diff --git a/pi/.pi/agent/extensions/tmux-status/README.md b/pi/.pi/agent/extensions/tmux-status/README.md
index b95aa0f..322990b 100644
--- a/pi/.pi/agent/extensions/tmux-status/README.md
+++ b/pi/.pi/agent/extensions/tmux-status/README.md
@@ -17,11 +17,27 @@ Each window combines its panes with priority **waiting > working > done > idle**
 
 ## Usage
 
-```
-set -g @pi_status_time '%s'
-set -g @pi_status_live '#{?#{e|>:#{@pi_status_until},#{T:@pi_status_time}},#{@pi_status},}'
-set -g @pi_status_badge '#{?#{m:*waiting*,#{P:#{E:@pi_status_live}}}, [pi:waiting],#{?#{m:*working*,#{P:#{E:@pi_status_live}}}, [pi:working],#{?#{m:*done*,#{P:#{E:@pi_status_live}}}, [pi:done],#{?#{m:*idle*,#{P:#{E:@pi_status_live}}}, [pi:idle],}}}}'
+Stow both the `pi` and `tmux` packages, then use:
+
+```tmux
+set -g status-interval 1
+set -g @pi_status_badge '#(sh ~/.config/tmux/scripts/pi-status.sh #{q:socket_path} #{window_id})'
 
 set -g window-status-format " #I #W#{E:@pi_status_badge} "
 set -g window-status-current-format " #{?window_zoomed_flag,*,} #I #W#{E:@pi_status_badge} "
 ```
+
+## Cached rendering
+
+Pi publishes pane-local state with a 20-second lease, renewed every five seconds.
+The tmux helper scans each window's panes in a background `#()` job, filters expired
+leases, and emits one badge. tmux caches that result per client/window and keeps
+showing it while the next job runs. Updates normally appear within about a second;
+exits, pane moves, and expired leases are picked up without a running Pi process.
+
+Status redraws only read the cached result: no nested pane loops or lease
+arithmetic run inside tmux's format-expansion time budget. A missing or empty
+badge cannot remove the window index or name. No cache files or daemon are needed.
+
+Reload tmux with **prefix+r** after updating. Existing Pi sessions can keep running;
+the pane status protocol is unchanged.
diff --git a/pi/.pi/agent/extensions/tmux-status/status.test.ts b/pi/.pi/agent/extensions/tmux-status/status.test.ts
index 1b13caf..73c3d46 100644
--- a/pi/.pi/agent/extensions/tmux-status/status.test.ts
+++ b/pi/.pi/agent/extensions/tmux-status/status.test.ts
@@ -1,8 +1,10 @@
 import assert from "node:assert/strict";
-import { execFile } from "node:child_process";
+import { execFile, spawn } from "node:child_process";
 import { mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
+import { fileURLToPath } from "node:url";
+import { setTimeout as delay } from "node:timers/promises";
 import { test } from "node:test";
 import { promisify } from "node:util";
 import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
@@ -168,10 +170,40 @@ test("tmux renders per-window aggregates, leases, pane moves, and ownership", as
   const config = await readFile(new URL("../../../../../tmux/.config/tmux/tmux.conf", import.meta.url), "utf8");
   // Exercise the repository's actual formats, without loading plugins or bindings.
   const formats = config.split("\n").filter((line) => /^set -g (?:@pi_status_|window-status-(?:current-)?format )/.test(line));
-  assert.equal(formats.length, 5);
+  assert.equal(formats.length, 3);
+  const helper = fileURLToPath(new URL("../../../../../tmux/.config/tmux/scripts/pi-status.sh", import.meta.url));
   const configFile = join(directory, "formats.conf");
-  await writeFile(configFile, formats.join("\n") + "\n");
+  const testConfig = formats.join("\n").replace("~/.config/tmux/scripts/pi-status.sh", `'${helper.replaceAll("'", "'\\''")}'`);
+  await writeFile(configFile, testConfig + "\n");
   await tmux("source-file", configFile);
+
+  // Keep a client alive: tmux's #() job cache belongs to the rendering client.
