites (v1.1.0 Track E, deferred)

scripts/measure_corpus.sh

@@ -111,6 +111,7 @@ WORKLOADS=(
   "calculator_root|calculator.wasm|2.3 MB component (root, large)"
   "simple_component|loom-core/tests/component_fixtures/simple.component.wasm|tiny component (adapter-heavy)"
   "calc_component|loom-core/tests/component_fixtures/calc.component.wasm|small component (adapter-heavy)"
+  "meld_fused|tests/corpus/meld_fused.wasm|real meld-fused multi-component core (Track 3 target — see tests/corpus/MELD_FUSED_README.md)"
 )
 
 # --- Helpers ---------------------------------------------------------------

tests/corpus/MELD_FUSED_README.md

@@ -0,0 +1,125 @@
+# tests/corpus/meld_fused.wasm — placeholder (not yet built)
+
+> **Status: MISSING.** This fixture is referenced by `scripts/measure_corpus.sh`
+> but has not yet been produced. This README documents exactly what is
+> required so the next operator can land it without guesswork.
+
+## Why this fixture is needed
+
+LOOM v1.0.5 Track 3 (commit `27c0a01`, PR #132) added two passes that target
+the shapes a real `meld fuse` of multiple components produces:
+
+| Pass                          | Target shape                                                         |
+|-------------------------------|----------------------------------------------------------------------|
+| `inline_scalar_adapters`      | cross-memory scalar copy: `load(memA); load(memB); call; store(memB); store(memA)` |
+| `dedupe_function_bodies`      | two functions with identical `(signature, locals, body)`             |
+
+The existing single-component fixtures
+(`loom-core/tests/component_fixtures/simple.component.wasm` and
+`calc.component.wasm`) produce a single fused core when run through
+`meld fuse`, but neither imports from the other, so the resulting fused
+core contains **no cross-memory adapter** — exactly the shape Tier-1.1
+targets. Track 3 therefore fired byte-neutral on the v1.0.5 measurement
+corpus.
+
+A **multi-component** meld-fused fixture is what Track 3 needs to demonstrate
+its byte wins. The harness already supports it; only the fixture is missing.
+
+## What to build
+
+`tests/corpus/meld_fused.wasm` — a single **core module** (post-fusion)
+that:
+
+1. Validates via `wasm-tools validate`.
+2. Contains at least one **cross-memory scalar adapter** (the
+   `inline_scalar_adapters` target shape).
+3. Optionally, contains two functions with identical
+   `(signature, locals, body)` (the `dedupe_function_bodies` target).
+
+## How to build it
+
+### Inputs that won't work (and why)
+
+The two existing component fixtures
+(`loom-core/tests/component_fixtures/simple.component.wasm`,
+`calc.component.wasm`) are **independent**: neither imports the other. They
+both export only pure scalar `(i32, i32) -> i32` functions and import
+nothing. `meld fuse` on two independent components either rejects the
+input or produces trivial pass-through adapters with a single memory —
+no cross-memory shape, no dedup target.
+
+### Inputs that will work
+
+A pair of components where one **imports** an interface the other
+**exports**, and both perform some non-trivial body. Easiest path:
+
+1. Author a tiny `wit` interface (one function, e.g.
+   `add: func(a: s32, b: s32) -> s32`).
+2. Build a producer component (Rust + `cargo-component` or `wit-bindgen`)
+   that exports it.
+3. Build a consumer component that imports it and re-exports a wrapped
+   version.
+4. `meld fuse producer.component.wasm consumer.component.wasm
+   -o tests/corpus/meld_fused.wasm` (the consumer's memory and the
+   producer's memory are separate → cross-memory adapter shape).
+
+> **Constraint:** v1.0.5 Track E (this work) forbids pulling components
+> from crates.io. Build local fixtures or revive the v1.0.0 PR-Q fixture
+> set (some of those crates may already be in
+> `tests/corpus/rust-examples/`).
+
+### Toolchain
+
+- `meld` v0.x (`/Users/r/.cargo/bin/meld` per the v0.9.0 measurement notes).
+- `cargo component` or `wit-bindgen` for building components from Rust.
+- `wasm-tools` for validation and inspection.
+
+### Commands
+
+```bash
+# 1. Build the two components (toolchain-specific).
+# 2. Fuse them into a core module.
+meld fuse \
+    <producer>.component.wasm \
+    <consumer>.component.wasm \
+    -o tests/corpus/meld_fused.wasm
+
+# 3. Validate.
+wasm-tools validate tests/corpus/meld_fused.wasm
+
+# 4. Confirm the cross-memory adapter shape.
+wasm-tools print tests/corpus/meld_fused.wasm | grep -A 20 "adapter\|i32.load\|i32.store"
+
+# 5. Run the harness; the new row must be non-`n/a`.
+bash scripts/measure_corpus.sh
+```
+
+## Harness wiring
+
+`scripts/measure_corpus.sh` has been updated on this branch to include
+`meld_fused` in the `WORKLOADS` array. The row reports `n/a` until the
+fixture is produced and committed.
+
+## Honest stop-report from this branch
+
+This branch (`release/v1.1.0-pr-meld-fixture`) attempted to produce the
+fixture but was unable to invoke `meld` due to an environment permission
+restriction on the agent that authored it (Bash invocations of `meld`
+were denied). The agent's choice was either to (a) ship a fake/stub wasm
+that validates but doesn't contain the target shape, or (b) ship this
+placeholder doc + harness wiring so the next operator can complete the
+work in minutes. **Option (b) was chosen per
+`CLAUDE.md`: "A correct optimizer that handles 50% of cases is infinitely
+better than a fast optimizer that corrupts 1% of cases."** Shipping a
+fake fixture would silently change what Track 3 measures against —
+exactly the kind of "good enough" shortcut LOOM's mission forbids.
+
+## Verification once the fixture lands
+
+Run `loom optimize tests/corpus/meld_fused.wasm -o /tmp/meld_fused.loom.wasm`
+both **with** and **without** Track 3 passes
+(`inline_scalar_adapters` / `dedupe_function_bodies`) and confirm the
+byte delta is strictly negative with the passes enabled. The
+expected effect on a fixture with one cross-memory adapter and one
+dedup target is **non-zero**, breaking the byte-neutral measurement
+recorded in `docs/measurements/v0.9.0-corpus-baseline.md`.