feat: add inline icons for edit

src/frontmatter/frontmatterFields.ts

@@ -0,0 +1,60 @@
+import {
+	extractFrontmatterBlock,
+	findFieldLineRange,
+	findFieldRange,
+	type TextRange,
+} from "./frontmatterBlock";
+
+export { findFieldLineRange, findFieldRange };
+export type { TextRange };
+
+export type ReplaceFrontmatterFieldResult =
+	| { ok: true; content: string; range: TextRange }
+	| { ok: false; reason: "no-frontmatter" | "no-field" };
+
+/**
+ * Replace a scalar frontmatter field value on its line.
+ * Does not re-serialize YAML; only rewrites the value after `:`.
+ */
+export function replaceFrontmatterField(
+	content: string,
+	key: string,
+	value: string,
+): ReplaceFrontmatterFieldResult {
+	const block = extractFrontmatterBlock(content);
+	if (!block || block.closeLine < 0) {
+		return { ok: false, reason: "no-frontmatter" };
+	}
+
+	const lineRange = findFieldLineRange(content, key);
+	if (!lineRange) {
+		return { ok: false, reason: "no-field" };
+	}
+
+	const lines = content.split(/\r?\n/);
+	const line = lines[lineRange.startLine] ?? "";
+	const colonIndex = line.indexOf(":");
+	if (colonIndex < 0) {
+		return { ok: false, reason: "no-field" };
+	}
+
+	const prefix = line.slice(0, colonIndex + 1);
+	const spacing = line.slice(colonIndex + 1).match(/^\s*/)?.[0] ?? " ";
+	const newLine = `${prefix}${spacing || " "}${value}`;
+	lines[lineRange.startLine] = newLine;
+
+	const eol = content.includes("\r\n") ? "\r\n" : "\n";
+	const next = lines.join(eol);
+
+	const valueRange = findFieldRange(next, key);
+	return {
+		ok: true,
+		content: next,
+		range: valueRange ?? {
+			startLine: lineRange.startLine,
+			startCol: 0,
+			endLine: lineRange.startLine,
+			endCol: newLine.length,
+		},
+	};
+}