feat(extension): derive the version as unpadded CalVer (milestone 318 step 8)

`1.0.<minutes since 2020>` -> `YYYY.M.D.HHMM` UTC, from the commit time of
the newest change to a packaged extension file. Same clock and same commit as
before; readable instead of opaque, and the same value the rest of the family
derives.

The hold on this step was two questions about AMO, and Mozilla's own docs
answer both:

    ^(0|[1-9][0-9]{0,8})([.](0|[1-9][0-9]{0,8})){0,3}$

  1. four all-numeric segments -> ACCEPTED ({0,3} more after the first).
  2. leading zeros              -> REJECTED. A segment is the single digit
     `0` or starts 1-9, so `08` and `0201` are refused. MDN says it in prose
     too: "Non-zero numbers must not include a leading zero."

So the documented fallback applies, extension only: the same numbers rendered
without the family's zero-padding. `2026.08.29.0201` and `2026.8.29.201` are
one value in two renderings — rule 148 defines comparison as numeric per
segment, under which they are equal — so nothing already published is
reordered, and left-padding each segment recovers the family string exactly.
HHMM stays one segment because AMO allows at most four.

The transition is safe in the other direction too: 2026 > 1, so every CalVer
outranks every published 1.0.x. build.yml's downgrade guard confirms it.

Also in scope:

* MAJOR.MINOR is gone. `cmd_major_minor`, `cmd_patch` and VERSION_EPOCH go
  with it, the committed version in manifest.json / package.json is now
  wholly inert, and ci.yml's MAJOR.MINOR-agreement check is retired rather
  than left running beside a fact that stopped existing (rule 22).
* ci.yml's `extension-version` lane now asserts Mozilla's regex verbatim
  instead of a loose `^[0-9]+(\.[0-9]+)*$` — which would have passed the
  padded shape. It also asserts YYYY.M.D.HHMM, because AMO would accept a
  regression to `1.0.<minutes>` while that orders below everything signed
  since. Checking here is the point: AMO 409s on re-signing, so a version it
  rejects is burned and cannot be reused.
* `artifacts.sh version extension` delegates to packaging.sh, so the two
  cannot answer differently. The direction matches the existing one —
  artifacts.sh already asks packaging.sh for the extension's path set.

#3156 is what makes this commit safe to make: packaging.sh is in web's path
set, so the web revision moves with the extension version and build-web
rebuilds instead of republishing an image bundling the previous XPI.

Scribe #3138.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.forgejo/workflows/build.yml

@@ -75,18 +75,23 @@ jobs:
           fetch-depth: 0
 
       # The version is DERIVED, not read from the repo (milestone 271 step 4,
-      # cut over 2026-08-27). `packaging.sh version` returns MAJOR.MINOR from
-      # manifest.json plus a patch component that is the commit TIME of the
-      # newest change to a PACKAGED extension file, in minutes since
-      # 2020-01-01 — family rule 149, never a commit count, which orders by
+      # cut over 2026-08-27). `packaging.sh version` returns `YYYY.M.D.HHMM`
+      # UTC — the commit TIME of the newest change to a PACKAGED extension
+      # file, per family rule 148/149. Never a commit count, which orders by
       # branch rather than by recency.
       #
-      # The committed "version" in manifest.json / package.json no longer
-      # decides anything: the stamp step below overwrites it in the working
-      # tree before web-ext ever reads it. It is deliberately NOT committed
-      # back — the commit carrying the bump would itself be a change to the
-      # extension and would move the version again. The repo holds the source;
-      # the build derives the label.
+      # Unpadded, and only here: AMO's grammar rejects a leading zero, so the
+      # extension renders rule 148's numbers without the family's padding
+      # (milestone 318 step 8). Same value, one character narrower per segment;
+      # ci.yml's extension-version lane checks the string against Mozilla's
+      # published regex before this job ever calls AMO.
+      #
+      # The committed "version" in manifest.json / package.json decides NOTHING
+      # — not even a MAJOR.MINOR prefix, which step 8 removed. The stamp step
+      # below overwrites it in the working tree before web-ext ever reads it,
+      # and it is deliberately NOT committed back: the commit carrying the bump
+      # would itself be a change to the extension and would move the version
+      # again. The repo holds the source; the build derives the label.
       - name: Derive extension version
         id: extver
         run: |

