ci: put Windows Go caches on the fast work disk via a setup-go-cache action - #3049
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…st OS endpoints Windows jobs have been finishing every step, including "Post Harden Runner" and "Complete job", and then never reporting a conclusion until GitHub cancels them 30-40 minutes later (0/day before harden-runner landed on the Windows legs on Aug 31; 5, 9, 23/day on Sept 1-3). Root cause: harden-runner's Windows post step waits at most 10 s for its agent, then kills it, and in the losing case the agent is still restoring the runner's DNS settings, leaving the adapter pointed at a DNS proxy that no longer exists. - Add .github/actions/windows-dns-guard: a scheduled-task watchdog that resets DNS only once harden-runner's post step has begun, the agent is gone, and 127.0.0.1 is still configured. Wired into every Windows leg. - Allowlist the Windows/macOS operating-system endpoints StepSecurity showed blocked on every job (NCSI probes, WNS, update/settings/telemetry, time sync, Sectigo OCSP/CRL, Apple update/CDN hosts); harden-runner stays in block mode everywhere. - Drop the GOPROXY "|direct" fallback in block-mode workflows: it only fans out to blocked vanity-import hosts. - Cancel superseded pull_request runs via a concurrency group. - Skip SARIF uploads on merge_group runs, whose synthetic ref cannot be scanned and was evicting PRs from the merge queue. Fix log: docs/fixes/2026-09-03-harden-runner-windows-dns-restore-race.md Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
The pool advertises four rotating names (0-3.pool.ntp.org); a single one was only what happened to be sampled. Push deferred until the first CI run of the guard finishes so its Windows data isn't cancelled by the new concurrency group. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
- Skip Harden Runner on draft-PR Windows jobs: every other Windows step (including checkout) is already skipped there, so its post step would race the agent's DNS restore with no guard available. - Run the guard's scheduled task as the runner's own Administrator account (S4U) instead of SYSTEM; it grants nothing the job does not already have. - Wrap the plain go mod download steps in pre-commit.yml and codeql.yml with go-mod-download-retry now that GOPROXY has no direct fallback. - Measurement query: filter to Windows jobs and tolerate fractional-second timestamps. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
…hards
Phase 2 (part 1) of the CI-stability plan, stacked on the Phase 1 branch.
Windows Defender: on the Windows shards "Set up Go" averages 5.2 min
(max 10.5) restoring a 1.9 GB go-build+mod cache; the download is ~20 s,
the rest is tar/zstd extraction with Defender's real-time scanner
inspecting every extracted file, and the same scanner holding handles on
fresh test files surfaces as testing.TempDir cleanup failures
("unlinkat ... being used by another process"). Add a continue-on-error
pwsh step to every Windows leg of test.yml (build, terraform-registry-cache,
test, mock) and to setup-go-cache-warmup.yml that excludes D:\a,
C:\hostedtoolcache\windows, the Go caches, and the temp dirs, plus go.exe
as a process. These are ephemeral VMs and the step does not touch
harden-runner's egress policy.
Restore-only toolchain cache: the repo's Actions cache is 18.9 GB across
17 refs/pull/N/merge-scoped entries against a 10 GB LRU quota, so the
static atmos-toolchain-<os>-<arch>-v2 key never hits ("Cache not found
for input keys" on every shard), then all 10 shards race to save it
("Unable to reserve cache with key ...") and "Post Cache Atmos toolchain"
costs 43 s avg / 3 min max per shard for nothing. Add an opt-in
restore-only input (default 'false') to actions/cache/action.yml that
switches to actions/cache/restore at the same pinned SHA, keep cache-hit
and key outputs working, document it in the README, and set it on the
test job's "Cache Atmos toolchain" step for all three OSes.
terraform-registry-cache stays the single writer per OS and is unchanged.
