refactor: migrate to gitea actions

.dockerignore

@@ -0,0 +1,5 @@
+.git
+.gitea
+Jenkinsfile
+README.md
+**/__pycache__

.gitea/workflows/build.yml

@@ -0,0 +1,80 @@
+name: Build OpenWrt Rust SDK images
+
+on:
+  workflow_dispatch:
+    inputs:
+      targets:
+        description: 'Comma-separated targets, or all'
+        default: 'x86/64,mediatek/filogic,octeon/generic'
+        required: true
+        type: string
+      publish:
+        description: 'Publish the original Docker Hub tags (requires approval)'
+        default: false
+        type: boolean
+
+permissions:
+  contents: read
+
+jobs:
+  matrix:
+    runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.resolve.outputs.matrix }}
+    steps:
+      - uses: builtin:checkout
+      - name: Resolve targets and OpenWrt versions
+        id: resolve
+        env:
+          TARGETS: ${{ inputs.targets }}
+        run: python3 ci/matrix.py
+
+  build:
+    needs: matrix
+    runs-on: ubuntu-latest
+    timeout-minutes: 360
+    strategy:
+      fail-fast: true
+      max-parallel: 1
+      matrix: ${{ fromJSON(needs.matrix.outputs.matrix) }}
+    env:
+      SAFE_TARGET: ${{ matrix.target }}
+      VERSION: ${{ matrix.version }}
+    steps:
+      - uses: builtin:checkout
+      - name: Prepare persistent cache and bounded builder
+        run: sh ci/setup-builder.sh
+      - name: Build SDK image
+        run: |
+          docker buildx build --builder openwrt-sdk-rust --load --progress plain \
+            --network host --allow network.host \
+            --no-cache-filter configured,sdk \
+            --build-arg SAFE_TARGET="$SAFE_TARGET" \
+            --build-arg VERSION="$VERSION" \
+            --build-arg JOBS=8 \
+            --build-arg SCCACHE_REDIS_ENDPOINT=redis://127.0.0.1:6379 \
+            --tag "lochnair/openwrt-sdk-rust:${SAFE_TARGET}-${VERSION}" .
+      - name: Verify SDK image
+        run: |
+          docker run --rm "lochnair/openwrt-sdk-rust:${SAFE_TARGET}-${VERSION}" sh -ec '
+            sccache --version
+            grep -qx "CONFIG_RUST_SCCACHE=y" .config
+            rustc=$(find staging_dir -type f -path "*/host/bin/rustc")
+            test -x "$rustc"
+            "$rustc" -vV
+            "$(dirname "$rustc")/cargo" --version
+          '
+          sh ci/verify-cache.sh "lochnair/openwrt-sdk-rust:${SAFE_TARGET}-${VERSION}"
+      - name: Publish Docker Hub tag
+        if: inputs.publish == true
+        env:
+          DOCKERHUB_USERNAME: ${{ secrets.DOCKERHUB_USERNAME }}
+          DOCKERHUB_TOKEN: ${{ secrets.DOCKERHUB_TOKEN }}
+        shell: bash
+        run: |
+          set -euo pipefail
+          DOCKER_CONFIG=$(mktemp -d)
+          export DOCKER_CONFIG
+          trap 'rm -rf "$DOCKER_CONFIG"' EXIT
+          printf '%s' "$DOCKERHUB_TOKEN" | docker login --username "$DOCKERHUB_USERNAME" --password-stdin
+          docker push "lochnair/openwrt-sdk-rust:${SAFE_TARGET}-${VERSION}"

Dockerfile

@@ -1,13 +1,35 @@
 ARG SAFE_TARGET
 ARG VERSION
 
-FROM ghcr.io/openwrt/sdk:${SAFE_TARGET}-${VERSION}
+FROM ghcr.io/openwrt/sdk:${SAFE_TARGET}-${VERSION} AS tooling
 
