test(public-safety): pin what a compacted value returns over its budget

tests/control_plane/test_public_safety_text_budget.py

@@ -0,0 +1,81 @@
+"""Budget rules for the shared public-safety text surface.
+
+``compact_text`` is the bound every projection spends before it hands a value to
+a host, a dashboard or another tool, and 202 production call sites pass it an
+explicit ``limit``. These cases pin what a caller reads back when a value does
+not fit: how much survives, where the ellipsis goes, and that the refusal rules
+still fire inside the kept prefix.
+"""
+
+import pytest
+
+from loopx.control_plane.runtime.public_safety import (
+    compact_text,
+    public_safe_compact_text,
+)
+
+# A synthetic credential shape, never a real one: enough of the pattern to be
+# refused and nothing else.
+SYNTHETIC_CREDENTIAL = "token=" + "abcdefghijklmn"
+
+
+@pytest.mark.parametrize("limit", [2, 3, 5, 12, 40])
+def test_a_value_over_budget_keeps_the_head_and_exactly_one_ellipsis(
+    limit: int,
+) -> None:
+    text = "y" * 80
+
+    compacted = compact_text(text, limit=limit)
+
+    assert compacted == text[: limit - 1] + "…"
+    assert len(compacted) == limit
+    assert compacted.endswith("…")
+
+
+def test_whitespace_is_collapsed_before_the_budget_is_spent() -> None:
+    raw = "  padded   value  "
+
+    assert len(raw) > 14
+    assert compact_text(raw, limit=14) == "padded value"
+    assert "…" not in compact_text(raw, limit=14)
+
+
+def test_a_value_that_exactly_fits_is_returned_without_an_ellipsis() -> None:
+    text = "abcdefghij"
+
+    assert compact_text(text, limit=len(text)) == text
+    assert len(compact_text(text, limit=len(text) - 1)) == len(text) - 1
+
+
+def test_the_ellipsis_replaces_a_character_rather_than_adding_one() -> None:
+    compacted = compact_text("alpha  beta\tgamma " + "x" * 40, limit=12)
+
+    assert compacted == "alpha beta…"
+    assert len(compacted) <= 12
+
+
+def test_values_are_coerced_before_the_budget_and_the_empty_stays_empty() -> None:
+    assert compact_text(123456, limit=3) == "12…"
+    assert compact_text(None, limit=5) == ""
+    assert public_safe_compact_text(None, limit=20) is None
+
+
+def test_default_budget_is_two_hundred_twenty_characters() -> None:
+    compacted = public_safe_compact_text("w" * 400)
+
+    assert compacted is not None
+    assert len(compacted) == 220
+    assert compacted.endswith("…")
+
+
+def test_a_credential_inside_the_kept_prefix_is_still_refused() -> None:
+    assert (
+        public_safe_compact_text(
+            f"note {SYNTHETIC_CREDENTIAL}",
+            limit=len(SYNTHETIC_CREDENTIAL) + 8,
+        )
+        is None
+    )
+    assert public_safe_compact_text("note ordinary prose", limit=40) == (
+        "note ordinary prose"
+    )