perf(campaign): share linear collision-safe attachment naming

Release v0.1.29. Coordinated integrity review: GovOPlaN/govoplan-core#298.

tests/test_filename_allocator.py

@@ -0,0 +1,75 @@
+from pathlib import Path
+import random
+import unittest
+
+from govoplan_campaign.backend.services.filenames import FilenameAllocator
+from govoplan_campaign.backend.services.zip_service import _normalized_members
+
+
+def legacy_names(names):
+    used = set()
+    result = []
+    for name in names:
+        path = Path(name)
+        candidate = name
+        counter = 2
+        while candidate.casefold() in used:
+            candidate = f"{path.stem} ({counter}){path.suffix}"
+            counter += 1
+        used.add(candidate.casefold())
+        result.append(candidate)
+    return result
+
+
+class FilenameAllocatorTests(unittest.TestCase):
+    def test_exact_equivalence_with_colliding_suffixes_case_unicode_and_multiple_dots(
+        self,
+    ):
+        choices = [
+            "report.pdf",
+            "REPORT.PDF",
+            "report (2).pdf",
+            "report (3).pdf",
+            "report (2) (2).pdf",
+            ".hidden",
+            "a.tar.gz",
+            "A.TAR.GZ",
+            "Straße.txt",
+            "STRASSE.txt",
+            "readme",
+        ]
+        rng = random.Random(42)
+        for _ in range(30):
+            names = [rng.choice(choices) for _ in range(200)]
+            allocator = FilenameAllocator()
+            self.assertEqual(
+                legacy_names(names), [allocator.allocate(name) for name in names]
+            )
+
+    def test_zip_and_message_names_preserve_every_input_and_sequence(self):
+        names = ["a.pdf", "A.pdf", "a (2).pdf", "a.pdf"]
+        paths = [Path(f"/synthetic/{index}/source") for index in range(len(names))]
+        members = _normalized_members(list(zip(paths, names)))
+        self.assertEqual(paths, [path for path, _ in members])
+        self.assertEqual(legacy_names(names), [name for _, name in members])
+        self.assertEqual("a.pdf", FilenameAllocator().allocate("a.pdf"))
+
+    def test_many_collisions_have_linear_membership_work(self):
+        class CountingSet(set):
+            probes = 0
+
+            def __contains__(self, item):
+                self.probes += 1
+                return super().__contains__(item)
+
+        allocator = FilenameAllocator()
+        allocator.used = CountingSet()
+        for _ in range(10000):
+            last = allocator.allocate("report.pdf")
+        self.assertEqual("report (10000).pdf", last)
+        self.assertEqual(10000, len(allocator.used))
+        self.assertEqual(19999, allocator.used.probes)
+
+
+if __name__ == "__main__":
+    unittest.main()