diff --git a/apps/desktop/electron/renderer-log.test.ts b/apps/desktop/electron/renderer-log.test.ts
index 5140020227..f120e56fbb 100644
--- a/apps/desktop/electron/renderer-log.test.ts
+++ b/apps/desktop/electron/renderer-log.test.ts
@@ -2,51 +2,85 @@ import { describe, expect, it, vi } from 'vitest'
 
 import { attachRendererConsoleCapture, formatRendererBoundaryReport, formatRendererConsoleLine } from './renderer-log'
 
+type ConsoleMessageEvent = {
+  level?: unknown
+  message?: unknown
+  sourceId?: unknown
+  lineNumber?: unknown
+}
+
+type ConsoleMessageHandler = (event: ConsoleMessageEvent) => void
+
+function createWindowHarness() {
+  let handler: ConsoleMessageHandler | undefined
+
+  const win = {
+    webContents: {
+      on: (_event: 'console-message', listener: ConsoleMessageHandler) => {
+        handler = listener
+      }
+    }
+  }
+
+  return { win, getHandler: () => handler }
+}
+
 describe('formatRendererConsoleLine', () => {
-  it('formats the canonical Electron 36+ details shape at error level', () => {
+  it('formats the canonical Electron console-message event at error level', () => {
     const line = formatRendererConsoleLine('hud', {
-      level: 3,
+      level: 'error',
       message: 'Minified React error #310',
-      sourceUrl: 'file:///app/index.js',
+      sourceId: 'file:///app/index.js',
       lineNumber: 13
     })
 
     expect(line).toBe('[renderer console:hud] Minified React error #310 (file:///app/index.js:13)')
   })
 
-  it('formats the deprecated positional shape at error level', () => {
-    const line = formatRendererConsoleLine('main', 3, 'boom', 7, 'file:///app/vendor.js')
-
-    expect(line).toBe('[renderer console:main] boom (file:///app/vendor.js:7)')
+  it('drops a canonical non-error string level', () => {
+    expect(
+      formatRendererConsoleLine('main', { level: 'info', message: 'x', sourceId: 's', lineNumber: 1 })
+    ).toBeNull()
   })
 
-  it('drops non-error levels in both shapes', () => {
-    expect(formatRendererConsoleLine('main', { level: 1, message: 'x', sourceUrl: 's', lineNumber: 1 })).toBeNull()
-    expect(formatRendererConsoleLine('main', 2, 'warn', 1, 's')).toBeNull()
+  it('drops malformed event objects', () => {
+    expect(formatRendererConsoleLine('main', {})).toBeNull()
   })
 })
 
 describe('attachRendererConsoleCapture', () => {
-  it('logs error-level messages and skips the rest', () => {
+  it('registers a single-argument listener, logs errors, and skips the rest', () => {
     const log = vi.fn()
-    let handler: ((...args: unknown[]) => void) | undefined
+    const capture = createWindowHarness()
 
-    const win = {
-      webContents: {
-        on: (_event: string, listener: (...args: unknown[]) => void) => {
-          handler = listener
-        }
-      }
-    }
+    attachRendererConsoleCapture(capture.win, 'quick-entry', log)
 
-    attachRendererConsoleCapture(win, 'quick-entry', log)
+    const handler = capture.getHandler()
+    expect(handler).toHaveLength(1)
 
-    handler?.({}, { level: 3, message: 'crash', sourceUrl: 'src', lineNumber: 2 })
-    handler?.({}, { level: 0, message: 'debug', sourceUrl: 'src', lineNumber: 3 })
+    handler?.({ level: 'error', message: 'crash', sourceId: 'src', lineNumber: 2 })
+    handler?.({ level: 'debug', message: 'debug', sourceId: 'src', lineNumber: 3 })
 
     expect(log).toHaveBeenCalledTimes(1)
     expect(log).toHaveBeenCalledWith('[renderer console:quick-entry] crash (src:2)')
   })
+
+  it('reports signature drift once across renderer windows', () => {
+    const log = vi.fn()
+    const firstCapture = createWindowHarness()
+    const secondCapture = createWindowHarness()
+
+    attachRendererConsoleCapture(firstCapture.win, 'main', log)
+    attachRendererConsoleCapture(secondCapture.win, 'hud', log)
+
+    firstCapture.getHandler()?.({})
+    secondCapture.getHandler()?.({})
+
+    expect(log).toHaveBeenCalledTimes(1)
+    expect(log).toHaveBeenCalledWith(
+      '[renderer console] Electron console-message signature drift detected; renderer errors may not be captured'
+    )
+  })
 })
 
 describe('formatRendererBoundaryReport', () => {
diff --git a/apps/desktop/electron/renderer-log.ts b/apps/desktop/electron/renderer-log.ts
index d3a97c6daa..8ac948e15a 100644
--- a/apps/desktop/electron/renderer-log.ts
+++ b/apps/desktop/electron/renderer-log.ts
@@ -15,53 +15,75 @@
  * tokens or PII we never want on disk.
  */
 
