Reject weak repaint history anchors

server/resize.test.mjs

@@ -268,6 +268,16 @@ try {
       repaintArchiveView('deep history\nshared transcript\n[old 160x40]\n',
         'shared transcript\n[new 90x24]\n').archive
       === 'deep history\nshared transcript\n[new 90x24]\n');
+    const poem = '❯ write me a poem about silicon\n\n● Silicon\n\n'
+      + 'Second most common thing underfoot, plain as the beach you forget while you walk it —\n'
+      + 'Someone thought to melt it, draw it out into a single perfect column, one lattice unbroken.\n';
+    const volatilePrefix = repaintArchiveView(
+      `older unique turn\n${poem}✻ Worked for 8s\n[old footer]\n`,
+      `✻ Worked for 2s\n${poem}✻ Worked for 8s\n[new footer]\n`,
+    ).archive;
+    check('a volatile leading status cannot anchor after and duplicate the repainted turn',
+      volatilePrefix.split('❯ write me a poem about silicon').length - 1 === 1
+      && volatilePrefix.includes('[new footer]') && !volatilePrefix.includes('[old footer]'));
     check('zooming wide again exposes the archive without growing it',
       repaintArchiveView(narrowView.archive, wide).archive === wide);
   }
@@ -418,8 +428,13 @@ try {
     // either the old frame or its welcome banner.
     const checkpoint = path.join(DATA_DIR, 'state', 'terminal-history', `${id}.json`);
     check('terminal history is checkpointed durably', await waitFor(() => fs.existsSync(checkpoint)));
-    const restarted = await view(id, 150, 40, true);
-    const resumed = await waitFor(async () => (await gridText(id)).includes('[fixture 150x40]'));
+    // A mobile pane opens its socket with xterm's provisional 80x24 geometry,
+    // then reports the measured phone grid as soon as layout settles. Exercise
+    // that change while the resumed TUI is still repainting, not only after the
+    // startup transaction has committed.
+    const restarted = await view(id, 80, 24, true);
+    restarted.resize(40, 28);
+    const resumed = await waitFor(async () => (await gridText(id)).includes('[fixture 40x28]'));
     const startupCommitted = await waitFor(() => restarted.frames.some((frame) =>
       frame.t === 'grid' && frame.reset));
     await sleep(350);

server/src/runner.js

@@ -297,8 +297,48 @@ export function repaintArchiveView(archive, visible, fallbackHistory = '') {
   if (!visible) return { archive, history: logicalHistory(archive) };
   const leading = visible.match(/^(?:[ \t]*\n)*/)?.[0].length || 0;
   const candidate = visible.slice(leading);
-  const match = candidate ? longestPrefixOccurrence(candidate, archive) : { length: 0, end: -1 };
-  const minimum = Math.min(12, candidate.trim().length, archive.trim().length);
+  let match = candidate ? longestPrefixOccurrence(candidate, archive) : { length: 0, end: -1 };
+
+  // A few shared characters are not a safe repaint boundary in a substantial
+  // screen. Claude's randomized status lines, for example, all begin with
+  // "Worked for ". Anchoring a fresh screen there can retain the old turn that
+  // precedes a later status line, then append that same turn again. Require a
+  // meaningful overlap for long screens, while still accepting complete short
+  // prompts in small panes.
+  const archiveContentLength = archive.trim().length;
+  const confidence = (tail) => Math.min(
+    64,
+    archiveContentLength,
+    Math.max(12, Math.floor(tail.trim().length / 2)),
+  );
+  let minimum = confidence(candidate);
+
+  // A repaint may start with one volatile row before its stable transcript.
+  // If the first row offers only a weak match, advance by logical lines until
+  // the first substantial overlap is found. The visible grid is bounded to 500
+  // rows, and the cap keeps a maliciously fragmented screen from repeatedly
+  // scanning a large archive.
+  if (match.length < minimum) {
+    let offset = 0;
+    for (let attempts = 0; attempts < 32;) {
+      const newline = candidate.indexOf('\n', offset);
+      if (newline < 0) break;
+      offset = newline + 1;
+      const tail = candidate.slice(offset);
+      if (!tail.trim()) break;
+      const nextBreak = tail.indexOf('\n');
+      const firstLine = tail.slice(0, nextBreak < 0 ? undefined : nextBreak);
+      if (firstLine.trim().length < 12) continue;
+      attempts++;
+      const next = longestPrefixOccurrence(tail, archive);
+      const nextMinimum = confidence(tail);
+      if (next.length >= nextMinimum) {
+        match = next;
+        minimum = nextMinimum;
+        break;
+      }
+    }
+  }
   let history = fallbackHistory;
   if (match.length >= minimum && minimum > 0) {
     const archiveOffset = match.end - match.length + 1;