.forgejo/workflows/ci.yml

@@ -2,7 +2,7 @@ name: CI
 
 # CI lanes per FabledRulebook/forgejo.md "CI philosophy":
 #   - lint: ruff only, no dep install — fast-fail for the common lint bounce.
-#   - extension-version: the derived version resolves and MAJOR.MINOR agrees.
+#   - extension-version: the derived version resolves and is a shape AMO takes.
 #   - backend-lint-and-test: `pytest -m "not integration"`, no service containers.
 #   - frontend-build: vitest unit + vite build.
 #   - integration: pgvector + redis service containers; alembic + `pytest -m integration`.
@@ -58,9 +58,12 @@ jobs:
   # the extension.yml suite runs on node:24-slim, which is exactly why
   # version.spec.js sticks to packaging.sh's git-free subcommands.
   #   1. the derivation actually resolves on this commit
-  #   2. MAJOR.MINOR agrees between the two files — the one part still hand-set,
-  #      and packaging.sh reads it from manifest.json ALONE, so a divergence
-  #      ships a version package.json disagrees with
+  #   2. the derived string is one AMO will accept, checked against Mozilla's
+  #      own published grammar rather than a loose "digits and dots"
+  #
+  # The MAJOR.MINOR-agreement check that used to be (2) is gone with milestone
+  # 318 step 8: the committed version no longer seeds anything, so there is no
+  # hand-set part left for the two files to disagree about.
   #
   # Deliberately NOT checked here: that the derived value beats what has already
   # been signed. That guard belongs in build.yml, where it compares against the
@@ -85,27 +88,38 @@ jobs:
           # busybox sh on the act_runner — no bashisms (family rule).
           VERSION=$(sh extension/scripts/packaging.sh version)
           echo "derived: $VERSION"
-          # The shape AMO accepts, and the shape build.yml will stamp.
-          if ! echo "$VERSION" | grep -qE '^[0-9]+(\.[0-9]+)*$'; then
-            echo "ERROR: derived version '$VERSION' is not plain dotted-numeric."
-            echo "AMO would reject it, and build.yml stamps it verbatim."
+
+          # Mozilla's published grammar for AMO, transcribed verbatim from
+          # MDN's manifest.json/version page:
+          #
+          #     ^(0|[1-9][0-9]{0,8})([.](0|[1-9][0-9]{0,8})){0,3}$
+          #
+          # Not the looser `^[0-9]+(\.[0-9]+)*$` this lane used to carry. That
+          # one passes `2026.08.29.0201`, which AMO REJECTS — a segment must be
+          # the single digit 0 or start 1-9 — and it also passes five segments,
+          # where AMO allows four. Both would surface as a failed sign with the
+          # version already burned: AMO 409s on re-signing, so a rejected value
+          # cannot be reclaimed and cannot be reused. This lane is the cheap
+          # place to find out. (#3138, milestone 318 step 8.)
+          if ! echo "$VERSION" | grep -qE '^(0|[1-9][0-9]{0,8})(\.(0|[1-9][0-9]{0,8})){0,3}$'; then
+            echo "ERROR: derived version '$VERSION' is not a version AMO accepts."
+            echo "AMO's grammar: ^(0|[1-9][0-9]{0,8})([.](0|[1-9][0-9]{0,8})){0,3}$"
+            echo "Most likely cause: a zero-padded segment (08, 0201). The rest"
+            echo "of the family pads; the extension must not — see packaging.sh."
             exit 1
           fi
-          mm() { grep -E '"version"' "$1" | head -1 | sed -E 's/.*"version"[[:space:]]*:[[:space:]]*"([0-9]+\.[0-9]+).*/\1/'; }
-          MAN=$(mm extension/manifest.json)
-          PKG=$(mm extension/package.json)
-          test -n "$MAN" || { echo "ERROR: no parseable version in extension/manifest.json"; exit 1; }
-          test -n "$PKG" || { echo "ERROR: no parseable version in extension/package.json"; exit 1; }
-          if [ "$MAN" != "$PKG" ]; then
-            echo "ERROR: MAJOR.MINOR disagrees between the two files."
-            echo "  extension/manifest.json = $MAN  <- packaging.sh reads MAJOR.MINOR from here"
-            echo "  extension/package.json  = $PKG"
-            echo "Only MAJOR.MINOR is hand-set. The patch component is derived from"
-            echo "commit time and overwritten at build time, so the committed patch"
-            echo "numbers are inert — but MAJOR.MINOR still ships. Set both the same."
+
+          # ...and the shape this project actually derives. AMO would happily
+          # take `1.0.3500147` too, so the grammar check alone would not notice
+          # a regression to the pre-318 shape — which orders BELOW everything
+          # signed since, and is unrecoverable once Firefox has the higher one.
+          if ! echo "$VERSION" | grep -qE '^20[0-9][0-9]\.[0-9]{1,2}\.[0-9]{1,2}\.[0-9]{1,4}$'; then
+            echo "ERROR: derived version '$VERSION' is not YYYY.M.D.HHMM."
+            echo "Rule 148's CalVer is what build.yml signs; the old"
+            echo "1.0.<minutes> shape would order below every ext-2026.* release."
             exit 1
           fi
-          echo "OK: MAJOR.MINOR $MAN, derived version $VERSION"
+          echo "OK: derived version $VERSION"
 
