Sitemaps: every entry carries an honest lastmod (item changes, release time for static pages) (#46)

ddiff --git a/README.md b/README.md
iindex c8ae132..6353de4 100644
---- a/README.md
++++ b/README.md
@@@ -138,13 +138,15 @@ deployment has no instruments (editors add them), no documents until the source
  | `/api/health`, `/api/ready`, `/release.json`, `POST /release-metrics`, `/metrics` | health, readiness, release, open tabs' update reports (counted in `/metrics`), metrics (loopback only) |
  | `POST /internal/events` | signed OpenVibe.Events deliveries (`sources.*`, and the two ADR-033 account events), host-local |
  
++Sitemap entries carry lastmod from each instrument's latest recorded change.
++
  ### Discoverability (roadmap §32)
  
  - Instrument pages go through the `openvibe-publishing/seo` gate. Financial information is a
    **sensitive** category: a page is `noindex` (`unreviewed_sensitive`) until a person-reviewed
    context is published, `noindex` when its newest monetary observation is older than
    `TRADE_PRICE_MAX_AGE_SEC` (`stale_price`), and `thin` below `TRADE_GATE_MIN_WORDS` of context.
--- The sitemap lists indexable instrument pages only, `lastmod` = the context's real publication time.
++- The sitemap lists indexable instrument pages only, `lastmod` = the instrument's latest recorded change.
  - JSON-LD: `WebPage` (+ `Corporation` with `tickerSymbol` for equities) and breadcrumbs, from real
    fields only. No price, offer, rating or invented date.
  - Every instrument page has a JSON twin with the same data (`/i/:symbol.json`).
ddiff --git a/server/http/discovery.js b/server/http/discovery.js
iindex 5e6e61a..937652d 100644
---- a/server/http/discovery.js
++++ b/server/http/discovery.js
@@@ -10,7 +10,7 @@
   *   GET /sitemap.xml                       sitemap index
   *   GET /sitemaps/instruments.xml          INDEXABLE instrument pages only (the gate decides:
   *                                          person-reviewed context, no stale price); lastmod = the
-- *                                          context's real publication time
++ *                                          latest instrument, observation or document change
   *   GET /feed.xml | /atom.xml | /feed.json recent public documents across instruments
   *   GET /i/:symbol/documents.xml|.atom|.json  one instrument's documents
   *
@@@ -103,18 +103,29 @@ function createDiscovery(ctx) {
          }));
      });
  
++    async function pageChanges() {
++        const rows = await store.db.prepare(`SELECT instrument_id, MAX(changed_at) AS changed_at FROM (
++            SELECT instrument_id, recorded_at AS changed_at FROM trade_market_observations
++            UNION ALL SELECT instrument_id, updated_at AS changed_at FROM trade_source_documents
++        ) changes GROUP BY instrument_id`).all();
++        return new Map(rows.map((r) => [r.instrument_id, r.changed_at]));
++    }
++    const pageLastmod = (instrument, changes) => Math.max(instrument.updated_at || 0, instrument.context_published_at || 0, changes.get(instrument.id) || 0);
++
      define(router, 'get', '/sitemap.xml', 'sitemapIndex', async (_req, res) => {
          const active = await instruments.active();
          const decisions = await Promise.all(active.map(async (i) => await indexing.decide(i)));
--        const times = active.filter((i, n) => decisions[n].indexable && i.context_published_at).map((i) => i.context_published_at);
++        const changes = await pageChanges();
++        const times = active.filter((i, n) => decisions[n].indexable).map((i) => pageLastmod(i, changes)).filter(Boolean);
          const newest = times.length ? new Date(Math.max(...times)).toISOString() : null;
          xml(res, seo.sitemapIndex([{ loc: abs('/sitemaps/instruments.xml'), ...(newest ? { lastmod: newest } : {}) }]));
      });
  
