diff --git a/docs/activity-trace.md b/docs/activity-trace.md
index 09b114e9..873f5651 100644
--- a/docs/activity-trace.md
+++ b/docs/activity-trace.md
@@ -307,10 +307,13 @@ checks are scans: every call to `trace`, `codePoints`, `controlOffset`,
 and the probe categories are named so a probe deleted in a refactor fails the
 suite instead of quietly reducing a count.
 
-One call is exempt and pinned by its exact text: the OSC 0 `log.debug` line
-renders a code point into a template literal on every title, whatever the trace
-is doing. It predates this feature (c07ab13, 2026-03) and is on `main`; the
-exemption exists so that it stays the only one.
+One call is exempt from that guard and pinned by its exact text: the OSC 0
+`log.debug` line renders a code point into a template literal, and it carries
+the debug-log guard `if (LOG_DEBUG_ON)` rather than `if (TRACE.on)` — a
+packaged build logs at `info`, so the line and its code point are inert there.
+`test/osc-debug-log-guards.test.js` pins that guard, and every other debug line
+on the PTY data path with it. The exemption above exists so that this stays the
+only one.
 
 This matters because of
 [ADR 0002](decisions/0002-discrete-steps-sidebar-animations.md) — the
diff --git a/main.js b/main.js
index 772da514..ee0cb94b 100644
--- a/main.js
+++ b/main.js
@@ -30,6 +30,7 @@ if (process.env.SWITCHBOARD_DATA_DIR) {
 
 log.transports.file.level = app.isPackaged ? 'info' : 'debug';
 log.transports.console.level = app.isPackaged ? 'info' : 'debug';
+const LOG_DEBUG_ON = log.transports.file.level === 'debug' || log.transports.console.level === 'debug';
 
 // Opt-in activity trace — see docs/activity-trace.md.
 const activityTrace = require('./activity-trace');
@@ -2170,12 +2171,12 @@ function wireSessionPty(session, sessionId, ptyProcess) {
         // Detect Claude CLI busy state from the OSC 0 title — see .ai/contexts/ipc-bridge.md
         if (code === '0') {
           const { busy: isBusy, idle: isIdle, via } = classifyTitleActivity(payload, { allowFallback: !session.isPlainTerminal });
-          log.debug(`[OSC 0] session=${currentId} cp=${codePoints(payload, 1)} rule=${via} busy=${isBusy} idle=${isIdle} wasBusy=${!!session._cliBusy}`);
+          if (LOG_DEBUG_ON) log.debug(`[OSC 0] session=${currentId} cp=${codePoints(payload, 1)} rule=${via} busy=${isBusy} idle=${isIdle} wasBusy=${!!session._cliBusy}`);
           if (TRACE.on) trace('osc.title', currentId, { cp: codePoints(payload, 3), title: payload.slice(0, 60), busy: isBusy, idle: isIdle, rule: via, was: !!session._cliBusy, decision: busyDecision(isBusy, isIdle, !!session._cliBusy) });
           if (isBusy && !session._cliBusy) {
             session._cliBusy = true;
             session._oscIdle = false;
-            log.debug(`[OSC 0] session=${currentId} → BUSY`);
+            if (LOG_DEBUG_ON) log.debug(`[OSC 0] session=${currentId} → BUSY`);
             if (TRACE.on) trace('busy.emit', currentId, { busy: true, via: 'osc0', sent: !!(mainWindow && !mainWindow.isDestroyed()) });
             if (mainWindow && !mainWindow.isDestroyed()) {
               mainWindow.webContents.send('cli-busy-state', currentId, true);
@@ -2183,7 +2184,7 @@ function wireSessionPty(session, sessionId, ptyProcess) {
           } else if (isIdle && session._cliBusy) {
             session._cliBusy = false;
             session._oscIdle = true;
-            log.debug(`[OSC 0] session=${currentId} → IDLE`);
+            if (LOG_DEBUG_ON) log.debug(`[OSC 0] session=${currentId} → IDLE`);
             if (TRACE.on) trace('busy.emit', currentId, { busy: false, via: 'osc0', sent: !!(mainWindow && !mainWindow.isDestroyed()) });
             if (mainWindow && !mainWindow.isDestroyed()) {
               mainWindow.webContents.send('cli-busy-state', currentId, false);
@@ -2199,12 +2200,12 @@ function wireSessionPty(session, sessionId, ptyProcess) {
         if (payload.startsWith('4;')) {
           const level = payload.split(';')[1];
           if (level === '0') continue; // 4;0 is also used for clearing, making it unreliable as an idle signal
-          log.debug(`[OSC 9;4] session=${currentId} level=${level} payload="${payload}" wasBusy=${!!session._cliBusy}`);
+          if (LOG_DEBUG_ON) log.debug(`[OSC 9;4] session=${currentId} level=${level} payload="${payload}" wasBusy=${!!session._cliBusy}`);
           if (TRACE.on) trace('osc.progress', currentId, { level, payload: payload.slice(0, 60), was: !!session._cliBusy, decision: progressDecision(level, !!session._cliBusy) });
           if ((level === '1' || level === '2' || level === '3') && !session._cliBusy) {
             session._cliBusy = true;
             session._oscIdle = false;
-            log.debug(`[OSC 9;4] session=${currentId} → BUSY`);
+            if (LOG_DEBUG_ON) log.debug(`[OSC 9;4] session=${currentId} → BUSY`);
             if (TRACE.on) trace('busy.emit', currentId, { busy: true, via: 'osc9.4', sent: !!(mainWindow && !mainWindow.isDestroyed()) });
             if (mainWindow && !mainWindow.isDestroyed()) {
               mainWindow.webContents.send('cli-busy-state', currentId, true);
diff --git a/test/activity-trace-probe-guards.test.js b/test/activity-trace-probe-guards.test.js
index 080476f5..4b85affc 100644
--- a/test/activity-trace-probe-guards.test.js
+++ b/test/activity-trace-probe-guards.test.js
@@ -132,13 +132,12 @@ test('every trace() call in main.js is guarded, except the IPC forwarder', () =>
   assert.equal(looseTrace.length, 1, 'the renderer forwarder is the only unguarded call');
 });
 
