Merge branch 'entry-content-visibility'

With logs up to ~25 000 entries, eagerly painting every grid cell
caused multi-second freezes on page load. Add content-visibility:
auto to the line-number and content cells so the browser defers
their layout / paint until they scroll into view.

The rule lives on the cells (not on .entry itself) because .entry
uses display: contents and produces no box of its own.
contain-intrinsic-size: auto 1.5em lets the browser remember
measured heights after first paint and uses ~one line tall as the
initial placeholder for never-seen cells.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/public/css/iblogs.css

@@ -950,6 +950,24 @@ main {
     width: 100%;
 }
 
+/*
+ * Skip layout / paint of off-screen log cells until they scroll into
+ * view. With logs running up to ~25 000 entries the eager render of
+ * every cell is what causes the multi-second freeze on initial load.
+ *
+ * `.entry` itself is `display: contents` (no box), so the rule has to
+ * land on the actual grid items it produces. `contain-intrinsic-size:
+ * auto 1.5em` lets the browser remember measured heights after first
+ * paint and falls back to ~one line tall as the placeholder for
+ * never-seen cells. Multi-line stack traces correct on first pass; the
+ * scroll position adjusts once.
+ */
+.log-inner .line-number-container,
+.log-inner .line-content {
+    content-visibility: auto;
+    contain-intrinsic-size: auto 1.5em;
+}
+
 .log-inner .entry.entry-error .line-content,
 .log-inner .entry.entry-error .line-number-container{
     background-color: var(--error-bg);
@@ -1153,6 +1171,17 @@ main {
         0 6px 16px color-mix(in srgb, var(--accent) 25%, transparent);
 }
 
+/*
+ * The header error-count chip is informational only — the smart fold is
+ * applied automatically on page load and folds can only be expanded
+ * individually. Strip the .btn cursor / hover affordance so the chip
+ * doesn't read as interactive.
+ */
+#error-toggle {
+    cursor: default;
+    pointer-events: none;
+}
+
 .log-inner .level {
     display: block;
     white-space: pre-wrap;

web/public/js/log.js

@@ -48,48 +48,44 @@ function scrollToHeight(top, smoothScrollLimit = 10000) {
 }
 
 /*
- * Error collapse toggle.
+ * Smart fold around errors.
  *
- * Smart fold: every entry within ±ERROR_WINDOW_SIZE of an error stays
- * visible; runs of non-error entries with no nearby errors collapse into
- * a draggable fold bar. Vertical drag on the bar progressively reveals or
- * re-hides lines; a click without drag reveals the next DEFAULT_CLICK_REVEAL
- * lines.
+ * Every entry within ±ERROR_WINDOW_SIZE of an error stays visible; runs of
+ * non-error entries with no nearby errors collapse into a draggable fold
+ * bar. Vertical drag on the bar progressively reveals or re-hides lines;
+ * a click without drag reveals the next DEFAULT_CLICK_REVEAL lines.
+ *
+ * The fold is applied automatically on page load when the log contains
+ * errors. Folds can only be expanded individually — there is no
+ * "unfold everything" path. The error-count chip in the header is purely
+ * informational; it is not interactive.
  */
 const ERROR_WINDOW_SIZE = 25;
 const PIXELS_PER_LINE_DRAG = 6;
 const DEFAULT_CLICK_REVEAL = 25;
 const DRAG_PIXEL_THRESHOLD = 3;
 
-const toggleErrorsButton = document.getElementById("error-toggle");
-if (toggleErrorsButton) {
-    toggleErrorsButton.addEventListener("click", toggleErrors);
-}
+applySmartFold();
 
-function toggleErrors() {
-    if (toggleErrorsButton.classList.contains("toggled")) {
-        toggleErrorsButton.classList.remove("toggled");
-        uncollapseAllErrors();
-    } else {
-        toggleErrorsButton.classList.add("toggled");
-        collapseAllErrors();
-    }
-}
-
-function collapseAllErrors() {
+function applySmartFold() {
     const lines = Array.from(document.querySelectorAll('.log-inner > .entry'));
     const total = lines.length;
     if (!total) return;
 
-    // Pass 1: mark entries within ±ERROR_WINDOW_SIZE of any error.
+    // Pass 1: mark entries within ±ERROR_WINDOW_SIZE of any error. If the
+    // log has no errors, every entry stays visible (we never produce one
+    // giant fold spanning the whole log).
     const mustShow = new Array(total).fill(false);
+    let sawError = false;
     for (let i = 0; i < total; i++) {
         if (lines[i].classList.contains("entry-error")) {
+            sawError = true;
             const lo = Math.max(0, i - ERROR_WINDOW_SIZE);
             const hi = Math.min(total - 1, i + ERROR_WINDOW_SIZE);
             for (let j = lo; j <= hi; j++) mustShow[j] = true;
         }
     }
+    if (!sawError) return;
 
     // Pass 2: hide unmarked entries; emit a fold bar at the START of each run.
     let runEntries = [];
@@ -110,11 +106,6 @@ function collapseAllErrors() {
     flushRun();
 }
 
-function uncollapseAllErrors() {
-    document.querySelectorAll(".log-inner > .entry").forEach(line => line.style.removeProperty("display"));
-    document.querySelectorAll(".collapsed-lines").forEach(bar => bar.remove());
-}
-
 function createFoldBar(entries) {
     const bar = document.createElement("div");
     bar.classList.add("collapsed-lines", "collapsed-lines-foldable");