feat(v2): implement session persistence, file watcher, and markdown viewer

Phase 4 complete (MVP ship):
- SessionDb (rusqlite, WAL mode): sessions + layout_state tables, CRUD
- FileWatcherManager (notify v6): watch files, emit Tauri change events
- MarkdownPane: marked.js rendering with Catppuccin styles, live reload
- Layout store wired to persistence (addPane/removePane/setPreset persist)
- restoreFromDb() on startup restores panes in layout order
- Sidebar "M" button opens file picker for markdown files
- New adapters: session-bridge.ts, file-bridge.ts
- Deps: rusqlite (bundled), dirs 5, notify 6, marked

v2/src/lib/components/Layout/TilingGrid.svelte

@@ -2,6 +2,7 @@
   import PaneContainer from './PaneContainer.svelte';
   import TerminalPane from '../Terminal/TerminalPane.svelte';
   import AgentPane from '../Agent/AgentPane.svelte';
+  import MarkdownPane from '../Markdown/MarkdownPane.svelte';
   import {
     getPanes,
     getGridTemplate,
@@ -54,9 +55,15 @@
               cwd={pane.cwd}
               onExit={() => removePane(pane.id)}
             />
+          {:else if pane.type === 'markdown'}
+            <MarkdownPane
+              paneId={pane.id}
+              filePath={pane.cwd ?? ''}
+              onExit={() => removePane(pane.id)}
+            />
           {:else}
             <div class="placeholder">
-              <p>{pane.type} pane — coming in Phase 4</p>
+              <p>{pane.type} pane — coming soon</p>
             </div>
           {/if}
         </PaneContainer>

v2/src/lib/components/Markdown/MarkdownPane.svelte

@@ -0,0 +1,196 @@
+<script lang="ts">
+  import { onMount, onDestroy } from 'svelte';
+  import { marked } from 'marked';
+  import { watchFile, unwatchFile, onFileChanged, type FileChangedPayload } from '../../adapters/file-bridge';
+
+  interface Props {
+    filePath: string;
+    paneId: string;
+    onExit?: () => void;
+  }
+
+  let { filePath, paneId, onExit }: Props = $props();
+
+  let renderedHtml = $state('');
+  let error = $state('');
+  let unlisten: (() => void) | undefined;
+
+  function renderMarkdown(source: string): void {
+    try {
+      renderedHtml = marked.parse(source, { async: false }) as string;
+      error = '';
+    } catch (e) {
+      error = `Render error: ${e}`;
+    }
+  }
+
+  onMount(async () => {
+    try {
+      const content = await watchFile(paneId, filePath);
+      renderMarkdown(content);
+
+      unlisten = await onFileChanged((payload: FileChangedPayload) => {
+        if (payload.pane_id === paneId) {
+          renderMarkdown(payload.content);
+        }
+      });
+    } catch (e) {
+      error = `Failed to open file: ${e}`;
+    }
+  });
+
+  onDestroy(() => {
+    unlisten?.();
+    unwatchFile(paneId).catch(() => {});
+  });
+</script>
+
+<div class="markdown-pane">
+  {#if error}
+    <div class="error">{error}</div>
+  {:else}
+    <div class="markdown-body">
+      {@html renderedHtml}
+    </div>
+  {/if}
+  <div class="file-path">{filePath}</div>
+</div>
+
+<style>
+  .markdown-pane {
+    display: flex;
+    flex-direction: column;
+    height: 100%;
+    background: var(--bg-primary);
+    color: var(--text-primary);
+  }
+
+  .markdown-body {
+    flex: 1;
+    overflow-y: auto;
+    padding: 16px 20px;
+    font-size: 14px;
+    line-height: 1.6;
+  }
+
+  .markdown-body :global(h1) {
+    font-size: 1.6em;
+    font-weight: 700;
+    margin: 0.8em 0 0.4em;
+    color: var(--ctp-lavender);
+    border-bottom: 1px solid var(--border);
+    padding-bottom: 0.3em;
+  }
+
+  .markdown-body :global(h2) {
+    font-size: 1.3em;
+    font-weight: 600;
+    margin: 0.7em 0 0.3em;
+    color: var(--ctp-blue);
+  }
+
+  .markdown-body :global(h3) {
+    font-size: 1.1em;
+    font-weight: 600;
+    margin: 0.6em 0 0.3em;
+    color: var(--ctp-sapphire);
+  }
+
+  .markdown-body :global(p) {
+    margin: 0.5em 0;
+  }
+
+  .markdown-body :global(code) {
+    background: var(--bg-surface);
+    padding: 1px 5px;
+    border-radius: 3px;
+    font-family: var(--font-mono);
+    font-size: 0.9em;
+    color: var(--ctp-green);
+  }
+
+  .markdown-body :global(pre) {
+    background: var(--bg-surface);
+    padding: 12px 14px;
+    border-radius: var(--border-radius);
+    overflow-x: auto;
+    font-size: 12px;
+    line-height: 1.5;
+    margin: 0.6em 0;
+  }
+
+  .markdown-body :global(pre code) {
+    background: none;
+    padding: 0;
+    color: var(--text-primary);
+  }
+
+  .markdown-body :global(blockquote) {
+    border-left: 3px solid var(--ctp-mauve);
+    margin: 0.5em 0;
+    padding: 4px 12px;
+    color: var(--text-secondary);
+  }
+
+  .markdown-body :global(ul), .markdown-body :global(ol) {
+    padding-left: 24px;
+    margin: 0.4em 0;
+  }
+
+  .markdown-body :global(li) {
+    margin: 0.2em 0;
+  }
+
+  .markdown-body :global(a) {
+    color: var(--ctp-blue);
+    text-decoration: none;
+  }
+
+  .markdown-body :global(a:hover) {
+    text-decoration: underline;
+  }
+
+  .markdown-body :global(table) {
+    border-collapse: collapse;
+    width: 100%;
+    margin: 0.5em 0;
+    font-size: 13px;
+  }
+
+  .markdown-body :global(th), .markdown-body :global(td) {
+    border: 1px solid var(--border);
+    padding: 6px 10px;
+    text-align: left;
+  }
+
+  .markdown-body :global(th) {
+    background: var(--bg-surface);
+    font-weight: 600;
+  }
+
+  .markdown-body :global(hr) {
+    border: none;
+    border-top: 1px solid var(--border);
+    margin: 1em 0;
+  }
+
+  .markdown-body :global(img) {
+    max-width: 100%;
+    border-radius: var(--border-radius);
+  }
+
+  .file-path {
+    border-top: 1px solid var(--border);
+    padding: 4px 12px;
+    font-size: 10px;
+    font-family: var(--font-mono);
+    color: var(--text-muted);
+    flex-shrink: 0;
+  }
+
+  .error {
+    color: var(--ctp-red);
+    padding: 16px;
+    font-size: 13px;
+  }
+</style>

