spikes: six v3 spikes (V8 harness, WASI shell, git, builder, http hook, esbuild)

Throwaway prototypes for Sausage v3. Plan and decisions:
~/research/sausage-v3/PLAN.md. Results and evidence: the spike READMEs.

spikes/s2-shell/patch-brush.nu

@@ -0,0 +1,16 @@
+#!/usr/bin/env nu
+# Apply the experiment only to the pinned scratch checkout.
+def main [] {
+    let root = '/tmp/s2-shell/brush'
+    let revision = (^git -C $root rev-parse HEAD | str trim)
+    if $revision != '943553433ae04f5b3bd55d2cf207e39eb9ef2af7' { error make {msg: 'unexpected brush revision'} }
+    let core = ($root | path join brush-core)
+    cp ($env.FILE_PWD | path join guest-process.rs) ($core | path join src sys wasm process.rs)
+    cp ($env.FILE_PWD | path join process.wit) ($core | path join s2-process.wit)
+    let manifest = ($core | path join Cargo.toml)
+    let text = (open --raw $manifest)
+    let marker = "[target.'cfg(target_family = \"wasm\")'.dependencies]"
+    if not ($text | str contains 'wit-bindgen =') {
+        $text | str replace $marker ($marker + "\nwit-bindgen = \"0.46\"\nserde_json = \"1\"") | save -f $manifest
+    }
+}