Merge PR #4111: fix(edit): guard apply_patch against clobber and swallowed multi-file failures (@roboomp)

packages/coding-agent/src/edit/index.ts

@@ -138,6 +138,7 @@ async function executeApplyPatchPerFile(
 
 	const perFileResults: EditToolPerFileResult[] = [];
 	const contentTexts: string[] = [];
+	let errorCount = 0;
 
 	for (let i = 0; i < fileEntries.length; i++) {
 		const { path, run } = fileEntries[i];
@@ -169,6 +170,29 @@ async function executeApplyPatchPerFile(
 			const displayErrorText = err instanceof HashlineMismatchError ? err.displayMessage : undefined;
 			perFileResults.push({ path, diff: "", isError: true, errorText, displayErrorText });
 			contentTexts.push(`Error editing ${path}: ${errorText}`);
+			errorCount++;
+			// Later entries were authored assuming this file's post-state; a
+			// partial cascade after failure typically compounds damage. Stop
+			// here, report applied vs. skipped, and let the caller re-issue
+			// only the failed and unapplied files. Matches
+			// `executeSinglePathEntries` semantics.
+			if (i > 0) {
+				const appliedPaths = fileEntries
+					.slice(0, i)
+					.map(e => e.path)
+					.join(", ");
+				contentTexts.push(`Files already applied: ${appliedPaths}.`);
+			}
+			if (i + 1 < fileEntries.length) {
+				const skippedPaths = fileEntries
+					.slice(i + 1)
+					.map(e => e.path)
+					.join(", ");
+				contentTexts.push(
+					`Files NOT applied: ${skippedPaths}; re-read the affected files and re-issue only the failed and unapplied files.`,
+				);
+			}
+			break;
 		}
 
 		// Emit partial result after each file so UI shows progressive completion
@@ -197,6 +221,10 @@ async function executeApplyPatchPerFile(
 			firstChangedLine: perFileResults.find(r => r.firstChangedLine)?.firstChangedLine,
 			perFileResults,
 		}),
+		// Any per-file failure marks the aggregate result as an error so the
+		// agent loop and renderer take the error branch instead of treating
+		// a mixed partial application as a successful edit.
+		...(errorCount > 0 ? { isError: true } : {}),
 	};
 }
 

packages/coding-agent/src/edit/modes/patch.ts

@@ -1492,6 +1492,14 @@ async function applyNormalizedPatch(input: PatchInput, options: ApplyPatchOption
 		if (destPath === absolutePath) {
 			throw new ApplyPatchError("rename path is the same as source path");
 		}
+		// The `*** Move to` / rename contract is strictly non-overwriting:
+		// reject before the update path reads or writes anything, so both
+		// source and pre-existing destination remain untouched. Callers who
+		// really need to replace the destination must delete it in an
+		// earlier hunk.
+		if (await fs.exists(destPath)) {
+			throw new ApplyPatchError(`Cannot rename ${input.path} to ${input.rename}: destination already exists.`);
+		}
 	}
 
 	// Handle CREATE operation
@@ -1499,6 +1507,15 @@ async function applyNormalizedPatch(input: PatchInput, options: ApplyPatchOption
 		if (!input.diff) {
 			throw new ApplyPatchError("Create operation requires diff (file content)");
 		}
+		// The `*** Add File` / create contract is strictly non-overwriting:
+		// reject before mkdir/write so pre-existing content stays intact and
+		// the caller can re-issue as an explicit `*** Update File` (or a
+		// delete+add pair) if overwrite is genuinely intended.
+		if (await fs.exists(absolutePath)) {
+			throw new ApplyPatchError(
+				`Cannot create ${input.path}: file already exists. Use *** Update File to modify it in place.`,
+			);
+		}
 		// Strip + prefixes if present (handles diffs formatted as additions)
 		const normalizedContent = normalizeCreateContent(input.diff);
 		const content = normalizedContent.endsWith("\n") ? normalizedContent : `${normalizedContent}\n`;