+# The SDK runs on amd64 even when compiling for another OpenWrt target.
+USER root
+RUN curl -fsSL https://github.com/mozilla/sccache/releases/download/v0.18.0/sccache-v0.18.0-x86_64-unknown-linux-musl.tar.gz -o /tmp/sccache.tar.gz && \
+    echo '45f1447fbe231e3037bde351ef70677dd212216c8d62ae7ca409fecc4d6acc89  /tmp/sccache.tar.gz' | sha256sum -c - && \
+    tar -xzf /tmp/sccache.tar.gz -C /tmp && \
+    install -m 0755 /tmp/sccache-v0.18.0-x86_64-unknown-linux-musl/sccache /usr/local/bin/sccache && \
+    rm -rf /tmp/sccache.tar.gz /tmp/sccache-v0.18.0-x86_64-unknown-linux-musl
+USER buildbot
+
+FROM tooling AS configured
+ARG SAFE_TARGET
+ARG VERSION
+ENV SCCACHE_REDIS_KEY_PREFIX=openwrt-rust:${SAFE_TARGET}-${VERSION}: \
+    CARGO_INCREMENTAL=0
+COPY --chmod=0755 ci/build-rust.sh /usr/local/bin/build-rust
 RUN ./scripts/feeds update packages && \
     ./scripts/feeds install rust && \
+    printf '\nCONFIG_RUST_SCCACHE=y\n' >> .config && \
     make defconfig && \
-    sed -i 's/--set=llvm.download-ci-llvm=true/--set=llvm.download-ci-llvm=false/g' feeds/packages/lang/rust/Makefile; \
+    grep -qx 'CONFIG_RUST_SCCACHE=y' .config && \
-    { make package/rust/host/compile -j$(nproc) || \
+    sed -i 's/--set=llvm.download-ci-llvm=true/--set=llvm.download-ci-llvm=false/g' feeds/packages/lang/rust/Makefile && \
-      make package/rust/host/compile -j1 V=sc; } && \
+    sed -i '/--set=llvm.download-ci-llvm=false/a\	--set=build.ccache=sccache \\' feeds/packages/lang/rust/Makefile && \
-    rm -rf build_dir/host/rustc-*/rustc-*/build \
+    sed -i '/^define Host\/Compile/i RUST_BUILD_JOBS ?= 8' feeds/packages/lang/rust/Makefile && \
-           dl/rustc-*.tar.*
+    sed -i 's/--build-dir /--jobs=$(RUST_BUILD_JOBS) --build-dir /' feeds/packages/lang/rust/Makefile
+
+FROM configured AS sdk
+ARG JOBS=8
+# A non-secret endpoint on the runner; do not persist it in the published image.
+ARG SCCACHE_REDIS_ENDPOINT
+RUN build-rust

