diff --git a/src/renderer/src/components/terminal-pane/pty-connection.test.ts b/src/renderer/src/components/terminal-pane/pty-connection.test.ts
index 1a7d768fcc0..c51539cd048 100644
--- a/src/renderer/src/components/terminal-pane/pty-connection.test.ts
+++ b/src/renderer/src/components/terminal-pane/pty-connection.test.ts
@@ -141,6 +141,7 @@ function createPane(paneId: number) {
       onData: vi.fn(() => ({ dispose: vi.fn() })),
       onResize: vi.fn(() => ({ dispose: vi.fn() }))
     },
+    container: { dataset: {} },
     fitAddon: {
       fit: vi.fn()
     }
diff --git a/src/renderer/src/components/terminal-pane/pty-connection.ts b/src/renderer/src/components/terminal-pane/pty-connection.ts
index 4f43abc56a3..ce27e9a7b00 100644
--- a/src/renderer/src/components/terminal-pane/pty-connection.ts
+++ b/src/renderer/src/components/terminal-pane/pty-connection.ts
@@ -10,7 +10,7 @@ import { createIpcPtyTransport } from './pty-transport'
 import { shouldSeedCacheTimerOnInitialTitle } from './cache-timer-seeding'
 import type { PtyConnectionDeps } from './pty-connection-types'
 import { safeFit } from '@/lib/pane-manager/pane-tree-ops'
-import { getFitOverrideForPane, bindPanePtyId } from '@/lib/pane-manager/mobile-fit-overrides'
+import { getFitOverrideForPty, bindPanePtyId } from '@/lib/pane-manager/mobile-fit-overrides'
 import { isPaneReplaying, replayIntoTerminal, replayIntoTerminalAsync } from './replay-guard'
 import {
   paneLeafId,
@@ -212,7 +212,8 @@ export function connectPanePty(
   }
 
   const onPtySpawn = (ptyId: string): void => {
-    bindPanePtyId(pane.id, ptyId)
+    bindPanePtyId(pane.id, ptyId, deps.tabId)
+    pane.container.dataset.ptyId = ptyId
     deps.syncPanePtyLayoutBinding(pane.id, ptyId)
     deps.updateTabPtyId(deps.tabId, ptyId)
     // Spawn completion is when a pane gains a concrete PTY ID. The initial
@@ -395,8 +396,10 @@ export function connectPanePty(
   const onResizeDisposable = pane.terminal.onResize(({ cols, rows }) => {
     // Why: when a mobile-fit override is active, the PTY is already at the
     // correct phone dimensions. Suppress resize forwarding to avoid spurious
-    // SIGWINCH signals that could cause TUI flicker.
-    if (getFitOverrideForPane(pane.id)) {
+    // SIGWINCH signals that could cause TUI flicker. Uses the transport's
+    // ptyId directly to avoid pane ID collisions across tabs.
+    const currentPtyId = transport.getPtyId()
+    if (currentPtyId && getFitOverrideForPty(currentPtyId)) {
       return
     }
     transport.resize(cols, rows)
@@ -557,7 +560,8 @@ export function connectPanePty(
         startFreshSpawn()
         return
       }
-      bindPanePtyId(pane.id, ptyId)
+      bindPanePtyId(pane.id, ptyId, deps.tabId)
+      pane.container.dataset.ptyId = ptyId
       deps.syncPanePtyLayoutBinding(pane.id, ptyId)
       deps.updateTabPtyId(deps.tabId, ptyId)
 
@@ -648,7 +652,8 @@ export function connectPanePty(
 
       // Why: when a mobile-fit override is active, skip sending desktop dims
       // to the PTY — the PTY is already at phone dimensions and must stay there.
-      if (!getFitOverrideForPane(pane.id)) {
+      const reattachPtyId = transport.getPtyId()
+      if (!reattachPtyId || !getFitOverrideForPty(reattachPtyId)) {
         transport.resize(cols, rows)
       }
       // Why: POSIX only delivers SIGWINCH when terminal dimensions actually
diff --git a/src/renderer/src/components/terminal-pane/terminal-appearance.ts b/src/renderer/src/components/terminal-pane/terminal-appearance.ts
index 861d5987f6c..b9b87976070 100644
--- a/src/renderer/src/components/terminal-pane/terminal-appearance.ts
+++ b/src/renderer/src/components/terminal-pane/terminal-appearance.ts
@@ -10,7 +10,7 @@ import {
 } from '@/lib/terminal-theme'
 import { buildFontFamily } from './layout-serialization'
 import { captureScrollState, restoreScrollState, safeFit } from '@/lib/pane-manager/pane-tree-ops'
-import { getFitOverrideForPane } from '@/lib/pane-manager/mobile-fit-overrides'
+import { getFitOverrideForPty } from '@/lib/pane-manager/mobile-fit-overrides'
 import type { PtyTransport } from './pty-transport'
 import type { EffectiveMacOptionAsAlt } from '@/lib/keyboard-layout/detect-option-as-alt'
 import { HEX_COLOR_RE } from '../../../../shared/color-validation'
@@ -231,7 +231,8 @@ export function applyTerminalAppearance(
     // Why: skip PTY resize when a mobile-fit override is active — the PTY
     // is already at the correct phone dimensions and must not be resized
     // back to desktop dimensions by an appearance change.
-    if (transport?.isConnected() && !getFitOverrideForPane(pane.id)) {
+    const appearancePtyId = transport?.getPtyId()
+    if (transport?.isConnected() && (!appearancePtyId || !getFitOverrideForPty(appearancePtyId))) {
       transport.resize(pane.terminal.cols, pane.terminal.rows)
       maybePushMode2031Flip(pane.id, appearance.mode, transport, paneMode2031, paneLastThemeMode)
     }
diff --git a/src/renderer/src/lib/pane-manager/mobile-fit-overrides.ts b/src/renderer/src/lib/pane-manager/mobile-fit-overrides.ts
index 3c10f129e18..7e5a781a081 100644
--- a/src/renderer/src/lib/pane-manager/mobile-fit-overrides.ts
+++ b/src/renderer/src/lib/pane-manager/mobile-fit-overrides.ts
@@ -10,7 +10,9 @@ type FitOverride = {
 }
 
