fix: a head nobody could name is not behind, so take latest is not offered without one

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/DiffDrawer.svelte

@@ -53,6 +53,7 @@
 				versions?: DiffVersionOption[]
 				onTakeLatest?: (head?: string) => void | Promise<void>
 				draftBase?: string
+				deployedHead?: string
 				draft: DiffData | undefined
 				current: DiffData
 				path?: string
@@ -140,16 +141,22 @@
 		}
 	}
 
-	/** The version this drawer presents as the deployed head, when it has a list to say
-	 *  so. Both the action's gate and the base it adopts hang off it, so "take latest"
-	 *  means the version the reader is looking at. */
+	/** The version this drawer presents as the deployed head: the one its list marks, else
+	 *  the head the editor knows. Both the action's gate and the base it adopts hang off
+	 *  it, so "take latest" means the version the reader is looking at. */
 	const headShown = $derived.by(() =>
-		data?.mode === 'normal' ? data.versions?.find((v) => v.isHead)?.id : undefined
+		data?.mode === 'normal'
+			? (data.versions?.find((v) => v.isHead)?.id ?? data.deployedHead)
+			: undefined
 	)
-	/** Behind as the drawer can see it: a base that is not the head on display. With no
-	 *  version list there is nothing to compare, so the editor's own gate stands. */
+	/** Behind as the drawer can see it. Unknown counts as not behind: offering to adopt a
+	 *  head nobody could name would move the base to a version never shown. */
 	const behindShown = $derived.by(
-		() => data?.mode === 'normal' && (headShown == null || data.draftBase !== headShown)
+		() =>
+			data?.mode === 'normal' &&
+			data.draftBase != null &&
+			headShown != null &&
+			data.draftBase !== headShown
 	)
 
 	let takingLatest = $state(false)
@@ -174,6 +181,7 @@
 					loadVersion?: (id: string) => Promise<Value | undefined>
 					onTakeLatest?: (head?: string) => void | Promise<void>
 					draftBase?: string
+					deployedHead?: string
 					draft?: Value | undefined
 					current: Value
 					defaultDiffType?: 'deployed' | 'draft'
@@ -195,6 +203,7 @@
 				loadVersion,
 				onTakeLatest,
 				draftBase,
+				deployedHead,
 				draft,
 				current,
 				button
@@ -213,6 +222,7 @@
 				versions,
 				onTakeLatest,
 				draftBase,
+				deployedHead,
 				draft: draft ? prepareDiff(draft) : undefined,
 				current: prepareDiff(current),
 				path: draft?.path || deployed?.path,

frontend/src/lib/components/FlowBuilder.svelte

@@ -1176,6 +1176,7 @@
 			versions: await deployedVersionOptions(),
 			onTakeLatest,
 			draftBase: draftBaseVersion,
+			deployedHead: version != null ? String(version) : undefined,
 			loadVersion: async (id) => {
 				const v = await FlowService.getFlowVersion({
 					workspace: opWorkspace!,

frontend/src/lib/components/ScriptBuilder.svelte

@@ -900,6 +900,7 @@
 			versions: await deployedVersionOptions(headHash),
 			onTakeLatest,
 			draftBase: draftBaseHash,
+			deployedHead: headHash,
 			loadVersion: async (hash) => {
 				const v = await ScriptService.getScriptByHash({ workspace: opWorkspace!, hash })
 				return replaceFalseWithUndefined({

frontend/src/lib/components/diff_drawer.ts

@@ -33,8 +33,12 @@ export type DiffDrawerDiff =
 			 *  the base adopted is the one the reader just looked at. */
 			onTakeLatest?: (head?: string) => void | Promise<void>
 			/** The version the draft forked from. The drawer offers `onTakeLatest` only
-			 *  while it differs from the head on display. */
+			 *  while it differs from the head, and passes that head to it. */
 			draftBase?: string
+			/** The deployed head as the editor knows it, used when no `versions` list
+			 *  loaded. Without either, the drawer cannot tell whether the draft is behind
+			 *  and offers nothing. */
+			deployedHead?: string
 			draft?: Value | undefined
 			current: Value
 			defaultDiffType?: 'deployed' | 'draft'

frontend/src/lib/components/raw_apps/RawAppEditorHeader.svelte

@@ -465,6 +465,7 @@
 			versions: await deployedVersionOptions(),
 			onTakeLatest,
 			draftBase: draftBaseVersion,
+			deployedHead: deployedVersionShown != null ? String(deployedVersionShown) : undefined,
 			loadVersion: async (id) => {
 				const v = await AppService.getAppByVersion({ workspace: opWorkspace!, id: Number(id) })
 				// Same normalization as `syncWithDeployed`, so switching versions doesn't