Fix scrollbar gutter

.claude/CLAUDE.md

@@ -121,6 +121,16 @@ markup for it. The one that has already bitten us:
   this; it parses the templates structurally, so extend it there if you find
   another flex-container component with the same trap.
 
+- **Tabler shifts the whole page sideways when a scrollbar appears.** It ships
+  `@media (min-width:992px) { :root { margin-left: calc(100vw - 100%) } }`; `100vw`
+  counts the scrollbar and `100%` doesn't, so any page tall enough to scroll slides
+  right by the scrollbar width with an unpainted strip down the left edge. It reads
+  as page-specific (the tall tabs of a section show it, the short ones don't), but
+  it's every scrollable page. `app.css` overrides it and reserves the space with
+  `scrollbar-gutter: stable` instead; `TestE2ENoLeftGutterWhenScrollbarAppears`
+  locks it in. Override in `app.css` rather than editing `tabler.min.css` — that
+  file's hash is pinned by `internal/licenses`.
+
 - **A `<button>` centers its text.** Invisible on a normal button, wrong the
   moment you use one as a full-width row (`d-flex w-100`, e.g. a `list-group-item`
   that expands a collapse): the label sits centered while every neighboring row is

internal/e2e/page_gutter_test.go

@@ -0,0 +1,79 @@
+//go:build browser
+
+package e2e
+
+import (
+	"crypto/rand"
+	"fmt"
+	"testing"
+
+	"github.com/chromedp/chromedp"
+	meshcore "github.com/meshcore-go/meshcore-go"
+
+	"github.com/MeshTender/MeshTender/internal/store"
+)
+
+// TestE2ENoLeftGutterWhenScrollbarAppears: a page long enough to scroll must still
+// start at the left edge of the window.
+//
+// Tabler ships `@media (min-width:992px) { :root { margin-left: calc(100vw - 100%) } }`
+// — 100vw counts the scrollbar and 100% doesn't, so any scrollable page gets a left
+// margin the width of the scrollbar, sliding the whole layout (navbar included) right
+// and leaving an unpainted strip down the left edge. app.css overrides it and reserves
+// the space with scrollbar-gutter instead.
+//
+// It has to be a browser test: it only reproduces at a viewport wide enough for the
+// media query AND tall enough content to produce a real scrollbar, which is also why
+// it looked page-specific — the short tabs of the same section were fine.
+func TestE2ENoLeftGutterWhenScrollbarAppears(t *testing.T) {
+	srv := newE2EServer(t)
+	owner, cookie := srv.login(t, "gutteruser")
+	org, err := srv.store.CreateOrg(srv.ctx, "Gutter Org", owner.ID)
+	if err != nil {
+		t.Fatalf("create org: %v", err)
+	}
+	// Enough rows that the list is taller than the window.
+	for i := 0; i < 30; i++ {
+		id, err := meshcore.GenerateLocalIdentity(rand.Reader)
+		if err != nil {
+			t.Fatalf("generate identity: %v", err)
+		}
+		if _, err := srv.store.CreateRepeater(srv.ctx, &store.Repeater{
+			OwnerID: owner.ID, Name: fmt.Sprintf("Rep %02d", i), PublicKeyHex: id.String(),
+			RadioFreqHz: 869525000, RadioBwHz: 250000, RadioSF: 11, RadioCR: 5,
+		}); err != nil {
+			t.Fatalf("create repeater: %v", err)
+		}
+	}
+
+	bctx, cancel, watch := startBrowser(t)
+	defer cancel()
+
+	var scrollbar, navLeft int
+	var htmlMargin string
+	if err := chromedp.Run(bctx,
+		// Above the 992px breakpoint the Tabler rule applies; below it, it doesn't.
+		chromedp.EmulateViewport(1280, 700),
+		setSessionCookie(cookie),
+		chromedp.Navigate(srv.appURL+"/orgs/"+org.Slug+"/repeaters"),
+		chromedp.WaitVisible(`#rep-list`, chromedp.ByQuery),
+		chromedp.Evaluate(`window.innerWidth - document.documentElement.clientWidth`, &scrollbar),
+		chromedp.Evaluate(`getComputedStyle(document.documentElement).marginLeft`, &htmlMargin),
+		chromedp.Evaluate(`Math.round(document.querySelector('header.navbar').getBoundingClientRect().left)`, &navLeft),
+	); err != nil {
+		t.Fatalf("browser run: %v", err)
+	}
+	watch.assertClean(t)
+
+	// Guard the guard: with no scrollbar the margin is 0 anyway and this proves nothing.
+	if scrollbar == 0 {
+		t.Skip("no classic scrollbar in this browser, so the rule cannot misfire")
+	}
+	if htmlMargin != "0px" {
+		t.Errorf("html margin-left = %s with a %dpx scrollbar; the page is pushed off the left edge",
+			htmlMargin, scrollbar)
+	}
+	if navLeft != 0 {
+		t.Errorf("navbar starts at x=%d, want 0 — there is a gutter down the left of the page", navLeft)
+	}
+}

internal/web/static/app.css

@@ -239,3 +239,29 @@ code.pubkey {
 .footer-centered .row {
   justify-content: center;
 }
+
+/* Undo Tabler's scrollbar compensation, which shifts the whole page sideways.
+   @media (min-width:992px) it sets `:root { margin-left: calc(100vw - 100%) }` —
+   100vw includes the scrollbar, 100% doesn't, so a page long enough to scroll gets a
+   left margin the width of the scrollbar. The intent is to stop layout shifting when
+   a scrollbar appears, but the result is that every scrollable page sits ~15px right
+   of the window with an unpainted strip down the left edge, navbar included (it was
+   visible on the org Repeaters and Configuration tabs, and absent on the shorter Home
+   and Members tabs, which is what made it look page-specific).
+
+   scrollbar-gutter reserves the space on the correct side instead: no shift when the
+   scrollbar appears, no gutter on the left. Where it isn't supported the declaration
+   is ignored, which lands on the plain browser behavior rather than back on the
+   sideways shift. Overlay scrollbars (macOS, mobile) take no space at all, so the
+   gutter is a no-op there.
+
+   Overriding here rather than editing tabler.min.css keeps that file byte-identical
+   to the audited upstream artifact (internal/licenses pins its hash). */
+:root {
+  scrollbar-gutter: stable;
+}
+@media (min-width: 992px) {
+  :root {
+    margin-left: 0;
+  }
+}