From 6f00cc35560bf9d4a12ee428743b655dfb9c9ce2 Mon Sep 17 00:00:00 2001
From: Chris Wanstrath <chris@ozmm.org>
Date: Mon, 16 Mar 2026 20:06:33 -0700
Subject: [PATCH] Add sccache as Rust build cache in container environment

Speeds up repeated cargo builds across sessions by caching
compilation artifacts on the persistent mount.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 src/vm.ts | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/vm.ts b/src/vm.ts
index 5a4bb29..dedf38c 100644
--- a/src/vm.ts
+++ b/src/vm.ts
@@ -15,6 +15,8 @@ const CONTAINER_ENV = {
   CARGO_HOME: "/sandlot/.cargo",
   GOROOT: "/sandlot/.go",
   GOPATH: "/sandlot/.gopath",
+  RUSTC_WRAPPER: "/sandlot/.cargo/bin/sccache",
+  SCCACHE_DIR: "/sandlot/.sccache",
 }
 
 /** Translate a host path to its corresponding container path. */
@@ -174,6 +176,16 @@ async function installPersistentTooling(log?: (msg: string) => void): Promise<vo
     await $`container exec --user ${USER} ${CONTAINER_NAME} bash -c ${`echo -e '${cargoConfig}' > /sandlot/.cargo/config.toml`}`.quiet()
   }
 
+  // sccache — skip if already installed on the persistent mount
+  const hasSccache = await $`container exec --user ${USER} ${CONTAINER_NAME} test -x /sandlot/.cargo/bin/sccache`.nothrow().quiet()
+  if (hasSccache.exitCode !== 0) {
+    log?.("Installing sccache")
+    await run(
+      $`container exec --user ${USER} ${CONTAINER_NAME} env ${`RUSTUP_HOME=${CONTAINER_ENV.RUSTUP_HOME}`} ${`CARGO_HOME=${CONTAINER_ENV.CARGO_HOME}`} ${`PATH=${CONTAINER_ENV.CARGO_HOME}/bin:$PATH`} cargo install sccache --locked`,
+      "sccache installation")
+    await $`container exec --user ${USER} ${CONTAINER_NAME} bash -c ${"mkdir -p /sandlot/.sccache"}`.nothrow().quiet()
+  }
+
   // Go — skip if already installed on the persistent mount
   const hasGo = await $`container exec --user ${USER} ${CONTAINER_NAME} test -x /sandlot/.go/bin/go`.nothrow().quiet()
   if (hasGo.exitCode !== 0) {
@@ -314,7 +326,7 @@ export async function claude(workdir: string, opts?: { prompt?: string; print?:
   systemPromptLines.push(
     "The host's ~/.sandlot is mounted at /sandlot.",
     "Bun is installed at ~/.local/bin/bun. Use bun instead of node/npm.",
-    "Rust (cargo/rustc) is installed at /sandlot/.cargo/. Go is installed at /sandlot/.go/.",
+    "Rust (cargo/rustc) is installed at /sandlot/.cargo/. Go is installed at /sandlot/.go/. sccache is configured as RUSTC_WRAPPER for build caching.",
   )
   if (opts?.print) {
     systemPromptLines.push("IMPORTANT: Do not use plan mode. Do not call the EnterPlanMode tool. Proceed directly with the task.")