Fix: exclude next-period start from relative date-range filters (#13381)

* Fix: exclude next-period start from relative date-range filters

Tantivy's [lo TO hi] range is inclusive on both ends, but computed upper
bounds (keyword ranges, YYYY/YYYYMM/YYYYMMDD tokens) represent the start of
the next period. Use half-open [lo TO hi} for those so e.g. "previous month"
no longer matches the 1st of the current month.

* Adds a regression test down to the second check for the hi range

src/documents/search/_dates.py

@@ -43,8 +43,16 @@ def _fmt(dt: datetime) -> str:
 
 
 def _iso_range(lo: datetime, hi: datetime) -> str:
-    """Format a [lo TO hi] range string in ISO 8601 for Tantivy query syntax."""
-    return f"[{_fmt(lo)} TO {_fmt(hi)}]"
+    """
+    Format a half-open ``[lo TO hi)`` range in ISO 8601 for Tantivy query syntax.
+
+    ``hi`` is always the exclusive ceiling of a computed period (the start of
+    the *next* day/week/month/quarter/year), so the closing bracket must be
+    the Tantivy exclusive-range brace ``}`` rather than ``]`` — otherwise the
+    first instant of the following period (e.g. the 1st of next month) is
+    incorrectly included in the match.
+    """
+    return f"[{_fmt(lo)} TO {_fmt(hi)}}}"
 
 
 def _quarter_start(d: date) -> date:

src/documents/search/_translate.py

@@ -566,6 +566,17 @@ def translate_range(field: str, lo: str, hi: str, tz: tzinfo) -> str:
         lo_pair, hi_pair = hi_pair, lo_pair
 
     lo_iso = _fmt(lo_pair[0]) if lo_pair is not None else OPEN_LO
-    hi_iso = _fmt(hi_pair[1]) if hi_pair is not None else OPEN_HI
 
-    return f"{field}:[{lo_iso} TO {hi_iso}]"
+    # A bound resolves to (floor, ceil) where floor == ceil for an exact instant
+    # (a full ISO datetime, "now", or a "+/-N unit" offset) and floor != ceil for
+    # a coarser period token (year/month/day precision). Only the latter needs a
+    # half-open close: its ceil is the start of the *next* period and must be
+    # excluded, or that instant (e.g. the 1st of next month) wrongly matches.
+    if hi_pair is not None:
+        hi_iso = _fmt(hi_pair[1])
+        hi_close = "]" if hi_pair[0] == hi_pair[1] else "}"
+    else:
+        hi_iso = OPEN_HI
+        hi_close = "]"
+
+    return f"{field}:[{lo_iso} TO {hi_iso}{hi_close}"