      define(router, 'get', '/sitemaps/instruments.xml', 'instrumentSitemap', async (_req, res) => {
++        const changes = await pageChanges();
          const entries = (await Promise.all((await instruments.active()).map(async (i) => ({
              loc: urls.instrument(i),
--            ...(i.context_published_at ? { lastmod: new Date(i.context_published_at).toISOString() } : {}),
++            ...(pageLastmod(i, changes) ? { lastmod: new Date(pageLastmod(i, changes)).toISOString() } : {}),
              decision: await indexing.decide(i),
          }))));
          xml(res, seo.sitemap(entries).files[0]);
ddiff --git a/test/pages.test.js b/test/pages.test.js
iindex 59528fd..f62c318 100644
---- a/test/pages.test.js
++++ b/test/pages.test.js
@@@ -5,6 +5,17 @@
   * endpoints answer; the historical marketplace branch is recorded as an open question, not built.
   */
  const assert = require('assert');
++
++function assertSitemapLastmods(xml, tag = 'url') {
++    const entries = [...xml.matchAll(new RegExp(`<${tag}>([\\s\\S]*?)</${tag}>`, 'g'))];
++    for (const [, body] of entries) {
++        const match = /<lastmod>(\d{4}-\d{2}-\d{2})<\/lastmod>/.exec(body);
++        assert.ok(match, body);
++        assert.strictEqual(new Date(match[1]).toISOString().slice(0, 10), match[1]);
++    }
++    return entries;
++}
++
  const fs = require('fs');
  const path = require('path');
  const { boot, check, done } = require('./helpers/boot');
@@@ -72,6 +83,7 @@ const WORDS = (n) => Array.from({ length: n }, (_, i) => `word${i}`).join(' ');
          assert.ok(/automated-consumer policy/.test(robots));
          assert.ok((await t.get('/sitemap.xml')).text.includes('https://openvibe.trade/sitemaps/instruments.xml'));
          assert.ok(!(await t.get('/sitemaps/instruments.xml')).text.includes('<loc>'), 'no indexable instrument yet');
++        assertSitemapLastmods((await t.get('/sitemaps/instruments.xml')).text);
          assert.ok((await t.get('/llms.txt')).text.startsWith('# OpenVibe.Trade'));
      });
  
@@@ -122,6 +134,14 @@ const WORDS = (n) => Array.from({ length: n }, (_, i) => `word${i}`).join(' ');
          await t.instrument({ symbol: 'OTHR', name: 'Other Co' });
          const pub = await t.get('/editor/i/ACME/context', { as: t.editor, form: { _csrf: t.csrf(t.editor), body: `Acme's price is stated by the source. ${WORDS(70)}`, cite: `observation:${observation.id}`, publish: '1' } });
          assert.ok(/n=context_published/.test(pub.headers.get('location')), 'the context published');
++        const map = (await t.get('/sitemaps/instruments.xml')).text;
++        assert.strictEqual(assertSitemapLastmods(map).length, 1);
++        const instrument = await t.ctx.store.db.prepare("SELECT id, updated_at, context_published_at FROM trade_instruments WHERE symbol = 'ACME'").get();
++        const observationTime = await t.ctx.store.db.prepare('SELECT MAX(recorded_at) AS at FROM trade_market_observations WHERE instrument_id = ?').get(instrument.id);
++        const documentTime = await t.ctx.store.db.prepare('SELECT MAX(updated_at) AS at FROM trade_source_documents WHERE instrument_id = ?').get(instrument.id);
++        const expected = new Date(Math.max(instrument.updated_at, instrument.context_published_at || 0, observationTime.at || 0, documentTime.at || 0)).toISOString().slice(0, 10);
++        assert.ok(map.includes(`<loc>https://openvibe.trade/i/ACME</loc><lastmod>${expected}</lastmod>`));
++        assertSitemapLastmods((await t.get('/sitemap.xml')).text, 'sitemap');
          const after = await t.get('/llms-full.txt');
          assert.ok(after.text.includes('https://openvibe.trade/i/ACME'));
          assert.ok(after.text.includes('### ACME — Acme Corp'));