What causes "Expected ${OPENER} on input line ${index + 1}." in can1357/oh-my-pi?

Start the payload with a « (or §path + «) opener line before any content.

Expected ${OPENER} on input line ${index + 1}.

Error message

Expected ${OPENER} on input line ${index + 1}.

What it means

The parser starts in the "outside" state: before the first « opener, the only legal non-empty input is the opener itself. Any other non-blank line before the first operation is rejected with this error, stating the 1-based input line number where the unexpected content was found. Blank lines are tolerated so leading whitespace does not break payloads.

Source

Thrown at packages/coding-agent/src/edit/sloppy.ts:1340

		}
		if (
			parsedOpener === false &&
			(trimmed.startsWith(OPENER) ||
				(trimmed.startsWith(REWRITE_HEADER) && trimmed !== REWRITE_HEADER && !registerReference))
		) {
			throw new Error(
				`Invalid control line ${JSON.stringify(trimmed)}; use only ${OPENER}, ${OPENER}*, ${REWRITE_HEADER}, or ${REWRITE_HEADER}N in REWRITE.`,
			);
		}
		if (state === "outside") {
			if (parsedOpener !== false) {
				allMatches = parsedOpener === 0;
				patternLines = [];
				rewriteLines = [];
				referenceSeparator = undefined;
				state = "pattern";
			} else if (trimmed !== "") {
				throw new Error(`Expected ${OPENER} on input line ${index + 1}.`);
			}
			continue;
		}

		if (state === "pattern") {
			const accumulated = patternLines.join("\n");
			const markersBalanced = (accumulated.match(/⟪/gu) || []).length === (accumulated.match(/⟫/gu) || []).length;
			if (trimmed === REWRITE_HEADER) {
				state = "rewrite";
			} else if (trimmed === "***" && markersBalanced && patternLines.some(entry => entry.trim() !== "")) {
				// A bare *** after MATCH content is an apply-patch-habit separator.
				state = "rewrite";
			} else if (trimmed === SELECT_CLOSE && markersBalanced && patternLines.some(entry => entry.trim() !== "")) {
				// A lone ⟫ after balanced selections is a mistyped » separator.
				state = "rewrite";
			} else if (registerReference && markersBalanced) {
				if (!patternLines.some(entry => entry.trim() !== "")) {
					throw new Error(`${trimmed} is valid only in REWRITE, never MATCH.`);

View on GitHub (pinned to 9690622007)

Solutions

Start the payload with a « (or §path + «) opener line before any content.
Delete any preamble text/prose before the first opener.
If the content before the first opener is meaningful, move it inside the first operation's MATCH block.

Example fix

// before
Here are the changes:
«
pattern
»
replacement

// after
«
pattern
»
replacement

Defensive patterns

Strategy: validation

Validate before calling

const firstContent = body.split("\n").find(l => l.trim() !== "");
if (firstContent !== undefined && !(firstContent.trim() === "«" || firstContent.trim() === "«*" || /^§/.test(firstContent.trim()))) {
  throw new Error("payload must start with a « opener");
}

Type guard

const startsWithOpener = (body: string): boolean => {
  const l = body.split("\n").find(x => x.trim() !== "");
  return l !== undefined && (l.trim() === "«" || l.trim() === "«*");
};

Try / catch

catch (err) {
  if (err instanceof Error && err.message.includes("Expected « on input line")) {
    // drop leading prose/headers before the first « and retry
  }
}

Prevention

Begin every payload directly with « — no explanations, headers, or diff markers before it.
Trim prose from LLM output before passing the body to the applier.
Use §path headers (which the section splitter consumes) for file targeting.

When it happens

Trigger: Passing a section body that starts with prose, a file path line, a diff header (--- a/...), or any other text before the first « opener line to the sloppy apply routine.

Common situations: Models prefixing payloads with explanations or «file» headers; tooling stripping the opener when slicing the body; pasted payloads that lost the first « line; bodies that include diff-style headers.

Related errors

AI-assisted analysis of can1357/oh-my-pi@9690622007 (2026-08-31). Data as JSON: /api/errors/4e5a065cc7be27a9. Report an issue: GitHub.