diff --git a/frontend/src/lib/components/apps/editor/AppEditorHeader.svelte b/frontend/src/lib/components/apps/editor/AppEditorHeader.svelte
index 6b4481c826..1085fc06e8 100644
--- a/frontend/src/lib/components/apps/editor/AppEditorHeader.svelte
+++ b/frontend/src/lib/components/apps/editor/AppEditorHeader.svelte
@@ -63,7 +63,7 @@
 	import LazyModePanel from './contextPanel/LazyModePanel.svelte'
 	import type { DiffDrawerI } from '$lib/components/diff_drawer'
 	import AppEditorHeaderDeploy from './AppEditorHeaderDeploy.svelte'
-	import { computeSecretUrl } from './appDeploy.svelte'
+	import { computeSecretUrl, versionThisDeployWrote } from './appDeploy.svelte'
 	import { updatePolicy } from './appPolicy'
 	import { editInForkAllowed, editInForkLabel, openEditInFork } from '$lib/utils/editInFork'
 	import { isCloudHosted } from '$lib/cloud'
@@ -392,7 +392,7 @@
 			workspace: $workspaceStore!,
 			path: npath
 		})
-		version = appHistory[0]?.version
+		version = versionThisDeployWrote(appHistory, $userStore?.username)
 		// Re-pin the fork base to the just-deployed head: the editor stays open, so a
 		// follow-up deploy (or a new edit) would otherwise compare against the now-
 		// superseded base and falsely warn. parent_version is in
diff --git a/frontend/src/lib/components/apps/editor/appDeploy.svelte.ts b/frontend/src/lib/components/apps/editor/appDeploy.svelte.ts
index 122c42bcf9..b071166dee 100644
--- a/frontend/src/lib/components/apps/editor/appDeploy.svelte.ts
+++ b/frontend/src/lib/components/apps/editor/appDeploy.svelte.ts
@@ -1,7 +1,28 @@
-import { base } from "$lib/base"
-import { workspaceStore } from "$lib/stores"
-import { get } from "svelte/store"
+import { base } from '$lib/base'
+import { workspaceStore } from '$lib/stores'
+import { get } from 'svelte/store'
 
 export function computeSecretUrl(secretUrl: string) {
-    return `${window.location.origin}${base}/public/${get(workspaceStore)}/${secretUrl}`
+	return `${window.location.origin}${base}/public/${get(workspaceStore)}/${secretUrl}`
+}
+
+/**
+ * The version a just-finished deploy wrote, read back from the history it lands in.
+ * The deploy and this read are two requests, so someone else's deploy in between is the
+ * newest entry too; taking it would make their version the fork base of content it never
+ * contained, and the next deploy would find base === head and overwrite them with no
+ * warning. A head this caller did not write therefore yields `undefined`: an unknown
+ * base, which the timestamps still cover, rather than a wrong one.
+ *
+ * Author is all the history can be matched on (`deployment_msg` is written later, by the
+ * dependency job), so a second deploy by the same user inside that window still reads as
+ * this one's.
+ */
+export function versionThisDeployWrote(
+	history: { version: number; created_by?: string }[] | undefined,
+	deployedBy: string | undefined
+): number | undefined {
+	const head = history?.[0]
+	if (!head || !deployedBy || head.created_by !== deployedBy) return undefined
+	return head.version
 }
diff --git a/frontend/src/lib/components/apps/editor/appDeploy.test.ts b/frontend/src/lib/components/apps/editor/appDeploy.test.ts
new file mode 100644
index 0000000000..184df32a96
--- /dev/null
+++ b/frontend/src/lib/components/apps/editor/appDeploy.test.ts
@@ -0,0 +1,16 @@
+import { describe, it, expect } from 'vitest'
+import { versionThisDeployWrote } from './appDeploy.svelte'
+
+describe('versionThisDeployWrote', () => {
+	it('takes the head this deploy wrote', () => {
+		expect(versionThisDeployWrote([{ version: 7, created_by: 'alice' }], 'alice')).toBe(7)
+	})
+
+	it('claims nothing when another deploy landed on top', () => {
+		// The base would otherwise be a version this content never contained, and the
+		// next deploy would find base === head and overwrite it unwarned.
+		expect(versionThisDeployWrote([{ version: 8, created_by: 'bob' }], 'alice')).toBe(undefined)
+		expect(versionThisDeployWrote([], 'alice')).toBe(undefined)
+		expect(versionThisDeployWrote([{ version: 7, created_by: 'alice' }], undefined)).toBe(undefined)
+	})
+})
diff --git a/frontend/src/lib/components/raw_apps/RawAppEditorHeader.svelte b/frontend/src/lib/components/raw_apps/RawAppEditorHeader.svelte
index 538f433dbb..58c13fd88c 100644
--- a/frontend/src/lib/components/raw_apps/RawAppEditorHeader.svelte
+++ b/frontend/src/lib/components/raw_apps/RawAppEditorHeader.svelte
@@ -70,6 +70,7 @@
 	// `runtime.syncPreviewWithDeployed`, which discards the fork draft + reloads
 	// the preview to the deployed version.
 	import { AIBtnClasses } from '../copilot/chat/AIButtonStyle'
+	import { versionThisDeployWrote } from '../apps/editor/appDeploy.svelte'
 	import { stripRawAppDiffNoise } from './utils'
 	import type { RawAppData } from './dataTableRefUtils'
 	import { editInForkAllowed, editInForkLabel, openEditInFork } from '$lib/utils/editInFork'
@@ -544,7 +545,8 @@
 			workspace: opWorkspace!,
 			path: npath
 		})
-		version = appHistory[0]?.version
+		// Only a version this deploy can claim becomes the draft's base below.
+		version = versionThisDeployWrote(appHistory, $userStore?.username)
 
 		closeSaveDrawer()
 		sendUserToast('App deployed successfully')