fix(debug): distinguish empty-log from missing-log in report placeholder

Copilot on #14138 flagged that the share report says '(file not found)'
when the log exists but is empty (either because the primary is empty
and no .1 rotation exists, or in the rare race where the file is
truncated between _resolve_log_path() and stat()).

- Split _primary_log_path() out of _resolve_log_path so both can share
  the LOG_FILES/home math without duplication.
- _capture_log_snapshot now reports '(file empty)' when the primary
  path exists on disk with zero bytes, and keeps '(file not found)'
  for the truly-missing case.

Tests: rename test_returns_none_for_empty → test_empty_primary_reports_file_empty
with the new assertion, plus a race-path test that monkeypatches
_resolve_log_path to exercise the size==0 branch directly.

hermes_cli/debug.py

@@ -332,24 +332,29 @@ class LogSnapshot:
     tail_text: str
     full_text: Optional[str]
 
-def _resolve_log_path(log_name: str) -> Optional[Path]:
-    """Find the log file for *log_name*, falling back to the .1 rotation.
-
-    Returns the path if found, or None.
-    """
+def _primary_log_path(log_name: str) -> Optional[Path]:
+    """Where *log_name* would live if present. Doesn't check existence."""
     from hermes_cli.logs import LOG_FILES
 
     filename = LOG_FILES.get(log_name)
-    if not filename:
+    return (get_hermes_home() / "logs" / filename) if filename else None
+
+
+def _resolve_log_path(log_name: str) -> Optional[Path]:
+    """Find the log file for *log_name*, falling back to the .1 rotation.
+
+    Returns the first non-empty candidate (primary, then .1), or None.
+    Callers distinguish 'empty primary' from 'truly missing' via
+    :func:`_primary_log_path`.
+    """
+    primary = _primary_log_path(log_name)
+    if primary is None:
         return None
 
-    log_dir = get_hermes_home() / "logs"
-    primary = log_dir / filename
     if primary.exists() and primary.stat().st_size > 0:
         return primary
 
-    # Fall back to the most recent rotated file (.1).
-    rotated = log_dir / f"{filename}.1"
+    rotated = primary.parent / f"{primary.name}.1"
     if rotated.exists() and rotated.stat().st_size > 0:
         return rotated
 
@@ -370,12 +375,15 @@ def _capture_log_snapshot(
     """
     log_path = _resolve_log_path(log_name)
     if log_path is None:
-        return LogSnapshot(path=None, tail_text="(file not found)", full_text=None)
+        primary = _primary_log_path(log_name)
+        tail = "(file empty)" if primary and primary.exists() else "(file not found)"
+        return LogSnapshot(path=None, tail_text=tail, full_text=None)
 
     try:
         size = log_path.stat().st_size
         if size == 0:
-            return LogSnapshot(path=log_path, tail_text="(file not found)", full_text=None)
+            # race: file was truncated between _resolve_log_path and stat
+            return LogSnapshot(path=log_path, tail_text="(file empty)", full_text=None)
 
         with open(log_path, "rb") as f:
             if size <= max_bytes: