feat: dist upgrade --latest downloads and verifies the release from the feed, --expect pins the version (#161)

Files changed:
- CHANGES.md
- INSTALL.md
- VERSION
- instructions/upgrade-instance.md
- tools/CONTRACT.md
- tools/chemenu/commands/dist_cmd.py
- tools/chemenu/commands/version_cmd.py
- tools/chemenu/tests/test_cli.py
- tools/chemenu/tests/test_dist_upgrade.py
- tools/chemenu/version.py

CHANGES.md

@@ -59,13 +59,14 @@ concern - readable here, never shipped as something to parse.
 
 ---
 
-## 7.1.0-beta.31 - 2026-09-26 - new_page/type_resolver comments no longer claim only entities declare a layout:
+## 7.1.0-beta.32 - 2026-09-29 - dist upgrade --latest: one-command update from the release feed
 
 **Author:** Torben Nehmer
 
 <!-- wikitool:bumps -->
 **High impact**
 - wikitool: one data record per command - `-h`, index and CONTRACT.md render from cli_contract (Gitea #121 Phase 1)
+- dist upgrade --latest: one-command update from the release feed
 
 **Medium impact**
 - CalDAV task-tracker provider (Nextcloud Tasks, iOS Reminders); review reports unknown-value findings instead of skipping them
@@ -102,6 +103,50 @@ concern - readable here, never shipped as something to parse.
 - new_page/type_resolver comments no longer claim only entities declare a layout:
 <!-- /wikitool:bumps -->
 
+### dist upgrade --latest: one-command update from the release feed (Gitea #161)
+
+Updating a tarball instance took a manual detour: `version notes`, then fetching the `.tar.gz` and
+its `.sha256` from the release page by hand, then `dist upgrade <tarball>`. `dist upgrade --latest`
+now does the middle part. It asks the release feed (`update_url` from the stamp,
+`$WIKITOOL_UPDATE_URL` and `$WIKITOOL_UPDATE_TOKEN` as before) which release is latest, downloads
+the release's archive and checksum into a scratch directory, verifies the archive against the
+checksum, and hands over to the existing upgrade path unchanged - classification,
+`--keep-local`/`--take-release`, migration report and every refusal are the same code. `<source>`
+becomes optional; exactly one of it and `--latest` must be given.
+
+The order is what matters. The local preconditions run first, then the feed is asked, and the
+version it reports is judged **before any download**: already installed is a success no-op, an
+older version is a downgrade refusal, a `-beta.N` version needs `--pre`. Only then are the two
+assets looked up - by exact name, `chemenu-stack-<version>.tar.gz` and its `.sha256`, in the
+`assets` of the release object the version query already returned, using the feed's own
+`browser_download_url` values; no URL is composed. A release missing either asset is refused
+before the first download with the assets it does have and its release page named. The checksum
+is mandatory on this path (a `<source>` archive without a sibling `.sha256` is still only a
+WARN), and the archive's own `VERSION` must equal the feed's version, otherwise nothing is
+applied. `--dry-run` downloads and verifies too - classification needs the tree - and removes
+everything again; the scratch directory goes away on every exit.
+
+`--expect <version>` (only with `--latest`) closes the gap between reading the notes and applying
+the update: the feed only offers its *latest* release, so if a newer one appeared since
+`version notes` was read, the run refuses before downloading anything and names both versions.
+`instructions/upgrade-instance.md` passes the version from step 2 in the dry run and in the real
+run. The comparison is on parsed versions, so a `v` prefix does not matter.
+
+`$WIKITOOL_UPDATE_TOKEN` is sent to an asset download only when the asset URL has the feed's
+scheme, host and port, and as an unredirected header, so a redirect cannot carry it elsewhere.
+There is no https enforcement: the checksum comes from the same host as the archive and protects
+against transfer errors, not against a compromised feed - `INSTALL.md` says so.
+
+The asset names are a Python constant (`version.ARCHIVE_NAME`) that a test ties to
+`.gitea/workflows/release.yml`, so renaming them in one place fails the suite instead of the next
+upgrade. `dist upgrade` is now `network: yes` in its record and in the pinned set in `test_cli.py`,
+the `version check` record's "never reached implicitly" note names the one explicit exception, the
+`fetch_latest` docstring says "three commands", and `tools/CONTRACT.md` is regenerated. The tests
+run against a local `http.server` that logs every request and its `Authorization` header, so the
+token rule and the "no asset request before the checks pass" rule are asserted on the wire. The
+`upstream merge` pointers in the `dist upgrade` record and failure message stay as they are; they
+belong to the separate work on the clone path.
+
 ### new_page/type_resolver comments no longer claim only entities declare a layout:
 
 Two code comments - `new_page.py`'s module docstring and `TypeResolver.get_layout`'s - still said

INSTALL.md

@@ -152,12 +152,14 @@ tools/wikitool version         # was läuft hier, und woher kommt es
 tools/wikitool version check   # gibt es ein neueres Release?
 ```
 
-`version check` und `version notes` sind die einzigen Befehle, die ins Netz gehen, und beide
+`version check`, `version notes` und `dist upgrade --latest` sind die einzigen Befehle, die
-fragen denselben Release-Feed der Ursprungs-Instanz (`$WIKITOOL_UPDATE_URL` überschreibt; sonst
+ins Netz gehen, und alle drei fragen denselben Release-Feed der Ursprungs-Instanz
-der Wert aus dem Stamp). `version check` ist dafür da; `version notes` greift nur dann darauf
+(`$WIKITOOL_UPDATE_URL` überschreibt; sonst der Wert aus dem Stamp). `version check` ist dafür da;
-zurück, wenn die lokale `CHANGES.md` den Eintrag nicht hat - auf einer Instanz also immer, siehe
+`version notes` greift nur dann darauf zurück, wenn die lokale `CHANGES.md` den Eintrag nicht
-unten - und sagt vorher auf stderr, welche URL es fragt. Ein nicht erreichbarer Feed wird als
+hat - auf einer Instanz also immer, siehe unten - und sagt vorher auf stderr, welche URL es
-Fehler gemeldet - **nie** als „aktuell" und nie als „keine Notes".
+fragt; `dist upgrade` fragt den Feed nur, wenn `--latest` dasteht, und lädt dann auch das Release
+herunter (siehe „Eine Instanz aktualisieren"). Ein nicht erreichbarer Feed wird als Fehler
+gemeldet - **nie** als „aktuell" und nie als „keine Notes".
 
 **Was die Versionsnummer aussagt:** kompatibel ist, was in der *linkesten von Null
 verschiedenen Stelle* übereinstimmt. `0.1.3 → 0.1.4` ist ein sicheres Update, `0.1.3 → 0.2.0`
@@ -203,9 +205,32 @@ Agent-Sitzung ausgeführt wird; eine zweite Fassung derselben Schrittfolge an di
 genau die Kopie, die irgendwann auseinanderläuft. Wer den Lauf selbst fahren will, liest dieselbe
 Datei.
 
-Was dieses Dokument beiträgt, ist die Entscheidung *davor* - welches Release, ob überhaupt, woher
+Was dieses Dokument beiträgt, ist die Entscheidung *davor* - welches Release, ob überhaupt, und
-der Tarball kommt (§ „Version und Updates" und Weg A oben) - und der eine Sonderfall, den die
+wem die Instanz als Quelle vertraut - und zwei Sonderfälle, die die Instruktion nicht abdecken
-Instruktion nicht abdecken kann, weil es sie dort noch nicht gibt:
+kann, weil es sie dort noch nicht gibt.
+
+**Das Release kommt mit einem Befehl.** `tools/wikitool dist upgrade --latest --expect <version>`
+fragt den Release-Feed, lädt Tarball und `.sha256` in ein Arbeitsverzeichnis, prüft den Tarball
+gegen die Summe und wendet ihn an; das Arbeitsverzeichnis verschwindet bei jedem Ausgang wieder,
+auch bei `--dry-run`. `<version>` ist die, die `version notes` gedruckt hat: der Feed kennt nur
+sein *neuestes* Release, und `--expect` verweigert den Lauf **vor** dem Download, wenn inzwischen
+ein neueres erschienen ist, statt es ungelesen einzuspielen. Beides zusammen entscheidet vor dem
+Download über „schon aktuell", Downgrade und Vor-Release (`-beta.N` braucht `--pre`); fehlt dem
+Release der Tarball oder die Summe, bricht der Befehl vor dem ersten Download ab und nennt die
+Release-Seite. Wer offline arbeitet oder einen Tarball vom Betreiber bekommen hat, gibt statt
+`--latest` weiter die Datei an (`dist upgrade <tarball>`).