   backend-lint-and-test:
     runs-on: python-ci

ci-requirements.md

@@ -71,12 +71,25 @@ per `docs/process.md`'s "add deps to the image when used by >1 project".
   published bytes?"*, not *"is this file copied in?"* — which is why the script
   keeps two lists rather than one.
 - **The shipped extension version is derived, not committed.** It is the commit
-  TIME of the newest packaged-extension change (minutes since 2020-01-01, per
-  family rule 149 — never a commit count, which orders by branch rather than by
-  recency). `build.yml`'s `sign-extension` computes it and stamps it into
-  `extension/manifest.json` + `package.json` in the working tree before signing;
-  the stamp is never committed. Treat the version in the repo as a base: only
-  its MAJOR.MINOR is read, and its patch component is inert.
+  TIME of the newest packaged-extension change, rendered `YYYY.M.D.HHMM` UTC
+  (family rules 148/149 — never a commit count, which orders by branch rather
+  than by recency). `build.yml`'s `sign-extension` computes it and stamps it
+  into `extension/manifest.json` + `package.json` in the working tree before
+  signing; the stamp is never committed. The version in the repo is **wholly
+  inert** — since milestone 318 step 8 there is no hand-set MAJOR.MINOR either.
+- **The extension is the one artifact that does not zero-pad, and that is not a
+  drift** (#3138). Mozilla's grammar for AMO is
+  `^(0|[1-9][0-9]{0,8})([.](0|[1-9][0-9]{0,8})){0,3}$` — a segment is the single
+  digit `0` or starts 1-9, and there are at most four. `2026.08.29.0201` is
+  rejected; `2026.8.29.201` is the same value one character narrower per
+  segment, and rule 148 defines comparison as numeric per segment, so nothing is
+  reordered. `ci.yml`'s `extension-version` lane asserts the derived string
+  against that exact regex, plus a `YYYY.M.D.HHMM` shape check that would catch
+  a regression to the pre-318 `1.0.<minutes>` — which AMO would accept and which
+  orders below everything already signed. Checking here is the whole point: AMO
+  409s on re-signing, so a version it rejects is burned and cannot be reused.
+  `scripts/artifacts.sh version extension` **delegates** to `packaging.sh` so
+  the two cannot answer differently.
 - Every job that derives anything checks out with `fetch-depth: 0` — all four
   `build.yml` jobs, `ci.yml`'s `extension-version` and `backend-lint-and-test`
   (for `tests/test_artifact_paths.py` and `test_artifact_identity.py`), and

