refactor(cleanup): simplify pass on the R-a diff

engine-compare imports the coordinator's title limit and trim instead
of a copy whose reason went with Arm B; the autonomy gate exports one
parser and its test runs in-process with two CLI runs; one import
scanner in lib-imports; the fenced-section walker shared from
tests/helpers/md-section.mjs instead of six copies; plan-gate hash
in-process; living-paths scans once; routing drops the orchestrator
filter whose files are gone; small leftovers removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/helpers/md-section.mjs

@@ -0,0 +1,26 @@
+// tests/helpers/md-section.mjs
+// The text of one markdown section, for the prose-pin tests.
+
+import { strict as assert } from 'node:assert';
+import { findSection } from '../../lib/parsers/plan-schema.mjs';
+
+/**
+ * The text of a heading's section (level from its #-count), up to the next
+ * heading of the same or a higher level outside a fence. The heading must exist.
+ * @param {string} text
+ * @param {string} heading - e.g. `## Phase 8 — Final report`
+ * @returns {string}
+ */
+export function sectionText(text, heading) {
+  const level = heading.match(/^#+/)[0].length;
+  const s = findSection(text, heading.replace(/^#+ /, ''), level);
+  assert.ok(s, `missing ${heading}`);
+  const lines = s.text.split('\n');
+  let fenced = false;
+  for (let i = 1; i < lines.length; i++) {
+    if (/^\s{0,3}(`{3,}|~{3,})/.test(lines[i])) fenced = !fenced;
+    const m = !fenced && lines[i].match(/^(#+) /);
+    if (m && m[1].length < level) return lines.slice(0, i).join('\n');
+  }
+  return s.text;
+}