+
+**Was die Prüfsumme leistet - und was nicht.** Die `.sha256` liegt beim selben Feed wie der
+Tarball. Sie schützt vor einer beschädigten Übertragung, nicht vor einem Feed, der selbst
+kompromittiert ist: die Echtheit eines Releases beruht auf dem Vertrauen in den Host, dessen
+Feed die Instanz fragt (`update_url` im Stamp). Es gibt keinen https-Zwang; wer einen
+`http://`-Feed konfiguriert, tut das bewusst. `$WIKITOOL_UPDATE_TOKEN` geht nur an Downloads
+auf demselben Host wie der Feed.
+
+**Beim ersten Sprung auf ein Release, das `--latest` kennt, gibt es die Option in der Instanz
+noch nicht** - die Instruktion, die dort steht, gehört zum Release, das die Instanz verlässt.
+Dann den Tarball einmal von Hand holen (Weg A oben), prüfen und `dist upgrade <tarball>` geben;
+ab dem Release danach trägt die Instanz `--latest` selbst.
 
 **Beim ersten Sprung auf `4.5.0` oder höher gibt es `dist upgrade` in der Instanz noch nicht** -
 es kam erst mit `4.5.0`. Dann das Werkzeug aus dem entpackten *neuen* Tarball verwenden, gegen die
@@ -233,9 +258,9 @@ sind. Einer Instanz, die älter ist als `.wikitool-kb.json`, fehlt die Datei gan
 **Fallstricke.** Eine Instanz ohne lokale `.wikitool-release.json` (oder eine ohne `files`-Block,
 aus der Zeit vor `4.5.0`) hat für `dist upgrade` keine Basis, gegen die es eine lokale Änderung
 erkennen könnte, und verweigert den Tausch - dafür gibt es heute keine Reparatur.
-Der Befehl lädt selbst nichts herunter: `<tarball-oder-verzeichnis>` muss vorher aus Weg A
+Mit `<tarball-oder-verzeichnis>` lädt der Befehl selbst nichts herunter; die Datei muss vorher
-geholt werden, und ein Tarball muss genau ein Top-Level-Verzeichnis enthalten - die Form, in der
+aus Weg A geholt werden. Nur `--latest` lädt, und ein Tarball muss in beiden Fällen genau ein
-`.gitea/workflows/release.yml` es baut.
+Top-Level-Verzeichnis enthalten - die Form, in der `.gitea/workflows/release.yml` es baut.
 
 Vor `4.5.0` stand hier ein rein manueller Ablauf (Maschinerie von Hand kopieren, `kb/CONTRACT.md`
 eingeschlossen, sha256-Vergleich von Hand). `dist upgrade` ersetzt genau diesen Teil; wer ihn

VERSION

@@ -1 +1 @@
-7.1.0-beta.31
+7.1.0-beta.32

instructions/upgrade-instance.md

@@ -81,14 +81,25 @@ fresh clone ([bootstrap.md](bootstrap.md)), and not for the clone-with-upstream
    step 12's, run against the migration documents this instance already has. An `offered` upgrade
    listed separately blocks nothing and is decided later, in step 12.
 
-4. **Fetch the tarball and verify it.** `dist upgrade` downloads nothing; the file has to be
+4. **Nothing to fetch by hand.** `dist upgrade --latest` asks the release feed for the latest
-   there already. Take the `.tar.gz` and its `.sha256` from the release page found in step 2 and
+   release, downloads its `.tar.gz` and `.sha256` into a scratch directory, checks the archive
-   check them before unpacking. A tarball must unpack to exactly one top-level directory.
+   against the checksum and removes both again - all inside the calls of steps 5 to 7. Note the
+   version step 2's `version notes` printed: steps 5 to 7 pass it as `--expect`, so a release that
+   appeared in the meantime is refused before anything is downloaded, rather than applied unread.
+
+   The offline alternative is the tarball path: with the feed unreachable, or an archive the
+   operator supplies, take the `.tar.gz` and its `.sha256` from the release page named in step 2,
+   check the archive against the checksum before unpacking, and pass the file as `<tarball>`
+   where the steps below say `--latest --expect <version>`. A tarball must unpack to exactly one
+   top-level directory. The checksum comes from the same host as the archive, so it catches a
+   damaged transfer, not a compromised host - who is trusted to publish releases is the
+   operator's decision, made before this file starts ([INSTALL.md](../INSTALL.md) § "Version und
+   Updates").
 
 5. **Dry-run the swap and read all four counts:**
 
    ```bash
-   tools/wikitool dist upgrade <tarball> --dry-run
+   tools/wikitool dist upgrade --latest --expect <version from step 2> --dry-run
    ```
 
    `unchanged` / `new` / `locally changed` / `removed from the release`. `unchanged` needs no
@@ -115,7 +126,7 @@ fresh clone ([bootstrap.md](bootstrap.md)), and not for the clone-with-upstream
    file reset and another kept. Preview it before it writes:
 
    ```bash
-   tools/wikitool dist upgrade <tarball> --dry-run --take-release <path> [--take-release <path>]
+   tools/wikitool dist upgrade --latest --expect <version from step 2> --dry-run --take-release <path> [--take-release <path>]
    ```
 
    The preview marks every named path as one it would overwrite from the release, and a path that
@@ -134,7 +145,7 @@ fresh clone ([bootstrap.md](bootstrap.md)), and not for the clone-with-upstream
 
    ```bash
    git rev-parse --short HEAD          # the pre-swap commit; keep it
-   tools/wikitool dist upgrade <tarball> [--take-release <path>] [--keep-local]
+   tools/wikitool dist upgrade --latest --expect <version from step 2> [--take-release <path>] [--keep-local]
    ```
 
    It writes, and commits nothing.

tools/CONTRACT.md

@@ -2418,7 +2418,7 @@ Apply a stack update `dist export` produced - the write half of `version check`.
 
 **SYNOPSIS**
 
-- `wikitool dist upgrade <source> [--dry-run] [--keep-local] [--take-release <path>]... [--prune] [--pre]`
+- `wikitool dist upgrade (<source> | --latest [--expect <version>]) [--dry-run] [--keep-local] [--take-release <path>]... [--prune] [--pre]`
 
 **PROPERTIES**
 
@@ -2426,23 +2426,30 @@ Apply a stack update `dist export` produced - the write half of `version check`.
 - idempotent: no
 - atomic: Yes for every refusal - nothing is written. Once writing starts it is a plain sequential file copy with no partial-state cleanup: an interruption mid-copy (killed process, disk full) can leave the tree part-old, part-new
 - budget: counted
-- network: no
+- network: yes
 
 **EXAMPLES**
 
 - `tools/wikitool dist upgrade ../chemenu-7.1.0.tar.gz --dry-run`
 - `tools/wikitool dist upgrade ../chemenu-7.1.0.tar.gz`
 - `tools/wikitool dist upgrade ../chemenu-7.1.0.tar.gz --take-release tools/README.md`
+- `tools/wikitool dist upgrade --latest --expect 8.0.0 --dry-run`
 
 **EXIT STATUS**
 
 - 0    success
 - 0    The source's version equals the installed one - a no-op success
+- 1    Both `<source>` and `--latest`, or neither; or `--expect` without `--latest`
 - 1    Local `VERSION` missing, or no local `.wikitool-release.json` with a `files` block
 - 1    `.wikitool-kb.json` is missing
 - 1    A migration is already outstanding against the *installed* machinery
 - 1    The working tree is dirty
 - 1    `<source>` does not exist, fails its `.sha256`, or does not unpack to exactly one top-level directory
+- 1    `--latest`: the release feed cannot be reached, or answers with something that is not a release
+- 1    `--latest --expect`: the feed's latest release is another version than the one expected; nothing was downloaded
+- 1    `--latest`: the release publishes no archive or no `.sha256` under the expected name; nothing was downloaded
+- 1    `--latest`: an asset download fails, or the archive fails its `.sha256`
+- 1    `--latest`: the downloaded archive's `VERSION` is not the version the feed announced
 - 1    The source carries no `VERSION`, `.wikitool-release.json` or `files` block
 - 1    The source's version is older than the installed one, or a pre-release without `--pre`
 - 1    A `--take-release` path this run does not classify as locally changed - the one refusal a `--dry-run` also raises
@@ -2450,11 +2457,17 @@ Apply a stack update `dist export` produced - the write half of `version check`.
