[jdx]

https://entire.io/gh/jdx/mise/trails/609

Every backend that downloads through mise's HTTP client fetched its artifact again on each install, and nothing checked what a restored or shared cache handed back (discussion 14217). This PR adds one content-addressed download store, $MISE_CACHE_DIR/downloads-cas, that re-hashes what it holds before using it, and says plainly what that does and doesn't protect.

Revalidated downloads (all HTTP-client callers, on by default). A finished download is kept with the ETag or Last-Modified value the server sent. The next request for the same URL is conditional; on 304 Not Modified mise uses the kept file after hashing it again, so nothing is transferred. A file that no longer matches is dropped and downloaded again. This covers github, aqua, http, the core tools, plugin archives, the registry, brew, remote task files and the rest without per-backend wiring. Servers that send no validator aren't cached.

Pinned reuse, no network (http, github, aqua, packslip). A checksum a tool pinned, in its options, in mise.lock, or as a packslip's signed digest, names the stored file, which is used without any request even if the URL changed. The pin is still verified after the download as before.

No extra copy. Files are stored once, by hash, under their own file name (installers read the format and the binary's name from it). The four pinning backends download into the store and the file in downloads is a hard link to it, so the archive takes no extra space; across devices it falls back to a copy. I checked that these install paths only read the downloaded file (raw binaries are copied and the copy is made executable), and a stored file is hashed again before every reuse, so an in-place change would cost a re-download, never a wrong install. Partial downloads now resume from the store's staging area.

Turn it all off with download_cache = false (MISE_DOWNLOAD_CACHE=0). The store holds up to 2 GiB, least recently used first. always_keep_download is deprecated (warns from 2026.11.0, removed 2027.11.0): downloads are kept in the store instead.

Trust. The recorded hash lives beside the file, so it catches damage but not a cache whose file and metadata were both replaced; without a pinned checksum a writable cache is trusted, and the docs say so. The extracted http-tarballs tree from shared_extraction (opt-in) is still trusted as is.

Docs. A "Restored caches and installed tools" section in the lockfile docs explains why mise can't validate an installed tree (installs are mutable on purpose, and source-built tools differ from their tarball) and what to do instead, with warnings on the http shared-extraction note and the GitHub Actions section.

Tested with unit tests of the 304 path, a tampered stored file, pinned reuse and the linked download, plus e2e tests for pinned and unpinned reinstalls with the server stopped and a tampered entry. The http, aqua, github and packslip e2e groups pass except test_http_compressed_binaries, which fails here removing a system-wide install under /usr/local/share/mise. Clippy with -D warnings is clean.

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Note

Medium Risk
Changes core download/install paths and trust assumptions for cached bytes; mitigated by re-hash on use and pin verification, but writable shared caches remain a security consideration documented in this PR.

Overview
Adds a content-addressed download cache ($MISE_CACHE_DIR/downloads-cas, toggle download_cache / MISE_DOWNLOAD_CACHE, default on) integrated into mise’s shared HTTP downloader.

Reuse behavior: Finished downloads are stored by BLAKE3 with URL and pin indexes. Repeat requests send conditional headers and skip the body on 304 Not Modified; tools with a pinned checksum (algo:hex from options, lockfile, or packslip digest) can be served with no network. Blobs are re-hashed before reuse; bad entries are dropped and fetched again.

API surface: New download_file_pinned, download_file_with_pin, and download_file_linked (hard-link into install paths where possible). http, github, aqua, and packslip install paths use linked downloads with pinned checksums; other HTTP callers get copy-out caching and revalidation. Partial/resume state moves under the cache incoming staging area.

Settings & docs: always_keep_download is deprecated in favor of the cache (2 GiB LRU eviction). Docs warn that restored CI caches and shared extraction stores are trusted as-is, not re-checked against mise.lock.

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📝 Walkthrough

Walkthrough

The documentation explains that lockfile checksums apply to downloaded artifacts, not restored caches or installed files. It describes cache safeguards and states that files already in the shared HTTP tarball store are not checked again against lockfile checksums.

Changes

Cache checksum documentation

Layer / File(s)	Summary
Checksum and cache guidance docs/dev-tools/mise-lock.md, docs/continuous-integration.md, docs/dev-tools/backends/http.md	The lockfile documentation describes checksum limits, cache safeguards, and verification options. The CI and HTTP backend documentation warn that restored caches and files in the shared store are not rechecked against lockfile checksums.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~4 minutes

Change: Other

Suggested reviewers: marukome0743

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Merge Risk: 🔵 Low · up to 2311d

The documentation could overstate protection in two narrow cases: a same-key GitLab writer can replace both cached files and their manifest, and an HTTP artifact without an existing checksum is not compared with a pinned value. Clarify these limitations; the risk is bounded to users relying on these safeguards.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Title check		The title describes reusing downloads that a server confirms are unchanged. The pull request instead documents trust boundaries for restored caches, installed tools, and the shared extraction store.	Replace the title with a concise description of the documentation change, such as "docs(lock): explain trust in restored caches and shared extraction".

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Check name	Status	Explanation
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.

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Actionable comments posted: 1

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Review comments at @docs/dev-tools/mise-lock.md:
- Around line 445-446: Update the `mise install --locked` guidance to clarify
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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @docs/dev-tools/mise-lock.md:
- Around line 430-431: Update the cache-integrity guidance around the manifest
in the mise cache documentation: require storing the expected manifest in
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contents against it, rather than relying on a co-located manifest that can be
replaced with the cache. If documenting an equivalent provider guarantee, make
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[github-actions]

Instruction counts

benchmark	trend	instructions	Δ	wall (min)	Δ
env	▁▂▅▄▄█	27,906,088 → 27,978,472	+0.26%	19.87 → 19.31ms	-2.80%
hook-env	▁▁█▇▇█	30,009,065 → 30,021,801	+0.04%	20.85 → 20.55ms	-1.44%
ls	▁▁▅▆▇█	32,137,059 → 32,205,130	+0.21%	21.57 → 21.72ms	+0.71%
registry	▃▄▁▄▂█	40,209,044 → 40,319,258	+0.27%	17.76 → 18.14ms	+2.13%
startup	▅▆▂▁▅█	11,082,838 → 11,100,389	+0.16%	12.09 → 12.10ms	+0.15%

No instruction-count regression above 1%.

_{Only instruction counts gate. Wall clock is shown for context — on identical hardware it moves 4-20% run to run.}

_{Measured by tak — instruction-counted CLI benchmarks, stored in this repository's git notes.}

_{86d168375de5 vs bd9c6e287ea5 · measured on the runner, not pushed to the history.}