diff --git a/internal/check-tab-radius-token.mjs b/internal/check-tab-radius-token.mjs
new file mode 100644
index 000000000..db5c2b924
--- /dev/null
+++ b/internal/check-tab-radius-token.mjs
@@ -0,0 +1,176 @@
+#!/usr/bin/env node
+/**
+ * check-tab-radius-token.mjs — the vertical tab rows must read the shared radius token, not a
+ * hard-coded pill.
+ *
+ * THE DEFECT THIS EXISTS FOR. The tabs shipped at border-radius:999px — a full stadium on a 48px
+ * row — under a real instruction to imitate the YouTube active row. Measured against the rest of
+ * the product that is the only thing shaped that way: .vtl-collapse is 8px, the filter toggles in
+ * library/components/search are 8px, and 8px is already the most common radius in the layout file.
+ * The Driver reversed it: "there is nowhere else in the app that has that same roundedness."
+ *
+ * ★ WHY A GATE AND NOT JUST THE FIX. The 999px rationale is still in the file, kept deliberately as
+ * history. A superseded rationale that still reads as current is exactly how a reversed decision
+ * gets quietly undone — the same trap another agent hit today with a stale "navy pin >= 7:1 PASS"
+ * acceptance line that no longer described anything that ships. A future reader who trusts that
+ * comment would restore the pill and believe they were fixing a regression.
+ *
+ * WHAT IT ASSERTS, and why each assertion is here rather than the obvious one:
+ *   A. .vtl-tab declares its radius through var(--vtl-radius,…), not a literal. Asserting the
+ *      TOKEN rather than the value "8px" is the point: the Driver's requirement is that the tabs,
+ *      the collapse button and the filter toggles agree, which a shared knob guarantees and three
+ *      matching literals only coincidentally satisfy.
+ *   B. The token's fallback equals .vtl-collapse's literal radius, READ FROM THE FILE. A hard-coded
+ *      expectation of 8px here would pass while the collapse button moved to 10px and the two
+ *      surfaces silently diverged — the gate would be asserting a number instead of the rule.
+ *   C. Neither .vtl-tab copy carries a pill radius (anything >= 100px). This is the actual
+ *      regression: a literal reintroduced beside the token would leave A passing.
+ *
+ * NOT ASSERTED, deliberately: .vtl-cap keeps border-radius:999px and should. The complaint was
+ * about the ratio of radius to size — a 16px badge at 999px is a chip, a 48px row at 999px is a
+ * stadium. A gate that banned 999px everywhere would over-apply the correction.
+ *
+ * ★ BOTH COPIES. VerticalTabsLayout.vue carries this CSS TWICE (VTL_SHADOW_CSS and the scoped
+ * <style> block) and they must stay byte-identical. Every .vtl-tab occurrence is checked, so a fix
+ * applied to only one copy fails here rather than shipping correct in one host and wrong in the
+ * other.
+ *
+ * NEGATIVE-TESTED: replacing the token with border-radius:999px in either copy exits 1 naming the
+ * line. Restoring exits 0. Run `bun run check:tab-radius:self-test` to re-prove it — an in-memory
+ * poisoning, so a crash can never leave the tree edited.
+ */
+import { readFileSync } from 'node:fs'
+import { resolve, dirname, join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const ROOT = resolve(dirname(fileURLToPath(import.meta.url)), '..')
+const FILE = join(ROOT, 'library/layouts/VerticalTabsLayout.vue')
+const REL = 'library/layouts/VerticalTabsLayout.vue'
+
+const fail = (m) => { console.error('TAB-RADIUS: FAIL — ' + m); process.exit(1) }
+
+// A pill is any radius at least half the row height; 48px rows make 100px a safe floor that still
+// catches 999px, 9999px and the occasional 50vh.
+const PILL_MIN = 100
+
+function auditLines(lines) {
+  const problems = []
+
+  // ── the reference: .vtl-collapse's literal radius, read from the file, never assumed ──────────
+  const collapse = []
+  lines.forEach((ln, i) => {
+    if (!/^\s*\.vtl-collapse\s*\{/.test(ln)) return
+    const m = ln.match(/border-radius:\s*([^;]+);/)
+    if (m) collapse.push({ line: i + 1, value: m[1].trim() })
+  })
+  if (!collapse.length) {
+    problems.push('could not find a .vtl-collapse rule with a border-radius to use as the reference.\n' +
+      '    This gate derives the expected value from the collapse button rather than hard-coding it,\n' +
+      '    because the rule is "the tabs agree with the collapse button", not "the tabs are 8px".')
+    return problems
+  }
+  const reference = collapse[0].value
+  if (collapse.some((c) => c.value !== reference)) {
+    problems.push('the .vtl-collapse copies disagree with each other: ' +
+      collapse.map((c) => `:${c.line}=${c.value}`).join(' vs ') +
+      '\n    Fix that first — the reference this gate measures against is not self-consistent.')