+  const client = spawn("tmux", ["-S", socket, "-C", "attach-session", "-t", "check"], {
+    stdio: ["pipe", "pipe", "pipe"],
+  });
+  t.after(() => { client.stdin.end(); client.kill(); });
+  let output = "";
+  client.stdout.on("data", (chunk) => { output += chunk.toString(); });
+  const render = async (target: string, format: string) => {
+    const marker = `render-${Math.random()}:`;
+    client.stdin.write(`display-message -p -t ${target} '${marker}${format.replaceAll("'", "'\\''")}'\n`);
+    for (let attempt = 0; attempt < 100; attempt++) {
+      const line = output.split("\n").find((line) => line.startsWith(marker));
+      if (line !== undefined) return line.slice(marker.length).trim();
+      await delay(10);
+    }
+    throw new Error(`Control client did not render: ${output}`);
+  };
+  const eventually = async (target: string, format: string, expected: RegExp) => {
+    let row = "";
+    for (let attempt = 0; attempt < 50; attempt++) {
+      row = await render(target, format);
+      if (expected.test(row)) return row;
+      await delay(100);
+    }
+    assert.match(row, expected);
+    return row;
+  };
   const failures: unknown[] = [];
   const run: RunTmux = async (args) => {
     try {
@@ -187,7 +219,11 @@ test("tmux renders per-window aggregates, leases, pane moves, and ownership", as
     statuses.push(status);
     return status;
   };
-  const badge = (target: string) => tmux("display-message", "-p", "-t", target, "#{E:@pi_status_badge}");
+  const badge = async (target: string) => {
+    const window = await tmux("display-message", "-p", "-t", target, "#{window_id}");
+    const { stdout } = await exec("sh", [helper, socket, window], { timeout: 3_000 });
+    return stdout.trim();
+  };
   const first = create(pane1, "first");
   const second = create(pane2, "second");
   await first.start("idle");
@@ -205,13 +241,13 @@ test("tmux renders per-window aggregates, leases, pane moves, and ownership", as
   assert.equal(await badge(pane1), "[pi:done]");
   for (const option of ["window-status-format", "window-status-current-format"]) {
     const format = await tmux("show-options", "-gv", option);
-    const rendered = await tmux("display-message", "-p", "-t", pane1, format);
-    assert.match(rendered, /0 editor\s+\[pi:done\]/, "Pi status follows the window name inline");
+    await eventually(pane1, format, /0 editor\s+\[pi:done\]/);
   }
   const windowList = "#{W:#{E:window-status-format},#{E:window-status-current-format}}";
   assert.equal(await tmux("display-message", "-p", "-t", pane1, "#{window_name}"), "editor");
   await tmux("set-option", "-p", "-t", pane1, "@pi_status_until", "1");
   assert.equal(await badge(pane1), "", "expired leases disappear without a running extension");
+  await eventually(pane1, "#{E:window-status-format}", /^0 editor$/);
   await first.update("working");
   const otherPane = await tmux("new-window", "-d", "-P", "-F", "#{pane_id}", "-n", "other", "/bin/sh");
   assert.equal(await badge(otherPane), "", "unrelated windows have no badge");
@@ -225,11 +261,40 @@ test("tmux renders per-window aggregates, leases, pane moves, and ownership", as
   assert.equal(await badge(otherPane), "[pi:waiting]", "old runtimes cannot alter a successor");
   const third = create(pane2, "third");
   await third.start("done");
-  const row = await tmux("display-message", "-p", "-t", pane2, windowList);
+  const row = await eventually(pane2, windowList, /0 editor \[pi:done\].*1 other \[pi:waiting\]/);
   assert.match(row, /0 editor \[pi:done\]/);
   assert.match(row, /1 other \[pi:waiting\]/, "background windows have inline badges too");
+
+  // A blocked refresh must retain the previous result, never the window label.
