Add landing screen as the app's entry point

Introduce a simple, show-don't-tell entry screen that lowers the "what
counts as a protocol" barrier and frames the activity as a short journey:

- Lead line "Examine the protocols around you" over a rotating, cross-fading
  list of deliberately diverse examples (traffic, code, kitchens, ritual,
  governance, play)
- Prominent "Begin" CTA above a three-step path: Describe / Understand / Share
- "About the Bicorder" link opens the existing help modal

Shown on first arrival; returning users with a reading in progress skip
straight to the diagnostic (computed synchronously, no flash). Remove the
now-redundant inline description from the focused flow.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

bicorder-app/src/App.svelte

@@ -9,6 +9,7 @@
   import FormRecommendation from './components/FormRecommendation.svelte';
   import AnalysisTransitionBanner from './components/AnalysisTransitionBanner.svelte';
   import HamburgerMenu from './components/HamburgerMenu.svelte';
+  import Landing from './components/Landing.svelte';
   import { BicorderClassifier } from './bicorder-classifier';
 
   // Load bicorder data and model from build-time constants
@@ -30,6 +31,32 @@
   let refreshKey = 0; // Used to force component refresh in focused mode
   let isHelpOpen = false;
 
+  // Show the landing screen on first arrival. Returning users who already have
+  // a reading in progress skip straight to the diagnostic. Computed
+  // synchronously (not in onMount) so the landing never flashes for them.
+  function hasReadingInProgress(): boolean {
+    if (typeof localStorage === 'undefined') return false;
+    try {
+      const saved = localStorage.getItem('bicorder-state');
+      if (!saved) return false;
+      const s = JSON.parse(saved);
+      const hasProtocol = !!s?.metadata?.protocol;
+      const hasValue = s?.diagnostic?.some(
+        (set: any) => set?.gradients?.some((g: any) => g?.value !== null && g?.value !== undefined)
+      );
+      return hasProtocol || hasValue;
+    } catch {
+      return false;
+    }
+  }
+
+  let started = hasReadingInProgress();
+
+  function startReading() {
+    started = true;
+    currentScreen = 0;
+  }
+
   // Screen types
   type Screen =
     | { type: 'metadata' }
@@ -432,6 +459,9 @@
 
 <HelpModal bind:isOpen={isHelpOpen} />
 
+{#if !started}
+  <Landing on:begin={startReading} on:about={openHelp} />
+{:else}
 <main>
   <div class="header">
     <div class="header-left">
@@ -519,12 +549,6 @@
 
   {:else}
     <!-- FOCUSED MODE: Show one screen at a time -->
-    {#if currentScreen === 0}
-      <div class="description">
-        <p>A diagnostic tool for the study of protocols</p>
-      </div>
-    {/if}
-
     <div class="focused-container">
       {#if currentScreenData.type === 'metadata'}
         <div class="focused-screen">
@@ -679,6 +703,7 @@
     </div>
   {/if}
 </main>
+{/if}
 