Fix log: docs/fixes/2026-09-03-windows-defender-exclusions-and-restore-only-toolchain-cache.md
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Add-MpPreference -ExclusionProcess 'go.exe' matches on image name only, not path, so it would exempt any binary named go.exe from real-time scanning regardless of where it actually lives - including one planted by a compromised dependency during go build/go generate. The path exclusions already in this step cover the actual scanning cost (file I/O in the Go caches and workspace), so removing the process exclusion gives up nothing measured. (Skipped a second CodeRabbit finding on this PR: it asked test/ terraform-registry-cache to needs: a "cache-writer" job that doesn't exist in this file - terraform-registry-cache itself is the writer, and test is deliberately parallel to it so 30 shards don't wait on or race the single writer job. Making test depend on it would serialize two long-running job groups that currently run concurrently.) Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
…efender-restore-only-cache # Conflicts: # .github/workflows/setup-go-cache-warmup.yml # .github/workflows/test.yml # docs/fixes/2026-09-03-harden-runner-windows-dns-restore-race.md
…verted)" This reverts commit 145a8c4.
GitHub's own actions/runner-images build script already disables
real-time monitoring and excludes C:\ and D:\ entirely on windows-latest
images, before any workflow step runs. Confirmed live via a temporary
diagnostic step (Get-MpComputerStatus/Get-MpPreference) on an actual
windows-latest runner: RealTimeProtectionEnabled was already False and
ExclusionPath already {C:\, D:\} before our own Add-MpPreference calls,
which only added redundant subpaths already covered by the existing C:\
exclusion. Since Defender was never doing real-time scanning to begin
with, it wasn't the cause of the measured Windows slowdown this step was
meant to fix - that root cause is still open.
Splits the fix-log doc accordingly: the restore-only-toolchain-cache half
(unrelated, unaffected) moves to its own file; a new doc records the
Defender investigation and reversal so it isn't re-attempted blind later.
Restoring our ~1.9 GB go-build+mod cache on windows-2025 hosted runners is ~6.5 minutes of pure tar extraction (download is ~16 s) - 40-60% of every Windows acceptance shard's wall time. Iterating on that through the full Tests suite costs a whole run per experiment. This workflow restores the SAME production setup-go archive under one tar configuration per matrix leg (gnu-tar = exactly what test.yml does today; bsdtar = the proposed fix via a PROGRAMFILES override + System32-first PATH, using only released @actions/cache code), asserts a real cache hit so a miss can never masquerade as a fast restore, prints which tar was actually selected, and writes each leg's "Set up Go" duration to the step summary. A second job reports C:/D: disk topology and a small-file write benchmark on each, to settle whether the D:\ that windows-2025-vs2026 still exposes is a distinct (fast) disk or a path onto the same volume. Evidence for the two measured causes: actions/runner-images#12416/#12647 (D: removed on Windows Server 2025; C: ~540 IOPS, won't-fix) and actions/cache#752 / actions/toolkit#2379 (MSYS GNU tar ~4x slower than native bsdtar on many-small-files archives; PR unmerged). Windows Defender is not a factor: real-time monitoring is disabled at the image level.
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Included review availability: Your plan provides up to 4 included reviews per hour; 2 remain after this review. 📝 WalkthroughWalkthroughThe PR centralizes Windows GNU tar and Go cache setup, moves Go temporary directories to the runner work disk, adopts the action across workflows, adds restore-only cache behavior, exports cache metadata for nested actions, and documents the changes. ChangesCache workflow updates
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🟡 Moderate · up to This change updates CI cache setup and restore behavior, but open CI-configuration and benchmark concerns remain, and the test-runtime argument log can lose newline distinctions. These issues should be resolved before merge to avoid misleading test or performance results and CI behavior. Sequence Diagram(s)sequenceDiagram
participant Workflow
participant setup_go_cache
participant windows_gnu_tar
participant actions_setup_go
Workflow->>setup_go_cache: Configure Go cache
setup_go_cache->>windows_gnu_tar: Set GNU tar on Windows
setup_go_cache->>actions_setup_go: Set up Go and restore cache
actions_setup_go-->>Workflow: Return setup outputs
sequenceDiagram
participant Workflow
participant CachePaths
participant GITHUB_ENV
participant CacheAction
Workflow->>CachePaths: Generate cache metadata
CachePaths->>GITHUB_ENV: Write ATMOS_CACHE_* variables
Workflow->>CacheAction: Invoke cache action with mode
CacheAction->>GITHUB_ENV: Read cache metadata
CacheAction-->>Workflow: Restore or restore and save cache
Suggested labels: Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 42.86% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 14 functions across 6 files. (9 skipped: 9 unsupported.)
✨ Finishing Touches 💡 1📝 Generate docstrings 💡
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In @.github/workflows/cache-perf.yml:
- Line 40: Update the workflow trigger configuration around workflow_dispatch so
pull requests run the required unit tests, integration tests, golangci-lint, and
coverage reporting while preserving manual dispatch for this lab; if these
checks belong in the owning PR workflow instead, add or reference them there
rather than leaving pull-request coverage absent.
- Around line 222-224: Update the drive benchmark loop to deduplicate drive
letters derived from LOCALAPPDATA and RUNNER_TEMP before creating benchmark
directories or running measurements, so each distinct available drive is
benchmarked once. Preserve the existing missing-drive skip behavior.
- Around line 161-164: Guard the jobs API lookup before calculating $secs:
validate that $job, $step, $step.started_at, and $step.completed_at are present,
using a bounded retry for transiently incomplete results or an explicit error
when they remain unavailable. Only perform the datetime subtraction after all
required values have been validated.
- Around line 79-80: Add go.dev:443 to the network allowlist used by the
setup-go workflow, alongside the existing storage.googleapis.com:443 and
google.golang.org:443 entries, so the Go download fallback remains permitted.
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workflow_dispatch only resolves workflows that already exist on the default branch, which would have meant merging the lab before running a single experiment. A push trigger runs the pushed branch's own copy of the file, so every push to a *ci-cache-perf* branch now runs it directly - edit, push, read the step summary, repeat. A per-ref concurrency group lets a newer push supersede a stale in-flight run. workflow_dispatch is kept for once the file is on main.
The first run missed on both legs: main's setup-go archive is evicted by the 10 GB LRU churn, and the only surviving entries are PR-scoped, which other branches cannot read. A seed job per cache layout now populates a real go-build+mod archive (go mod download + go build ./...) that setup-go's post step saves under this branch, so the timed legs always restore something real. The topology job measured D: as a separate disk with ~8.8x the small-file write rate of C: (4,545 vs 515 files/s), so a third leg relocates GOCACHE and GOMODCACHE to D:\a\ before setup-go (actions/setup-go#515). It needs its own seed: the cache version hashes the restore paths and the archive holds absolute paths, so seed and restore must agree on layout. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
…composite The second run lost the D: seed's archive before its restore leg ran: this repo's cache sits at the 10 GB quota (9.9 GB across 5 entries, ~1.8 GB per Windows setup-go archive), so every save evicts the least recently used entries, and the restore legs waited on both seeds - nine minutes during which the D: archive was the oldest unread entry. Now each layout is its own seed -> restore pair, so a restore starts (and touches its archive) seconds after its seed saved it. Each layout also gets its own cache key via a marker file hashed through cache-dependency-path. The shared step sequence moves into .github/actions/cache-perf-lab, which times the restore with its own clock since the jobs API does not list nested composite steps. Measured so far (both seeds through bsdtar): the cache save dropped from 590 s on C: to 175 s on D:, and go build ./... from 599 s to 455 s. On C:, gnu-tar restored in 276 s and bsdtar in 295 s. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
…numbers Run 2's "bsdtar" legs silently used GNU tar: a step-level PROGRAMFILES override does not take effect on Windows runners (the process keeps its own ProgramFiles value), so @actions/cache's hardcoded %PROGRAMFILES%\Git\usr\bin\tar.exe existence check kept passing. The composite now takes tar: gnu|bsd and, for bsd, renames Git's tar.exe aside for the job and puts C:\Windows\System32 first on PATH, so the toolkit's PATH lookup lands on bsdtar. Nothing else in the job needs Git's tar. Measured so far with GNU tar on both sides: restore 276 s on C: vs 94 s on D: (same 1.7 GB archive); save 590 s vs 175 s; go build 599 s vs 455 s. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
