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>

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