v2/src/lib/components/Sidebar/SessionList.svelte

@@ -33,15 +33,46 @@
       title: `Agent ${num}`,
     });
   }
+
+  let fileInputEl: HTMLInputElement | undefined = $state();
+
+  function openMarkdown() {
+    fileInputEl?.click();
+  }
+
+  function handleFileSelect(e: Event) {
+    const input = e.target as HTMLInputElement;
+    const file = input.files?.[0];
+    if (!file) return;
+
+    // Tauri file paths from input elements include the full path
+    const path = (file as any).path ?? file.name;
+    const id = crypto.randomUUID();
+    addPane({
+      id,
+      type: 'markdown',
+      title: file.name,
+      cwd: path,
+    });
+    input.value = '';
+  }
 </script>
 
 <div class="session-list">
   <div class="header">
     <h2>Sessions</h2>
     <div class="header-buttons">
+      <button class="new-btn" onclick={openMarkdown} title="Open markdown file">M</button>
       <button class="new-btn" onclick={newAgent} title="New agent (Ctrl+Shift+N)">A</button>
       <button class="new-btn" onclick={newTerminal} title="New terminal (Ctrl+N)">+</button>
     </div>
+    <input
+      bind:this={fileInputEl}
+      type="file"
+      accept=".md,.markdown,.txt"
+      onchange={handleFileSelect}
+      style="display: none;"
+    />
   </div>
 
   <div class="layout-presets">
@@ -65,7 +96,7 @@
       {#each panes as pane (pane.id)}
         <li class="pane-item" class:focused={pane.focused}>
           <button class="pane-btn" onclick={() => focusPane(pane.id)}>
-            <span class="pane-icon">{pane.type === 'terminal' ? '>' : pane.type === 'agent' ? '*' : '#'}</span>
+            <span class="pane-icon">{pane.type === 'terminal' ? '>' : pane.type === 'agent' ? '*' : pane.type === 'markdown' ? 'M' : '#'}</span>
             <span class="pane-name">{pane.title}</span>
           </button>
           <button class="remove-btn" onclick={() => removePane(pane.id)}>&times;</button>