…action New .github/actions/setup-go-cache: pinned actions/setup-go with caching, plus one Windows-specific step before it - relocate GOCACHE and GOMODCACHE onto the runner's work disk (derived from RUNNER_TEMP) when that is a different drive from LOCALAPPDATA, where Go's defaults live. On windows-latest that is D:, a separate disk with ~8.8x the small-file write rate of C:. No-op on Linux/macOS or on an image without the split. Measured with the cache-perf lab on our ~1.7 GB go-build+mod archive: restore 276 s -> 94 s, save 590 s -> 175 s, go build ./... 599 s -> 455 s. All eight setup-go call sites in test.yml that run on v5.6.0 (or on Windows) and the cache-warmup workflow now use the action, so the pattern lives in one place; the Linux-only coverage job stays on setup-go v6. terraform-registry-cache moves from setup-go v6 to the action's v5.6.0. The lab's D: layout now runs this exact action, so cache-perf.yml keeps measuring what production runs. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
… at the GNU tar steps Run 4 of the lab settles the tar question: with real bsdtar (Git's tar renamed aside) the restore takes 353 s on C: and 117 s on D: against GNU tar's 264 s and 94 s, because @actions/cache's bsdtar path decompresses the whole archive to a .tar on disk before extracting. The GNU tar steps stay, now with the measured justification instead of the unmeasured 2024 belief; the lab keeps the bsdtar leg for re-checks. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Erik Osterman (Cloud Posse) (osterman)
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The lab did its job (four runs, every number in docs/fixes/2026-09-04-windows-go-caches-on-fast-disk.md) and is not worth maintaining on main. It remains in this branch's history at 8fe6ed6 if it is ever needed again. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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…Args A same-PR fix for a CodeRabbit finding (encoding ambiguity: a literal "\n" in an argument vs. an actual embedded newline) escaped backslash before newline/tab. That broke every Windows path argument recorded through this helper: every consumer (pkg/runner/step, cmd/custom_command_*_test.go, pkg/container, pkg/workflow) reads the log with a plain strings.Split on tabs and compares fields directly against real filesystem paths -- none of them decode escapes back out. Confirmed via TestCustomCommandContainerBuildPassesWithBlockToDocker failing deterministically (not flaky -- reproduced on rerun) on the Windows acceptance shard with every path separator doubled. The encoding ambiguity CodeRabbit flagged is real but was never exploitable: no caller has ever decoded this format. Revert rather than add a decoder nobody needs, restoring the behavior every existing consumer already depends on.
…apse action.yml bash actions/cache/action.yml's meta/validate/export steps (~35 lines of hand-rolled bash) existed only because a nested composite's post step can't see the outer step's steps.*.outputs (actions/runner#2800), so the action re-derived and re-wrote the same key/path/restore-keys to $GITHUB_ENV by hand -- duplicating, less safely, what pkg/github/actions already does correctly for $GITHUB_OUTPUT (collision-safe delimiter generation, tested). - cmd/ci/cache/paths.go: emitGitHubCachePaths now also writes ATMOS_CACHE_KEY/ATMOS_CACHE_PATH/ATMOS_CACHE_RESTORE_KEYS to $GITHUB_ENV (via the same env.Output/ghactions.FormatValue used for $GITHUB_OUTPUT) whenever $GITHUB_ENV is set, with explicit empty-key/empty-paths validation replacing the old bash checks. - errors/errors.go: new ErrCachePathsRequired sentinel, alongside the existing ErrCacheKeyRequired. - actions/cache/action.yml: meta+validate+export collapse into the one `atmos ci cache paths --format=github` line the action already mostly was. The CR/LF and delimiter-collision finding classes from the previous commit can't recur now that this is one tested Go code path instead of every consumer's own bash.
