feat: major explorer performance overhaul, stream preview, and e2e testing

- Replace structuredClone with fast JSON clone (4x faster record cloning)
- Sample-based estimateSize instead of scanning all records (~600x faster)
- Stabilize wrappedDispatch with useRef to prevent cascading re-executions
- Remove unused useState from useExecution to eliminate full-screen re-renders
- Memoize 8 components with React.memo (TitleBar, ForkTabs, StageList, etc.)
- Add stream preview to AddStageModal and EditStageModal (Tab to toggle, Enter to zoom)
- Split useInput hooks to fix typing garble when TextInput is active
- Fix fuzzy search ranking: name-first matching with +200 bonus, minScore threshold
- Fix fromps race condition: skip UPDATE_STAGE_ARGS when args unchanged
- Fix undo/redo stale cache: clear cache and lastError on UNDO/REDO
- Fix execution not retrying after error + args edit (stageFingerprint dep)
- Fix disabled first stage showing 0 records
- Fix welcome screen 'n' key not working
- Rename tui → explorer throughout codebase
- Add tmux-based e2e test harness and 10 smoke tests (RUN_E2E=1 to enable)
- Add comprehensive unit tests: executor, reducer, fuzzy-match, unicode, etc.
- Add executor benchmark script

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: benbernard

bin/recs-tui.ts

@@ -99,19 +99,79 @@ if (command === "story") {
   process.exit(0);
 }
 
-// Handle TUI subcommand
-if (command === "tui") {
-  const tuiArgs = args.slice(1);
-  // Re-exec via recs-tui.ts with remaining args
-  const { join } = await import("node:path");
-  const tuiEntry = join(import.meta.dir, "recs-tui.ts");
-  const proc = Bun.spawn(["bun", "run", tuiEntry, ...tuiArgs], {
-    stdin: "inherit",
-    stdout: "inherit",
-    stderr: "inherit",
-  });
-  const code = await proc.exited;
-  process.exit(code);
+// Handle Explorer subcommand
+if (command === "explorer") {
+  const explorerArgs = args.slice(1);
+  // Dynamically import the explorer entry point so it works in compiled binaries
+  const explorerModule = await import("../src/explorer/index.tsx");
+  const launchExplorer = explorerModule.launchExplorer;
+  type ExplorerOptions = import("../src/explorer/index.tsx").ExplorerOptions;
+  const { SessionManager } = await import("../src/explorer/session/session-manager.ts");
+
+  const sessionManager = new SessionManager();
+
+  // Handle --list
+  if (explorerArgs.includes("--list")) {
+    const sessions = await sessionManager.list();
+    if (sessions.length === 0) {
+      console.log("No saved sessions.");
+    } else {
+      console.log("Saved sessions:\n");
+      for (const s of sessions) {
+        const label = s.name || s.sessionId;
+        console.log(`  ${label}`);
+        console.log(`    ${s.stageCount} stages, last used ${formatAge(Date.now() - s.lastAccessedAt)}`);
+        console.log();
+      }
+    }
+    process.exit(0);
+  }
+
+  // Handle --clean
+  if (explorerArgs.includes("--clean")) {
+    const removed = await sessionManager.clean();
+    console.log(removed === 0
+      ? "No sessions to clean up."
+      : `Removed ${removed} session${removed === 1 ? "" : "s"} older than 7 days.`);
+    process.exit(0);
+  }
+
+  // Parse explorer options
+  const explorerOptions: ExplorerOptions = {};
+  for (let i = 0; i < explorerArgs.length; i++) {
+    const arg = explorerArgs[i]!;
+    if (arg === "--session" || arg === "-s") {
+      explorerOptions.sessionId = explorerArgs[++i];
+    } else if (arg === "--pipeline" || arg === "-p") {
+      explorerOptions.pipeline = explorerArgs[++i];
+    } else if (arg === "--help" || arg === "-h") {
+      console.log(`Usage: recs explorer [options] [inputfile]
+
+Options:
+  --session, -s <id>     Resume a saved session
+  --pipeline, -p <cmd>   Start with an initial pipeline command
+  --list                 List saved sessions
+  --clean                Remove sessions older than 7 days
+
+Supported file types: .csv, .tsv, .xml, .jsonl, .json, .ndjson`);
+      process.exit(0);
+    } else if (!arg.startsWith("-")) {
+      explorerOptions.inputFile = arg;
+    }
+  }
+
+  try {
+    await launchExplorer(explorerOptions);
+  } catch (err) {
+    process.stderr.write(
+      `\nExplorer error: ${err instanceof Error ? err.message : String(err)}\n`,
+    );
+    if (err instanceof Error && err.stack) {
+      process.stderr.write(err.stack + "\n");
+    }
+    process.exit(1);
+  }
+  process.exit(0);
 }
 
 // Handle alias management subcommand
@@ -194,3 +254,10 @@ if (!noUpdateCheck && shouldCheck(getConfigDir())) {
 }
 
 process.exit(exitCode);
+
+function formatAge(ms: number): string {
+  if (ms < 60_000) return "just now";
+  if (ms < 3_600_000) return `${Math.floor(ms / 60_000)}m ago`;
+  if (ms < 86_400_000) return `${Math.floor(ms / 3_600_000)}h ago`;
+  return `${Math.floor(ms / 86_400_000)}d ago`;
+}