Reduce terminal flicker in the dor file picker

docs/specs/dor-tool.md

@@ -232,6 +232,7 @@ Source of truth: `BUILTIN_HANDLERS` in `dor-tools-builtin/src/file-viewer-format
 
 - **Must list the files under the resolved CWD as git does in a work tree** — tracked and untracked, less ignored and deleted. Outside one, a walk lists each work tree it reaches likewise and skips dot-entries, `node_modules`, and the macOS home `Library`.
 - **Must offer the highlighted file's `tool.openHandlers` answer in order**: what [Opening local files](#opening-local-files) selects, then later matching rules' `tool` and `preview`, then each built-in supporting it — each once, with what it runs and the rule or built-in that offers it.
+- **Must preserve the query and selected file across terminal resizes.**
 
 Source of truth: `runFilePicker` in `dor/src/commands/open-picker.ts`; `listOpenHandlers` in `lib/src/host/tool-open.ts`.
 

dor/src/commands/fuzzy.ts

@@ -208,6 +208,11 @@ export class Ranker {
     this.schedule();
   }
 
+  /** One bounded slice now, so a frame drawn right away shows matches. */
+  seed(): void {
+    if (this.scanning) this.step(SLICE_MS);
+  }
+
   /** Ranks everything listed so far, now: Enter opens what is best. */
   flush(): void {
     this.step(Infinity);

dor/src/commands/open-picker.ts

@@ -68,6 +68,8 @@ export function runFilePicker(options: PickerOptions): Promise<PickerChoice | nu
   let handlerRows = new Map<number, number>();
   let listRows = 0;
   let redrawTimer: ReturnType<typeof setTimeout> | undefined;
+  let previousLines: string[] = [];
+  let previousSize = '';
   const listing = new AbortController();
 
   return new Promise((resolve) => {
@@ -194,6 +196,9 @@ export function runFilePicker(options: PickerOptions): Promise<PickerChoice | nu
         }
         if (done) return;
       }
+      // A query edit restarts ranking; without a slice now, this frame would
+      // paint an empty list until the deferred scan catches up.
+      ranker.seed();
       render();
     };
 
@@ -241,10 +246,20 @@ export function runFilePicker(options: PickerOptions): Promise<PickerChoice | nu
         lines.push(dim(clip(hints().join('  '), columns)));
       }
 
-      let out = `${CSI}?2026h${CSI}?25l`;
-      lines.forEach((line, index) => { out += `${CSI}${index + 1};1H${line}${SGR.reset}${CSI}K`; });
-      out += `${CSI}1;${3 + displayWidth(shown)}H${CSI}?25h${CSI}?2026l`;
-      terminal.write(out);
+      // Handler replies and ranking ticks often change nothing visible. Keep
+      // those frames silent, and leave unchanged rows alone on real updates.
+      // A resize invalidates the cache because the terminal may reflow rows.
+      // Erasing before writing keeps a character in the last column, where an
+      // erase after it would land on that character.
+      const size = `${columns}x${rows}`;
+      let out = '';
+      lines.forEach((line, index) => {
+        if (size === previousSize && line === previousLines[index]) return;
+        out += `${CSI}${index + 1};1H${CSI}2K${line}${SGR.reset}`;
+      });
+      previousLines = lines;
+      previousSize = size;
+      if (out) terminal.write(`${CSI}?2026h${CSI}?25l${out}${CSI}1;${3 + displayWidth(shown)}H${CSI}?25h${CSI}?2026l`);
     };
 
     const renderPanel = (width: number): Line[] => {

dor/test/open-picker.test.mjs

@@ -6,7 +6,7 @@ import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 import { runCli } from '../dist/cli.js';
 import { fuzzyMatch, Ranker } from '../dist/commands/fuzzy.js';
-import { parseKeys } from '../dist/commands/open-picker.js';
+import { parseKeys, runFilePicker } from '../dist/commands/open-picker.js';
 import { listFiles } from '../dist/commands/file-list.js';
 import { execFileSync } from 'node:child_process';
 import { setImmediate } from 'node:timers/promises';
@@ -75,14 +75,19 @@ test('parseKeys decodes keys, mouse, paste, and a lone escape', () => {
 