extension/README.md

@@ -38,27 +38,42 @@ npm run build                # unsigned XPI in web-ext-artifacts/
 - [ ] Subscriptions list: popup → "Sources" tab → list renders
 - [ ] Check now: click play icon on source row → no error toast
 
-## Versioning — don't hand-edit the patch number
+## Versioning — the committed number decides nothing
 
 The shipped version is **derived**, not committed. `scripts/packaging.sh
-version` returns `MAJOR.MINOR` from `manifest.json` plus a patch component
-that is the commit *time* of the newest change to a packaged extension file,
-in minutes since 2020-01-01. `build.yml` computes it and stamps it into both
+version` returns `YYYY.M.D.HHMM` in UTC: the commit *time* of the newest change
+to a packaged extension file. `build.yml` computes it and stamps it into both
 `manifest.json` and `package.json` at build time. The stamp is never
 committed — the commit carrying it would itself be a change to the extension,
 which would move the version again.
 
 So:
 
-- **Editing the patch number does nothing.** It is overwritten before web-ext
-  ever reads it. There is no bump to make, and none to forget.
-- **MAJOR.MINOR is still yours.** It carries the deliberate meaning, it is read
-  from `manifest.json` alone, and CI fails the `extension-version` lane if the
-  two files disagree on it.
+- **Editing the version does nothing.** All of it is overwritten before web-ext
+  ever reads it. There is no bump to make, and none to forget. There is no
+  hand-set part left either: MAJOR.MINOR went away with milestone 318 step 8.
 - `npm run build` locally produces an XPI labelled with the *committed*
   version, since nothing stamped it. Fine for loading into a test profile; not
   what ships.
 
+**Why the extension is the one artifact that does not zero-pad.** Every other
+FC artifact emits rule 148's `YYYY.MM.DD.HHMM`. AMO will not take it: Mozilla's
+grammar for addons.mozilla.org is
+
+```
+^(0|[1-9][0-9]{0,8})([.](0|[1-9][0-9]{0,8})){0,3}$
+```
+
+— each segment is the single digit `0` or starts 1-9, so `08` and `0201` are
+rejected, and at most four segments are allowed. The extension therefore emits
+**the same numbers unpadded**: `2026.8.29.201` where the rest of the family
+says `2026.08.29.0201`. Rule 148 already defines comparison as numeric per
+segment, under which the two are equal, so nothing is reordered by the choice
+and left-padding each segment recovers the family string exactly. `ci.yml`'s
+`extension-version` lane checks the derived string against that regex on every
+push — the cheap place to find out, because AMO 409s on re-signing and a
+rejected version is burned for good.
+
 Why commit time and not a commit count: a count is per-branch, so `dev` and
 `main` count different histories of the same code and their versions end up
 ordered by which branch accumulated more commits rather than by which is newer.

extension/scripts/packaging.sh

@@ -60,7 +60,7 @@ NOT_PACKAGED_BUILD='web-ext-artifacts node_modules'
 NOT_VERSION_RELEVANT='package.json package-lock.json README.md .gitignore vitest.config.js test test/**'
 
 usage() {
-  echo "usage: packaging.sh {ignore|pathspec|version|major-minor|patch}" >&2
+  echo "usage: packaging.sh {ignore|pathspec|version}" >&2
   exit 2
 }
 
