diff --git a/ui-tui-opentui-v2/src/entry/main.tsx b/ui-tui-opentui-v2/src/entry/main.tsx
index c1a30d53d7c..f0163fc3d97 100644
--- a/ui-tui-opentui-v2/src/entry/main.tsx
+++ b/ui-tui-opentui-v2/src/entry/main.tsx
@@ -32,6 +32,7 @@ import { getLog } from '../boundary/log.ts'
 import { acquireRenderer } from '../boundary/renderer.ts'
 import { makeAppLayer } from '../boundary/runtime.ts'
 import { nthAssistantResponse } from '../logic/copy.ts'
+import { envFlag } from '../logic/env.ts'
 import { createPromptHistory, dirHistoryPersister, loadDirHistory } from '../logic/history.ts'
 import { createPasteStore } from '../logic/pastes.ts'
 import { mapResumeHistory, mapSessionList } from '../logic/resume.ts'
@@ -461,16 +462,14 @@ function streamHello(controller: FakeGatewayController): void {
   controller.emit({ type: 'message.complete' })
 }
 
-const TRUE_RE = /^(?:1|true|yes|on)$/i
-
 if (import.meta.main) {
-  const fake = TRUE_RE.test(process.env.HERMES_TUI_FAKE?.trim() ?? '')
+  const fake = envFlag(process.env.HERMES_TUI_FAKE, false)
   const cols = process.stdout.columns || 80
   const initialPrompt = process.env.HERMES_TUI_PROMPT?.trim() || process.argv.slice(2).join(' ').trim()
   const resumeId = process.env.HERMES_TUI_RESUME?.trim()
   // Mouse on by default (opencode parity: wheel-scroll the transcript, drag the
   // scrollbar, click-to-expand tools, text-aware selection). HERMES_TUI_MOUSE=0 opts out.
-  const mouse = !/^(?:0|false|no|off)$/i.test(process.env.HERMES_TUI_MOUSE?.trim() ?? '')
+  const mouse = envFlag(process.env.HERMES_TUI_MOUSE, true)
   const base = { mouse, fake, cols }
   const withPrompt = initialPrompt ? { ...base, initialPrompt } : base
   const input: TuiInput = resumeId ? { ...withPrompt, resumeId } : withPrompt
diff --git a/ui-tui-opentui-v2/src/logic/env.ts b/ui-tui-opentui-v2/src/logic/env.ts
new file mode 100644
index 00000000000..294e5c69ef2
--- /dev/null
+++ b/ui-tui-opentui-v2/src/logic/env.ts
@@ -0,0 +1,16 @@
+/**
+ * env — shared boolean env-flag parsing (one source for the TRUE/FALSE regexes).
+ *
+ * Recognized truthy values: 1/true/yes/on; falsy: 0/false/no/off (case-insensitive,
+ * surrounding whitespace trimmed). Anything else (incl. unset) is "unrecognized".
+ */
+export const TRUE_RE = /^(?:1|true|yes|on)$/i
+export const FALSE_RE = /^(?:0|false|no|off)$/i
+
+/** Parse a boolean env var; returns `fallback` when unset/unrecognized. */
+export function envFlag(value: string | undefined, fallback: boolean): boolean {
+  const v = value?.trim() ?? ''
+  if (TRUE_RE.test(v)) return true
+  if (FALSE_RE.test(v)) return false
+  return fallback
+}
diff --git a/ui-tui-opentui-v2/src/logic/theme.ts b/ui-tui-opentui-v2/src/logic/theme.ts
index e273a98f345..7d20013b8e2 100644
--- a/ui-tui-opentui-v2/src/logic/theme.ts
+++ b/ui-tui-opentui-v2/src/logic/theme.ts
@@ -14,6 +14,8 @@
  * ui-tui/src/gatewayTypes.ts). Keep this port in sync if that contract changes.
  */
 
+import { FALSE_RE, TRUE_RE } from './env.ts'
+
 export interface ThemeColors {
   primary: string
   accent: string
@@ -317,9 +319,6 @@ export const LIGHT_THEME: Theme = {
   bannerHero: ''
 }
 
-const TRUE_RE = /^(?:1|true|yes|on)$/
-const FALSE_RE = /^(?:0|false|no|off)$/
-
 const LIGHT_DEFAULT_TERM_PROGRAMS = new Set<string>(['Apple_Terminal'])
 
 const LUMA_LIGHT_THRESHOLD = 0.6
diff --git a/ui-tui-opentui-v2/src/test/env.test.ts b/ui-tui-opentui-v2/src/test/env.test.ts
new file mode 100644
index 00000000000..cf510b8ae76
--- /dev/null
+++ b/ui-tui-opentui-v2/src/test/env.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, test } from 'bun:test'
+
+import { envFlag } from '../logic/env.ts'
+
+describe('envFlag', () => {
+  test('recognizes truthy values regardless of case/whitespace', () => {
+    for (const v of ['1', 'true', 'yes', 'on', 'TRUE', 'Yes', ' on ']) {
+      expect(envFlag(v, false)).toBe(true)
+    }
+  })
+
+  test('recognizes falsy values regardless of case/whitespace', () => {
+    for (const v of ['0', 'false', 'no', 'off', 'FALSE', 'No', ' off ']) {
+      expect(envFlag(v, true)).toBe(false)
+    }
+  })
+
+  test('returns fallback when unset', () => {
+    expect(envFlag(undefined, true)).toBe(true)
+    expect(envFlag(undefined, false)).toBe(false)
+    expect(envFlag('', true)).toBe(true)
+    expect(envFlag('   ', false)).toBe(false)
+  })
+
+  test('returns fallback for unrecognized garbage', () => {
+    expect(envFlag('maybe', true)).toBe(true)
+    expect(envFlag('maybe', false)).toBe(false)
+    expect(envFlag('2', true)).toBe(true)
+    expect(envFlag('enabled', false)).toBe(false)
+  })
+})