 
 **ON FAILURE**
 
+- Both `<source>` and `--latest`, or neither; or `--expect` without `--latest` -> Not transient - name exactly one source, and pass `--expect` only with `--latest`
 - Local `VERSION` missing, or no local `.wikitool-release.json` with a `files` block -> Not transient - fix the named precondition and retry. A checkout with shared git history takes stack updates with `wikitool upstream merge` instead
 - `.wikitool-kb.json` is missing -> Run `wikitool migrate baseline <version>`, then retry
 - A migration is already outstanding against the *installed* machinery -> Finish it first - `wikitool migrate status` names it - then retry
 - The working tree is dirty -> Commit or stash first, then retry
 - `<source>` does not exist, fails its `.sha256`, or does not unpack to exactly one top-level directory -> Fix the path or re-download the release archive, then retry
+- `--latest`: the release feed cannot be reached, or answers with something that is not a release -> Transient - retry once; then report the URL from the message, or take the release page's archive by hand and pass it as `<source>`
+- `--latest --expect`: the feed's latest release is another version than the one expected; nothing was downloaded -> Not transient - read `wikitool version notes` for the version the message names, then either expect that one or stop
+- `--latest`: the release publishes no archive or no `.sha256` under the expected name; nothing was downloaded -> Not transient - the message lists the assets present and the release page; report it there rather than upgrading without the checksum
+- `--latest`: an asset download fails, or the archive fails its `.sha256` -> Retry once; if it fails again, report the exact message - do not fall back to an unchecked archive
+- `--latest`: the downloaded archive's `VERSION` is not the version the feed announced -> Not transient - an inconsistent release; report it against the release page
 - The source carries no `VERSION`, `.wikitool-release.json` or `files` block -> Point `<source>` at a distribution export, then retry
 - The source's version is older than the installed one, or a pre-release without `--pre` -> Not transient - choose another source, or pass `--pre` for a pre-release
 - A `--take-release` path this run does not classify as locally changed - the one refusal a `--dry-run` also raises -> Correct it against the locally-changed list the refusal prints, then retry
@@ -2466,7 +2479,9 @@ Apply a stack update `dist export` produced - the write half of `version check`.
 
 **NOTES**
 
-- Never downloads anything: `<source>` is an already-fetched export directory or `.tar.gz` release archive. An archive is verified against a sibling `.sha256` if one is present (a missing one is a WARN, not a block) and must unpack to exactly one top-level directory - the shape `.gitea/workflows/release.yml` packs.
+- Exactly one of `<source>` and `--latest` names the release. `<source>` is an already-fetched export directory or `.tar.gz` release archive and touches no network: the archive is verified against a sibling `.sha256` if one is present (a missing one is a WARN, not a block) and must unpack to exactly one top-level directory - the shape `.gitea/workflows/release.yml` packs.
+- `--latest` asks the release feed (`update_url` of the local stamp, overridable with `$WIKITOOL_UPDATE_URL`; `$WIKITOOL_UPDATE_TOKEN` is sent along) which release is latest, checks that version - `--expect`, a downgrade, a pre-release without `--pre`, already installed - before any download, then downloads the archive and its `.sha256` into a scratch directory removed on every exit. The checksum is mandatory here (a release without one, or an archive that fails it, is an error, not a WARN) and the archive's own `VERSION` must equal the feed's version. The asset URLs are the feed's own `browser_download_url` values, and the token reaches an asset download only if it is on the feed's origin. The checksum protects against transfer errors, not against a feed that is itself compromised - authenticity is the trust in the feed's host.
+- `--expect <version>` (only with `--latest`) pins the release the feed may announce: a different latest version is refused before anything is downloaded. Pass the version `wikitool version notes` was read for, in the dry run and in the real run alike.
 - The write set is exactly the *new* `.wikitool-release.json`'s `files` block, minus what an export re-seeds from a blank template every time (`kb/log.md`, `raw/.gitkeep`) or seeds once and the instance owns from then on (`.wikitool-kb.json`, `CHANGES.md`), plus the stamp itself, always rewritten.
 - Every candidate path is classified against the *local* `.wikitool-release.json`'s recorded digest: unchanged is overwritten silently, absent from the old stamp is created, and locally modified or locally deleted is **never** silently overwritten.
 - Locally changed files abort the run with the full list; the abort text names the three answers with the command line filled in, and none of them is the default.
@@ -2478,13 +2493,14 @@ Apply a stack update `dist export` produced - the write half of `version check`.
 - Reports, but does not block on, a crossed compatibility boundary.
 - The local preconditions - `VERSION`, the release stamp, `.wikitool-kb.json`, no outstanding migration, a clean working tree - are checked before the source is read. Not being a git repository at all is a WARN, not a refusal.
 - Never touches git - no commit, no push.
-- `--dry-run` classifies and reports without writing; a pre-release (`-beta.N`) source needs `--pre`.
+- `--dry-run` classifies and reports without writing; a pre-release (`-beta.N`) source needs `--pre`. With `--latest` it still downloads and verifies the archive - that is the only way to classify - and removes it again.
 - An interrupted write is not resumed automatically: compare the tree against the printed classification and finish or revert by hand.
 - The closing report names `instructions/upgrade-instance.md`, which carries the order for everything after the swap and resumes at `instructions sync`.
 
 **SEE ALSO**
 
 - `wikitool version check` - finds out whether an update exists
+- `wikitool version notes` - the notes of the release `--expect` should name
 - `instructions/upgrade-instance.md` - the order after the swap
 - `INSTALL.md` § "Version und Updates" - which release, whether to take it, where the tarball comes from
 - `wikitool upstream merge` - the update path for a checkout with shared git history
@@ -2571,8 +2587,8 @@ Ask the origin's release feed whether a newer stack exists.
 **NOTES**
 
 - Asks the release feed for its latest release and compares it with `VERSION`: `state` is `current`, `update`, `migration` (the step crosses a compatibility boundary) or `ahead`.
-- The only command whose whole job is the network call - `version notes` reaches the same feed too, but only as a fallback on a distributed instance.
+- The only command whose whole job is the network call - `version notes` reaches the same feed too, but only as a fallback on a distributed instance, and `dist upgrade --latest` asks it which release to download.
-- Never reached implicitly from another command, needs no key, and times out after `--timeout` seconds (default 10).
+- Never reached implicitly from another command (`dist upgrade` asks only when passed `--latest`), needs no key, and times out after `--timeout` seconds (default 10).
 - The feed is `--url`, else `$WIKITOOL_UPDATE_URL`, else the release stamp's, else the built-in origin. `$WIKITOOL_UPDATE_TOKEN` is only needed if that feed is not readable anonymously.
 - For `update` or `migration` it prints that applying the release is a separate, manual step (`INSTALL.md` § "Eine Instanz aktualisieren").
 - Read-only; exempt from the Iteration Budget Gate.

tools/chemenu/commands/dist_cmd.py

@@ -736,8 +736,8 @@ def run_export(target: Path, dry_run: bool = False, origin: Optional[Origin] = N
 # modified/deleted file is never silently overwritten: the run aborts unless
 # `--keep-local` keeps it or `--take-release <path>` names it, which is the
 # difference between a file the instance means to carry and one that drifted.
-# This never calls a release feed; the caller supplies an already-downloaded
+# The classification never touches the network: the tree or archive it works
-# tree or archive.
+# on is either supplied by the caller or fetched by `--latest` beforehand.
 
 
 @dataclass(frozen=True)
@@ -867,6 +867,87 @@ def _resolved_source(source: Path):
         yield _extract_single_top_level_dir(source, Path(tmp))
 
 
+def _version_gate(
+    new_version: "version_mod.Version",
+    local_version: "version_mod.Version",
+    allow_pre: bool,
+    origin: str,
+) -> bool:
+    """The three version refusals shared by a source tree and the feed: a
+    candidate without `--pre`, a downgrade, an equal version. `True` means go
+    on; `False` means the run ended successfully as a no-op. `origin` names
+    what reported the version, for the message."""
+    if new_version.is_prerelease and not allow_pre:
+        fail(
+            f"{origin} reports {new_version}, a running candidate (-beta.N). "
+            "`.gitea/workflows/release.yml` never publishes one, so it can only come from a "
+            "dev checkout or a hand-made release - pass --pre if that is deliberate."
+        )
+    if new_version < local_version:
+        fail(f"{origin} reports {new_version}, older than the installed {local_version} - refusing a downgrade.")
+    if new_version == local_version:
+        success(f"Already at {local_version}. Nothing to do.")
+        return False
+    return True
+
+
+def _query_feed(
+    stamp: dict,
+    local_version: "version_mod.Version",
+    allow_pre: bool,
+    expect: Optional["version_mod.Version"],
+) -> Optional[tuple["version_mod.LatestRelease", str, Optional[str]]]:
+    """Ask the release feed which release is latest and decide, before any
+    download, whether there is anything to fetch. Returns the release with the
+    feed URL and token, or `None` when the installed version is already it."""
