diff --git a/scripts/checkedReadMigration.test.ts b/scripts/checkedReadMigration.test.ts
index dc088dde..f927e5f8 100644
--- a/scripts/checkedReadMigration.test.ts
+++ b/scripts/checkedReadMigration.test.ts
@@ -82,6 +82,7 @@ function makeSession() {
 		askClose: async () => 'discard' as const,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/scripts/documentEncodingRoundTrip.test.ts b/scripts/documentEncodingRoundTrip.test.ts
index e9e60cd3..914fdcc7 100644
--- a/scripts/documentEncodingRoundTrip.test.ts
+++ b/scripts/documentEncodingRoundTrip.test.ts
@@ -92,6 +92,7 @@ function makeSession() {
 		askClose: async () => 'discard' as const,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/scripts/explicitSaveCancelsAutoSave.test.ts b/scripts/explicitSaveCancelsAutoSave.test.ts
index 0f06f764..ab92f5f2 100644
--- a/scripts/explicitSaveCancelsAutoSave.test.ts
+++ b/scripts/explicitSaveCancelsAutoSave.test.ts
@@ -99,6 +99,7 @@ function makeSession() {
 		askClose: async () => 'discard' as const,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/scripts/externalChangeReload.test.ts b/scripts/externalChangeReload.test.ts
index 5907c808..11dd2d9f 100644
--- a/scripts/externalChangeReload.test.ts
+++ b/scripts/externalChangeReload.test.ts
@@ -53,6 +53,7 @@ function makeSession() {
 		askClose: async () => 'discard' as const,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/scripts/lossySaveRefusalScope.test.ts b/scripts/lossySaveRefusalScope.test.ts
index 1faeff67..e9cff2da 100644
--- a/scripts/lossySaveRefusalScope.test.ts
+++ b/scripts/lossySaveRefusalScope.test.ts
@@ -88,6 +88,7 @@ function makeSession() {
 		askClose: async () => 'discard' as const,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/scripts/oneWritePerTabInFlight.test.ts b/scripts/oneWritePerTabInFlight.test.ts
index 0ff20b1d..cfb7744c 100644
--- a/scripts/oneWritePerTabInFlight.test.ts
+++ b/scripts/oneWritePerTabInFlight.test.ts
@@ -116,6 +116,7 @@ function makeSession() {
 		askClose: async () => 'discard' as const,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/scripts/pathIdentityCaseFolding.test.ts b/scripts/pathIdentityCaseFolding.test.ts
index 2aae2a8d..be6bb0c0 100644
--- a/scripts/pathIdentityCaseFolding.test.ts
+++ b/scripts/pathIdentityCaseFolding.test.ts
@@ -121,6 +121,7 @@ function makeSession() {
 		askClose: async () => 'discard' as const,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/scripts/reopenDirtyDocument.test.ts b/scripts/reopenDirtyDocument.test.ts
index c986f2a5..c6a3d9b4 100644
--- a/scripts/reopenDirtyDocument.test.ts
+++ b/scripts/reopenDirtyDocument.test.ts
@@ -80,6 +80,7 @@ function makeSession() {
 		askClose: async () => 'discard' as const,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/scripts/taskToggleLineEndings.test.ts b/scripts/taskToggleLineEndings.test.ts
index 022702a1..0de66501 100644
--- a/scripts/taskToggleLineEndings.test.ts
+++ b/scripts/taskToggleLineEndings.test.ts
@@ -70,6 +70,7 @@ function makeSession() {
 		askClose: async () => 'discard' as const,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/scripts/truncatedBufferGuard.test.ts b/scripts/truncatedBufferGuard.test.ts
index 1e24bbaa..13203164 100644
--- a/scripts/truncatedBufferGuard.test.ts
+++ b/scripts/truncatedBufferGuard.test.ts
@@ -49,6 +49,8 @@ const { createDocumentSession } = await import('../src/lib/sessions/documentSess
 const viewer = readSource(new URL('../src/lib/MarkdownViewer.svelte', import.meta.url));
 
 const errors: string[] = [];
+/** Non-failure notices the session raised, in order. */
+const notices: string[] = [];
 /** What the close dialog answers next. Set per test. */
 let closeAnswer: 'save' | 'discard' | 'cancel' = 'discard';
 
