feat: add history session resume UI and API

Add GET /api/history/sessions endpoint that scans Claude conversation
files for resume. Add welcome overlay UI with clickable history items.
Path decoding validates existence via fs.access with HOME fallback.

src/web/public/index.html

@@ -256,6 +256,10 @@
             <div class="welcome-qr-inner" id="welcomeQrInner"></div>
             <div class="welcome-qr-url" id="welcomeQrUrl"></div>
           </div>
+          <div class="history-sessions" id="historySessions" style="display:none">
+            <h3 class="history-title">Resume Conversation</h3>
+            <div class="history-list" id="historyList"></div>
+          </div>
           <p class="welcome-hint">Or press <kbd>Ctrl</kbd>+<kbd>Enter</kbd> to start</p>
           <button class="welcome-ralph-link" onclick="app.showRalphWizard()">Start Ralph Loop &rarr;</button>
         </div>

src/web/public/styles.css

@@ -2080,6 +2080,70 @@ body {
   text-align: center;
 }
 
+/* History sessions panel */
+.history-sessions {
+  margin-top: 1.5rem;
+  width: 100%;
+  max-width: 560px;
+}
+
+.history-title {
+  font-size: 0.85rem;
+  color: var(--text-dim);
+  margin-bottom: 0.5rem;
+  font-weight: 500;
+  text-align: left;
+}
+
+.history-list {
+  display: flex;
+  flex-direction: column;
+  gap: 0.35rem;
+  max-height: 240px;
+  overflow-y: auto;
+}
+
+.history-item {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  padding: 0.5rem 0.75rem;
+  background: var(--bg-input);
+  border: 1px solid var(--border);
+  border-radius: 6px;
+  cursor: pointer;
+  transition: border-color 0.15s, background 0.15s;
+  text-align: left;
+}
+
+.history-item:hover {
+  border-color: var(--accent);
+  background: var(--bg-hover);
+}
+
+.history-item-dir {
+  flex: 1;
+  font-size: 0.8rem;
+  color: var(--text);
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.history-item-meta {
+  font-size: 0.7rem;
+  color: var(--text-muted);
+  white-space: nowrap;
+}
+
+.history-item-size {
+  font-size: 0.7rem;
+  color: var(--text-dim);
+  white-space: nowrap;
+  min-width: 45px;
+  text-align: right;
+}
+
 .welcome-hint {
   color: var(--text-muted);
   font-size: 0.8rem;

src/web/routes/session-routes.ts

@@ -144,6 +144,7 @@ export function registerSessionRoutes(
       claudeMode: claudeModeConfig.claudeMode,
       allowedTools: claudeModeConfig.allowedTools,
       openCodeConfig: mode === 'opencode' ? body.openCodeConfig : undefined,
+      resumeSessionId: body.resumeSessionId,
     });
 
     ctx.addSession(session);
@@ -922,4 +923,67 @@ export function registerSessionRoutes(
       return createErrorResponse(ApiErrorCode.OPERATION_FAILED, getErrorMessage(err));
     }
   });
+
+  // ═══════════════════════════════════════════════════════════════
+  // History — list past Claude conversations for resume
+  // ═══════════════════════════════════════════════════════════════
+
+  app.get('/api/history/sessions', async () => {
+    const projectsDir = join(process.env.HOME || '/tmp', '.claude', 'projects');
+    const results: Array<{
+      sessionId: string;
+      workingDir: string;
+      projectKey: string;
+      sizeBytes: number;
+      lastModified: string;
+    }> = [];
+
+    try {
+      const projectDirs = await fs.readdir(projectsDir);
+      for (const projDir of projectDirs) {
+        const projPath = join(projectsDir, projDir);
+        const stat = await fs.stat(projPath).catch(() => null);
+        if (!stat?.isDirectory()) continue;
+
+        // Decode project key to working dir. The encoding replaces '/' with '-',
+        // which is lossy when path components contain '-'. Do naive decode first,
+        // then verify it exists. Fall back to HOME if the decoded path is invalid.
+        const naiveDecode = projDir.replace(/^-/, '/').replace(/-/g, '/');
+        const dirExists = await fs
+          .access(naiveDecode)
+          .then(() => true)
+          .catch(() => false);
+        const workingDir = dirExists ? naiveDecode : process.env.HOME || '/tmp';
+
+        const entries = await fs.readdir(projPath);
+        for (const entry of entries) {
+          if (!entry.endsWith('.jsonl')) continue;
+          const sessionId = entry.replace('.jsonl', '');
+          // Only valid UUIDs
+          if (!/^[a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12}$/.test(sessionId)) continue;
+
+          const filePath = join(projPath, entry);
+          const fileStat = await fs.stat(filePath).catch(() => null);
+          if (!fileStat) continue;
+          // Skip tiny files (empty or just init)
+          if (fileStat.size < 500) continue;
+
+          results.push({
+            sessionId,
+            workingDir,
+            projectKey: projDir,
+            sizeBytes: fileStat.size,
+            lastModified: fileStat.mtime.toISOString(),
+          });
+        }
+      }
+    } catch {
+      // Projects dir may not exist
+    }
+
+    // Sort by lastModified descending
+    results.sort((a, b) => new Date(b.lastModified).getTime() - new Date(a.lastModified).getTime());
+
+    return { sessions: results.slice(0, 50) };
+  });
 }