+    url = version_mod.update_url(stamp)
+    token = os.environ.get(version_mod.UPDATE_TOKEN_ENV, "").strip() or None
+    console.print(f"Asking the release feed {url}", highlight=False)
+    try:
+        release = version_mod.fetch_latest_assets(url, token)
+    except version_mod.VersionError as exc:
+        fail(str(exc))
+    if expect is not None and release.version != expect:
+        fail(
+            f"The feed's latest release is {release.version}, not the expected {expect} - "
+            "nothing was downloaded. The feed moved on since the notes were read, or "
+            f"the wrong version was named: read `wikitool version notes` for {release.version} "
+            "before deciding to go there instead."
+        )
+    if not _version_gate(release.version, local_version, allow_pre, "the release feed"):
+        return None
+    return release, url, token
+
+
+@contextmanager
+def _downloaded_source(release: "version_mod.LatestRelease", feed_url: str, token: Optional[str]):
+    """Yield the directory of the release the feed announced: download its
+    archive and checksum into a scratch directory, hold the archive to the
+    checksum (a missing checksum is an error, never a WARN), and unpack it.
+    A release without both assets is refused before the first download. The
+    scratch directory is removed on every exit, `--dry-run` included."""
+    archive_url, sum_url = _asset_urls(release)
+    with tempfile.TemporaryDirectory(prefix="wikitool-upgrade-") as tmp:
+        archive = Path(tmp) / release.archive_name
+        checksum = archive.with_name(archive.name + version_mod.CHECKSUM_SUFFIX)
+        for url, dest in ((archive_url, archive), (sum_url, checksum)):
+            console.print(f"Downloading {url}", highlight=False)
+            try:
+                version_mod.download_asset(url, dest, version_mod.token_for_asset(feed_url, url, token))
+            except version_mod.VersionError as exc:
+                fail(str(exc))
+        _verify_sha256_sidecar(archive)
+        yield _extract_single_top_level_dir(archive, Path(tmp) / "unpacked")
+
+
+def _asset_urls(release: "version_mod.LatestRelease") -> tuple[str, str]:
+    try:
+        return release.asset_urls()
+    except version_mod.VersionError as exc:
+        fail(str(exc))
+        raise  # unreachable: fail() raises typer.Exit
+
+
 def _git_working_tree_status() -> Optional[str]:
     """`git status --porcelain` for `config.ROOT`, or None if it is not a git
     repository at all - which is a valid, if unprotected, state for a tarball
@@ -907,7 +988,7 @@ def _resolve_take_release(
 
 
 def _refusal_for_blocked(
-    source: Path, undecided: list[str], classification: FileClassification
+    target: str, undecided: list[str], classification: FileClassification
 ) -> str:
     """The abort text for blocked paths no flag has answered for.
 
@@ -927,9 +1008,9 @@ def _refusal_for_blocked(
         f"{len(undecided)} locally changed file(s) (listed above) would be silently "
         f"overwritten. Nothing was written, and none of these three is the default:\n"
         f"  - take the release's version and discard the local change:\n"
-        f"      dist upgrade {rel_path(source)} --take-release {paths}\n"
+        f"      dist upgrade {target} --take-release {paths}\n"
         f"  - keep every local change and upgrade around them ({kept_again}):\n"
-        f"      dist upgrade {rel_path(source)} --keep-local\n"
+        f"      dist upgrade {target} --keep-local\n"
         f"  - reconcile them by hand first, then re-run."
     )
 
@@ -984,8 +1065,8 @@ def _report_plan(
     path="dist upgrade",
     summary="Apply a stack update `dist export` produced - the write half of `version check`.",
     synopsis=(cli_contract.Variant(
-        usage="dist upgrade <source> [--dry-run] [--keep-local] [--take-release <path>]... "
+        usage="dist upgrade (<source> | --latest [--expect <version>]) [--dry-run] "
-        "[--prune] [--pre]",
+        "[--keep-local] [--take-release <path>]... [--prune] [--pre]",
     ),),
     properties=cli_contract.Properties(
         effect=cli_contract.Effect.WRITE,
@@ -994,12 +1075,28 @@ def _report_plan(
         "sequential file copy with no partial-state cleanup: an interruption mid-copy "
         "(killed process, disk full) can leave the tree part-old, part-new",
         budget=cli_contract.Budget.COUNTED,
+        network=cli_contract.Network.YES,
     ),
     notes=(
-        "Never downloads anything: `<source>` is an already-fetched export directory or "
+        "Exactly one of `<source>` and `--latest` names the release. `<source>` is an "
-        "`.tar.gz` release archive. An archive is verified against a sibling `.sha256` if one "
+        "already-fetched export directory or `.tar.gz` release archive and touches no network: "
-        "is present (a missing one is a WARN, not a block) and must unpack to exactly one "
+        "the archive is verified against a sibling `.sha256` if one is present (a missing one "
-        "top-level directory - the shape `.gitea/workflows/release.yml` packs.",
+        "is a WARN, not a block) and must unpack to exactly one top-level directory - the "
+        "shape `.gitea/workflows/release.yml` packs.",
+        "`--latest` asks the release feed (`update_url` of the local stamp, overridable with "
+        "`$WIKITOOL_UPDATE_URL`; `$WIKITOOL_UPDATE_TOKEN` is sent along) which release is "
+        "latest, checks that version - `--expect`, a downgrade, a pre-release without `--pre`, "
+        "already installed - before any download, then downloads the archive and its "
+        "`.sha256` into a scratch directory removed on every exit. The checksum is mandatory "
+        "here (a release without one, or an archive that fails it, is an error, not a WARN) "
+        "and the archive's own `VERSION` must equal the feed's version. The asset URLs are the "
+        "feed's own `browser_download_url` values, and the token reaches an asset download only "
+        "if it is on the feed's origin. The checksum protects against transfer errors, not "
+        "against a feed that is itself compromised - authenticity is the trust in the feed's "
+        "host.",
+        "`--expect <version>` (only with `--latest`) pins the release the feed may announce: a "
+        "different latest version is refused before anything is downloaded. Pass the version "
+        "`wikitool version notes` was read for, in the dry run and in the real run alike.",
         "The write set is exactly the *new* `.wikitool-release.json`'s `files` block, minus "
         "what an export re-seeds from a blank template every time (`kb/log.md`, "
         "`raw/.gitkeep`) or seeds once and the instance owns from then on "
@@ -1029,7 +1126,8 @@ def _report_plan(
         "Not being a git repository at all is a WARN, not a refusal.",
         "Never touches git - no commit, no push.",
         "`--dry-run` classifies and reports without writing; a pre-release (`-beta.N`) source "
-        "needs `--pre`.",
+        "needs `--pre`. With `--latest` it still downloads and verifies the archive - that is "
+        "the only way to classify - and removes it again.",
         "An interrupted write is not resumed automatically: compare the tree against the "
         "printed classification and finish or revert by hand.",
         "The closing report names `instructions/upgrade-instance.md`, which carries the order "
@@ -1041,6 +1139,11 @@ def _report_plan(
             reaction="",
             code=0,
         ),
+        cli_contract.Failure(
+            cause="Both `<source>` and `--latest`, or neither; or `--expect` without `--latest`",
+            reaction="Not transient - name exactly one source, and pass `--expect` only with "
+            "`--latest`",
+        ),
         cli_contract.Failure(
             cause="Local `VERSION` missing, or no local `.wikitool-release.json` with a `files` "
             "block",
@@ -1064,6 +1167,34 @@ def _report_plan(
             "one top-level directory",
             reaction="Fix the path or re-download the release archive, then retry",
         ),
+        cli_contract.Failure(
+            cause="`--latest`: the release feed cannot be reached, or answers with something "
+            "that is not a release",
+            reaction="Transient - retry once; then report the URL from the message, or take the "
+            "release page's archive by hand and pass it as `<source>`",
+        ),
+        cli_contract.Failure(
+            cause="`--latest --expect`: the feed's latest release is another version than the "
+            "one expected; nothing was downloaded",
+            reaction="Not transient - read `wikitool version notes` for the version the message "
+            "names, then either expect that one or stop",
+        ),
+        cli_contract.Failure(
+            cause="`--latest`: the release publishes no archive or no `.sha256` under the "
+            "expected name; nothing was downloaded",
+            reaction="Not transient - the message lists the assets present and the release page; "
+            "report it there rather than upgrading without the checksum",
+        ),
+        cli_contract.Failure(
+            cause="`--latest`: an asset download fails, or the archive fails its `.sha256`",
+            reaction="Retry once; if it fails again, report the exact message - do not fall back "
+            "to an unchecked archive",
+        ),
+        cli_contract.Failure(
+            cause="`--latest`: the downloaded archive's `VERSION` is not the version the feed "
+            "announced",
+            reaction="Not transient - an inconsistent release; report it against the release page",
+        ),
         cli_contract.Failure(
             cause="The source carries no `VERSION`, `.wikitool-release.json` or `files` block",
             reaction="Point `<source>` at a distribution export, then retry",
@@ -1091,12 +1222,14 @@ def _report_plan(
         "tools/wikitool dist upgrade ../chemenu-7.1.0.tar.gz --dry-run",
         "tools/wikitool dist upgrade ../chemenu-7.1.0.tar.gz",
         "tools/wikitool dist upgrade ../chemenu-7.1.0.tar.gz --take-release tools/README.md",
+        "tools/wikitool dist upgrade --latest --expect 8.0.0 --dry-run",
     ),
     never=(
         "Never treat any of the three answers to locally changed files as the default.",
     ),
     see_also=(
         "`wikitool version check` - finds out whether an update exists",
+        "`wikitool version notes` - the notes of the release `--expect` should name",
         "`instructions/upgrade-instance.md` - the order after the swap",
         "`INSTALL.md` § \"Version und Updates\" - which release, whether to take it, where "
         "the tarball comes from",
@@ -1106,8 +1239,17 @@ def _report_plan(
 ))
 @app.command("upgrade")
 def upgrade_command(
-    source: Path = typer.Argument(
+    source: Optional[Path] = typer.Argument(
-        ..., help="An extracted distribution directory, or a release .tar.gz archive"
+        None, help="An extracted distribution directory, or a release .tar.gz archive - or use --latest"
+    ),
+    latest: bool = typer.Option(
+        False, "--latest",
+        help="Download the release the feed announces as latest instead of naming a <source>",
+    ),
+    expect: Optional[str] = typer.Option(
+        None, "--expect",
+        help="With --latest: refuse, before downloading anything, unless the feed's latest release "
+        "is this version (the one `version notes` was read for)",
     ),
     dry_run: bool = typer.Option(
         False, "--dry-run", help="Classify and report, without writing anything"
@@ -1133,8 +1275,10 @@ def upgrade_command(
 ):
     """Apply a stack update `dist export` produced - the write half of `version check`.
