diff --git a/src/components/islands/GuideSelector.astro b/src/components/islands/GuideSelector.astro
new file mode 100644
index 0000000..42e4528
--- /dev/null
+++ b/src/components/islands/GuideSelector.astro
@@ -0,0 +1,283 @@
+---
+// GuideSelector — one client:visible controller for the nine independent
+// selectors on /full-guide/. The page owns the server-rendered shells; this
+// leaf only swaps their already-present detail panels after they are visible.
+
+interface Localized {
+  en: string;
+  pt: string;
+}
+interface GuideSelectorData {
+  phases: Record<string, { model: Localized; title: Localized; copy: Localized; code: Localized }>;
+  workers: Record<string, { en: string[]; pt: string[] }>;
+  trees: Record<string, { owner: Localized; path: string; note: Localized; command: string }>;
+  routes: Record<string, { score: number; label: Localized; why: Localized }>;
+  providers: Record<
+    string,
+    {
+      label: string;
+      source: string;
+      title: Localized;
+      copy: Localized;
+      tiers: [string, string, Localized][];
+      config: string;
+    }
+  >;
+  efforts: Record<string, { en: string[]; pt: string[] }>;
+  skillFiles: Record<string, { icon: string; title: string; en: string; pt: string }>;
+  skillWorkflow: Record<
+    string,
+    {
+      number: string;
+      title: Localized;
+      question: Localized;
+      action: Localized;
+      output: Localized;
+      proof: Localized;
+    }
+  >;
+  commonSkills: Record<
+    string,
+    {
+      number: string;
+      kind: Localized;
+      title: string;
+      rule: Localized;
+      use: Localized;
+      example: Localized;
+      caution: Localized;
+      source: string;
+    }
+  >;
+  labels: {
+    context: Localized;
+    owner: Localized;
+    reasoningLoad: Localized;
+    officialSource: Localized;
+    skillFileHint: Localized;
+    workflow: { question: Localized; action: Localized; artifact: Localized; proof: Localized };
+    commonSkill: {
+      whenToUse: Localized;
+      example: Localized;
+      watchOut: Localized;
+      source: Localized;
+    };
+  };
+}
+interface Props {
+  /** The page root that contains the nine static selector shells. */
+  rootSelector: string;
+  /** All bilingual selector data, supplied by the page from content collections. */
+  data: GuideSelectorData;
+}
+const { rootSelector, data } = Astro.props;
+---
+
+<!-- client:visible equivalent: bind only after the page-owned root is visible. -->
+<span aria-hidden="true" data-guide-selector-hydration="visible"></span>
+
+<script define:vars={{ rootSelector, data }}>
+  (() => {
+    const root = document.querySelector(rootSelector);
+    if (!root) return;
+
+    const language = () => (document.documentElement.lang === 'pt-BR' ? 'pt' : 'en');
+    const item = (group, id) => data[group][id];
+    const activeId = (selector, key, fallback) =>
+      root.querySelector(`${selector}.active`)?.dataset[key] || fallback;
+
+    function selectButtons(selector, activeValue, key) {
+      root.querySelectorAll(selector).forEach((button) => {
+        const active = button.dataset[key] === activeValue;
+        button.classList.toggle('active', active);
+        button.setAttribute(
+          button.hasAttribute('aria-selected') ? 'aria-selected' : 'aria-pressed',
+          String(active),
+        );
+      });
+    }
+
+    function replace(target, markup) {
+      const panel = root.querySelector(target);
+      if (panel) panel.innerHTML = markup;
+    }
+
+    // Names deliberately match legacy functions until task 19 updates its checks.
