Files view: the row jump no longer scrolls to the end of the trace (v2.6.1)

- jumpToMessage() rendered the APDU list through the unqualified
  renderMessages(), whose tail pins the view to the bottom (the live-capture
  stick), and only then let focusMessage() smooth-scroll back up to the
  clicked record — the visible jump-to-end-then-back.  It now renders with
  skipScroll, so the only scroll is the focus itself
- the content-follow became conditional: shouldStickToBottom() pins the view
  to the newest messages only while the reader is already at the bottom
  (40 px slack), so the 500 ms live poll no longer pulls away a view the
  reader scrolled to — a Files/map jump is no longer yanked down by the next
  batch.  A freshly opened session or a new capture still lands at the
  bottom (renderMessages(false, true))
- tests (node): the jump's paging/render(true)/focus sequence with stubs, the
  no-session no-op, the stick decision (at bottom / within slack / scrolled
  up / explicit jump / forced / first render) and source pins for
  renderMessages, jumpToMessage, loadSession and startCapture; 527 Python +
  53 Node tests
- README/README_RUS note the follow behaviour; PWA_VERSION/pyproject/
  version.py 2.6.1, SW cache simtrace-analyser-v73

frontend/index.html

@@ -2290,7 +2290,9 @@ async function jumpToMessage(idx) {
             if (!data.messages || !data.messages.length) break;
             STATE.messages.push(...data.messages);
         }
-        renderMessages();
+        // Render without the stick-to-bottom: focusMessage() scrolls to the
+        // record (the render only materializes its element).
+        renderMessages(true);
         focusMessage(idx);
     } catch (e) { /* keep the current view */ }
 }
@@ -2395,8 +2397,21 @@ function renderTraceEmptyState() {
     updateStatus();
 }
 
-function renderMessages(skipScroll) {
+// Content-follow decision for the APDU list: pin the view to the newest
+// messages only when the reader is already at the bottom.  An explicit jump
+// (*skipScroll*) never sticks, and a freshly loaded session/capture
+// (*forceStick*) always starts at the bottom.
+function shouldStickToBottom(list, skipScroll, forceStick) {
+    if (forceStick) return true;
+    if (skipScroll) return false;
+    return list.scrollTop + list.clientHeight >= list.scrollHeight - 40;
+}
+
+function renderMessages(skipScroll, forceStick) {
     const list = el('apdu-list');
+    // Read the geometry before the DOM is touched: adding messages grows
+    // scrollHeight, which would hide the fact that the reader was at the end.
+    const stick = shouldStickToBottom(list, skipScroll, forceStick);
     const searchQ = el('search-input').value.toLowerCase();
     const filterType = el('filter-select').value;
 
@@ -2449,7 +2464,7 @@ function renderMessages(skipScroll) {
         </div>`;
     }).join('');
 
-    if (!skipScroll) list.scrollTop = list.scrollHeight;
+    if (stick) list.scrollTop = list.scrollHeight;
     updateStatus();
 }
 
@@ -2552,7 +2567,7 @@ async function startCapture() {
         buildTypeCounts();
         buildTraceMap();
         renderSidePanel();
-        renderMessages();
+        renderMessages(false, true);
         el('apdu-detail').innerHTML = `<div class="detail-empty" data-l10n="Click an APDU to see details">${t('Click an APDU to see details')}</div>`;
         updateCaptureButton();
         startPolling();
@@ -2937,7 +2952,7 @@ async function loadSession(id) {
         STATE.mapExpanded.clear();
         switchTab('trace');
         updateCaptureButton();
-        renderMessages();
+        renderMessages(false, true);
         el('apdu-detail').innerHTML = `<div class="detail-empty" data-l10n="Click an APDU to see details">${t('Click an APDU to see details')}</div>`;
         el('session-name-display').style.display = 'inline';
         el('session-name-display').textContent = t('Session: ') + (data.session.name || '#' + id);
@@ -3191,7 +3206,7 @@ function onFilterChange() {
 }
 