README.md

@@ -1 +1,128 @@
-# openwrt-sdk-rust
+# openwrt-sdk-rust
+
+Builds the OpenWrt SDK with its Rust host toolchain installed. Gitea Actions
+resolves `stable_version` and `oldstable_version` from OpenWrt's `.versions.json`.
+The default targets remain `x86/64,mediatek/filogic,octeon/generic`; dispatch with
+`targets=all` to use upstream `dump-target-info.pl`, or supply a comma-separated
+list. Images still use `ghcr.io/openwrt/sdk:<target-with-dashes>-<version>` and
+publish to `lochnair/openwrt-sdk-rust:<target-with-dashes>-<version>` on Docker Hub.
+No `latest` tag or additional registry is introduced.
+
+## Runner setup and cutover
+
+The workflow uses `ubuntu-latest` on the existing TheBeast runner, currently
+the only runner. Its job image and access to the persistent Docker daemon were
+verified; no additional runner, label, capacity change, or restart is required.
+`builtin:checkout` uses the existing Runner 5 checkout support.
+
+Enable repository Actions and set `DOCKERHUB_USERNAME` and `DOCKERHUB_TOKEN`
+secrets with push permission to `lochnair/openwrt-sdk-rust`. Jenkins' credential
+ID is not reusable in Gitea. The workflow is manually dispatched, matching the
+parameterized Jenkins job; there are no PR, push, or scheduled publication
+triggers. `publish=false` is the safe validation default. Dispatch
+`publish=true` only after publication is approved. Login uses a temporary job
+directory, and each successfully built and checked image is pushed under its
+original tag. Before any push, `ci/verify-cache.sh` uses the installed SDK rustc
+in two disposable containers and requires a Redis miss followed by a hit.
+
+Run a non-publishing dispatch for the default six combinations, then an
+approved publishing dispatch. Check the pulled image's Rust/Cargo installation
+and downstream package build before disabling the old Jenkins job and deleting
+`Jenkinsfile`. Do not retire Jenkins before this acceptance run. No Jenkins
+plugins or credentials are used by the new workflow.
+
+## Persistent compilation cache
+
+`ci/setup-builder.sh` provisions one Redis service and one reusable BuildKit
+builder on that daemon. Redis uses the named volume `openwrt-rust-sccache`, AOF
+persistence (`appendfsync everysec`), a 6 GiB LRU cache, an 8 GiB memory limit,
+and one CPU. Jobs and build containers can disappear without losing it. A
+machine crash can lose up to the most recent second of cache writes; eviction
+or lost entries cause recompilation. Do not run `docker compose down -v` or
+prune this volume. BuildKit's layer cache is separate and may be garbage
+collected without clearing sccache.
+
+The cache joins the existing `gitea-runner-jobs` network and exposes port 6379
+only on loopback. BuildKit uses host networking to reach it; package containers
+use its Docker DNS name. This is a trusted-runner cache: do not attach untrusted
+PR containers or public networks to it. No password or endpoint is baked into
+published SDK images. Consumers outside this runner can use their own Redis
+endpoint. Each target/OpenWrt version has its own key prefix; sccache also
+hashes Rust compiler version and shared libraries, compilation arguments
+(including target and flags), source and dependency contents. Different Rust
+versions/toolchains therefore miss rather than reuse incompatible objects.
+
+The shared BuildKit worker executes one build step at a time, even across
+simultaneous dispatches. It is limited to eight CPUs and 20 GiB RAM with no
+swap. Make and Rust bootstrap both receive eight jobs; the original `-j1 V=sc`
+diagnostic retry also reduces bootstrap/Ninja to one job. Rust
+build-directory/archive cleanup remains. BuildKit
+layer storage has a 50 GiB GC budget. Matrix jobs also run one at a time and
+stop scheduling on a failure, as Jenkins' sequential stage loop did.
+
+OpenWrt integration was inspected in the SDK's pinned packages feed:
+
+- `rust-values.mk` **unexports `RUSTC_WRAPPER`**. Setting it in the workflow
+  alone does not enable caching. `CONFIG_RUST_SCCACHE=y` makes OpenWrt inject
+  `CARGO_INCREMENTAL=0`, `RUSTC_WRAPPER=sccache`, and `SCCACHE_DIR` into host
+  and package Cargo invocations. The Dockerfile enables and checks that option.
+- The base SDK has no sccache binary. We install the pinned 0.18.0 amd64-musl
+  release and verify its SHA-256 before using it.
+- Rust bootstrap wraps rustc itself. We also set `build.ccache=sccache` in
+  its configure arguments so stage-zero compilation and LLVM use sccache,
+  retaining `llvm.download-ci-llvm=false`. The inherited wrapper is forwarded
+  by bootstrap through `RUSTC_WRAPPER_REAL` where applicable.
+- sccache is a compiler cache, not a Cargo target-directory cache. Linked
+  binaries, proc macros, some bootstrap work and incremental compilation are
+  not cacheable. SDK bootstrap and downstream dependencies can share storage
+  without necessarily sharing every compiled object. Every actual SDK build
+  prints statistics on success or failure; configured/compile layers are
+  rebuilt so stale Docker layer hits do not hide those statistics.
+
+Sources: [OpenWrt Rust configuration](https://github.com/openwrt/packages/blob/openwrt-24.10/lang/rust/rust-values.mk),
+[Rust bootstrap](https://github.com/rust-lang/rust/blob/1.90.0/src/bootstrap/src/core/build_steps/compile.rs),
+[sccache Redis](https://github.com/mozilla/sccache/blob/v0.18.0/docs/Redis.md),
+[Rust cache limitations](https://github.com/mozilla/sccache/blob/v0.18.0/docs/Rust.md).
+
+## Downstream OpenWrt packages
+
+Use the same persistent daemon and target/version image. For example, after
+installing the `sqm-autorate-rust` feed/package in the SDK:
+
+```sh
+docker run --rm --network gitea-runner-jobs --cpus 8 \
+  --memory 20g --memory-swap 20g \
+  -e SCCACHE_REDIS_ENDPOINT=redis://openwrt-rust-cache:6379 \
+  lochnair/openwrt-sdk-rust:x86-64-24.10.8 sh -ec '
+    # Install/update the downstream feed here before defconfig.
+    make defconfig
+    grep -qx "CONFIG_RUST_SCCACHE=y" .config
+    sccache --start-server
+    trap "sccache --show-stats; sccache --stop-server" EXIT
+    sccache --zero-stats
+    make package/sqm-autorate-rust/compile -j8 V=sc
+  '
+```
+
+Keep the image's cache prefix and enable `CONFIG_RUST_SCCACHE` after any
+downstream configuration replacement. Cache statistics belong to the current
+container's sccache server; `--zero-stats` does not erase cached objects.
+`sqm-autorate-rust` currently uses cross-rs to publish static binaries, not an
+OpenWrt SDK package workflow; that unrelated pipeline is unchanged. The package
+Makefile in `openwrt-feeds` already uses OpenWrt's `rust-package.mk`, so an SDK
+package job can use this cache without patching the package.
+
+For a local SDK build on the prepared runner:
+
+```sh
+sh ci/setup-builder.sh
+docker buildx build --builder openwrt-sdk-rust --load --progress plain \
+  --network host --allow network.host --no-cache-filter configured,sdk \
+  --build-arg SAFE_TARGET=x86-64 --build-arg VERSION=24.10.8 \
+  --build-arg JOBS=8 \
+  --build-arg SCCACHE_REDIS_ENDPOINT=redis://127.0.0.1:6379 \
+  -t lochnair/openwrt-sdk-rust:x86-64-24.10.8 .
+```
+
+See [validation results](ci/VALIDATION.md) for the checks performed and the
+remaining cutover acceptance.