 const overridesByPtyId = new Map<string, FitOverride>()
-const ptyIdByPaneId = new Map<number, string>()
+// Why: keyed by 'tabId:paneId' composite to avoid collisions when different
+// tabs have panes with the same numeric ID (pane IDs are per-tab, not global).
+const ptyIdByPaneKey = new Map<string, string>()
 
 // Why: the override maps are plain JS — React components that read them
 // (e.g. the desktop mobile-fit banner) have no way to know when entries
@@ -52,9 +54,12 @@ export function setFitOverride(
 
 export function getPaneIdsForPty(ptyId: string): number[] {
   const result: number[] = []
-  for (const [paneId, boundPtyId] of ptyIdByPaneId) {
+  for (const [key, boundPtyId] of ptyIdByPaneKey) {
     if (boundPtyId === ptyId) {
-      result.push(paneId)
+      const paneId = Number(key.split(':').pop())
+      if (!Number.isNaN(paneId)) {
+        result.push(paneId)
+      }
     }
   }
   return result
@@ -64,24 +69,32 @@ export function getFitOverrideForPty(ptyId: string): FitOverride | null {
   return overridesByPtyId.get(ptyId) ?? null
 }
 
-export function getFitOverrideForPane(paneId: number): FitOverride | null {
-  const ptyId = ptyIdByPaneId.get(paneId)
-  if (!ptyId) {
-    return null
+export function getFitOverrideForPane(paneId: number, tabId?: string): FitOverride | null {
+  if (tabId) {
+    const ptyId = ptyIdByPaneKey.get(`${tabId}:${paneId}`)
+    if (!ptyId) {
+      return null
+    }
+    return overridesByPtyId.get(ptyId) ?? null
   }
-  return overridesByPtyId.get(ptyId) ?? null
+  return null
 }
 
-export function bindPanePtyId(paneId: number, ptyId: string | null): void {
-  if (ptyId) {
-    ptyIdByPaneId.set(paneId, ptyId)
-  } else {
-    ptyIdByPaneId.delete(paneId)
+export function bindPanePtyId(paneId: number, ptyId: string | null, tabId?: string): void {
+  if (tabId) {
+    const key = `${tabId}:${paneId}`
+    if (ptyId) {
+      ptyIdByPaneKey.set(key, ptyId)
+    } else {
+      ptyIdByPaneKey.delete(key)
+    }
   }
 }
 
-export function unbindPane(paneId: number): void {
-  ptyIdByPaneId.delete(paneId)
+export function unbindPane(paneId: number, tabId?: string): void {
+  if (tabId) {
+    ptyIdByPaneKey.delete(`${tabId}:${paneId}`)
+  }
 }
 
 export function hydrateOverrides(
diff --git a/src/renderer/src/lib/pane-manager/pane-tree-ops.test.ts b/src/renderer/src/lib/pane-manager/pane-tree-ops.test.ts
index e52585fb05b..0a2450ba669 100644
--- a/src/renderer/src/lib/pane-manager/pane-tree-ops.test.ts
+++ b/src/renderer/src/lib/pane-manager/pane-tree-ops.test.ts
@@ -33,7 +33,7 @@ function createPane({
   return {
     id: 1,
     terminal: terminal as never,
-    container: {} as never,
+    container: { dataset: {} } as never,
     xtermContainer: {} as never,
     linkTooltip: {} as never,
     gpuRenderingEnabled: true,
diff --git a/src/renderer/src/lib/pane-manager/pane-tree-ops.ts b/src/renderer/src/lib/pane-manager/pane-tree-ops.ts
index 7e7d05bb6c1..721479d32a8 100644
--- a/src/renderer/src/lib/pane-manager/pane-tree-ops.ts
+++ b/src/renderer/src/lib/pane-manager/pane-tree-ops.ts
@@ -5,7 +5,7 @@ import type {
   PaneStyleOptions
 } from './pane-manager-types'
 import { createDivider } from './pane-divider'
-import { getFitOverrideForPane } from './mobile-fit-overrides'
+import { getFitOverrideForPty } from './mobile-fit-overrides'
 
 export { findLineByContent, captureScrollState, restoreScrollState } from './pane-scroll'
 
@@ -44,8 +44,10 @@ export function safeFit(pane: ManagedPane): void {
     // Why: when a mobile client has resized this PTY to phone dimensions,
     // the desktop must keep xterm at those dimensions instead of fitting to
     // the desktop pane geometry. This prevents desktop auto-fit from undoing
-    // the mobile resize.
-    const override = getFitOverrideForPane(pane.id)
+    // the mobile resize. Uses data-pty-id (set by bindPanePtyId) to look up
+    // the override by ptyId directly, avoiding pane ID collisions across tabs.
+    const ptyId = pane.container.dataset.ptyId
+    const override = ptyId ? getFitOverrideForPty(ptyId) : null
     if (override) {
       if (pane.terminal.cols !== override.cols || pane.terminal.rows !== override.rows) {
         pane.terminal.resize(override.cols, override.rows)