     \f
-    Never downloads anything: `source` is an already-fetched
+    `source` is an already-fetched export directory or `.tar.gz` archive;
-    export directory or `.tar.gz` archive. Writes exactly the new release
+    `--latest` instead downloads the archive and its checksum from the
+    release feed (`--expect <version>` pins which release that may be) and
+    holds it to the checksum before anything else. Writes exactly the new release
     stamp's `files` block, minus what an export re-seeds every time
     (`kb/log.md`, `raw/.gitkeep`) or seeds once and the instance owns from
     then on (`.wikitool-kb.json`, `CHANGES.md`), classifying every candidate
@@ -1155,19 +1299,41 @@ def upgrade_command(
         take_release=take_release,
         prune=prune,
         allow_pre=allow_pre,
+        latest=latest,
+        expect=expect,
     )
 
 
 def run_upgrade(
-    source: Path,
+    source: Optional[Path] = None,
     dry_run: bool = False,
     keep_local: bool = False,
     take_release: Optional[Sequence[str]] = None,
     prune: bool = False,
     allow_pre: bool = False,
+    latest: bool = False,
+    expect: Optional[str] = None,
 ) -> None:
     """The upgrade itself, free of Typer's option objects - see `run_export`
     for why this split exists."""
+    if latest == (source is not None):
+        fail(
+            "Name exactly one source: `<source>` (an export directory or a release .tar.gz "
+            "already on disk) or `--latest` (the release the feed announces). "
+            + ("Both were given." if latest else "Neither was given.")
+        )
+        return
+    expected_version = None
+    if expect is not None:
+        if not latest:
+            fail("--expect only makes sense with --latest: it pins the release the feed may announce.")
+            return
+        try:
+            expected_version = version_mod.Version.parse(expect)
+        except version_mod.VersionError as exc:
+            fail(f"--expect: {exc}")
+            return
+
     try:
         local_version = version_mod.read_version()
     except version_mod.VersionError as exc:
@@ -1223,7 +1389,19 @@ def run_upgrade(
         )
         return
 
-    with _resolved_source(source) as new_root:
+    feed = None
+    if latest:
+        feed = _query_feed(old_stamp, local_version, allow_pre, expected_version)
+        if feed is None:
+            return
+        release, feed_url, feed_token = feed
+        source_cm = _downloaded_source(release, feed_url, feed_token)
+        target = f"--latest --expect {release.version}"
+    else:
+        source_cm = _resolved_source(source)
+        target = rel_path(source)
+
+    with source_cm as new_root:
         version_path = new_root / version_mod.VERSION_FILENAME
         if not version_path.is_file():
             fail(f"{rel_path(new_root)} has no VERSION - not a distribution export.")
@@ -1234,18 +1412,16 @@ def run_upgrade(
             fail(str(exc))
             return
 
-        if new_version.is_prerelease and not allow_pre:
+        if feed is not None and new_version != feed[0].version:
             fail(
-                f"{new_version} is a running candidate (-beta.N). `.gitea/workflows/release.yml` "
+                f"The downloaded archive's VERSION says {new_version}, but the feed announced "
-                "never publishes one, so a candidate tree can only come from a dev checkout by "
+                f"{feed[0].version} (tag {feed[0].tag}) - this release is inconsistent, so "
-                "hand - pass --pre if that is deliberate."
+                "nothing was applied. Report it against the release page"
+                + (f" {feed[0].html_url}" if feed[0].html_url else "")
+                + "."
             )
             return
-        if new_version < local_version:
+        if not _version_gate(new_version, local_version, allow_pre, "the source"):
-            fail(f"{new_version} is older than the installed {local_version} - refusing a downgrade.")
-            return
-        if new_version == local_version:
-            success(f"Already at {local_version}. Nothing to do.")
             return
 
         stamp_path = new_root / version_mod.RELEASE_STAMP_FILENAME
@@ -1289,7 +1465,7 @@ def run_upgrade(
 
         undecided = [path for path in classification.blocked if path not in taken]
         if undecided and not keep_local:
-            fail(_refusal_for_blocked(source, undecided, classification))
+            fail(_refusal_for_blocked(target, undecided, classification))
             return
 
         to_write = sorted(classification.unchanged + classification.new + sorted(taken))

tools/chemenu/commands/version_cmd.py

@@ -29,6 +29,9 @@ number means, and `instructions/dev/version-parts.md` for the candidate model):
   stderr before asking and takes `--offline`. Both need no key, both time
   out, and a feed that cannot be reached is reported as an error rather than
   silently answered as "up to date" or "no notes".
+- `dist upgrade --latest` reaches the same feed as a third, equally explicit
+  caller: it asks which release is latest, then downloads that release's
+  assets. Only `version_mod` talks to the feed; this module is not involved.
 """
 from __future__ import annotations
 
@@ -158,8 +161,10 @@ def show_command(
         "is `current`, `update`, `migration` (the step crosses a compatibility boundary) or "
         "`ahead`.",
         "The only command whose whole job is the network call - `version notes` reaches the "
-        "same feed too, but only as a fallback on a distributed instance.",
+        "same feed too, but only as a fallback on a distributed instance, and `dist upgrade "
-        "Never reached implicitly from another command, needs no key, and times out after "
+        "--latest` asks it which release to download.",
+        "Never reached implicitly from another command (`dist upgrade` asks only when passed "
+        "`--latest`), needs no key, and times out after "
         "`--timeout` seconds (default 10).",
         "The feed is `--url`, else `$WIKITOOL_UPDATE_URL`, else the release stamp's, else the "
         "built-in origin. `$WIKITOOL_UPDATE_TOKEN` is only needed if that feed is not readable "

tools/chemenu/tests/test_cli.py

@@ -337,7 +337,8 @@ def test_every_gated_record_shows_its_re_run_after_exit_42():
 def test_network_yes_is_exactly_the_commands_that_can_reach_outside_this_checkout():
     """Gitea #144: `network:` means *any* reach outside this checkout - an HTTP call
     `wikitool` makes itself, or a git operation against a remote (fetch/ls-remote/push) -
-    not only the two `version_cmd.py` used to claim exclusivity for. Pinned as an explicit
+    not only the two `version_cmd.py` used to claim exclusivity for. `dist upgrade` is on the list
+    since `--latest`, which asks the release feed and downloads from it. Pinned as an explicit
     set so a command gaining or losing that reach is a deliberate edit here, not a silent
     drift between the property and what the command actually does."""
     expected = {
@@ -346,6 +347,7 @@ def test_network_yes_is_exactly_the_commands_that_can_reach_outside_this_checkou
         "upstream merge",
         "version check",
         "version notes",
+        "dist upgrade",
         "review",
         "task new",
         "task list",

tools/chemenu/tests/test_dist_upgrade.py

@@ -4,9 +4,13 @@ execution, and every refusal before anything is written. See Gitea #7."""
 from __future__ import annotations
 
 import hashlib
+import http.server
 import json
+import shutil
 import subprocess
 import tarfile
+import tempfile
+import threading
 from pathlib import Path
 
 import pytest
@@ -586,3 +590,426 @@ def test_tarball_sha256_sidecar_mismatch_is_refused(instance, tmp_path):
 
     with pytest.raises(typer.Exit):
         dist_cmd.run_upgrade(archive)
+
+
+# --- --latest: the release feed ---------------------------------------------
+#
+# A real `http.server` on 127.0.0.1 rather than a fetcher stub: the download
+# path is `urllib` streaming into a file, and the same-origin token rule is a
+# statement about which requests carry which header - both only observable on
+# the wire. Every server records `(path, Authorization)` for each request.