ci/VALIDATION.md

@@ -0,0 +1,89 @@
+# Migration validation — 2026-10-10
+
+Inspected the original Jenkinsfile, Dockerfile, downstream `sqm-autorate-rust`
+workflows and package Makefile, Terraform runner definition, and live TheBeast
+runner configuration before changing the repository.
+
+## Passed
+
+- YAML parsing; TOML parsing; `sh -n`; ShellCheck; `git diff --check`.
+- actionlint 1.7.12, excluding only its unsupported `builtin:checkout` action
+  syntax. The workflow uses the existing `ubuntu-latest` label. Gitea's documentation and the
+  existing downstream workflow confirm built-in checkout support.
+- Default matrix resolves six entries for stable 25.12.5 and oldstable 24.10.8.
+  `targets=all` ran upstream target discovery inside the actual job image and
+  resolved 194 entries. Empty/invalid targets fail. Every default base-image
+  tag was read successfully from GHCR.
+- Docker Compose configuration accepted; Redis healthy with its named volume,
+  AOF enabled and successful AOF writes. Service and bounded builder were
+  provisioned on TheBeast without changing the runner configuration.
+- Builder inspected: eight-CPU quota, 20 GiB memory/swap limit, one BuildKit
+  worker step, 50 GiB layer GC budget. A second disposable job container with
+  fresh Docker client configuration reused the existing daemon and builder.
+- Dockerfile build checks completed. Two expected advisory warnings: mandatory
+  base-image arguments have no defaults, and Docker's secret-name heuristic
+  mistakes the public `SCCACHE_REDIS_KEY_PREFIX` for a secret.
+- `configured` Dockerfile stage built for x86/64 on both OpenWrt releases.
+  Pinned feeds select Rust 1.94.0 on 25.12.5 and 1.90.0 on 24.10.8. Both retain
+  `CONFIG_RUST_SCCACHE=y` through defconfig and contain the explicit bootstrap
+  `build.ccache=sccache` setting with LLVM CI downloads disabled.
+- Actual OpenWrt make-variable expansion injects sccache into host and package
+  compilation, despite unexporting an inherited wrapper.
+- Real Cargo library compilation in Docker BuildKit: one Redis miss. A fresh
+  runtime container using the Docker-network endpoint: one hit, zero misses.
+- Recreated the newly provisioned Redis container using the same named volume;
+  a fresh compiler container still recorded one hit, zero misses. No existing
+  infrastructure containers were restarted.
+- Same source/cache namespace with GNU versus musl target: first musl build
+  missed; repetition hit. Rust 1.90.0 versus 1.91.0: first 1.91 build missed;
+  repetition hit. All probes reported zero cache read/write errors.
+- A disposable OpenWrt package used the real `Build/Compile/Cargo` helper,
+  SDK GCC/musl linker, OpenWrt LTO/optimization flags and a local Rust library
+  dependency. It built successfully in two separate containers: one dependency
+  miss, then one hit. The linked executable correctly remained non-cacheable.
+  This used a prebuilt Rust 1.90 toolchain for the probe, not a freshly compiled
+  SDK toolchain; it is not a full SDK/source-bootstrap acceptance result.
+- Retained `ci/verify-cache.sh` passed its separate-container miss/hit checks
+  against that prebuilt validation toolchain. Its original hardcoded SDK rustc
+  path was later corrected after the live mediatek/filogic build exposed the
+  target-specific staging layout; see the follow-up below.
+- Publication configuration checked: original Docker Hub namespace/tag format,
+  verification before push, explicit publish input, temporary credential
+  directory, no automatic publication trigger. No registry login or push was
+  attempted.
+
+## Remaining acceptance
+
+1. Enable repository Actions and configure the two Docker Hub secrets. No
+   runner configuration changes are required.
+2. Complete a non-publishing Gitea dispatch for the full default matrix.
+   The mediatek/filogic 24.10.8 job completed Rust source bootstrap and image
+   export; its corrected verification passed on the built image. Acceptance
+   for the other combinations remains pending.
+3. With explicit publication approval, run the publishing dispatch, pull the
+   resulting tags and build the downstream OpenWrt package with the new image.
+   Actual Docker Hub authorization and publication remain unverified.
+4. After acceptance, disable the old Jenkins job and remove `Jenkinsfile`.
+   It is deliberately retained until the replacement passes these checks.
+
+Remote test logs and disposable probe sources are under
+`/tmp/openwrt-sdk-rust-migration` in TheBeast's `gitea-runner` instance. The
+Redis volume/service and BuildKit builder remain available for the replacement
+pipeline; no cache volume or existing infrastructure was deleted.
+
+## Follow-up: mediatek/filogic 24.10.8 verification
+
+The supplied job 1602 log shows full SDK compilation and image export completed
+successfully. Verification failed with exit 127 because it assumed
+`staging_dir/host/bin/rustc`. Inspection of that exact built image reproduced
+the failure and located Rust/Cargo in
+`staging_dir/target-aarch64_cortex-a53_musl/host/bin` instead. Both the workflow
+and retained cache probe now resolve the unique executable compiler from the
+SDK staging tree, rather than assuming a shared host directory.
+
+Reran the corrected verification on that image: Rust 1.90.0 and Cargo 1.90.0
+execute successfully. The retained cache probe reports one Redis miss in its
+first container and one hit in a fresh second container, with zero cache
+read/write errors. ShellCheck, actionlint (excluding only Gitea's built-in
+checkout syntax), and `git diff --check` pass. No rebuild or publication was
+performed for this fix.