@@ -71,6 +73,7 @@ function makeSession() {
 		askClose: async () => closeAnswer,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => notices.push('partialCopySaved'),
 	});
 }
 
@@ -78,6 +81,7 @@ function reset() {
 	tabManager.closeAll();
 	invokeCalls = [];
 	errors.length = 0;
+	notices.length = 0;
 	closeAnswer = 'discard';
 }
 
@@ -362,23 +366,49 @@ test('a task checkbox is not toggled into a partial buffer that already carries
 	assert.equal(tab.rawContent, edited, 'and the edits it carries must not be traded for the file’s tail');
 });
 
-test('Save As refuses to copy a partially loaded document', async () => {
-	// The copy would be silently short, and it is a NEW file — nothing about it
-	// says it is missing everything past 50KB. The guard sits before the dialog,
-	// so the user is not asked where to put a document that is not going to be
-	// written.
+test('Save As completes the buffer first, so the copy is whole when it can be', async () => {
+	// Reaching for Save As is not a reason to write less than the document. The
+	// tail is readable and the buffer is clean, so there is nothing stopping this
+	// copy from being the whole file — and nothing to warn about.
 	reset();
-	const { session } = await openPartial();
+	const { session, tab } = await openPartial();
+	handleInvoke = (cmd) => {
+		if (cmd === 'read_file_content_checked') return [FULL, false, 'UTF-8'];
+		if (cmd === 'save_file_content') return null;
+		if (cmd === 'canonicalize_path') return '/docs/copy.md';
+		if (cmd === 'plugin:dialog|save') return '/docs/copy.md';
+		throw new Error(`unexpected invoke: ${cmd}`);
+	};
+
+	assert.equal(await session.saveContentAs(), true);
+	assert.equal(invokeCalls.find((call) => call.cmd === 'save_file_content')?.args.content, FULL);
+	assert.deepEqual(notices, [], 'a whole copy is not worth a warning');
+	assert.notEqual(tab.isTruncated, true);
+});
+
+test('Save As is the way out of a partial buffer that carries edits', async () => {
+	// The one write a partial buffer may make. A copy is a NEW file at a path the
+	// user chose, so it destroys nothing they had — and refusing it too left the
+	// edits below with no exit at all, which is a worse answer than a short copy
+	// the user is told about. `refuseIfLossilyDecoded` has always reasoned this
+	// way, and this is the same trade.
+	reset();
+	const { session, tab } = await openPartial();
+	const edited = `${PARTIAL}edited`;
+	tabManager.updateTabRawContent(tab.id, edited);
+	// Completing the buffer is not on the table here: the tail is gone, and even
+	// if it were readable, reading it would discard the edits this is rescuing.
 	makeTailUnreadable();
 
-	assert.equal(await session.saveContentAs(), false, 'Save As must report failure rather than write a short copy');
-	assert.equal(wroteToDisk(), false, 'an incomplete copy must never be written');
-	assert.equal(
-		invokeCalls.some((call) => call.cmd.endsWith('dialog|save')),
-		false,
-		'and the Save As dialog is not opened for a write that cannot happen',
-	);
-	assert.deepEqual(errors, ['Refusing to save a partially loaded document']);
+	assert.equal(await session.saveContentAs(), true, 'the rescue must be allowed to happen');
+	assert.equal(invokeCalls.find((call) => call.cmd === 'save_file_content')?.args.content, edited);
+	assert.deepEqual(notices, ['partialCopySaved'], 'and the reader is told where the copy stops');
+	assert.deepEqual(errors, [], 'it is not a failure');
+	// The flag described the file the tab used to point at. It now points at the
+	// copy and holds all of it, so leaving the flag on would free the text and
+	// then trap it again — every later save refused, from a whole document.
+	assert.notEqual(tab.isTruncated, true);
+	assert.equal(await session.saveContent(tab.id), true, 'and the tab saves normally from here on');
 });
 