+
+
+class FeedServer:
+    def __init__(self) -> None:
+        self.routes: dict[str, tuple[int, bytes]] = {}
+        self.requests: list[tuple[str, str | None]] = []
+        outer = self
+
+        class Handler(http.server.BaseHTTPRequestHandler):
+            def do_GET(self):  # noqa: N802 - http.server's name
+                outer.requests.append((self.path, self.headers.get("Authorization")))
+                status, body = outer.routes.get(self.path, (404, b"not found"))
+                self.send_response(status)
+                self.send_header("Content-Length", str(len(body)))
+                self.end_headers()
+                self.wfile.write(body)
+
+            def log_message(self, *args):  # silence the test output
+                pass
+
+        self.httpd = http.server.HTTPServer(("127.0.0.1", 0), Handler)
+        self.thread = threading.Thread(target=self.httpd.serve_forever, kwargs={"poll_interval": 0.01}, daemon=True)
+        self.thread.start()
+
+    @property
+    def base(self) -> str:
+        return f"http://127.0.0.1:{self.httpd.server_address[1]}"
+
+    def stop(self) -> None:
+        self.httpd.shutdown()
+        self.httpd.server_close()
+
+    def paths(self) -> list[str]:
+        return [path for path, _ in self.requests]
+
+    def asset_paths(self) -> list[str]:
+        return [path for path in self.paths() if path.startswith("/assets/")]
+
+
+@pytest.fixture
+def feed(monkeypatch: pytest.MonkeyPatch):
+    server = FeedServer()
+    monkeypatch.setenv("WIKITOOL_UPDATE_URL", f"{server.base}/feed")
+    yield server
+    server.stop()
+
+
+@pytest.fixture
+def other_origin():
+    server = FeedServer()
+    yield server
+    server.stop()
+
+
+@pytest.fixture
+def scratch_tmp(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Path:
+    """Redirect `tempfile` into a directory the test can inspect afterwards."""
+    scratch = tmp_path / "scratch-tmp"
+    scratch.mkdir()
+    monkeypatch.setattr(tempfile, "tempdir", str(scratch))
+    return scratch
+
+
+def _publish(
+    feed: FeedServer,
+    tmp_path: Path,
+    version: str,
+    files: dict[str, str] | None = None,
+    *,
+    tag: str | None = None,
+    inner_version: str | None = None,
+    checksum: str | None = "ok",
+    archive: bool = True,
+    asset_server: FeedServer | None = None,
+) -> str:
+    """Serve `version` as the feed's latest release and return its archive name.
+
+    `inner_version` is what the archive's own VERSION says (default: the same),
+    `checksum` is `"ok"`, `"wrong"` or `None` for no `.sha256` asset."""
+    name = f"chemenu-stack-{version}"
+    tree = _release(
+        tmp_path, f"served-{name}", inner_version or version,
+        files or {"AGENTS.md": "core v2\n", "tools/wikitool": "#!/bin/sh\n"},
+    )
+    packed = tmp_path / f"{name}.tar.gz"
+    with tarfile.open(packed, "w:gz") as tf:
+        tf.add(tree, arcname=name)
+    data = packed.read_bytes()
+    digest = hashlib.sha256(data).hexdigest() if checksum == "ok" else "0" * 64
+    holder = asset_server or feed
+    assets = []
+    if archive:
+        holder.routes[f"/assets/{name}.tar.gz"] = (200, data)
+        assets.append({"name": f"{name}.tar.gz", "browser_download_url": f"{holder.base}/assets/{name}.tar.gz"})
+    if checksum is not None:
+        holder.routes[f"/assets/{name}.tar.gz.sha256"] = (200, f"{digest}  {name}.tar.gz\n".encode())
+        assets.append({
+            "name": f"{name}.tar.gz.sha256",
+            "browser_download_url": f"{holder.base}/assets/{name}.tar.gz.sha256",
+        })
+    feed.routes["/feed"] = (
+        200,
+        json.dumps({
+            "tag_name": tag or f"v{version}",
+            "html_url": f"{feed.base}/releases/tag/v{version}",
+            "assets": assets,
+        }).encode(),
+    )
+    return name
+
+
+def _stamp_version(instance: Path) -> str:
+    return json.loads((instance / version_mod.RELEASE_STAMP_FILENAME).read_text())["version"]
+
+
+def test_latest_downloads_verifies_and_applies_the_feeds_release(instance, tmp_path, feed, scratch_tmp):
+    name = _publish(feed, tmp_path, "1.1.0")
+
+    dist_cmd.run_upgrade(latest=True)
+
+    assert (instance / "AGENTS.md").read_text(encoding="utf-8") == "core v2\n"
+    assert _stamp_version(instance) == "1.1.0"
+    assert feed.paths() == ["/feed", f"/assets/{name}.tar.gz", f"/assets/{name}.tar.gz.sha256"]
+    assert list(scratch_tmp.iterdir()) == []
+    recorded = json.loads((instance / version_mod.RELEASE_STAMP_FILENAME).read_text())["files"]
+    assert recorded
+    for relative, digest in recorded.items():
+        assert _digest((instance / relative).read_text(encoding="utf-8")) == digest
+
+
+def test_latest_yields_the_same_tree_as_the_archive_it_downloaded(instance, tmp_path, feed, monkeypatch):
+    name = _publish(feed, tmp_path, "1.1.0")
+    served = tmp_path / f"{name}.tar.gz"
+    snapshot = tmp_path / "instance-copy"
+    shutil.copytree(instance, snapshot)
+
+    dist_cmd.run_upgrade(latest=True)
+    via_feed = {p.relative_to(instance): p.read_bytes() for p in instance.rglob("*") if p.is_file()}
+
+    monkeypatch.setattr(config, "ROOT", snapshot)
+    dist_cmd.run_upgrade(served)
+    via_archive = {p.relative_to(snapshot): p.read_bytes() for p in snapshot.rglob("*") if p.is_file()}
+
+    assert via_feed == via_archive
+
+
+def test_latest_dry_run_downloads_writes_nothing_and_cleans_up(instance, tmp_path, feed, scratch_tmp):
+    name = _publish(feed, tmp_path, "1.1.0")
+
+    dist_cmd.run_upgrade(latest=True, dry_run=True)
+
+    assert (instance / "AGENTS.md").read_text(encoding="utf-8") == "core\n"
+    assert _stamp_version(instance) == "1.0.0"
+    assert f"/assets/{name}.tar.gz" in feed.paths()
+    assert list(scratch_tmp.iterdir()) == []
+
+
+def test_latest_already_current_is_a_no_op_without_any_download(instance, tmp_path, feed):
+    _publish(feed, tmp_path, "1.0.0")
+
+    dist_cmd.run_upgrade(latest=True)
+
+    assert feed.paths() == ["/feed"]
+    assert _stamp_version(instance) == "1.0.0"
+
+
+def test_latest_older_than_installed_is_a_downgrade_refusal_before_any_download(instance, tmp_path, feed, capsys):
+    _publish(feed, tmp_path, "0.9.0")
+
+    with pytest.raises(typer.Exit) as excinfo:
+        dist_cmd.run_upgrade(latest=True)
+
+    assert excinfo.value.exit_code == 1
+    assert "downgrade" in capsys.readouterr().out
+    assert feed.asset_paths() == []
+
+
+def test_latest_prerelease_needs_pre_and_is_refused_before_any_download(instance, tmp_path, feed):
+    _publish(feed, tmp_path, "1.1.0-beta.1")
+
+    with pytest.raises(typer.Exit):
+        dist_cmd.run_upgrade(latest=True)
+    assert feed.asset_paths() == []
+
+    dist_cmd.run_upgrade(latest=True, allow_pre=True)
+    assert _stamp_version(instance) == "1.1.0-beta.1"
+
+
+@pytest.mark.parametrize("missing", ["checksum", "archive"])
+def test_latest_release_without_an_asset_is_refused_before_any_download(
+    instance, tmp_path, feed, capsys, missing
+):
+    _publish(
+        feed, tmp_path, "1.1.0",
+        checksum=None if missing == "checksum" else "ok",
+        archive=missing != "archive",
+    )
+
+    with pytest.raises(typer.Exit) as excinfo:
+        dist_cmd.run_upgrade(latest=True)
+
+    assert excinfo.value.exit_code == 1
+    out = " ".join(capsys.readouterr().out.split())
+    assert "chemenu-stack-1.1.0.tar.gz" in out
+    assert "assets present" in out
+    assert "/releases/tag/v1.1.0" in out
