diff --git a/mobile/app/h/[hostId]/session/[worktreeId].tsx b/mobile/app/h/[hostId]/session/[worktreeId].tsx
index 8b032c3ad99..05fff5e7cb0 100644
--- a/mobile/app/h/[hostId]/session/[worktreeId].tsx
+++ b/mobile/app/h/[hostId]/session/[worktreeId].tsx
@@ -1377,7 +1377,10 @@ export default function SessionScreen() {
         {
           terminal: handle,
           client: { id: deviceTokenRef.current!, type: 'mobile' as const },
-          viewport: viewportRef.current ?? undefined,
+          viewport: nativeChatTerminalStream.mobileNativeChatSubscribeViewport(
+            covered,
+            viewportRef.current
+          ),
           capabilities: nativeChatTerminalStream.mobileNativeChatTerminalCapabilities(covered)
         },
         (result) => {
@@ -2455,6 +2458,7 @@ export default function SessionScreen() {
     terminalFrameHeightRef,
     viewportRef,
     viewportMeasuredRef,
+    nativeChatCoveredRef: showNativeChatRef,
     clientRef,
     deviceTokenRef,
     initializedHandlesRef,
diff --git a/mobile/src/session/mobile-native-chat-terminal-stream.test.ts b/mobile/src/session/mobile-native-chat-terminal-stream.test.ts
index cc92c6b3aca..9b751c5af75 100644
--- a/mobile/src/session/mobile-native-chat-terminal-stream.test.ts
+++ b/mobile/src/session/mobile-native-chat-terminal-stream.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, it } from 'vitest'
 import {
   isTerminalCoveredByNativeChat,
+  mobileNativeChatSubscribeViewport,
   mobileNativeChatTerminalCapabilities,
   resolveMobileNativeChatTerminalStreamAction
 } from './mobile-native-chat-terminal-stream'
@@ -34,6 +35,17 @@ describe('mobile native-chat terminal stream lifecycle', () => {
     expect(mobileNativeChatTerminalCapabilities(false)).toEqual({ terminalBinaryStream: 1 })
   })
 
+  it('omits the viewport from a covered lease subscribe so the host keeps desktop dims', () => {
+    // Why: handleMobileSubscribe phone-fits the PTY whenever a viewport is present,
+    // even for a lease-only subscribe — entering chat must not resize the terminal.
+    expect(mobileNativeChatSubscribeViewport(true, { cols: 40, rows: 60 })).toBeUndefined()
+    expect(mobileNativeChatSubscribeViewport(false, { cols: 40, rows: 60 })).toEqual({
+      cols: 40,
+      rows: 60
+    })
+    expect(mobileNativeChatSubscribeViewport(false, null)).toBeUndefined()
+  })
+
   it('records a cold-start cover before WebView readiness so return refreshes', () => {
     expect(
       resolveMobileNativeChatTerminalStreamAction({
diff --git a/mobile/src/session/mobile-native-chat-terminal-stream.ts b/mobile/src/session/mobile-native-chat-terminal-stream.ts
index 387fe9c3580..d96ced2a6f6 100644
--- a/mobile/src/session/mobile-native-chat-terminal-stream.ts
+++ b/mobile/src/session/mobile-native-chat-terminal-stream.ts
@@ -35,3 +35,11 @@ export function mobileNativeChatTerminalCapabilities(covered: boolean): {
     ? { terminalBinaryStream: 1, mobileInputLeaseOnly: 1 }
     : { terminalBinaryStream: 1 }
 }
+
+// Why: a covered subscribe is only an input lease — carrying phone dims would make the host phone-fit a PTY native chat never renders.
+export function mobileNativeChatSubscribeViewport(
+  covered: boolean,
+  viewport: { cols: number; rows: number } | null
+): { cols: number; rows: number } | undefined {
+  return covered ? undefined : (viewport ?? undefined)
+}
diff --git a/mobile/src/terminal/terminal-viewport-refit.test.ts b/mobile/src/terminal/terminal-viewport-refit.test.ts
index de63099155b..5312e64d188 100644
--- a/mobile/src/terminal/terminal-viewport-refit.test.ts
+++ b/mobile/src/terminal/terminal-viewport-refit.test.ts
@@ -135,6 +135,18 @@ describe('terminal viewport refit', () => {
     expect(timerBody).toContain('if (!decision.shouldRefit)')
   })
 
+  it('suppresses refits while native chat covers the active terminal', () => {
+    // Why: native chat renders the transcript, not the grid — a refit there would
+    // reflow the desktop PTY to phone dims the user never sees.
+    const timerStart = hookSource.indexOf('refitTimerRef.current = setTimeout(')
+    const coveredCheck = hookSource.indexOf('if (nativeChatCoveredRef.current)', timerStart)
+    const measureIndex = hookSource.indexOf('measureFitDimensions', timerStart)
+    expect(timerStart).toBeGreaterThanOrEqual(0)
+    expect(coveredCheck).toBeGreaterThan(timerStart)
+    expect(measureIndex).toBeGreaterThan(coveredCheck)
+    expect(sessionSource).toContain('nativeChatCoveredRef: showNativeChatRef')
+  })
+
   it('is wired into the session screen', () => {
     expect(sessionSource).toContain('useTerminalViewportRefit({')
     expect(sessionSource).toContain('tabStripVisible: terminals.length > 1')
diff --git a/mobile/src/terminal/terminal-viewport-refit.ts b/mobile/src/terminal/terminal-viewport-refit.ts
index 6194fabc675..3091ac8c301 100644
--- a/mobile/src/terminal/terminal-viewport-refit.ts
+++ b/mobile/src/terminal/terminal-viewport-refit.ts
@@ -23,6 +23,8 @@ type TerminalViewportRefitOptions = {
   terminalFrameHeightRef: RefObject<number>
   viewportRef: RefObject<TerminalViewportDims | null>
   viewportMeasuredRef: RefObject<boolean>
+  // Why: while native chat covers the active terminal, a refit would push phone dims into a PTY nobody on this device is viewing.
+  nativeChatCoveredRef: RefObject<boolean>
   clientRef: RefObject<RpcClient | null>
   deviceTokenRef: RefObject<string | null>
   initializedHandlesRef: RefObject<Set<string>>
@@ -51,6 +53,7 @@ export function useTerminalViewportRefit(
     terminalFrameHeightRef,
     viewportRef,
     viewportMeasuredRef,
+    nativeChatCoveredRef,
     clientRef,
     deviceTokenRef,
     initializedHandlesRef,
@@ -99,6 +102,10 @@ export function useTerminalViewportRefit(
         if (!handle) {
           return
         }
+        // Why: the trigger already marked the viewport stale, and the return-to-terminal resubscribe re-measures — refitting now would resize a covered PTY.
+        if (nativeChatCoveredRef.current) {
+          return
+        }
         const ref = terminalRefs.current.get(handle)
         if (!ref) {
           return
@@ -171,6 +178,7 @@ export function useTerminalViewportRefit(
       terminalFrameHeightRef,
       viewportRef,
       viewportMeasuredRef,
+      nativeChatCoveredRef,
       clientRef,
       deviceTokenRef,
       initializedHandlesRef,