@@ -86,36 +86,48 @@ cmd_pathspec() {
   echo
 }
 
-# MAJOR.MINOR stays hand-set in manifest.json — it's the part that carries
-# deliberate meaning. Only the patch component is derived.
-cmd_major_minor() {
-  root=$(git rev-parse --show-toplevel)
-  grep -E '"version"' "$root/extension/manifest.json" \
-    | head -1 \
-    | sed -E 's/.*"version"[[:space:]]*:[[:space:]]*"([0-9]+)\.([0-9]+).*/\1.\2/'
+# Strip leading zeros from one segment, leaving at least one digit.
+#
+# This exists for AMO and nothing else. Mozilla's version grammar for
+# addons.mozilla.org is documented as
+#
+#     ^(0|[1-9][0-9]{0,8})([.](0|[1-9][0-9]{0,8})){0,3}$
+#
+# — each segment is either the single digit `0` or starts 1-9, so `08` and
+# `0201` are rejected outright, while `0` itself is fine. MDN states it in
+# prose too: "Non-zero numbers must not include a leading zero."
+#
+# POSIX sh has no trim-loop, hence the while.
+unpad() {
+  s=$1
+  while [ "${#s}" -gt 1 ]; do
+    case "$s" in
+      0*) s=${s#0} ;;
+      *)  break ;;
+    esac
+  done
+  printf '%s' "$s"
 }
 
-# 2020-01-01T00:00:00Z — the anchor for the derived patch component. Fixed
-# forever; moving it would renumber every version downwards.
-VERSION_EPOCH=1577836800
-
-# Minutes since VERSION_EPOCH of the LATEST commit that touched a PACKAGED
-# extension file.
+# The extension's version: `YYYY.M.D.HHMM`, UTC, derived from the commit TIME
+# of the newest change to a PACKAGED extension file.
 #
-# Time-derived, per family rule 149: an artifact's ordering key must never be a
-# commit count. A count is per-branch — `dev` and `main` count different
-# histories of the same code — so the moment BOTH channels publish, their
-# versions order by which branch accumulated more commits rather than by which
-# is newer. A squash-merge makes that permanent: main gains one commit where dev
-# gained five, so dev climbs away from main and a dev install can never cross
-# back. That is Roundtable's 2026-08-24 incident (`versionCode` was the branch's
-# commit count) in a different repo. Measured here on 2026-08-27: main=23,
-# dev=24 under the old formula — one apart, which is exactly how the inversion
-# stays invisible until it strands somebody.
+# THE ONE DELIBERATE DEPARTURE FROM THE FAMILY SHAPE, and it is a rendering
+# difference only. Rule 148 says `YYYY.MM.DD.HHMM` zero-padded, and every other
+# FC artifact emits exactly that. AMO's grammar (see unpad) forbids the padding,
+# and AMO is not negotiable: a rejected version is burned, since AMO 409s on
+# re-signing a version it has already seen. So the extension emits THE SAME
+# NUMBERS unpadded — 2026.08.29.0201 and 2026.8.29.201 are one value in two
+# renderings, and rule 148 already specifies comparison as numeric per segment,
+# under which they are equal. Nothing published is reordered by the choice, and
+# left-padding each segment recovers the family string exactly.
+#
+# HHMM is one segment, not two, because AMO allows at most FOUR. Unpadded that
+# reads oddly (00:14 -> `14`, midnight -> `0`) but stays strictly increasing
+# within a day, which is all the ordering needs.
 #
 # Why the commit's time and not the build's:
-#   * MONOTONIC — max() over a set that only ever gains members. Verified
-#     across all 24 extension-touching commits: zero non-monotonic steps.
+#   * MONOTONIC — max() over a set that only ever gains members.
 #   * STABLE while the extension is unchanged, so an unchanged extension keeps
 #     its version, the ext-<version> signature cache still hits, and AMO is
 #     called once per extension CHANGE rather than once per push. Build-time
@@ -126,32 +138,40 @@ VERSION_EPOCH=1577836800
 #     produced for byte-identical code. Same code, same version, one signing.
 #   * REPRODUCIBLE — any checkout of a commit yields that commit's version.
 #
+# Never a commit count (family rule 149): a count is per-branch, so `dev` and
+# `main` count different histories of the same code and order by which branch
+# accumulated more commits rather than by which is newer. A squash-merge makes
+# that permanent. Roundtable's 2026-08-24 incident, in a different repo.
+#
 # Requires real history: a depth-1 clone sees one commit and will derive a wrong
 # (too low) value. Every consumer must check out with fetch-depth: 0.
-cmd_patch() {
+#
+# Formatted through git rather than date(1): busybox date does not reliably
+# accept `-d @<epoch>`, and git's --date=format-local is available wherever git
+# is. TZ=UTC so the value does not depend on the runner's timezone.
+cmd_version() {
   root=$(git rev-parse --show-toplevel)
   # Unquoted on purpose: the pathspec must word-split into separate args.
   # Globbing is already off script-wide (set -euf above).
   # shellcheck disable=SC2046
-  ts=$(cd "$root" && git log --format=%ct HEAD -- extension/ $(cmd_pathspec) \
-       | sort -n | tail -1)
-  if [ -z "$ts" ]; then
+  sha=$(cd "$root" && git log --format='%ct %H' HEAD -- extension/ $(cmd_pathspec) \
+        | sort -n | tail -1 | cut -d' ' -f2)
+  if [ -z "$sha" ]; then
     echo "packaging.sh: no commit touches a packaged extension file" >&2
     exit 1
   fi
-  echo $(( (ts - VERSION_EPOCH) / 60 ))
-}
-
-cmd_version() {
-  echo "$(cmd_major_minor).$(cmd_patch)"
+  padded=$(cd "$root" && TZ=UTC git show -s --format=%cd \
+           --date='format-local:%Y.%m.%d.%H%M' "$sha")
+  # Rebinding the function's own positional params, which are unused here.
+  # shellcheck disable=SC2046
+  set -- $(echo "$padded" | tr '.' ' ')
+  echo "$(unpad "$1").$(unpad "$2").$(unpad "$3").$(unpad "$4")"
 }
 