 function fakeTerminal({ columns = 120, rows = 20 } = {}) {
   let onInput;
+  let onResize;
   let output = '';
+  let taken = 0;
   return {
     columns: () => columns,
     rows: () => rows,
     write: (text) => { output += text; },
-    listen(input) { onInput = input; return () => { onInput = undefined; }; },
+    listen(input, resize) { onInput = input; onResize = resize; return () => { onInput = undefined; onResize = undefined; }; },
     send(chunk) { onInput(chunk); },
+    resize(width, height) { columns = width; rows = height; onResize(); },
     get output() { return output; },
+    /** Output written since the previous call. */
+    take() { const text = output.slice(taken); taken = output.length; return text; },
     get listening() { return onInput !== undefined; },
   };
 }
@@ -114,6 +119,73 @@ async function until(predicate, label) {
   assert.fail(`timed out waiting for ${label}`);
 }
 
+/** The rows a frame repainted, in order. */
+const paintedRows = (text) => [...text.matchAll(/\x1b\[(\d+);1H/g)].map(match => Number(match[1]));
+
+test('picker redraws only changed rows, skips identical frames, and repaints after resize', async () => {
+  const terminal = fakeTerminal({ columns: 60, rows: 8 });
+  const result = runFilePicker({
+    terminal,
+    fixedTool: 'builtin:file',
+    async listFiles(onFiles) { onFiles(['a'.repeat(58), 'b.ts']); return { truncated: false }; },
+    async handlers() { assert.fail('fixed handler needs no lookup'); },
+  });
+  try {
+    await until(() => terminal.output.includes('2/2'), 'completed listing');
+    // The query/count row and the first file fill the terminal width, so an
+    // erase after either would delete its last character.
+    assert.doesNotMatch(terminal.take(), /\x1b\[K/, 'rows are erased only before they are written');
+    terminal.send('\x1b[A'); // Already at the top.
+    terminal.resize(60, 8);
+    assert.equal(terminal.take(), '', 'unchanged frames emit no bytes or cursor toggles');
+
+    terminal.send('\x1b[B');
+    const update = terminal.take();
+    assert.deepEqual(paintedRows(update), [2, 3]);
+    assert.ok(update.endsWith('\x1b[1;3H\x1b[?25h\x1b[?2026l'), 'returns the cursor to the query');
+
+    terminal.send('b');
+    const filtered = terminal.take();
+    assert.match(filtered, /\x1b\[2;1H\x1b\[2K[^H]*b\x1b\[0m\x1b\[1m\.ts/, 'shorter replacement clears the old row first');
+    assert.doesNotMatch(filtered, /0…\/2/, 'typing does not paint an empty list before ranking');
+    terminal.resize(120, 10);
+    const wide = terminal.take();
+    assert.deepEqual(paintedRows(wide), [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
+    assert.match(wide, /Opens with/);
+    terminal.resize(60, 6);
+    const narrow = terminal.take();
+    assert.deepEqual(paintedRows(narrow), [1, 2, 3, 4, 5, 6]);
+    assert.match(narrow, /1;4H/, 'query cursor survives resize');
+    terminal.send('\r');
+    assert.deepEqual(await result, { file: 'b.ts' });
+  } finally {
+    if (terminal.listening) terminal.send('\x03');
+    await result;
+  }
+});
+
+test('handler replies leave unchanged file rows alone', async () => {
+  const terminal = fakeTerminal({ columns: 60 });
+  let reply;
+  const result = runFilePicker({
+    terminal,
+    async listFiles(onFiles) { onFiles(['a.ts', 'b.ts']); return { truncated: false }; },
+    handlers: () => new Promise(resolve => { reply = resolve; }),
+  });
+  try {
+    await until(() => reply !== undefined, 'handler request');
+    terminal.take();
+    reply({ handlers: HANDLERS, config: '/config', warnings: [], target: '/a.ts', directory: false });
+    await until(() => terminal.output.includes('builtin:file'), 'handler reply');
+    const update = terminal.take();
+    assert.doesNotMatch(update, /a\.ts|b\.ts/);
+    assert.deepEqual(paintedRows(update), [19, 20]);
+  } finally {
+    terminal.send('\x03');
+    await result;
+  }
+});
+
 async function withTree(run) {
   const dir = await mkdtemp(join(tmpdir(), 'dor-picker-'));
   try {