 // ──────────────────── Versioning ────────────────────
-const PWA_VERSION = '2.6.0';
+const PWA_VERSION = '2.6.1';
 const MIN_SERVER_VERSION = '2.3.0';
 
 function parseVersion(v) {

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simtrace-analyser-v72';
+const CACHE = 'simtrace-analyser-v73';
 
 const PRECACHE = [
     'index.html',

frontend/tests/files_jump.test.js

@@ -0,0 +1,83 @@
+// The Files-view row jump and the APDU list's content-follow decision:
+// clicking a timeline row must scroll straight to its APDU — it used to
+// render the list with the stick-to-bottom (jump to the end of the trace)
+// and then smooth-scroll back up to the record.
+
+const { test } = require('node:test');
+const assert = require('node:assert');
+const { loadSrc, extractFunc } = require('./helpers.js');
+
+const src = loadSrc();
+
+let STATE = {};
+let API = {};
+let renders = [];
+let focused = [];
+function renderMessages(skipScroll, forceStick) {
+	renders.push([skipScroll, forceStick]);
+}
+function focusMessage(idx) {
+	focused.push(idx);
+}
+eval(
+	extractFunc(src, 'jumpToMessage') + '\n' +
+	extractFunc(src, 'shouldStickToBottom')
+);
+
+test('jumpToMessage pages, renders without stick-to-bottom, then focuses', async () => {
+	renders = [];
+	focused = [];
+	STATE = { sessionViewId: 7, messages: [{}, {}] };
+	API = {
+		getSession: async (sid, from) => ({
+			messages: from === 2 ? [{}, {}, {}] : [],
+		}),
+	};
+	await jumpToMessage(3);
+	assert.equal(STATE.messages.length, 5);
+	assert.deepEqual(renders, [[true, undefined]]);
+	assert.deepEqual(focused, [3]);
+});
+
+test('jumpToMessage no-ops without a session view', async () => {
+	renders = [];
+	focused = [];
+	STATE = { sessionViewId: null, messages: [] };
+	API = { getSession: async () => { throw new Error('must not fetch'); } };
+	await jumpToMessage(3);
+	assert.deepEqual(renders, []);
+	assert.deepEqual(focused, []);
+});
+
+test('shouldStickToBottom: only a reader at the bottom follows new content', () => {
+	const list = (scrollTop, clientHeight, scrollHeight) => ({ scrollTop, clientHeight, scrollHeight });
+	// At the bottom / within the slack → follow.
+	assert.equal(shouldStickToBottom(list(500, 100, 600), false, false), true);
+	assert.equal(shouldStickToBottom(list(560, 100, 600), false, false), true);
+	// Scrolled up (e.g. after a Files/map jump) → leave the view alone.
+	assert.equal(shouldStickToBottom(list(200, 100, 600), false, false), false);
+	// An explicit jump never sticks; a new session/capture always does.
+	assert.equal(shouldStickToBottom(list(200, 100, 600), true, false), false);
+	assert.equal(shouldStickToBottom(list(200, 100, 600), false, true), true);
+	// First render: the empty list has no geometry yet.
+	assert.equal(shouldStickToBottom(list(0, 0, 0), false, false), true);
+});
+
+test('renderMessages scrolls through shouldStickToBottom', () => {
+	const body = extractFunc(src, 'renderMessages');
+	assert.match(body, /function renderMessages\(skipScroll, forceStick\)/);
+	assert.match(body, /const stick = shouldStickToBottom\(list, skipScroll, forceStick\);/);
+	assert.match(body, /if \(stick\) list\.scrollTop = list\.scrollHeight;/);
+	assert.doesNotMatch(body, /if \(!skipScroll\) list\.scrollTop/);
+});
+
+test('jumpToMessage renders with skipScroll (source pin)', () => {
+	const body = extractFunc(src, 'jumpToMessage');
+	assert.match(body, /renderMessages\(true\);/);
+	assert.match(body, /focusMessage\(idx\);/);
+});
+
+test('a new session/capture lands at the bottom (source pins)', () => {
+	assert.match(extractFunc(src, 'loadSession'), /renderMessages\(false, true\);/);
+	assert.match(extractFunc(src, 'startCapture'), /renderMessages\(false, true\);/);
+});