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.

tests/hermes_cli/test_debug.py

@@ -158,14 +158,27 @@ class TestCaptureLogSnapshot:
         assert snap.full_text is None
         assert snap.tail_text == "(file not found)"
 
-    def test_returns_none_for_empty(self, hermes_home):
-        # Truncate agent.log to empty
+    def test_empty_primary_reports_file_empty(self, hermes_home):
+        """Empty primary (no .1 fallback) surfaces as '(file empty)', not missing."""
         (hermes_home / "logs" / "agent.log").write_text("")
 
         from hermes_cli.debug import _capture_log_snapshot
         snap = _capture_log_snapshot("agent", tail_lines=10)
         assert snap.full_text is None
-        assert snap.tail_text == "(file not found)"
+        assert snap.tail_text == "(file empty)"
+
+    def test_race_truncate_after_resolve_reports_empty(self, hermes_home, monkeypatch):
+        """If the log is truncated between resolve and stat, say 'empty', not 'missing'."""
+        log_path = hermes_home / "logs" / "agent.log"
+        from hermes_cli import debug
+
+        monkeypatch.setattr(debug, "_resolve_log_path", lambda _name: log_path)
+        log_path.write_text("")
+
+        snap = debug._capture_log_snapshot("agent", tail_lines=10)
+        assert snap.path == log_path
+        assert snap.full_text is None
+        assert snap.tail_text == "(file empty)"
 
     def test_truncates_large_file(self, hermes_home):
         """Files larger than max_bytes get tail-truncated."""