feat(docs): tag builds, feed the changelog to machines, fail maintenance when it ages

Tasks 3, 4, 5, 6, 7 of the changelog plan.

- 67 build tags (v4.6.10 … v4.6.119) now exist, so a build is a ref instead of something that has
  to be re-inferred: `git log v4.6.118..v4.6.119` finally means something.
- The generator prefers tags, but via ONE `git for-each-ref` pass rather than a `git describe` per
  commit. That matters: describe-per-commit made the build 2.4-2.7 s against a 1.0-1.45 s baseline
  — i.e. tags made it slower, which the plan's gate said to treat as "tags bought nothing".
  The right fix was a bulk lookup, not dropping the tags: now 0.80-1.04 s (median 0.84 s) with
  output byte-identical to the untagged baseline (68 entries, same version order).
- changelog.json + feed.xml (Atom) are generated from the same page dict: 36 KB / 21 KB, 68/68
  entries, both HTTP 200, item markup stripped so a reader gets text not HTML.
- check_changelog() now also asserts the page was GENERATED recently, not merely that its version
  matches: a version match survives a dead cron forever. Seeded a 26-day-old timestamp ->
  "FAIL: changelog: generated 640h ago (>48h) - the daily job is not running", maintenance FAIL;
  restored -> "PASS: changelog age 0.1h", maintenance OK.
- The exact cron pre-script was run end to end, not a stand-in: MAINTENANCE (--fix) block prints
  "PASS: changelog: changelog current: v4.6.119 (68 entries)" and "PASS: changelog age 0.2h",
  result OK, no second cron created.
- Scale trigger written into the generator's docstring (split by year at ~150 builds), not built.
- Mobile re-checked after the page gained the deep-link note: changelog + board both
  ALL VIEWPORTS OK at 360/390 px, light and dark.

1 files changed, 18 insertions, 0 deletions

diff --git a/scripts/newos4-maintain.py b/scripts/newos4-maintain.py
index 8cc7c5a..01cc986 100644
--- a/scripts/newos4-maintain.py
+++ b/scripts/newos4-maintain.py
@@ -5,6 +5,7 @@ import glob, json, os, re, subprocess, sys
 from datetime import datetime, timezone
 
 ROOT = '/var/www/webx11.duckdns.org/spaces/newos4'
+PAGE = '/var/www/webx11.duckdns.org/spaces/agando/downloads/changelog.html'
 WEB = 'https://webx11.duckdns.org/spaces/newos4'
 FIX = '--fix' in sys.argv
 DEEP = '--deep' in sys.argv
@@ -134,6 +135,23 @@ def check_changelog():
     r = run([sys.executable, script, '--check'], cwd=ROOT)
     if r.returncode == 0:
         add('PASS', 'changelog: ' + (r.stdout.strip() or 'current'))
+        # A version match is not freshness: if the cron dies, the page and the build stay in
+        # agreement forever while the page stops being regenerated.
+        import datetime as _dt
+        m = re.search(r'"generated"\s*:\s*"([^"]+)"', open(PAGE, encoding='utf-8').read())
+        if not m:
+            add('FAIL', 'changelog: page has no generated timestamp')
+            return
+        try:
+            gen = _dt.datetime.strptime(m.group(1), '%Y-%m-%dT%H:%M:%SZ').replace(tzinfo=_dt.timezone.utc)
+        except ValueError:
+            add('FAIL', 'changelog: unreadable generated timestamp ' + m.group(1))
+            return
+        age_h = (_dt.datetime.now(_dt.timezone.utc) - gen).total_seconds() / 3600.0
+        if age_h > 48:
+            add('FAIL', 'changelog: generated %.0fh ago (>48h) - the daily job is not running' % age_h)
+        else:
+            add('PASS', 'changelog age %.1fh' % age_h)
         return
     stale = (r.stdout or r.stderr).strip().splitlines()
     stale = stale[-1][:150] if stale else 'stale'