test(3516): add failing regression for missing gsd-update filter arm

Adds bug-3516-reapply-patches-gsd-update-filter.test.cjs — 7 tests that
assert all four exclusion patterns (gsd:update, gsd-update, GSD update,
gsd-install) are present in the git-enhanced two-way merge filter inside
get-shit-done/workflows/reapply-patches.md.

Two tests fail before the fix: 'filter excludes renamed gsd-update commits'
and 'all four expected exclusion patterns are present in the filter'.

tests/bug-3516-reapply-patches-gsd-update-filter.test.cjs

@@ -0,0 +1,123 @@
+// allow-test-rule: source-text-is-the-product
+// get-shit-done/workflows/reapply-patches.md is the installed runtime workflow —
+// its text IS the deployed behavioral contract for the --reapply flag.
+
+'use strict';
+
+/**
+ * Bug #3516: reapply-patches.md git-enhanced two-way merge filter misses
+ * commits authored by the renamed `/gsd-update` flow.
+ *
+ * The `grep -v` alternation on line 231 only included the legacy `gsd:update`
+ * marker. After the slash-command rename `/gsd:update` → `/gsd-update`, commits
+ * authored by the current flow fall through the filter and are misclassified as
+ * user customizations, prompting spurious merge conflicts during `--reapply`.
+ *
+ * Fix: add `gsd-update` arm to the alternation so both the legacy and current
+ * commit-message prefixes are excluded. `GSD update` and `gsd-install`
+ * exclusions are preserved.
+ *
+ * Per the repo's source-text-is-the-product exception: the workflow file's text
+ * IS the deployed behavioral contract. Structural assertion against the parsed
+ * shell command string is the correct test form here.
+ */
+
+const { describe, test, before } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+
+const WORKFLOW_PATH = path.join(
+  __dirname,
+  '..',
+  'get-shit-done',
+  'workflows',
+  'reapply-patches.md',
+);
+
+/**
+ * Extract the git log filter command from the workflow.
+ *
+ * Looks for the `grep -v "..."` shell snippet inside the Git-enhanced two-way
+ * merge section and returns the alternation string between the quotes.
+ * Returns null if the snippet is absent (signals a structural regression).
+ */
+function extractFilterAlternation(content) {
+  // Match the grep -v "..." line in the bash block
+  const match = content.match(/grep\s+-v\s+"([^"]+)"/);
+  if (!match) return null;
+  return match[1];
+}
+
+/**
+ * Parse the alternation string (pipe-delimited) into individual arms.
+ * Handles escaped pipes produced by shell regex syntax (`\|`).
+ */
+function parseAlternationArms(alternation) {
+  // Shell grep alternation uses \| (escaped pipe); split on that
+  return alternation.split(/\\\|/).map((arm) => arm.trim());
+}
+
+describe('Bug #3516: git-enhanced two-way merge filter includes gsd-update arm', () => {
+  let content;
+  let alternation;
+  let arms;
+
+  before(() => {
+    content = fs.readFileSync(WORKFLOW_PATH, 'utf8');
+    alternation = extractFilterAlternation(content);
+    arms = alternation ? parseAlternationArms(alternation) : [];
+  });
+
+  test('workflow file exists', () => {
+    assert.ok(
+      fs.existsSync(WORKFLOW_PATH),
+      'get-shit-done/workflows/reapply-patches.md must exist',
+    );
+  });
+
+  test('git-enhanced two-way merge section contains a grep -v filter', () => {
+    assert.ok(
+      alternation !== null,
+      'reapply-patches.md must contain a `grep -v "..."` filter in the git-enhanced two-way merge section',
+    );
+  });
+
+  test('filter excludes legacy gsd:update commits (back-compat)', () => {
+    assert.ok(
+      arms.some((arm) => arm === 'gsd:update'),
+      `filter must include 'gsd:update' arm for back-compat; got arms: ${JSON.stringify(arms)}`,
+    );
+  });
+
+  test('filter excludes renamed gsd-update commits (primary fix)', () => {
+    assert.ok(
+      arms.some((arm) => arm === 'gsd-update'),
+      `filter must include 'gsd-update' arm (renamed flow); got arms: ${JSON.stringify(arms)}`,
+    );
+  });
+
+  test('filter excludes GSD update commits (no regression)', () => {
+    assert.ok(
+      arms.some((arm) => arm === 'GSD update'),
+      `filter must include 'GSD update' arm; got arms: ${JSON.stringify(arms)}`,
+    );
+  });
+
+  test('filter excludes gsd-install commits (no regression)', () => {
+    assert.ok(
+      arms.some((arm) => arm === 'gsd-install'),
+      `filter must include 'gsd-install' arm; got arms: ${JSON.stringify(arms)}`,
+    );
+  });
+
+  test('all four expected exclusion patterns are present in the filter', () => {
+    const required = ['gsd:update', 'gsd-update', 'GSD update', 'gsd-install'];
+    const missing = required.filter((p) => !arms.some((arm) => arm === p));
+    assert.deepEqual(
+      missing,
+      [],
+      `filter is missing required exclusion patterns: ${JSON.stringify(missing)}; got arms: ${JSON.stringify(arms)}`,
+    );
+  });
+});