fix(#1778): use 1.6 named-flag frontmatter.set form in thread workflow (#1816)

* fix(#1778): use 1.6 named-flag frontmatter.set form in thread workflow

The thread workflow's CLOSE and RESUME branches called frontmatter.set with
the pre-1.6 fully-positional shape (frontmatter.set <file> <field> <value>).
Since 1.6 the dispatcher (gsd-tools.cjs) parses the file positionally and
reads field/value from the named flags --field/--value via parseNamedArgs;
the positional form leaves field/value undefined, cmdFrontmatterSet errors
'file, field, and value required', and the status/updated writes are
silently skipped. Closing a thread never marked it status: resolved and
resuming never marked it status: in_progress.

Switch all four sites (CLOSE status+updated, RESUME status+updated) to the
1.6 hybrid form that verify-work.md already uses:
  frontmatter.set <file> --field <field> --value <value>

Add a regression test with three guards: (1) behavioral — the named-flag
form writes the field while the positional form errors with the documented
message and does not mutate the file; (2) workflow parity — no workflow
under gsd-core/workflows/ emits the positional form, so a future edit that
reintroduces it anywhere fails CI; (3) thread-specific — CLOSE writes
status: resolved and RESUME writes status: in_progress via the named flags.

* docs(#1778): add changeset fragment for thread workflow frontmatter fix

* docs(#1778): fix unclosed inline-code backtick in changeset fragment

* fix(#1778): move regression into owning test + regen baselines

lint-regression-test-names rejects new bug-NNNN-*.test.cjs files; move the
#1778 regression (behavioral named-vs-positional + workflow-parity scan +
thread CLOSE/RESUME assertions) into tests/frontmatter-cli.test.cjs, the
canonical home for frontmatter CLI regressions, and delete the standalone
file. frontmatter-cli.test.cjs already carries the allow-test-rule exemption
for workflow .md content tests.

gsd-core/workflows/thread.md ships to every runtime and is size-tracked, so
recapture the 16 golden-install-parity fixtures (thread.md hash) and the
per-file workflow size baseline (thread.md 12400 -> 12464) via UPDATE_GOLDEN=1
and npm run size:baseline.

tests/frontmatter-cli.test.cjs

@@ -18,7 +18,7 @@ const assert = require('node:assert/strict');
 const fs = require('fs');
 const path = require('path');
 const os = require('os');
-const { runGsdTools } = require('./helpers.cjs');
+const { runGsdTools, parseFrontmatter } = require('./helpers.cjs');
 
