fix(design-ledger-gate): fail on unresolved merge conflict markers

tools/design-ledger-gate/index.test.ts

@@ -16,6 +16,7 @@
 import { describe, expect, test } from "bun:test";
 import {
 	type Changed,
+	conflictMarkerViolations,
 	type Deps,
 	evaluate,
 	HISTORICAL_CHAIN,
@@ -1038,3 +1039,64 @@ describe("runOnce", () => {
 		expect(await runOnce(d)).toBe(2);
 	});
 });
+
+describe("conflictMarkerViolations", () => {
+	test("flags git-style markers that leave every DL- row valid", () => {
+		// The dangerous shape: markers sit between rows, so id uniqueness, status
+		// grammar, and link resolution all still pass.
+		const text = [
+			"| DL-001 | a | Active (m, 2026-01-01) | [r](r.md) |",
+			"<<<<<<< HEAD",
+			"=======",
+			">>>>>>> theirs",
+		].join("\n");
+		const got = conflictMarkerViolations(LEDGER, text);
+		expect(got.map((v) => v.line)).toEqual([2, 3, 4]);
+		expect(got[0]?.message).toContain("unresolved merge conflict marker");
+	});
+
+	test("flags jj-style markers too", () => {
+		const text = [
+			"<<<<<<< conflict 1 of 1",
+			"%%%%%%% diff",
+			"+++++++ side",
+			">>>>>>> ends",
+		].join("\n");
+		expect(conflictMarkerViolations(LEDGER, text)).toHaveLength(4);
+	});
+
+	test("stays silent on ordinary prose", () => {
+		// Guards the false-positive edge: a table separator and a fenced diff both
+		// carry runs of = and +, but neither opens a conflict.
+		const text = ["| --- | --- |", "```diff", "+++ b/x", "```", "a === b"].join(
+			"\n",
+		);
+		expect(conflictMarkerViolations(LEDGER, text)).toEqual([]);
+	});
+	test("flags lengthened markers — both tools widen past 7", () => {
+		// A conflict whose hunk holds a marker-like run makes git and jj emit
+		// wider markers; an exact-7 match misses the conflict entirely.
+		const text = [
+			"<<<<<<<<<<< conflict 1 of 1",
+			"%%%%%%%%%%% diff",
+			"+++++++++++ side",
+			">>>>>>>>>>> ends",
+		].join("\n");
+		const got = conflictMarkerViolations(LEDGER, text);
+		expect(got).toHaveLength(4);
+		expect(got[0]?.message).toContain("<<<<<<<<<<<");
+	});
+
+	test("stays silent on a long setext underline", () => {
+		// Governed records carry 14-char `=` underlines, so `=` must stay exact.
+		const text = ["A heading", "==============", "", "body"].join("\n");
+		expect(conflictMarkerViolations(LEDGER, text)).toEqual([]);
+	});
+
+	test("stays silent on a marker shown as fenced example text", () => {
+		const text = ["```text", "<<<<<<< HEAD", ">>>>>>> theirs", "```"].join(
+			"\n",
+		);
+		expect(conflictMarkerViolations(LEDGER, text)).toEqual([]);
+	});
+});

tools/design-ledger-gate/index.ts

@@ -283,6 +283,37 @@ function splitLedgerRow(row: string): string[] {
 	return cells;
 }
 
+/**
+ * Unresolved merge markers in a governed file. The ledger is one append-only
+ * file every lane appends to, so conflicts are routine — and markers can leave
+ * every `| DL-` row syntactically valid, which passes every other check here.
+ */
+export function conflictMarkerViolations(
+	file: string,
+	text: string,
+): Violation[] {
+	const out: Violation[] = [];
+	let inFence = false;
+	text.split("\n").forEach((line, i) => {
+		if (/^\s*(```|~~~)/.test(line)) inFence = !inFence;
+		// A record may legitimately show a marker as fenced example text; the rest
+		// of this module skips fences for the same reason.
+		if (inFence) return;
+		// jj adds `%%%%%%%`/`+++++++` to git's three, and both tools LENGTHEN every
+		// marker past 7 when the conflicting hunk itself holds a marker-like run.
+		// `=` stays exact: governed records use long `=` setext underlines.
+		const m = /^(<{7,}|>{7,}|%{7,}|\+{7,}|={7})(\s|$)/.exec(line);
+		if (m) {
+			out.push({
+				file,
+				line: i + 1,
+				message: `unresolved merge conflict marker: ${m[1]}`,
+			});
+		}
+	});
+	return out;
+}
+
 /** Parse DECISIONS.md text into ledger rows (topic headings/prose skipped). */
 export function parseLedger(text: string): LedgerRow[] {
 	const rows: LedgerRow[] = [];
@@ -604,12 +635,16 @@ export async function runOnce(deps: Deps): Promise<number> {
 		});
 	}
 	const ledger = ledgerText === null ? [] : parseLedger(ledgerText);
+	if (ledgerText !== null) {
+		violations.push(...conflictMarkerViolations(DECISIONS_PATH, ledgerText));
+	}
 
 	const records: RecordHeader[] = [];
 	for (const path of recordFiles) {
 		const text = await readText(root, path);
 		if (text === null) continue; // listed but vanished — ignore
 		records.push(parseRecordHeader(path, text));
+		violations.push(...conflictMarkerViolations(path, text));
 	}
 
 	violations.push(