+  }
+
+  // ── the subject: every .vtl-tab rule (both synced copies) ────────────────────────────────────
+  const tabs = []
+  lines.forEach((ln, i) => {
+    // `.vtl-tab {` only — not .vtl-tab-badge, .vtl-tab-fallback, or .vtl-tab:hover
+    if (!/^\s*\.vtl-tab\s*\{/.test(ln)) return
+    const m = ln.match(/border-radius:\s*([^;]+);/)
+    tabs.push({ line: i + 1, value: m ? m[1].trim() : null })
+  })
+  if (!tabs.length) {
+    problems.push('found 0 `.vtl-tab {` rules in ' + REL + '.\n' +
+      '    A gate with nothing to assert is not passing; it is not running. If the class was\n' +
+      '    renamed, update this gate in the same commit.')
+    return problems
+  }
+  if (tabs.length < 2) {
+    problems.push(`found only ${tabs.length} \`.vtl-tab {\` rule. This file carries its CSS TWICE ` +
+      '(VTL_SHADOW_CSS and the scoped style block) and both must be present and identical — a\n' +
+      '    component that is correct in one host and wrong in the other is this repo\'s most\n' +
+      '    frequent defect shape.')
+  }
+
+  for (const t of tabs) {
+    if (!t.value) { problems.push(`${REL}:${t.line} — .vtl-tab declares no border-radius at all.`); continue }
+
+    // C. the regression: a pill literal reintroduced
+    const px = t.value.match(/^(\d+)px$/)
+    if (px && Number(px[1]) >= PILL_MIN) {
+      problems.push(`${REL}:${t.line} — .vtl-tab is back to a PILL (${t.value}).\n` +
+        '    The 999px stadium was SUPERSEDED on 2026-09-23. The YouTube rationale still in this\n' +
+        '    file is kept as history, NOT as a current instruction — do not restore the pill from it.\n' +
+        `    Expected: border-radius:var(--vtl-radius,${reference});`)
+      continue
+    }
+
+    // A. the token
+    const tok = t.value.match(/^var\(\s*--vtl-radius\s*,\s*([^)]+)\)$/)
+    if (!tok) {
+      problems.push(`${REL}:${t.line} — .vtl-tab uses the literal "${t.value}" instead of the shared token.\n` +
+        '    The requirement is that the tabs, the collapse button and the filter toggles AGREE.\n' +
+        '    A shared knob guarantees that; three matching literals only coincidentally satisfy it.\n' +
+        `    Expected: border-radius:var(--vtl-radius,${reference});`)
+      continue
+    }
+
+    // B. the fallback tracks the reference
+    if (tok[1].trim() !== reference) {
+      problems.push(`${REL}:${t.line} — the token fallback is ${tok[1].trim()} but .vtl-collapse ` +
+        `(line ${collapse[0].line}) is ${reference}.\n` +
+        '    These are the two surfaces the Driver named as needing to match. Change both or neither.')
+    }
+  }
+
+  // both copies must agree with each other
+  const distinct = [...new Set(tabs.map((t) => t.value))]
+  if (distinct.length > 1) {
+    problems.push('the two synced copies of .vtl-tab disagree: ' +
+      tabs.map((t) => `:${t.line}=${t.value}`).join(' vs ') +
+      '\n    Edit both or neither — check:synced-css enforces the same rule file-wide.')
+  }
+
+  return problems
+}
+
+// ── self-test: prove the gate catches the real regression, in memory ────────────────────────────
+if (process.argv.includes('--self-test')) {
+  const original = readFileSync(FILE, 'utf8')
+  if (auditLines(original.split('\n')).length) {
+    console.error('TAB-RADIUS SELF-TEST: FAIL — the tree is already failing; fix that first.')
+    process.exit(1)
+  }
+  const cases = [
+    ['pill-restored', (s) => s.replace('cursor:pointer; border-radius:var(--vtl-radius,8px); font:inherit;',
+      'cursor:pointer; border-radius:999px; font:inherit;')],
+    ['literal-instead-of-token', (s) => s.replace('cursor:pointer; border-radius:var(--vtl-radius,8px); font:inherit;',
+      'cursor:pointer; border-radius:8px; font:inherit;')],
+  ]
+  let bad = 0
+  for (const [name, poison] of cases) {
+    const mutated = poison(original)
+    if (mutated === original) { console.error(`  ${name}: POISON DID NOT APPLY — the gate proves nothing.`); bad++; continue }
+    const caught = auditLines(mutated.split('\n')).length > 0
+    console.log(`  ${name}: ${caught ? 'caught' : 'NOT CAUGHT'}`)
+    if (!caught) bad++
+  }
+  if (bad) { console.error(`TAB-RADIUS SELF-TEST: FAIL — ${bad} case(s) not caught.`); process.exit(1) }
+  console.log('TAB-RADIUS SELF-TEST: PASS — both regressions caught; tree untouched (poisoned in memory).')