ci/build-rust.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+set -eu
+
+: "${SCCACHE_REDIS_ENDPOINT:?Set the persistent sccache Redis endpoint}"
+: "${JOBS:=8}"
+case "$JOBS" in ''|*[!0-9]*|0) echo 'JOBS must be a positive integer' >&2; exit 1 ;; esac
+
+sccache --start-server
+trap 'sccache --show-stats; sccache --stop-server' EXIT
+sccache --zero-stats
+# Bootstrap/Ninja does not inherit Make's job count. Bound both explicitly.
+make package/rust/host/compile -j"$JOBS" RUST_BUILD_JOBS="$JOBS" || \
+    make package/rust/host/compile -j1 RUST_BUILD_JOBS=1 V=sc
+rm -rf build_dir/host/rustc-*/rustc-*/build dl/rustc-*.tar.*

ci/buildkitd.toml

@@ -0,0 +1,6 @@
+# Shared by all SDK jobs on this daemon, including simultaneous dispatches.
+[worker.oci]
+  max-parallelism = 1
+  gc = true
+  reservedSpace = "10GB"
+  maxUsedSpace = "50GB"

ci/cache.compose.yml

@@ -0,0 +1,40 @@
+services:
+  cache:
+    image: redis:7.4.6-alpine
+    container_name: openwrt-rust-cache
+    restart: unless-stopped
+    command:
+      - redis-server
+      - --appendonly
+      - 'yes'
+      - --appendfsync
+      - everysec
+      - --maxmemory
+      - 6gb
+      - --maxmemory-policy
+      - allkeys-lru
+      - --save
+      - ''
+    mem_limit: 8g
+    memswap_limit: 8g
+    cpus: 1
+    ports:
+      - '127.0.0.1:6379:6379'
+    volumes:
+      - cache:/data
+    networks:
+      - jobs
+    healthcheck:
+      test: ['CMD', 'redis-cli', 'ping']
+      interval: 5s
+      timeout: 3s
+      retries: 12
+
+volumes:
+  cache:
+    name: openwrt-rust-sccache
+
+networks:
+  jobs:
+    external: true
+    name: gitea-runner-jobs