+type ConsoleMessageLevel = 'info' | 'warning' | 'error' | 'debug'
+
+interface ConsoleMessageEventLike {
+  level?: unknown
+  message?: unknown
+  sourceId?: unknown
+  lineNumber?: unknown
+}
+
 interface ConsoleMessageDetails {
-  level: number
+  level: ConsoleMessageLevel
   message: string
-  sourceUrl: string
+  sourceId: string
   lineNumber: number
 }
 
 interface WebContentsLike {
-  on(event: 'console-message', listener: (...args: unknown[]) => void): unknown
+  on(event: 'console-message', listener: (event: ConsoleMessageEventLike) => void): unknown
 }
 
 interface WindowLike {
   webContents: WebContentsLike
 }
 
-/** Normalize Electron's two `console-message` signatures into one line, or
- *  null for non-error levels. Canonical (Electron 36+): `(event, details)`;
- *  deprecated positional: `(event, level, message, line, sourceId)`.
- *  `level` is numeric 0..3, where 3 === error. */
-export function formatRendererConsoleLine(
-  label: string,
-  detailsOrLevel: unknown,
-  message?: unknown,
-  line?: unknown,
-  sourceId?: unknown
-): string | null {
-  const details =
-    detailsOrLevel && typeof detailsOrLevel === 'object' ? (detailsOrLevel as ConsoleMessageDetails) : null
+let didReportConsoleMessageSignatureDrift = false
 
-  const level = details ? details.level : detailsOrLevel
+function isConsoleMessageDetails(value: unknown): value is ConsoleMessageDetails {
+  if (typeof value !== 'object' || value === null) {
+    return false
+  }
 
-  if (level !== 3) {
+  const event = value as ConsoleMessageEventLike
+  const isKnownLevel =
+    event.level === 'info' || event.level === 'warning' || event.level === 'error' || event.level === 'debug'
+
+  return (
+    isKnownLevel &&
+    typeof event.message === 'string' &&
+    typeof event.sourceId === 'string' &&
+    typeof event.lineNumber === 'number'
+  )
+}
+
+/** Format Electron's canonical console-message event object into one line, or
+ *  null for non-error or malformed events. Hermes's pinned Electron 40.x line
+ *  puts severity and source metadata on the event object itself; accepting one
+ *  listener argument also avoids Electron's deprecated positional
+ *  `(event, level, message, line, sourceId)` path. */
+export function formatRendererConsoleLine(label: string, details: ConsoleMessageEventLike): string | null {
+  if (!isConsoleMessageDetails(details) || details.level !== 'error') {
     return null
   }
 
-  const text = details ? details.message : message
-  const src = details ? details.sourceUrl : sourceId
-  const lineNo = details ? details.lineNumber : line
-
-  return `[renderer console:${label}] ${String(text)} (${String(src)}:${String(lineNo)})`
+  return `[renderer console:${label}] ${details.message} (${details.sourceId}:${String(details.lineNumber)})`
 }
 
 /** Attach the error-level console hook to a renderer window. `log` is the
  *  desktop.log sink (rememberLog in main.ts). */
 export function attachRendererConsoleCapture(win: WindowLike, label: string, log: (line: string) => void): void {
-  win.webContents.on('console-message', (_event, detailsOrLevel, message, line, sourceId) => {
-    const formatted = formatRendererConsoleLine(label, detailsOrLevel, message, line, sourceId)
+  win.webContents.on('console-message', (event) => {
+    if (!isConsoleMessageDetails(event)) {
+      if (!didReportConsoleMessageSignatureDrift) {
+        didReportConsoleMessageSignatureDrift = true
+        log('[renderer console] Electron console-message signature drift detected; renderer errors may not be captured')
+      }
+      return
+    }
+
+    const formatted = formatRendererConsoleLine(label, event)
 
     if (formatted !== null) {
       log(formatted)