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Inline comments:
In `@cmd/ci/cache/paths.go`:
- Line 164: Isolate GITHUB_ENV in the GitHub-format output-only tests so they
cannot append cache metadata to the runner’s real job environment file. Update
the shared test setup or each affected test to clear GITHUB_ENV while preserving
the existing GITHUB_OUTPUT behavior and the GetEnvPath handling in the
production path.
- Around line 169-170: Update the error return in the GITHUB_ENV export path to
wrap the underlying error with context identifying the GITHUB_ENV export, while
preserving the original error for unwrapping. Keep the preceding GITHUB_OUTPUT
error handling unchanged.
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…r; update stale regression test - cmd/ci/cache: this package's test binary runs inside real GitHub Actions CI, so every github-format test would otherwise inherit an ambient GITHUB_ENV left over from the job -- emitGitHubCachePaths writes to it whenever set, so an unrelated test could leak fixture cache metadata into the real job's environment file. initTestIO (called by every test in the package) now clears it by default; tests that specifically exercise the write path override it explicitly. Added a regression test proving initTestIO clears an ambient value. Also wrapped the GITHUB_ENV write's error so it's distinguishable from the preceding GITHUB_OUTPUT write's error. - cmd/docker_and_action_regression_test.go: TestAtmosCacheActionValidatesMetadataBeforeActionsCache asserted the exact bash validation strings the previous commit removed from action.yml (validation now lives in Go -- see TestEmitGitHubCachePaths_EmptyKey/_EmptyPaths). Failing across every acceptance shard and the race suite. Updated to check the real invariant -- metadata is still derived via `atmos ci cache paths --format=github` before either terminal cache step runs -- instead of bash string literals that no longer exist.
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Inline comments:
In `@cmd/ci/cache/paths_test.go`:
- Line 103: Initialize the command test kit with cmd.NewTestKit(t) before
calling initTestIO in this test, ensuring RootCmd flags and arguments are reset
between tests while preserving the existing helper setup.
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Erik Osterman (Cloud Posse) (osterman)
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Resolves conflicts against main's cache-action redesign (#3049) and the toolchain-env-export changes: this branch made no unique changes to actions/cache/action.yml (main is a strict superset), so took main's copy verbatim. Kept this branch's new ci-toolchain composite action step in test.yml in place of the old manual per-tool install + separate cache step. Kept main's fake_container_runtime.go recordArgs (no backslash-escaping, per the earlier revert that fixed Windows path-argument test breakage).
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Resolves conflicts in actions/cache/action.yml, actions/cache/README.md, .github/actions/setup-go-cache/action.yml, and the windows-go-caches fix doc against main's cache-action redesign (#3049): kept this branch's deprecated restore-only input (mapped to mode) and its wider conditions layered on top of main's redesigned structure, and kept this branch's fuller comments (the Linux race-job pin note; the stale setup-go v6 comment removal).