+  process.exit(0)
+}
+
+const problems = auditLines(readFileSync(FILE, 'utf8').split('\n'))
+if (problems.length) {
+  console.error(`TAB-RADIUS: FAIL — ${problems.length} problem(s).\n`)
+  for (const p of problems) console.error('  ✗ ' + p + '\n')
+  process.exit(1)
+}
+console.log('TAB-RADIUS: PASS — .vtl-tab reads var(--vtl-radius) in both synced copies, and the')
+console.log('  fallback matches .vtl-collapse. The .vtl-cap badge keeps its pill by design: the')
+console.log('  complaint was the ratio of radius to size, not the shape itself.')
diff --git a/package.json b/package.json
index c5f0c0add..ccd1d23d9 100644
--- a/package.json
+++ b/package.json
@@ -54,7 +54,7 @@
     "check:facet-changes-map:self-test": "node internal/check-facet-changes-map.mjs --self-test   # reverts the fix IN THE LIVE PAGE and requires the gate to FAIL. SELF_TEST_MODE=colour (default, isolates the colour assertion — the reported bug) | props | both | frozen (blocks the source update, isolating the set assertion). All four modes verified caught.",
     "check:heartbeat": "node internal/check-heartbeat-threshold.mjs   # the HEARTBEAT ZONE threshold (the choropleth's top bin) must come from config AND the shipped config must still render today's ramp. Two sides: (B) a configured threshold must MOVE the edge — catches re-hard-coding; (A2) dashboard.config.js's own map.* must still resolve to 5/20/60/150/Infinity — catches the shipped default silently changing. A2 was MISSING at first and heartbeatThreshold:999 shipped past this gate printing 'default ramp unchanged'. A grep for '150' cannot do either job: it false-positives on the legitimate default and false-negatives on a re-hard-coding at 200. run check:heartbeat:self-test for the NEGATIVE tests (3 cases).",
     "check:heartbeat:self-test": "node internal/check-heartbeat-threshold.mjs --self-test   # THREE regression cases, each required to fire ITS OWN assertion: [literal] resolver replaced by the old hard-coded array -> B; [shipped-default] dashboard.config.js heartbeatThreshold changed -> A2; [shipped-mode] heartbeatMode flipped to quantile -> A2. Poisons IN MEMORY, never the file. Testing that the FEATURE works is not testing that the REGRESSION is caught — this gate shipped with only the first and missed the second.",
-    "build:unlocked": "bun run check:template-literal && bun run check:mjs-parse && bun run check:sfc-parse && bun run clean && bun run token && for d in plugin-designs/*/; do BUNDLE=$(basename \"$d\") bun x vite build || exit 1; done && bun run tree && bun run check:drop && bun run check:parse && bun run verify && bun run check:sri && bun run check:public-hygiene && bun run check:label-joins && bun run check:facet-cascade && bun run check:facet-one-field && bun run check:heartbeat && bun run check:kpi-unit && bun run check:composite-reg && bun run check:descriptions && bun run check:no-abs-paths && bun run check:no-codename && bun run check:dep-names && bun run check:composite-srcs && bun run check:embed-targets && bun run check:nested-token && bun run gallery",
+    "build:unlocked": "bun run check:template-literal && bun run check:mjs-parse && bun run check:sfc-parse && bun run check:tab-radius && bun run clean && bun run token && for d in plugin-designs/*/; do BUNDLE=$(basename \"$d\") bun x vite build || exit 1; done && bun run tree && bun run check:drop && bun run check:parse && bun run verify && bun run check:sri && bun run check:public-hygiene && bun run check:label-joins && bun run check:facet-cascade && bun run check:facet-one-field && bun run check:heartbeat && bun run check:kpi-unit && bun run check:composite-reg && bun run check:descriptions && bun run check:no-abs-paths && bun run check:no-codename && bun run check:dep-names && bun run check:composite-srcs && bun run check:embed-targets && bun run check:nested-token && bun run gallery",
     "check:template-literal": "node internal/template-literal-check.mjs",
     "verify:map-paint": "node internal/verify-map-paint.mjs",
     "check:sri": "node internal/sri-consistency-check.mjs",
@@ -109,6 +109,8 @@
     "check:no-orphan-gates": "node internal/check-no-orphan-gates.mjs",
     "check:one-palette": "node internal/check-one-palette.mjs",
     "check:kpi-unit": "node internal/check-kpi-unit-once.mjs",
+    "check:tab-radius": "node internal/check-tab-radius-token.mjs",
+    "check:tab-radius:self-test": "node internal/check-tab-radius-token.mjs --self-test",
     "check:synced-css": "node internal/check-synced-css-copies.mjs",
     "check:composite-reg": "node internal/check-composite-registration.mjs",
     "check:filter-width": "node internal/check-filter-width-stable.mjs",
@@ -140,4 +142,4 @@
   "engines": {
     "node": ">=18.0.0"
   }
-}
+}
\ No newline at end of file