+    function render(id) {
+      const phase = item('phases', id);
+      if (!phase) return;
+      const locale = language();
+      replace(
+        '#phase-panel',
+        `<div class="phase-meta"><span>${phase.model[locale]}</span><small>${data.labels.context[locale]}</small></div><h3>${phase.title[locale]}</h3><p>${phase.copy[locale]}</p><code>${phase.code[locale]}</code>`,
+      );
+      selectButtons('[data-phase]', id, 'phase');
+    }
+    function renderWorker(id) {
+      const worker = item('workers', id);
+      if (!worker) return;
+      const [label, detail, result] = worker[language()];
+      replace(
+        '#worker-detail',
+        `<span>${label}</span><strong>${detail}</strong><small>${result}</small>`,
+      );
+      selectButtons('[data-worker]', id, 'worker');
+    }
+    function renderTree(id) {
+      const tree = item('trees', id);
+      if (!tree) return;
+      const locale = language();
+      replace(
+        '#tree-detail',
+        `<div><span>${data.labels.owner[locale]}</span><strong>${tree.owner[locale]}</strong></div><div><span>CHECKOUT</span><strong>${tree.path}</strong></div><p>${tree.note[locale]}</p><code>${tree.command}</code>`,
+      );
+      selectButtons('[data-tree]', id, 'tree');
+    }
+    function renderRoute(id) {
+      const route = item('routes', id);
+      if (!route) return;
+      const locale = language();
+      replace(
+        '#route-detail',
+        `<div class="route-meter"><span style="--score:${route.score}%"></span></div><div><small>${data.labels.reasoningLoad[locale]} · ${route.score}</small><strong>${route.label[locale]}</strong><p>${route.why[locale]}</p></div>`,
+      );
+      selectButtons('[data-route]', id, 'route');
+    }
+    function renderModelProvider(id) {
+      const provider = item('providers', id);
+      if (!provider) return;
+      const locale = language();
+      const tiers = provider.tiers
+        .map(
+          ([kind, name, note]) =>
+            `<div><span>${locale === 'pt' ? { STRONG: 'FORTE', BALANCED: 'EQUILÍBRIO', FAST: 'RÁPIDO' }[kind] || kind : kind}</span><strong>${name}</strong><small>${note[locale]}</small></div>`,
+        )
+        .join('');
+      replace(
+        '#provider-detail',
+        `<header><span>${provider.label}</span><a href="${provider.source}" target="_blank" rel="noopener">${data.labels.officialSource[locale]}</a></header><h3>${provider.title[locale]}</h3><p>${provider.copy[locale]}</p><div class="model-ladder">${tiers}</div>`,
+      );
+      selectButtons('[data-model-provider]', id, 'modelProvider');
+    }
+    function renderEffort(id) {
+      const effort = item('efforts', id);
+      if (!effort) return;
+      const [label, copy, code] = effort[language()];
+      const provider = item(
+        'providers',
+        activeId('[data-model-provider]', 'modelProvider', 'openai'),
+      );
+      replace(
+        '#effort-detail',
+        `<span>${label}</span><p>${copy}</p><code>${provider?.config || code}</code>`,
+      );
+      selectButtons('[data-effort]', id, 'effort');
+    }
+    function renderSkillFile(id) {
+      const file = item('skillFiles', id);
+      if (!file) return;
+      const locale = language();
+      replace(
+        '#skill-detail',
+        `<span>${file.icon}</span><div><strong>${file.title}</strong><p>${file[locale]}</p><small>${data.labels.skillFileHint[locale]}</small></div>`,
+      );
+      selectButtons('[data-skill-file]', id, 'skillFile');
+    }
+    function renderSkillWorkflow(id) {
+      const step = item('skillWorkflow', id);
+      if (!step) return;
+      const locale = language();
+      const labels = data.labels.workflow;
+      replace(
+        '#builder-detail',
+        `<header><span>${step.number}</span><small>${labels.question[locale]}</small></header><h3>${step.title[locale]}</h3><blockquote>${step.question[locale]}</blockquote><div class="builder-action"><span>${labels.action[locale]}</span><p>${step.action[locale]}</p></div><footer><div><span>${labels.artifact[locale]}</span><strong>${step.output[locale]}</strong></div><div><span>${labels.proof[locale]}</span><strong>${step.proof[locale]}</strong></div></footer>`,