ci/matrix.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+"""Resolve the same stable/oldstable x target matrix as Jenkins."""
+import json
+import os
+import re
+import subprocess
+import tempfile
+import urllib.request
+
+
+def resolve(versions, targets):
+    versions = [versions[k] for k in ("stable_version", "oldstable_version") if versions.get(k)]
+    if not versions:
+        raise ValueError("OpenWrt returned no stable or oldstable version")
+    targets = [t.strip() for t in targets.split(",") if t.strip()]
+    if not targets:
+        raise ValueError("No targets selected")
+    for target in targets:
+        if not re.fullmatch(r"[a-z0-9_+-]+/[a-z0-9_+-]+", target):
+            raise ValueError(f"Invalid target: {target!r}")
+    for version in versions:
+        if not re.fullmatch(r"[a-zA-Z0-9_.-]+", version):
+            raise ValueError(f"Invalid version: {version!r}")
+    return {"include": [{"target": t.replace("/", "-"), "version": v}
+                        for v in versions for t in dict.fromkeys(targets)]}
+
+
+if __name__ == "__main__":
+    with urllib.request.urlopen("https://downloads.openwrt.org/.versions.json", timeout=60) as response:
+        versions = json.load(response)
+    targets = os.environ.get("TARGETS", "x86/64,mediatek/filogic,octeon/generic")
+    if targets.strip() == "all":
+        with tempfile.TemporaryDirectory(prefix="openwrt-targets-") as source:
+            subprocess.run(["git", "clone", "--depth", "1", "https://github.com/openwrt/openwrt.git", source], check=True)
+            output = subprocess.check_output(["perl", "scripts/dump-target-info.pl", "targets"], cwd=source, text=True)
+            targets = ",".join(line.split()[0] for line in output.splitlines() if line.strip())
+    matrix = json.dumps(resolve(versions, targets), separators=(",", ":"))
+    print(matrix)
+    with open(os.environ["GITHUB_OUTPUT"], "a") as output:
+        output.write(f"matrix={matrix}\n")

ci/setup-builder.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -eu
+docker compose -p openwrt-rust -f ci/cache.compose.yml up -d --wait
+if ! docker buildx inspect openwrt-sdk-rust >/dev/null 2>&1; then
+    docker buildx create --name openwrt-sdk-rust --driver docker-container \
+        --driver-opt network=host,memory=20g,memory-swap=20g,cpu-period=100000,cpu-quota=800000 \
+        --buildkitd-config ci/buildkitd.toml \
+        --buildkitd-flags '--allow-insecure-entitlement network.host' || \
+        docker buildx inspect openwrt-sdk-rust
+fi
+docker buildx inspect openwrt-sdk-rust --bootstrap

ci/verify-cache.sh

@@ -0,0 +1,39 @@
+#!/bin/sh
+# Compile in two disposable containers: the second must read the first's cache.
+set -eu
+image=${1:?Usage: verify-cache.sh IMAGE}
+nonce=$(mktemp -d)
+trap 'rmdir "$nonce"' EXIT
+prefix="validation:${image##*:}:$(basename "$nonce"):"
+for expected in miss hit; do
+    docker run --rm -i --network gitea-runner-jobs --cpus 2 \
+        --memory 2g --memory-swap 2g \
+        -e SCCACHE_REDIS_ENDPOINT=redis://openwrt-rust-cache:6379 \
+        -e SCCACHE_REDIS_KEY_PREFIX="$prefix" -e EXPECTED="$expected" \
+        "$image" sh -es <<'PROBE'
+rustc=$(find /builder/staging_dir -type f -path '*/host/bin/rustc')
+test -x "$rustc"
+mkdir /tmp/sccache-probe
+cd /tmp/sccache-probe
+printf 'pub fn probe(n: u64) -> u64 { n.wrapping_mul(17) }\n' > probe.rs
+sccache --start-server
+trap 'sccache --stop-server' EXIT
+sccache --zero-stats
+sccache "$rustc" --crate-name ci_sccache_probe \
+    --crate-type rlib --emit link,dep-info --out-dir . probe.rs
+sccache --show-stats
+sccache --show-stats --stats-format json > stats.json
+python3 - <<'PY'
+import json
+import os
+
+data = json.load(open("stats.json"))
+assert data["cache_location"].startswith("redis,"), data
+stats = data["stats"]
+field = "cache_hits" if os.environ["EXPECTED"] == "hit" else "cache_misses"
+assert sum(stats[field]["counts"].values()) == 1, data
+assert stats["cache_read_errors"] == stats["cache_write_errors"] == 0, data
+print("Verified persistent cache", os.environ["EXPECTED"])
+PY
+PROBE
+done