 [ $# -ge 1 ] || usage
 case "$1" in
-  ignore)      cmd_ignore ;;
-  pathspec)    cmd_pathspec ;;
-  version)     cmd_version ;;
-  major-minor) cmd_major_minor ;;
-  patch)       cmd_patch ;;
-  *)           usage ;;
+  ignore)   cmd_ignore ;;
+  pathspec) cmd_pathspec ;;
+  version)  cmd_version ;;
+  *)        usage ;;
 esac

extension/test/version.spec.js

@@ -8,10 +8,10 @@ const EXT_DIR = path.join(path.dirname(fileURLToPath(import.meta.url)), '..')
 const read = (name) => JSON.parse(readFileSync(path.join(EXT_DIR, name), 'utf8'))
 const readText = (...seg) => readFileSync(path.join(EXT_DIR, ...seg), 'utf8')
 
-// Only the git-free subcommands are exercised here: `version`/`patch` shell out
-// to git, and the extension lane runs on node:24-bookworm-slim which may not
-// ship it. Those two are covered where git is guaranteed — ci.yml and build.yml
-// run on ci-python.
+// Only the git-free subcommands are exercised here: `version` shells out to
+// git, and the extension lane runs on node:24-bookworm-slim which may not ship
+// it. That one is covered where git is guaranteed — ci.yml's extension-version
+// lane and build.yml both run on ci-python.
 const packaging = (cmd) =>
   execFileSync('sh', [path.join(EXT_DIR, 'scripts', 'packaging.sh'), cmd], {
     cwd: EXT_DIR,
@@ -145,28 +145,33 @@ describe('consumers delegate rather than keeping their own copy', () => {
 })
 
 describe('extension version', () => {
-  const majorMinor = (v) => v.split('.').slice(0, 2).join('.')
+  // Mozilla's published grammar for addons.mozilla.org, transcribed from MDN's
+  // manifest.json/version page. Each segment is the single digit 0 or starts
+  // 1-9 — so no leading zeros — and there are at most four of them.
+  const AMO = /^(0|[1-9][0-9]{0,8})(\.(0|[1-9][0-9]{0,8})){0,3}$/
 