 test('answering “Save” to the close dialog cannot flush a partial buffer', async () => {
diff --git a/scripts/viewModeWithoutSaving.test.ts b/scripts/viewModeWithoutSaving.test.ts
index 2dac55d4..f7b69ad0 100644
--- a/scripts/viewModeWithoutSaving.test.ts
+++ b/scripts/viewModeWithoutSaving.test.ts
@@ -390,6 +390,7 @@ function makeSession(askClose: (title: string) => Promise<'save' | 'discard' | '
 		askClose,
 		onCloseSaveNewerEdits: () => {},
 		onCloseAutoSaveFailed: () => {},
+		onPartialCopySaved: () => {},
 	});
 }
 
diff --git a/src/lib/MarkdownViewer.svelte b/src/lib/MarkdownViewer.svelte
index 9a0d7a16..3e4a82f2 100644
--- a/src/lib/MarkdownViewer.svelte
+++ b/src/lib/MarkdownViewer.svelte
@@ -701,6 +701,9 @@ import { createDocumentSession, type LoadMarkdownOptions } from './sessions/docu
 			}),
 		onCloseSaveNewerEdits: () => addToast(t('toast.savedNewerEdits', settings.language), 'info'),
 		onCloseAutoSaveFailed: () => addToast(t('toast.autoSaveFailed', settings.language), 'error'),
+		// Not an error: the copy is the way out of a partial buffer, and it was
+		// written. What the reader needs is to know where it stops.
+		onPartialCopySaved: () => addToast(t('toast.partialCopySaved', settings.language), 'info'),
 	});
 
 	async function discardPersistedWindowState() {
diff --git a/src/lib/sessions/documentSession.svelte.ts b/src/lib/sessions/documentSession.svelte.ts
index 05b5f9c4..350f89e7 100644
--- a/src/lib/sessions/documentSession.svelte.ts
+++ b/src/lib/sessions/documentSession.svelte.ts
@@ -55,6 +55,12 @@ type DocumentSessionOptions = {
 	askClose: (title: string) => Promise<'save' | 'discard' | 'cancel'>;
 	onCloseSaveNewerEdits: () => void;
 	onCloseAutoSaveFailed: () => void;
+	/**
+	 * A Save As wrote a copy that stops where the load did. Not a failure — the
+	 * copy is the way out of a partial buffer — but the reader has to be told
+	 * what is in the file they just made.
+	 */
+	onPartialCopySaved: () => void;
 };
 