 // Track temp files for cleanup
 let tempFiles = [];
@@ -441,3 +441,88 @@ describe('Bug #1660: frontmatter set of an object-list field fails closed instea
     assert.ok(!parsed.error, 'an idempotent scalar-array set must not produce an error');
   });
 });
+
+// ─── #1778: thread workflow must use the 1.6 named-flag frontmatter.set form ─
+//
+// The thread workflow's CLOSE and RESUME branches previously invoked the
+// pre-1.6 positional shape (frontmatter.set <file> <field> <value>). Since 1.6
+// the dispatcher (gsd-tools.cjs) reads field/value from the named --field/
+// --value flags via parseNamedArgs; the positional form leaves field/value
+// undefined, cmdFrontmatterSet errors `file, field, and value required`, and
+// the status/updated writes are silently skipped — so closing a thread never
+// marked it status: resolved and resuming never marked it status: in_progress.
+describe('#1778: thread workflow uses the 1.6 named-flag frontmatter.set form', () => {
+  test('behavioral: named-flag form writes the field; positional form errors and does not mutate', () => {
+    // 1.6 named-flag form — must succeed and write status: resolved.
+    const goodFile = writeTempFile('---\nstatus: open\nupdated: "2025-01-01"\n---\n\n# thread body\n');
+    const good = runGsdTools(['frontmatter', 'set', goodFile, '--field', 'status', '--value', 'resolved']);
+    assert.ok(good.success, `named-flag form must succeed; stderr: ${good.error}`);
+    assert.strictEqual(
+      parseFrontmatter(fs.readFileSync(goodFile, 'utf-8')).status,
+      'resolved',
+      'named-flag form must write status: resolved into the file',
+    );
+
+    // Pre-1.6 positional form — must fail with the documented message and NOT mutate.
+    const badFile = writeTempFile('---\nstatus: open\nupdated: "2025-01-01"\n---\n\n# thread body\n');
+    const bad = runGsdTools(['frontmatter', 'set', badFile, 'status', 'resolved']);
+    assert.ok(!bad.success, 'positional form must fail (it is the bug being guarded against)');
+    assert.ok(
+      (bad.error + bad.output).includes('file, field, and value required'),
+      `positional form must error with the documented message; got:\n${bad.error}${bad.output}`,
+    );
+    assert.strictEqual(
+      parseFrontmatter(fs.readFileSync(badFile, 'utf-8')).status,
+      'open',
+      'positional form must NOT mutate the file (the silent-failure bug)',
+    );
+  });
+
+  test('workflow parity: no gsd-core/workflows/*.md emits the positional frontmatter.set form', () => {
+    const workflowsDir = path.join(__dirname, '..', 'gsd-core', 'workflows');
+    const files = fs.readdirSync(workflowsDir).filter((f) => f.endsWith('.md'));
+    assert.ok(files.length > 0, 'expected at least one workflow under gsd-core/workflows/');
+
+    const offenders = [];
+    for (const name of files) {
+      const full = path.join(workflowsDir, name);
+      const lines = fs.readFileSync(full, 'utf-8').split(/\r?\n/);
+      lines.forEach((line, i) => {
+        // Match any frontmatter.set invocation (dot or space form, with or
+        // without the `gsd_run query` prefix). The 1.6 contract requires
+        // --field AND --value on every set call; a set line missing --field
+        // is the pre-1.6 positional form (#1778).
+        if (!/frontmatter[.\s]+set\b/.test(line)) return;
+        if (!/--field\b/.test(line) || !/--value\b/.test(line)) {
+          offenders.push(`${name}:${i + 1}: ${line.trim()}`);
+        }
+      });
+    }
+
+    assert.deepStrictEqual(
+      offenders,
+      [],
+      `These workflow frontmatter.set invocations are missing the 1.6 --field/--value named flags (the #1778 positional-form bug):\n  ${offenders.join('\n  ')}\n\nUse: gsd_run query frontmatter.set <file> --field <field> --value <value>`,
+    );
+  });
+
+  test('thread workflow CLOSE writes status: resolved and RESUME writes status: in_progress via named flags', () => {
+    const src = fs.readFileSync(path.join(__dirname, '..', 'gsd-core', 'workflows', 'thread.md'), 'utf-8');
+
+    // CLOSE mode: status resolved + updated, both via named flags.
+    assert.ok(
+      /frontmatter\.set\s+\S*\.planning\/threads\/\{SLUG\}\.md\s+--field\s+status\s+--value\s+resolved\b/.test(src),
+      'CLOSE mode must invoke: frontmatter.set .planning/threads/{SLUG}.md --field status --value resolved',
+    );
+    assert.ok(
+      /frontmatter\.set\s+\S*\.planning\/threads\/\{SLUG\}\.md\s+--field\s+updated\s+--value\s+YYYY-MM-DD\b/.test(src),
+      'CLOSE mode must invoke: frontmatter.set .planning/threads/{SLUG}.md --field updated --value YYYY-MM-DD',
+    );
+
+    // RESUME mode: status in_progress + updated, both via named flags.
+    assert.ok(
+      /frontmatter\.set\s+\S*\.planning\/threads\/\{SLUG\}\.md\s+--field\s+status\s+--value\s+in_progress\b/.test(src),
+      'RESUME mode must invoke: frontmatter.set .planning/threads/{SLUG}.md --field status --value in_progress',
+    );
+  });
+});