fix: prune/retier no longer treat a foreign same-stem file as a rolled log

prune() and retier() matched any file starting with "<stem>." (minus the live
<stem>.log), with no check that the name actually has this lib's own rolled
shape (<stem>.<stamp>[.N].log[.gz]). Since v0.5.0 the default history_stem is
the cwd basename, so a project dropping its own same-stem file into log_dir
(e.g. proj.audit.log, proj.stats.json) got silently deleted by prune once it
aged past backup_count, or folded into retier's tier accounting (gzipped or
deleted as if it were a real roll). Candidates are now filtered through
_is_rolled_name before being treated as a roll.

Signed-off-by: disqualifier <dev@disqualifier.me>

src/log_setup/rotation.py

@@ -15,6 +15,7 @@ plain copy.
 
 import gzip
 import os
+import re
 import shutil
 import time
 from typing import Callable, Optional, Tuple
@@ -252,12 +253,17 @@ def retier(log_dir: str, stem: str, keep_uncompressed: int, keep_compressed: int
     ordering is by mtime, then by the roll counter parsed from the name, so a
     same-second burst (tied mtimes, counter-disambiguated stamps like run.<t>.log /
     run.<t>.1.log) still tiers newest-first rather than falling back to listdir order.
+
+    candidates are also checked against this lib's own rolled-file shape
+    (`<stem>.<stamp>[.N].log[.gz]`, see `_is_rolled_name`) - a foreign file that only
+    shares the `<stem>.` prefix (e.g. a project's own `<stem>.audit.log` dropped into
+    the same log_dir) is left alone rather than tiered/gzipped/deleted.
     """
     stem = os.path.basename(stem)
     try:
         names = [
             name for name in os.listdir(log_dir)
-            if name.startswith(f"{stem}.") and name != f"{stem}.log"
+            if name != f"{stem}.log" and _is_rolled_name(stem, name)
         ]
     except OSError:
         return
@@ -305,6 +311,23 @@ def retier(log_dir: str, stem: str, keep_uncompressed: int, keep_compressed: int
                 pass
 
 
+def _rolled_name_pattern(stem: str) -> "re.Pattern":
+    """compiled regex matching this lib's own rolled-file shape for stem
+
+    `<stem>.<Y-m-d_H-M-S>[.N].log[.gz]` - the uniform namer output from
+    make_history_namer/rotate_on_start (see attach_rolling). used to filter
+    prune/retier candidates so a foreign file merely sharing the `<stem>.` prefix
+    (e.g. a project's own `proj.audit.log` sitting beside its `proj.<stamp>.log`
+    rolls) is never mistaken for a roll and pruned/retiered/deleted.
+    """
+    return re.compile(rf"^{re.escape(stem)}\.\d{{4}}-\d{{2}}-\d{{2}}_\d{{2}}-\d{{2}}-\d{{2}}(?:\.\d+)?\.log(?:\.gz)?$")
+
+
+def _is_rolled_name(stem: str, name: str) -> bool:
+    """return whether name has this lib's own rolled-log shape for stem"""
+    return _rolled_name_pattern(stem).match(name) is not None
+
+
 def _roll_counter(path: str) -> int:
     """parse the same-second disambiguation counter out of a rolled filename
 
@@ -331,6 +354,11 @@ def prune(log_dir: str, stem: str, backup_count: int) -> None:
     FOOTGUN: `stem` is reduced to its basename so a `name` containing a directory (e.g.
     "sub/run") still matches the basenamed rolled files in log_dir - else nothing
     matches and old files pile up forever.
+
+    candidates are also checked against this lib's own rolled-file shape
+    (`<stem>.<stamp>[.N].log[.gz]`, see `_is_rolled_name`) - a foreign file that only
+    shares the `<stem>.` prefix (e.g. a project's own `<stem>.audit.log` dropped into
+    the same log_dir) is left alone rather than counted and deleted as a roll.
     """
     if backup_count <= 0:
         return
@@ -339,7 +367,7 @@ def prune(log_dir: str, stem: str, backup_count: int) -> None:
         entries = [
             os.path.join(log_dir, name)
             for name in os.listdir(log_dir)
-            if name.startswith(f"{stem}.") and name != f"{stem}.log"
+            if name != f"{stem}.log" and _is_rolled_name(stem, name)
         ]
     except OSError:
         return