 /**
@@ -557,7 +563,7 @@ export function createDocumentSession(options: DocumentSessionOptions) {
 		// a large file completes its buffer first. If one is ever missed, the
 		// write must fail loudly rather than silently truncate the document.
 		if (tab.isTruncated) {
-			options.onError('Refusing to save a partially loaded document', new Error(tab.path));
+			options.onError(t('toast.partialSaveBlocked', settings.language), tab.path);
 			return false;
 		}
 		let targetPath = tab.path;
@@ -625,11 +631,21 @@ export function createDocumentSession(options: DocumentSessionOptions) {
 	async function saveContentAs(): Promise<boolean> {
 		const tab = tabManager.activeTab;
 		if (!tab) return false;
-		// A partial buffer would produce a silently incomplete copy.
-		if (tab.isTruncated) {
-			options.onError('Refusing to save a partially loaded document', new Error(tab.path));
-			return false;
-		}
+		// A copy is a NEW file at a path the user chose, so unlike the ordinary
+		// save it cannot destroy anything they already have. That is what makes
+		// it the one write a partial buffer may make — and refusing it too, as
+		// this did, left a buffer that could go nowhere: not over the original,
+		// correctly, and not beside it either, so edits made in that state had
+		// no exit but the clipboard. The lossy-decode guard reasons the same way
+		// and has always pointed at Save As for the same reason.
+		//
+		// Completed first where that is possible, so the copy is whole whenever
+		// it can be. `ensureFullContent` declines on a dirty buffer — reading the
+		// file over unsaved edits would discard the very thing this rescue is
+		// for — and that is exactly the case where the copy really is short, so
+		// the user is told once it is written.
+		if (tab.isTruncated) await ensureFullContent(tab.id);
+		const copyIsPartial = tab.isTruncated === true;
 		const selected = await save({
 			filters: [
 				{ name: 'Markdown', extensions: ['md'] },
@@ -667,9 +683,22 @@ export function createDocumentSession(options: DocumentSessionOptions) {
 				tabManager.setTabDecodedLossy(tab.id, false);
 				tabManager.setTabEncoding(tab.id, 'UTF-8');
 				lossySaveWarnedTabs.delete(tab.id);
+				// And the same for the truncation flag, for the same reason: it
+				// described the file this tab used to point at. Whatever the buffer
+				// was a slice OF, it is the whole of what was just written, and the
+				// tab now points at that. Leaving it on would refuse every save from
+				// a tab holding a complete document — the rescue would free the text
+				// and then trap it again. Assigned rather than going through
+				// `setTabRawContent`, which would also reset the baseline the two
+				// lines below set on purpose.
+				tab.isTruncated = false;
 				options.saveRecentFile(selected);
 				tab.originalContent = snapshot;
 				tab.isDirty = tab.rawContent !== snapshot;
+				// Said after the write rather than before the dialog: nothing is lost
+				// by proceeding, and a reader who came here to rescue unsaved text
+				// still has to know that what landed on disk stops where the load did.
+				if (copyIsPartial) options.onPartialCopySaved();
 				return true;
 			} catch (error) {
 				clearSelfWrite(selected);
diff --git a/src/lib/utils/i18n.ts b/src/lib/utils/i18n.ts
index 0c92f22d..b4a5c9ed 100644
--- a/src/lib/utils/i18n.ts
+++ b/src/lib/utils/i18n.ts
@@ -273,6 +273,8 @@ export const translations: Record<LanguageCode, Translation> = {
             openExportedFileFailed: 'Could not open exported file',
             partialDocument: 'Cannot edit yet — this file is not fully loaded',
             lossySaveBlocked: 'Not saved: parts of this file could not be read in any encoding and became "�" when it was opened. Saving would destroy the original — use "Save As" to write a copy',
+            partialSaveBlocked: 'Not saved: only part of this file has loaded, and saving would truncate it — use "Save As" to write a copy',