+  const gate = join(directory, "block-refresh");
+  const started = join(directory, "refresh-started");
+  const slowHelper = join(directory, "slow-helper.sh");
+  const quote = (value: string) => `'${value.replaceAll("'", "'\\''")}'`;
+  await writeFile(slowHelper,
+    `if [ -f ${quote(gate)} ]; then\n` +
+    `  touch ${quote(started)}\n` +
+    `  while [ -f ${quote(gate)} ]; do sleep 0.05; done\n` +
+    `fi\nexec sh ${quote(helper)} "$@"\n`);
+  t.after(() => rm(gate, { force: true }));
+  await tmux("set-option", "-g", "@pi_status_badge", `#(sh ${quote(slowHelper)} #{q:socket_path} #{window_id})`);
+  await eventually(pane2, windowList, /0 editor \[pi:done\].*1 other \[pi:waiting\]/);
+  await writeFile(gate, "");
+  await replacement.update("working");
+  for (let attempt = 0; attempt < 50; attempt++) {
+    await render(pane2, windowList);
+    if (await readFile(started, "utf8").then(() => true, () => false)) break;
+    await delay(100);
+  }
+  await readFile(started, "utf8");
+  const cached = await render(pane2, "#{T:status-format[0]}");
+  assert.match(cached, /0 editor \[pi:done\]/);
+  assert.match(cached, /1 other \[pi:waiting\]/, "last badge survives an in-flight refresh");
+  await rm(gate);
+  await eventually(pane2, windowList, /1 other \[pi:working\]/);
+
   await replacement.stop();
   assert.equal(await badge(otherPane), "");
+  await eventually(pane2, windowList, /0 editor \[pi:done\]\s+1 other\s*$/);
   assert.equal(await tmux("show-options", "-p", "-t", pane1), "", "shutdown removes all pane-local state");
 
   assert.deepEqual(failures, [], "no tmux commands failed during the integration test");
diff --git a/tmux/.config/tmux/scripts/pi-status.sh b/tmux/.config/tmux/scripts/pi-status.sh
new file mode 100755
index 0000000..c960f6e
--- /dev/null
+++ b/tmux/.config/tmux/scripts/pi-status.sh
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+# tmux caches #() output while this job refreshes, keeping pane scans out of
+# status-line format expansion. Use IDs and an explicit socket for any server.
+[ "$#" -eq 2 ] || exit 1
+panes=$(tmux -S "$1" list-panes -t "$2" -F '#{@pi_status} #{@pi_status_until}' 2>/dev/null) || exit 1
+
+printf '%s\n' "$panes" | awk -v now="$(date +%s)" '
+    BEGIN {
+        priority["idle"] = 1
+        priority["done"] = 2
+        priority["working"] = 3
+        priority["waiting"] = 4
+    }
+    NF == 2 && $2 ~ /^[0-9]+$/ && $2 > now && priority[$1] > best {
+        best = priority[$1]
+        state = $1
+    }
+    END {
+        # A blank line explicitly clears a previously cached badge.
+        if (best) printf " [pi:%s]\n", state
+        else print ""
+    }
+'
diff --git a/tmux/.config/tmux/tmux.conf b/tmux/.config/tmux/tmux.conf
index 47e07ca..e4af4ef 100644
--- a/tmux/.config/tmux/tmux.conf
+++ b/tmux/.config/tmux/tmux.conf
@@ -66,10 +66,9 @@ set -g pane-border-status off
 set -g pane-border-format '#{pane_current_command} #{pane_current_path}'
 set -g window-status-separator " "
 
-# requires `.pi/agent/extensions/tmux-status`
-set -g @pi_status_time '%s'
-set -g @pi_status_live '#{?#{e|>:#{@pi_status_until},#{T:@pi_status_time}},#{@pi_status},}'
-set -g @pi_status_badge '#{?#{m:*waiting*,#{P:#{E:@pi_status_live}}}, [pi:waiting],#{?#{m:*working*,#{P:#{E:@pi_status_live}}}, [pi:working],#{?#{m:*done*,#{P:#{E:@pi_status_live}}}, [pi:done],#{?#{m:*idle*,#{P:#{E:@pi_status_live}}}, [pi:idle],}}}}'
+# Requires `.pi/agent/extensions/tmux-status`. #() caches the last result while
+# the helper refreshes; redraws never scan panes or evaluate their leases.
+set -g @pi_status_badge '#(sh ~/.config/tmux/scripts/pi-status.sh #{q:socket_path} #{window_id})'
 
 set -g window-status-format " #I #W#{E:@pi_status_badge} "
 set -g window-status-current-format " #{?window_zoomed_flag,*,} #I #W#{E:@pi_status_badge} "