+    assert feed.asset_paths() == []
+    assert _stamp_version(instance) == "1.0.0"
+
+
+def test_latest_checksum_mismatch_writes_nothing_and_cleans_up(instance, tmp_path, feed, scratch_tmp, capsys):
+    _publish(feed, tmp_path, "1.1.0", checksum="wrong")
+
+    with pytest.raises(typer.Exit) as excinfo:
+        dist_cmd.run_upgrade(latest=True)
+
+    assert excinfo.value.exit_code == 1
+    assert "does not match" in " ".join(capsys.readouterr().out.split())
+    assert (instance / "AGENTS.md").read_text(encoding="utf-8") == "core\n"
+    assert _stamp_version(instance) == "1.0.0"
+    assert list(scratch_tmp.iterdir()) == []
+
+
+def test_latest_archive_version_that_differs_from_the_feed_is_refused(instance, tmp_path, feed, scratch_tmp, capsys):
+    _publish(feed, tmp_path, "1.1.0", inner_version="1.2.0")
+
+    with pytest.raises(typer.Exit) as excinfo:
+        dist_cmd.run_upgrade(latest=True)
+
+    assert excinfo.value.exit_code == 1
+    out = " ".join(capsys.readouterr().out.split())
+    assert "1.2.0" in out and "1.1.0" in out
+    assert _stamp_version(instance) == "1.0.0"
+    assert list(scratch_tmp.iterdir()) == []
+
+
+def test_latest_asset_download_error_is_reported_with_its_url(instance, tmp_path, feed, capsys):
+    name = _publish(feed, tmp_path, "1.1.0")
+    del feed.routes[f"/assets/{name}.tar.gz"]
+
+    with pytest.raises(typer.Exit) as excinfo:
+        dist_cmd.run_upgrade(latest=True)
+
+    assert excinfo.value.exit_code == 1
+    assert f"/assets/{name}.tar.gz answered HTTP 404" in " ".join(capsys.readouterr().out.split())
+    assert _stamp_version(instance) == "1.0.0"
+
+
+def test_latest_unreachable_feed_is_an_error_naming_the_url(instance, monkeypatch, capsys):
+    monkeypatch.setenv("WIKITOOL_UPDATE_URL", "http://127.0.0.1:1/feed")
+
+    with pytest.raises(typer.Exit) as excinfo:
+        dist_cmd.run_upgrade(latest=True)
+
+    assert excinfo.value.exit_code == 1
+    assert "Could not reach http://127.0.0.1:1/feed" in " ".join(capsys.readouterr().out.split())
+
+
+def test_latest_respects_the_local_preconditions_before_asking_the_feed(instance, tmp_path, feed):
+    _publish(feed, tmp_path, "1.1.0")
+    (instance / "AGENTS.md").write_text("locally edited\n", encoding="utf-8")
+    subprocess.run(["git", "init", "-q"], cwd=instance, check=True)
+
+    with pytest.raises(typer.Exit):
+        dist_cmd.run_upgrade(latest=True)
+
+    assert feed.requests == []
+
+
+def test_latest_blocked_refusal_names_the_pinned_latest_invocation(instance, tmp_path, feed, capsys):
+    _publish(feed, tmp_path, "1.1.0")
+    (instance / "AGENTS.md").write_text("locally edited\n", encoding="utf-8")
+
+    with pytest.raises(typer.Exit):
+        dist_cmd.run_upgrade(latest=True)
+
+    out = " ".join(capsys.readouterr().out.split())
+    assert "dist upgrade --latest --expect 1.1.0 --take-release AGENTS.md" in out
+    assert "dist upgrade --latest --expect 1.1.0 --keep-local" in out
+
+
+def test_source_and_latest_together_or_neither_is_refused_before_any_check(instance, tmp_path, feed):
+    release = _release(tmp_path, "release", "1.1.0", {"AGENTS.md": "core\n"})
+
+    with pytest.raises(typer.Exit) as both:
+        dist_cmd.run_upgrade(release, latest=True)
+    with pytest.raises(typer.Exit) as neither:
+        dist_cmd.run_upgrade()
+
+    assert both.value.exit_code == 1 and neither.value.exit_code == 1
+    assert feed.requests == []
+
+
+# --- --expect ---------------------------------------------------------------
+
+
+@pytest.mark.parametrize("spelling", ["1.1.0", "v1.1.0"])
+def test_expect_matching_the_feed_proceeds(instance, tmp_path, feed, spelling):
+    _publish(feed, tmp_path, "1.1.0")
+
+    dist_cmd.run_upgrade(latest=True, expect=spelling)
+
+    assert _stamp_version(instance) == "1.1.0"
+
+
+def test_expect_mismatch_is_refused_before_any_download_naming_both_versions(instance, tmp_path, feed, capsys):
+    _publish(feed, tmp_path, "1.2.0")
+
+    with pytest.raises(typer.Exit) as excinfo:
+        dist_cmd.run_upgrade(latest=True, expect="1.1.0")
+
+    assert excinfo.value.exit_code == 1
+    out = " ".join(capsys.readouterr().out.split())
+    assert "1.2.0" in out and "1.1.0" in out and "version notes" in out
+    assert feed.asset_paths() == []
+    assert _stamp_version(instance) == "1.0.0"
+
+
+def test_expect_mismatch_wins_over_an_already_current_install(instance, tmp_path, feed):
+    _publish(feed, tmp_path, "1.0.0")
+
+    with pytest.raises(typer.Exit):
+        dist_cmd.run_upgrade(latest=True, expect="1.1.0")
+
+
+def test_expect_without_latest_is_refused(instance, tmp_path, feed):
+    release = _release(tmp_path, "release", "1.1.0", {"AGENTS.md": "core\n"})
+
+    with pytest.raises(typer.Exit) as excinfo:
+        dist_cmd.run_upgrade(release, expect="1.1.0")
+
+    assert excinfo.value.exit_code == 1
+    assert feed.requests == []
+
+
+def test_expect_that_is_not_a_version_is_refused(instance, feed):
+    with pytest.raises(typer.Exit):
+        dist_cmd.run_upgrade(latest=True, expect="latest")
+    assert feed.requests == []
+
+
+# --- the token --------------------------------------------------------------
+
+
+def test_token_goes_to_the_feed_and_same_origin_assets_only(instance, tmp_path, feed, other_origin, monkeypatch):
+    monkeypatch.setenv("WIKITOOL_UPDATE_TOKEN", "s3cret")
+    name = _publish(feed, tmp_path, "1.1.0")
+
+    dist_cmd.run_upgrade(latest=True)
+
+    assert {auth for _, auth in feed.requests} == {"token s3cret"}
+    assert f"/assets/{name}.tar.gz" in feed.paths()
+    assert other_origin.requests == []
+
+
+def test_token_is_withheld_from_an_asset_on_another_origin(instance, tmp_path, feed, other_origin, monkeypatch):
+    monkeypatch.setenv("WIKITOOL_UPDATE_TOKEN", "s3cret")
+    _publish(feed, tmp_path, "1.1.0", asset_server=other_origin)
+
+    dist_cmd.run_upgrade(latest=True)
+
+    assert _stamp_version(instance) == "1.1.0"
+    assert feed.requests == [("/feed", "token s3cret")]
+    assert len(other_origin.requests) == 2
+    assert {auth for _, auth in other_origin.requests} == {None}
+
+
+@pytest.mark.parametrize(
+    "feed_url, asset_url, sent",
+    [
+        ("https://git.example/api/v1/releases/latest", "https://git.example/dl/a.tar.gz", True),
+        ("https://git.example/api/v1/releases/latest", "https://git.example:443/dl/a.tar.gz", True),
+        ("https://git.example/api/v1/releases/latest", "http://git.example/dl/a.tar.gz", False),
+        ("https://git.example/api/v1/releases/latest", "https://cdn.example/dl/a.tar.gz", False),
+        ("http://git.example:3000/x", "http://git.example:3001/x", False),
+    ],
+)
+def test_token_for_asset_compares_scheme_host_and_port(feed_url, asset_url, sent):
+    assert version_mod.token_for_asset(feed_url, asset_url, "t") == ("t" if sent else None)
+    assert version_mod.token_for_asset(feed_url, asset_url, None) is None
+
+
+# --- the asset names --------------------------------------------------------
+
+
+def test_release_asset_names_match_the_workflow():
+    workflow = Path(__file__).resolve().parents[3] / ".gitea" / "workflows" / "release.yml"
+    if not workflow.is_file():
+        pytest.skip("a distributed instance carries no release workflow")
+    text = workflow.read_text(encoding="utf-8")
+
+    archive = version_mod.ARCHIVE_NAME.format(version="${VERSION}")
+    stem = archive.removesuffix(".tar.gz")
+    assert f'name="{stem}"' in text