+            partialCopySaved: 'Copy saved, but it holds only the part of the document that had loaded',
             encodingUnmappable: 'Not saved: {{encoding}} cannot represent every character this document now contains (an emoji, most likely). Use "Save As" to write a copy as UTF-8',
             restoreInterrupted: 'Markpad did not finish restoring your session last time',
             restoreInterruptedDeferred: 'Markpad did not finish opening {path} last time, so it was skipped. Open it yourself to try again'
@@ -603,6 +605,8 @@ export const translations: Record<LanguageCode, Translation> = {
 			openExportedFileFailed: '无法打开导出的文件',
 			partialDocument: '暂时无法编辑 — 文件尚未完整加载',
 			lossySaveBlocked: '未保存：此文件的部分内容无法用任何编码读取，打开时已变成“�”。直接保存会破坏原文件 — 请用“另存为”写入新文件',
+			partialSaveBlocked: '未保存：此文件只加载了一部分，保存会将其截断 —— 请用“另存为”写一份副本',
+			partialCopySaved: '副本已保存，但其中只包含已加载的那部分文档',
 			encodingUnmappable: '未保存：{{encoding}} 无法表示文档中新增的部分字符（多半是表情符号）。请用“另存为”写入一份 UTF-8 副本'
         },
         externalChange: {
@@ -888,6 +892,8 @@ export const translations: Record<LanguageCode, Translation> = {
             autoSaveFailed: '自動保存に失敗しました — 未保存の変更はメモリ内に残っています',
             savedNewerEdits: '保存しました — 新しい編集があるため編集モードを継続します',
             lossySaveBlocked: '保存しませんでした：このファイルの一部はどの文字コードでも読めず、開いた時点で「�」に置き換わっています。上書き保存すると元のファイルが壊れます —「名前を付けて保存」で新しいファイルに書き出してください',
+            partialSaveBlocked: '保存しませんでした：このファイルは一部しか読み込まれておらず、上書き保存すると切り詰められます —「名前を付けて保存」で複製を書き出してください',
+            partialCopySaved: '複製を保存しましたが、読み込めていた範囲のみが含まれています',
             encodingUnmappable: '保存しませんでした：{{encoding}} ではこの文書に含まれる一部の文字（多くは絵文字）を表現できません。「名前を付けて保存」で UTF-8 の複製を作成してください'
         },
         modal: {
@@ -1181,6 +1187,8 @@ export const translations: Record<LanguageCode, Translation> = {
             openExportedFileFailed: '無法開啟匯出的檔案',
             partialDocument: '尚無法編輯 — 此檔案尚未完全讀取',
             lossySaveBlocked: '未儲存：此檔案的部分內容無法用任何編碼讀取，開啟時已變成「�」。直接儲存會破壞原檔案 — 請用「另存新檔」寫入新檔案',
+            partialSaveBlocked: '未儲存：此檔案只讀取了一部分，儲存會將其截斷 —— 請用「另存新檔」寫一份副本',
+            partialCopySaved: '副本已儲存，但其中只包含已讀取的那部分文件',
             encodingUnmappable: '未儲存：{{encoding}} 無法表示此文件新增的部分字元（多半是表情符號）。請用「另存新檔」寫入一份 UTF-8 複本'
         },
         externalChange: {
@@ -1496,6 +1504,8 @@ export const translations: Record<LanguageCode, Translation> = {
             savedNewerEdits: '저장됨 — 새로운 편집이 있어 편집 모드를 유지합니다',
             openExportedFileFailed: '내보낸 파일을 열 수 없습니다',
             lossySaveBlocked: '저장하지 않음: 이 파일의 일부는 어떤 인코딩으로도 읽을 수 없어 열 때 "�"로 바뀌었습니다. 덮어쓰면 원본이 손상됩니다 — "다른 이름으로 저장"으로 새 파일에 저장하세요',
+            partialSaveBlocked: '저장하지 않음: 이 파일은 일부만 불러왔으며, 저장하면 잘려나갑니다 — "다른 이름으로 저장"으로 사본을 만드세요',
+            partialCopySaved: '사본을 저장했지만, 불러온 부분만 담겨 있습니다',
             encodingUnmappable: '저장하지 않음: {{encoding}}(으)로는 이 문서에 포함된 일부 문자(대개 이모지)를 표현할 수 없습니다. "다른 이름으로 저장"으로 UTF-8 사본을 만드세요'
         },
         modal: {
@@ -1775,6 +1785,8 @@ export const translations: Record<LanguageCode, Translation> = {
             autoSaveFailed: 'Автосохранение не удалось — несохранённые правки остались только в памяти',
             savedNewerEdits: 'Сохранено — остаюсь в режиме редактирования, так как есть более новые правки',
             lossySaveBlocked: 'Не сохранено: часть содержимого файла не читается ни в одной кодировке и при открытии стала «�». Сохранение уничтожит оригинал — используйте «Сохранить как» для записи копии',
+            partialSaveBlocked: 'Не сохранено: загружена только часть файла, сохранение обрежет его — используйте «Сохранить как» для создания копии',
+            partialCopySaved: 'Копия сохранена, но содержит только загруженную часть документа',
             encodingUnmappable: 'Не сохранено: кодировка {{encoding}} не может представить некоторые символы этого документа (скорее всего, эмодзи). Используйте «Сохранить как», чтобы записать копию в UTF-8'
         },
         modal: {