-  it('keeps the hand-set MAJOR.MINOR in lockstep across both files', () => {
-    // Narrowed from full-string equality at milestone 271 step 5. Since step 4
-    // the patch component is derived from commit time and stamped into both
-    // files at build time, so the committed patch numbers are inert — nothing
-    // reads them and they are not what ships. Asserting on them would fail for
-    // a difference that changes nothing.
+  it('keeps a committed version AMO would accept, though it ships nothing', () => {
+    // The committed value is wholly inert since milestone 318 step 8: there is
+    // no hand-set MAJOR.MINOR left for packaging.sh to read, and build.yml
+    // stamps the derived string over both files before web-ext sees them.
     //
-    // MAJOR.MINOR is the opposite: still hand-set, still shipped, and
-    // packaging.sh reads it from manifest.json ALONE. Let the two diverge and
-    // the extension ships a version package.json disagrees with, with no other
-    // signal.
-    expect(majorMinor(read('manifest.json').version))
-      .toBe(majorMinor(read('package.json').version))
+    // It is still asserted, for one reason: `npm run build` locally packages
+    // whatever is committed, so a value AMO would reject turns a local build
+    // into a confusing failure with no CI signal ahead of it. ci.yml checks
+    // the same grammar against the DERIVED value, which is the one AMO sees.
+    for (const file of ['manifest.json', 'package.json']) {
+      expect(read(file).version, `${file} version is not AMO-shaped`).toMatch(AMO)
+    }
   })
 
-  it('uses a plain dotted numeric version AMO will accept', () => {
-    // The committed value seeds MAJOR.MINOR, so it still has to parse even
-    // though its patch component never ships. ci.yml asserts the same shape on
-    // the DERIVED value, which is the one AMO actually sees.
-    expect(read('package.json').version).toMatch(/^\d+(\.\d+)*$/)
+  it('rejects the zero-padded family shape, which is why the extension unpads', () => {
+    // Guards the reason for the exception, not just its result. If this ever
+    // starts passing, someone has loosened the pattern and the next sign burns
+    // an AMO version to find out. (#3138.)
+    expect('2026.08.29.0201').not.toMatch(AMO)
+    expect('2026.8.29.201').toMatch(AMO)
+    // Five segments: AMO allows four.
+    expect('2026.8.29.2.1').not.toMatch(AMO)
   })
 
   it('declares manifest v3', () => {

scripts/artifacts.sh

@@ -170,6 +170,21 @@ cmd_revision() {
 # exists — at which point two lanes derive different answers for one source
 # and the shared-signature property is lost.
 cmd_version() {
+  # The extension is the one artifact this script does not FORMAT, only route.
+  # AMO's version grammar forbids leading zeros, so the extension emits the
+  # same numbers unpadded (#3138) — a rendering exception, documented in
+  # packaging.sh beside the signing step that has to obey it. Delegating keeps
+  # one answer per artifact: `artifacts.sh version extension` and
+  # `packaging.sh version` cannot drift into two.
+  #
+  # The direction is deliberate. artifacts.sh already asks packaging.sh for the
+  # extension's PATH SET (ext_paths above), so the version has to flow the same
+  # way; reversing it would have packaging.sh call back into this script, which
+  # would call packaging.sh for the paths again.
+  if [ "$1" = extension ]; then
+    sh "$ROOT/extension/scripts/packaging.sh" version
+    return
+  fi
   sha=$(echo "$(newest "$1")" | cut -d' ' -f2)
   # One git call for the whole string rather than four and a sed. git's
   # format-local takes the complete format, and doing it in pieces was only