-// One call predates the trace: the OSC 0 debug log renders a code point into a
-// template literal on every title, whatever the trace is doing. It is a real
-// cost on a hot path and it is not this feature's to remove — it came in with
-// c07ab13 (2026-03) and is on main. Pinned by its exact text so that it stays
-// the *only* exception: anything new fails the assertion below.
+// One call renders a code point outside the trace's guard: the OSC 0 debug log
+// sits under `if (LOG_DEBUG_ON)` instead, the debug-log guard, which
+// test/osc-debug-log-guards.test.js pins. Its exact text is pinned here so
+// that it stays the *only* exception: anything new fails the assertion below.
 const KNOWN_UNGUARDED_HELPERS = [
-  'log.debug(`[OSC 0] session=${currentId} cp=${codePoints(payload, 1)} rule=${via} busy=${isBusy} idle=${isIdle} wasBusy=${!!session._cliBusy}`);',
+  'if (LOG_DEBUG_ON) log.debug(`[OSC 0] session=${currentId} cp=${codePoints(payload, 1)} rule=${via} busy=${isBusy} idle=${isIdle} wasBusy=${!!session._cliBusy}`);',
 ];
 
 test('no trace payload helper is called outside a guard', () => {
diff --git a/test/osc-debug-log-guards.test.js b/test/osc-debug-log-guards.test.js
new file mode 100644
index 00000000..ed2182db
--- /dev/null
+++ b/test/osc-debug-log-guards.test.js
@@ -0,0 +1,62 @@
+// The debug lines on the PTY data path must cost nothing when debug logging
+// is off.
+//
+// `log.debug` decides at the transport whether to write, but its argument is
+// built by the caller either way: a template literal interpolating
+// `codePoints(payload, 1)` is rendered, handed to electron-log, walked through
+// the transports and dropped. A packaged build sets both transports to `info`
+// (main.js), so every one of these lines is discarded work there, and the CLI
+// emits an OSC title per spinner frame. `LOG_DEBUG_ON` is the guard, the same
+// shape as the `if (TRACE.on)` guard the probes on those lines already carry.
+//
+// This is a source scan, the house pattern for main.js (see
+// read-file-for-panel-bounds.test.js): main.js needs an Electron host, so the
+// only thing standing between the codebase and an unguarded hot-path debug
+// line is a read of the text.
+
+'use strict';
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+
+// Normalised: core.autocrlf=true and no .gitattributes means a fresh clone can
+// hand these tests CRLF while CI stays LF.
+const MAIN = fs.readFileSync(path.join(__dirname, '..', 'main.js'), 'utf8').replace(/\r\n/g, '\n');
+
+function ptyDataHandler() {
+  const start = MAIN.indexOf('function wireSessionPty(');
+  assert.notEqual(start, -1, 'wireSessionPty not found in main.js');
+  const end = MAIN.indexOf('\n}\n', start);
+  assert.notEqual(end, -1, 'end of wireSessionPty not found');
+  return MAIN.slice(start, end);
+}
+
+test('LOG_DEBUG_ON follows the transports rather than restating their condition', () => {
+  const m = MAIN.match(/^const LOG_DEBUG_ON = (.+);$/m);
+  assert.ok(m, 'LOG_DEBUG_ON must be declared');
+  assert.match(m[1], /transports\.file\.level/);
+  assert.match(m[1], /transports\.console\.level/);
+  assert.ok(
+    MAIN.indexOf('const LOG_DEBUG_ON') > MAIN.indexOf('log.transports.console.level ='),
+    'the flag must be read after the levels are set',
+  );
+});
+
+test('every debug line on the PTY data path is guarded', () => {
+  const lines = ptyDataHandler().split('\n');
+  const calls = lines.filter(l => l.includes('log.debug('));
+  assert.ok(calls.length >= 5, `expected the OSC debug lines to still be there, found ${calls.length}`);
+  for (const line of calls) {
+    assert.match(
+      line.trim(), /^if \(LOG_DEBUG_ON\) log\.debug\(/,
+      `an unguarded log.debug on the PTY data path builds its message on every frame: ${line.trim()}`,
+    );
+  }
+});
+
+test('the OSC 0 title line renders code points only under the guard', () => {
+  const line = ptyDataHandler().split('\n').find(l => l.includes('codePoints(payload, 1)'));
+  assert.ok(line, 'the OSC 0 debug line must still report the title code point');
+  assert.match(line.trim(), /^if \(LOG_DEBUG_ON\) log\.debug\(/);
+});