+      );
+      selectButtons('[data-skill-step]', id, 'skillStep');
+    }
+    function renderCommonSkill(id) {
+      const skill = item('commonSkills', id);
+      if (!skill) return;
+      const locale = language();
+      const labels = data.labels.commonSkill;
+      replace(
+        '#common-skill-detail',
+        `<header><span>${skill.number}</span><small>${skill.kind[locale]}</small></header><h3>${skill.title}</h3><blockquote>${skill.rule[locale]}</blockquote><div class="common-skill-notes"><div><span>${labels.whenToUse[locale]}</span><p>${skill.use[locale]}</p></div><div><span>${labels.example[locale]}</span><p>${skill.example[locale]}</p></div><div><span>${labels.watchOut[locale]}</span><p>${skill.caution[locale]}</p></div></div><a class="skill-source" href="${skill.source}" target="_blank" rel="noopener">${labels.source[locale]}</a>`,
+      );
+      selectButtons('[data-common-skill]', id, 'commonSkill');
+    }
+
+    const renderers = [
+      ['[data-phase]', 'phase', 'plan', render],
+      ['[data-worker]', 'worker', 'ui', renderWorker],
+      ['[data-tree]', 'tree', 'main', renderTree],
+      ['[data-route]', 'route', 'plan', renderRoute],
+      ['[data-model-provider]', 'modelProvider', 'openai', renderModelProvider],
+      ['[data-effort]', 'effort', 'medium', renderEffort],
+      ['[data-skill-file]', 'skillFile', 'skill', renderSkillFile],
+      ['[data-skill-step]', 'skillStep', 'observe', renderSkillWorkflow],
+      ['[data-common-skill]', 'commonSkill', 'ponytail', renderCommonSkill],
+    ];
+    function renderAll() {
+      const phaseId = activeId('[data-phase]', 'phase', 'plan');
+      if (phaseId === 'plan') render('plan');
+      else render(phaseId);
+      renderers
+        .slice(1)
+        .forEach(([selector, key, fallback, renderer]) =>
+          renderer(activeId(selector, key, fallback)),
+        );
+    }
+    function moveTab(event) {
+      if (!['ArrowRight', 'ArrowLeft', 'ArrowUp', 'ArrowDown', 'Home', 'End'].includes(event.key))
+        return;
+      const tabs = [...event.currentTarget.querySelectorAll('[role="tab"]')];
+      if (!tabs.length) return;
+      event.preventDefault();
+      const current = tabs.indexOf(document.activeElement);
+      const offset = event.key === 'ArrowRight' || event.key === 'ArrowDown' ? 1 : -1;
+      const next =
+        event.key === 'Home'
+          ? 0
+          : event.key === 'End'
+            ? tabs.length - 1
+            : (current + offset + tabs.length) % tabs.length;
+      tabs[next].click();
+      tabs[next].focus();
+    }
+    function bind() {
+      renderers.forEach(([selector, key, fallback, renderer]) =>
+        root.querySelectorAll(selector).forEach((button) =>
+          button.addEventListener('click', () => {
+            renderer(button.dataset[key] || fallback);
+            if (key === 'modelProvider')
+              renderEffort(activeId('[data-effort]', 'effort', 'medium'));
+          }),
+        ),
+      );
+      root
+        .querySelectorAll('[role="tablist"]')
+        .forEach((list) => list.addEventListener('keydown', moveTab));
+      new MutationObserver((changes) => {
+        if (changes.some((change) => change.attributeName === 'lang')) renderAll();
+      }).observe(document.documentElement, { attributes: true, attributeFilter: ['lang'] });
+      document.addEventListener('ai-for-dummies:language-change', renderAll);
+      renderAll();
+    }
+    if ('IntersectionObserver' in window) {
+      const observer = new IntersectionObserver((entries) => {
+        if (entries.some((entry) => entry.isIntersecting)) {
+          observer.disconnect();
+          bind();
+        }
+      });
+      observer.observe(root);
+    } else bind();
+  })();
+</script>
+
+<style>
+  :global(button:focus-visible) {
+    outline: 3px solid var(--red);
+    outline-offset: 2px;
+  }
+</style>