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what
.github/actions/setup-go-cache: pinnedactions/setup-gowith caching, plus one Windows-specific step before it - relocateGOCACHEandGOMODCACHEonto the runner's work disk (derived fromRUNNER_TEMP) when that is a different drive fromLOCALAPPDATA, where Go's defaults live. No-op on Linux/macOS or on any image without the split.setup-gocall site that runs on Windows or was on v5.6.0 (build,terraform-registry-cache,test,magefiles,floci-go,kubernetes-e2e,container-step, andsetup-go-cache-warmup.yml), so the pattern lives in one place.terraform-registry-cachemoves from setup-go v6 to the action's v5.6.0; the Linux-onlycoveragejob andsetup-atmos-buildstay on v6..github/actions/windows-gnu-tar(idempotent, no-op off Windows) issetup-go-cache's first step, and the publishedactions/cacheaction (behind every "Cache Atmos toolchain" step) carries the same step inline, since a published action cannot reference a local one; its README gains a Windows section. Every cache-using action now provisions its own tar, and the four hand-copied "Add GNU tar to PATH" steps with their unmeasured 2024 comment are gone.cache-perf.ymlworkflow that lived on this branch (seeded a real archive per cache layout, restored it under each tar/disk combination, timed theSet up Gostep; last at8fe6ed6384, removed before merge). Method and every number are in the fix-log.why
On
windows-latest, restoring our ~1.7 GB Go cache took 4-7 minutes per job and saving it 7-10, with the download at ~16 s: the time is tar writing ~200k small files onto C: (~540 IOPS). D: is a separate disk with ~8.8x the small-file write rate (4,545 vs 515 files/s), andRUNNER_TEMPalready lives there - but Go's default cache locations don't.Measured on the same archive,
Set up Gostep wall clock:Cache save (seed jobs, GNU tar): 590 s on C: vs 175 s on D:.
go mod download && go build ./...: 599 s vs 455 s.bsdtar was the original hypothesis (actions/cache#752, actions/toolkit#2379 report ~4x faster extraction) and it loses on both disks:
@actions/cache's bsdtar path decompresses the whole archive to acache.taron disk before extracting, and that extra multi-GB write costs more than the MSYS overhead it avoids. Along the way: main's Go cache never survives between runs because the repo sits at the 10 GB quota (every save evicts LRU entries; the onlysetup-go-Windowsentries that exist are PR-scoped), so the save speedup matters as much as the restore; and a step-levelPROGRAMFILESoverride silently does nothing on Windows runners, which made the first "bsdtar" runs measure GNU tar - only the tar command line in the log tells the truth.The cache version hashes the restore paths, so the first run after this lands is a one-time cold start for the Windows jobs.
Seen in production on this PR's own Tests run (33898160232):
Build (windows)took the cold miss and saved 1.84 GB in 156 s (main's last Windows build spent 416 s on that save from C:); all ten Windows acceptance shards then restored it in 90-116 s where the same restore took 4-7 minutes before.Full write-up:
docs/fixes/2026-09-04-windows-go-caches-on-fast-disk.md.Temp directories too. The action also points
GOTMPDIR,TEMPandTMPat the work disk (atD:\a\tmp, besideRUNNER_TEMP), since Go's build scratch and everyt.TempDir()the tests create otherwise land on the slow disk. Measured on the Windows acceptance shards' "Acceptance tests" step: 2,826 s summed across nine shards with temp on C: vs 2,171 s on D:, a 23% cut, largest on the fixture-heavy shards. (Not underRUNNER_TEMPitself: it isD:\a\_temp, and atmos's output layer mangles\_in printed paths - a Markdown-escape bug inpkg/ui, to be fixed separately - which the toolchain clean tests caught.)What this does not fix: the 10 GB cache quota. Four concurrent PR runs wrote ~15 GB of entries within seven minutes, and GitHub evicts by least recent access, so a freshly saved archive nobody has read yet is the first to go. In one run all ten Windows shards missed an archive the build job had saved two minutes earlier, and cold shards take 710-818 s for tests that take 180-280 s warm. The disk change makes every miss and save 2.7-3.8x cheaper; making them rare needs fewer bytes per run or a different backend for the Linux jobs (RunsOn's Magic Cache has no such quota). Documented in the fix-log as the follow-up.
Includes #3038. Both PRs extend the published
actions/cacheaction (#3038:restore-onlyinput so the acceptance shards restore the toolchain cache without each trying to save it; this PR: GNU tar step +cache-home), so #3038's branch is merged in here and the action carries both inputs. If this merges first, #3038 can be closed; if #3038 merges first, this rebases cleanly (verified withgit merge-treeagainst both).references
windows-lateststill has it)🤖 Generated with Claude Code
Summary by CodeRabbit
Performance
New Features
cache-homeoption.Maintenance
Documentation