test(session): cover historical catalog comparison failures

packages/test-support/session-snapshot/tests/normalize.spec.ts

@@ -684,6 +684,43 @@ describe('normalizeSessionSnapshot', () => {
     ].join('\n'))
   })
 
+  it('rejects an empty historical comparison input', () => {
+    expect(() => omitSubagentCatalogForHistoricalComparison('\n'))
+      .toThrow('session snapshot must start with a session header')
+  })
+
+  it('preserves snapshots and source references when no catalog fact is present', () => {
+    const normalized = [
+      { type: 'session', id: '{{session:1}}' },
+      { type: 'tool/call', data: { callId: 'result' } },
+      { type: 'tool/result', data: { callId: 'result' }, sourceEventSeqs: [0] },
+    ].map(record => JSON.stringify(record)).join('\n') + '\n'
+
+    expect(omitSubagentCatalogForHistoricalComparison(normalized)).toBe(normalized)
+  })
+
+  it.each(['0', 0.5, -1])('refuses malformed source references during historical comparison: %s', (source) => {
+    const normalized = [
+      { type: 'session', id: '{{session:1}}' },
+      { type: 'subagent/catalog', data: { childId: '{{session:2}}' } },
+      { type: 'tool/result', data: { callId: 'result' }, sourceEventSeqs: [source] },
+    ].map(record => JSON.stringify(record)).join('\n')
+
+    expect(() => omitSubagentCatalogForHistoricalComparison(normalized))
+      .toThrow('normalized sourceEventSeqs must contain non-negative safe integers')
+  })
+
+  it('refuses to remove a catalog fact cited by a retained event', () => {
+    const normalized = [
+      { type: 'session', id: '{{session:1}}' },
+      { type: 'subagent/catalog', data: { childId: '{{session:2}}' } },
+      { type: 'tool/result', data: { callId: 'result' }, sourceEventSeqs: [0] },
+    ].map(record => JSON.stringify(record)).join('\n')
+
+    expect(() => omitSubagentCatalogForHistoricalComparison(normalized))
+      .toThrow('historical comparison cannot omit cited catalog event 0')
+  })
+
   it('migrates and re-packs multi-session fixtures after relationship-preserving id redaction', () => {
     const raw = [
       JSON.stringify({ type: 'session', version: 0, id: '{{session:1}}', createdAt: 0, delegationDepth: 0 }),