+    assert archive.replace(stem, "${name}") in text
+    assert (archive + version_mod.CHECKSUM_SUFFIX).replace(stem, "${name}") in text
+
+
+def test_fetch_latest_assets_reads_urls_off_the_release_and_skips_malformed_entries():
+    payload = json.dumps({
+        "tag_name": "v1.1.0",
+        "assets": [
+            {"name": "a.tar.gz", "browser_download_url": "https://h/a"},
+            {"name": "no-url"},
+            "not an object",
+        ],
+    }).encode()
+
+    release = version_mod.fetch_latest_assets("https://h/feed", fetcher=lambda u, t, to: payload)
+
+    assert release.version == version_mod.Version.parse("1.1.0")
+    assert release.tag == "v1.1.0"
+    assert release.assets == {"a.tar.gz": "https://h/a"}
+    with pytest.raises(version_mod.VersionError, match="assets present: a.tar.gz"):
+        release.asset_urls()

tools/chemenu/version.py

@@ -37,7 +37,9 @@ import functools
 import json
 import os
 import re
+import shutil
 import urllib.error
+import urllib.parse
 import urllib.request
 from dataclasses import dataclass
 from pathlib import Path
@@ -349,12 +351,15 @@ def fetch_latest(
 
     The network call sits behind `fetcher` so every caller above this line -
     and every test - can run without a network. This is the one place that
-    talks to the **release feed**, and only two commands reach it: `version
+    talks to the **release feed**, and only three commands reach it: `version
-    check`, whose whole job it is, and `version notes` on a *distributed*
+    check`, whose whole job it is, `version notes` on a *distributed*
     instance, whose local `CHANGES.md` is a stub with no entry to print (see
-    `fetch_latest_notes`). Neither is implicit - `check` exists for the call,
+    `fetch_latest_notes`), and `dist upgrade --latest`, which asks the feed
-    and `notes` announces the URL it is asking before it asks, on stderr, and
+    which release to download (see `fetch_latest_assets`). None is implicit -
-    takes `--offline` for a caller that wants none of it.
+    `check` exists for the call, `notes` announces the URL it is asking before
+    it asks, on stderr, and takes `--offline` for a caller that wants none of
+    it, and `upgrade` reaches the feed only when the operator passes
+    `--latest`.
     """
     fetch = fetcher or _urlopen_fetch
     try:
@@ -462,6 +467,120 @@ def fetch_latest_notes(
     return version, body, (str(html_url) if html_url else None)
 
 
+# --- release assets --------------------------------------------------------
+#
+# `dist upgrade --latest` downloads the two assets `.gitea/workflows/release.yml`
+# attaches to every release. The names are that workflow's `name=` line plus
+# `.tar.gz` / `.tar.gz.sha256`; `test_release_asset_names_match_the_workflow`
+# ties this constant to the workflow so one cannot move without the other.
+
+ARCHIVE_NAME = "chemenu-stack-{version}.tar.gz"
+CHECKSUM_SUFFIX = ".sha256"
+DOWNLOAD_TIMEOUT = 60.0
+
+
+@dataclass(frozen=True)
+class LatestRelease:
+    """What the feed's latest release offers: its version, its tag as the feed
+    spells it, its own page, and every asset as `name -> download URL`."""
+
+    version: Version
+    tag: str
+    html_url: Optional[str]
+    assets: dict[str, str]
+
+    @property
+    def archive_name(self) -> str:
+        return ARCHIVE_NAME.format(version=self.version)
+
+    def asset_urls(self) -> tuple[str, str]:
+        """`(archive URL, checksum URL)`, read off the release object and never
+        composed. Raises `VersionError` naming the release page when either is
+        missing - an upgrade without its checksum is refused, not downgraded to
+        an unchecked one."""
+        archive = self.archive_name
+        wanted = (archive, archive + CHECKSUM_SUFFIX)
+        missing = [name for name in wanted if name not in self.assets]
+        if missing:
+            present = ", ".join(sorted(self.assets)) or "none"
+            page = f" - see the release page {self.html_url}" if self.html_url else ""
+            raise VersionError(
+                f"release {self.tag} does not publish {' and '.join(missing)} "
+                f"(assets present: {present}){page}"
+            )
+        return self.assets[wanted[0]], self.assets[wanted[1]]
+
+
+def fetch_latest_assets(
+    url: str,
+    token: Optional[str] = None,
+    timeout: float = 10.0,
+    fetcher: Optional[Fetcher] = None,
+) -> LatestRelease:
+    """`fetch_latest`'s version plus the release's assets, from the one
+    response - the asset URLs are the feed's own `browser_download_url`
+    values, never a path this code composes (AGENTS.md invariant 7)."""
+    version, captured = _fetch_latest_object(url, token, timeout, fetcher)
+    assets: dict[str, str] = {}
+    raw_assets = captured.get("assets")
+    if isinstance(raw_assets, list):
+        for entry in raw_assets:
+            if not isinstance(entry, dict):
+                continue
+            name = str(entry.get("name") or "").strip()
+            download = str(entry.get("browser_download_url") or "").strip()
+            if name and download:
+                assets[name] = download
+    html_url = captured.get("html_url") or captured.get("url")
+    return LatestRelease(
+        version=version,
+        tag=str(captured.get("tag_name") or "").strip(),
+        html_url=str(html_url) if html_url else None,
+        assets=assets,
+    )
+
+
+def _origin(url: str) -> tuple[str, str, int]:
+    parts = urllib.parse.urlsplit(url)
+    scheme = parts.scheme.lower()
+    default = {"http": 80, "https": 443}.get(scheme, 0)
+    return scheme, (parts.hostname or "").lower(), parts.port or default
+
+
+def token_for_asset(feed_url: str, asset_url: str, token: Optional[str]) -> Optional[str]:
+    """The token to send with an asset download: `token` when the asset is on
+    the feed's own origin (scheme, host, port), `None` otherwise. An asset URL
+    is data from a JSON answer, so the credential does not follow it to
+    another host."""
+    return token if token and _origin(feed_url) == _origin(asset_url) else None
+
+
+def download_asset(
+    url: str,
+    dest: Path,
+    token: Optional[str] = None,
+    timeout: float = DOWNLOAD_TIMEOUT,
+) -> None:
+    """Stream `url` into `dest`. `timeout` is a socket timeout per read, not a
+    deadline for the whole transfer. The token goes out as an *unredirected*
+    header, so a redirect to another host does not carry it along. Every
+    failure is a `VersionError` naming the URL."""
+    request = urllib.request.Request(url)
+    if token:
+        request.add_unredirected_header("Authorization", f"token {token}")
+    try:
+        with urllib.request.urlopen(request, timeout=timeout) as response:  # noqa: S310 - URL from the feed
+            with dest.open("wb") as out:
+                shutil.copyfileobj(response, out)
+    except urllib.error.HTTPError as exc:
+        hint = ""
+        if exc.code in (401, 403):
+            hint = f" - the download needs authentication; set ${UPDATE_TOKEN_ENV}"
+        raise VersionError(f"{url} answered HTTP {exc.code}{hint}") from exc
+    except (urllib.error.URLError, OSError, TimeoutError) as exc:
+        raise VersionError(f"Could not download {url}: {exc}") from exc
+
+
 # --- CHANGES.md ------------------------------------------------------------
 #
 # The changelog is prose and stays the author's job. What is mechanical is the