 <style>
   main {

bicorder-app/src/components/Landing.svelte

@@ -0,0 +1,216 @@
+<script lang="ts">
+  import { createEventDispatcher, onMount, onDestroy } from 'svelte';
+  import { fade } from 'svelte/transition';
+
+  const dispatch = createEventDispatcher<{ begin: void; about: void }>();
+
+  // A deliberately wide-ranging list — traffic, code, kitchens, ritual,
+  // governance, play — to show how capacious "protocol" really is.
+  const examples = [
+    'a four-way stop',
+    'tipping at a restaurant',
+    "Robert's Rules of Order",
+    'a sourdough starter passed between neighbors',
+    'code review on a pull request',
+    'a Quaker meeting for worship',
+    'queuing for the bus',
+    'how Wikipedia settles an edit war',
+    'a family holiday gift exchange',
+    'the handshake',
+    'academic peer review',
+    'trick-or-treating',
+    'a potluck dinner',
+    'jury deliberation',
+    "a city's recycling rules",
+    'an open-source contributor guide',
+  ];
+
+  let idx = 0;
+  let timer: ReturnType<typeof setInterval>;
+
+  onMount(() => {
+    timer = setInterval(() => {
+      idx = (idx + 1) % examples.length;
+    }, 2400);
+  });
+
+  onDestroy(() => clearInterval(timer));
+</script>
+
+<div class="landing">
+  <div class="title-block">
+    <div class="title-sm">Protocol</div>
+    <div class="title-lg">BICORDER</div>
+    <div class="motif" aria-hidden="true">[----#----]</div>
+  </div>
+
+  <div class="scan">
+    <span class="scan-label">Examine the protocols around you</span>
+    <span class="scan-example">
+      {#key idx}
+        <span in:fade={{ duration: 350 }}>{examples[idx]}</span>
+      {/key}
+    </span>
+  </div>
+
+  <button class="begin-btn" on:click={() => dispatch('begin')}>
+    Begin &rarr;
+  </button>
+
+  <ol class="steps">
+    <li>
+      <span class="step-n">1</span>
+      <span class="step-text"><strong>Describe</strong> a protocol around you</span>
+    </li>
+    <li>
+      <span class="step-n">2</span>
+      <span class="step-text"><strong>Understand</strong> how it works</span>
+    </li>
+    <li>
+      <span class="step-n">3</span>
+      <span class="step-text"><strong>Share</strong> your findings</span>
+    </li>
+  </ol>
+
+  <button class="about-link" on:click={() => dispatch('about')}>
+    About the Bicorder
+  </button>
+</div>
+
+<style>
+  .landing {
+    min-height: 100vh;
+    max-width: 640px;
+    margin: 0 auto;
+    padding: 2rem 1.5rem;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    text-align: center;
+    gap: 2rem;
+  }
+
+  .title-block {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+  }
+
+  .title-sm {
+    font-size: 1.1rem;
+    letter-spacing: 0.3rem;
+    opacity: 0.7;
+  }
+
+  .title-lg {
+    font-size: 2.4rem;
+    font-weight: bold;
+    letter-spacing: 0.4rem;
+  }
+
+  .motif {
+    font-family: 'Courier New', Courier, monospace;
+    font-size: 1.2rem;
+    letter-spacing: 0.15rem;
+    opacity: 0.4;
+    margin-top: 0.75rem;
+  }
+
+  .scan {
+    display: flex;
+    flex-direction: column;
+    gap: 0.6rem;
+  }
+
+  .scan-label {
+    font-size: 1.4rem;
+    font-weight: bold;
+    line-height: 1.4;
+  }
+
+  .scan-example {
+    /* Reserve space for up to two wrapped lines so the rotating example
+       never shifts the steps below it. */
+    display: flex;
+    align-items: flex-start;
+    justify-content: center;
+    min-height: 3.2rem;
+    font-size: 1.2rem;
+    opacity: 0.85;
+  }
+
+  .steps {
+    list-style: none;
+    margin: 0;
+    padding: 0;
+    display: flex;
+    flex-direction: column;
+    gap: 0.85rem;
+    text-align: left;
+  }
+
+  .steps li {
+    display: flex;
+    align-items: center;
+    gap: 0.85rem;
+    font-size: 1.05rem;
+  }
+
+  .step-n {
+    flex-shrink: 0;
+    width: 1.9rem;
+    height: 1.9rem;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    border: 2px solid var(--border-color);
+    border-radius: 50%;
+    font-weight: bold;
+    font-size: 0.95rem;
+  }
+
+  .step-text {
+    opacity: 0.9;
+  }
+
+  .begin-btn {
+    font-size: 1.15rem;
+    font-weight: bold;
+    letter-spacing: 0.1rem;
+    padding: 0.85rem 2.5rem;
+  }
+
+  .about-link {
+    background: none;
+    border: none;
+    min-height: auto;
+    min-width: auto;
+    padding: 0;
+    font-size: 0.85rem;
+    text-decoration: underline;
+    opacity: 0.55;
+    cursor: pointer;
+  }
+
+  .about-link:hover {
+    opacity: 0.9;
+    background: none;
+    color: var(--fg-color);
+  }
+
+  @media (max-width: 768px) {
+    .landing {
+      gap: 1.5rem;
+      padding: 1.5rem 1.25rem;
+    }
+
+    .title-lg {
+      font-size: 2rem;
+    }
+
+    .scan-label {
+      font-size: 1.2rem;
+    }
+  }
+</style>