fix(#1905): normalize hand-authored backstop marker so it can't degrade to green (#1909)

* fix(#1905): normalize hand-authored backstop marker so it can't degrade to green

A hand-authored non-inferable `backstop` truth with a stray trailing space (or
surrounding quotes) silently graded {status:green} instead of abstaining — the exact
#1154 false-pass. `truthVerification` returned null for any value != 'backstop'/'explicit',
and the frontmatter continuation-KV parser preserved the stray whitespace captured inside
the quotes. Normalize the marker before comparison (Postel) AND trim the continuation-KV
value at the parser (durable root cause; also cleans the sibling check_target path).

Regression: a trailing-space/quoted backstop truth now abstains (insufficient_spec),
end-to-end from a hand-authored must_haves.truths block (#1820 rail).

Refs #1905, epic #1904.

* chore(changeset): Fixed fragment for #1909 (backstop marker normalize)

tests/frontmatter.test.cjs

@@ -366,6 +366,22 @@ Body content.`;
     assert.strictEqual(result[1], 'Coverage exceeds 80%');
   });
 
+  test('trims a continuation-KV value so a quoted trailing space does not survive (#1905, root cause of the #1154 false-pass)', () => {
+    // A quoted value like `"backstop "` captures the inner trailing space in group 2; left untrimmed,
+    // a hand-authored non-inferable `backstop` marker (#1820 spec-optional rail) degrades to `'backstop '`,
+    // which `truthVerification` no longer recognizes → the truth silently grades green instead of abstaining.
+    // Whitespace is never semantic in a scalar KV value, so the parser must trim it.
+    const content = `---
+must_haves:
+  truths:
+    - statement: user data is never logged
+      verification: "backstop "
+---
+Body.`;
+    const result = parseMustHavesBlock(content, 'truths');
+    assert.strictEqual(result[0].verification, 'backstop', 'the captured value is trimmed, not left as "backstop "');
+  });
+
   test('extracts artifacts as object array', () => {
     const content = `---
 phase: 01