Initial commit: CI Agent competitive-intelligence monitoring app

FastAPI + Celery + Next.js + Postgres/Redis app with company monitoring,
source collection, LLM-based change analysis, enrichment, and account
security (Turnstile, escalating lockout, email verification).

apps/api/app/change_detection/structured_diff.py

@@ -0,0 +1,33 @@
+"""Layer 2: structured field comparison.
+
+Compares the *set* of items (job postings, press releases, filings,
+products - whatever the source's documents represent) between two
+snapshots' `structured_summary["urls"]`/`["titles"]`. This is what catches
+"a new job posting appeared" or "a press release was removed" without
+needing a bespoke parser per source type - collection_service already
+records the full current item set on every run, so this is a plain set
+diff between two runs.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+
+
+@dataclass(frozen=True)
+class StructuredDiff:
+    added: list[str] = field(default_factory=list)
+    removed: list[str] = field(default_factory=list)
+
+    @property
+    def has_changes(self) -> bool:
+        return bool(self.added or self.removed)
+
+
+def diff_item_sets(previous_urls: list[str], current_urls: list[str]) -> StructuredDiff:
+    previous_set = set(previous_urls)
+    current_set = set(current_urls)
+    return StructuredDiff(
+        added=sorted(current_set - previous_set),
+        removed=sorted(previous_set - current_set),
+    )