diff --git a/tests/tools/test_search_error_guard.py b/tests/tools/test_search_error_guard.py
index e045c8c3d524..8b827a6d4936 100644
--- a/tests/tools/test_search_error_guard.py
+++ b/tests/tools/test_search_error_guard.py
@@ -109,6 +109,26 @@ def test_truncation_no_false_error(self, method, tmp_path):
         assert res.error is None, f"truncated success wrongly errored: {res.error!r}"
         assert len(res.matches) == 5
 
+    def test_files_only_preserves_spaced_paths_end_to_end(self, method, tmp_path):
+        root = tmp_path / "workspace"
+        root.mkdir()
+        spaced = root / "Meeting Notes.txt"
+        nested_dir = root / "project files"
+        nested_dir.mkdir()
+        nested = nested_dir / "release notes.md"
+        spaced.write_text("needle\n")
+        nested.write_text("needle\n")
+
+        res = _search(
+            _ops(tmp_path), method, "needle", "workspace", output_mode="files_only"
+        )
+
+        assert res.error is None
+        assert set(res.files) == {
+            "workspace/Meeting Notes.txt",
+            "workspace/project files/release notes.md",
+        }
+
     def test_files_only_excludes_diagnostics(self, method, partial_error_tree):
         # files_only mode must not list a diagnostic line as a fake file path.
         res = _search(_ops(partial_error_tree), method, "needle",
@@ -216,3 +236,41 @@ def test_context_lines_and_separator_are_payload(self):
         assert diagnostics == ""
         assert "--" in payload
         assert "a.py-6-after" in payload
+
+    def test_files_only_preserves_spaced_paths(self):
+        # Regression: files_only output is one bare path per line and may
+        # contain spaces. The content-mode shape regex forbids whitespace, so
+        # without mode awareness these valid matches are silently dropped.
+        out = "normal.py\nMy Document.md\nsub/Meeting Notes.txt\nsub/clean.txt\n"
+        diagnostics, payload = _split_tool_diagnostics(out, output_mode="files_only")
+        assert diagnostics == ""
+        lines = payload.split("\n")
+        assert "My Document.md" in lines
+        assert "sub/Meeting Notes.txt" in lines
+        assert len(lines) == 4
+
+    def test_files_only_still_drops_regex_parse_error(self):
+        # The hard-error block (indented pattern + caret, trailing "error: ")
+        # must still be classified as diagnostics in files_only mode so a real
+        # failure is surfaced rather than returned as fake file paths.
+        out = "rg: regex parse error:\n    (?:[)\n       ^\nerror: unclosed character class\n"
+        diagnostics, payload = _split_tool_diagnostics(out, output_mode="files_only")
+        assert payload.strip() == ""
+        assert "regex parse error" in diagnostics
+
+    def test_files_only_keeps_path_named_like_error_summary(self):
+        # A file literally named "error: notes.md" is a valid match, not a
+        # diagnostic: outside an rg parse-error block, an "error:"-prefixed
+        # line is a real path and must be preserved.
+        out = "src/a.py\nerror: notes.md\nsrc/b.py\n"
+        diagnostics, payload = _split_tool_diagnostics(out, output_mode="files_only")
+        assert diagnostics == ""
+        assert "error: notes.md" in payload.split("\n")
+
+    def test_files_only_keeps_indented_path_outside_error_block(self):
+        # A path with leading whitespace is still a real match when no
+        # parse-error block is active; it must not be mistaken for a caret line.
+        out = "src/a.py\n  weird name.txt\nsrc/b.py\n"
+        diagnostics, payload = _split_tool_diagnostics(out, output_mode="files_only")
+        assert diagnostics == ""
+        assert "  weird name.txt" in payload.split("\n")
diff --git a/tools/file_operations.py b/tools/file_operations.py
index 994723cf583b..6591bdd8605a 100644
--- a/tools/file_operations.py
+++ b/tools/file_operations.py
@@ -345,7 +345,7 @@ def _search_stdout_and_limit(result: ExecuteResult) -> tuple[str, Optional[str]]
     return result.stdout, None
 
 
-def _split_tool_diagnostics(output: str) -> tuple[str, str]:
+def _split_tool_diagnostics(output: str, output_mode: str = "content") -> tuple[str, str]:
     """Separate rg/grep diagnostic lines from real match output.
 
     ``_exec`` runs commands with ``stderr=subprocess.STDOUT``, so error and
@@ -367,6 +367,7 @@ def _split_tool_diagnostics(output: str) -> tuple[str, str]:
     """
     diagnostics: list[str] = []
     payload: list[str] = []
+    in_rg_parse_error = False
     for line in output.split('\n'):
         if not line.strip():
             continue
@@ -379,6 +380,28 @@ def _split_tool_diagnostics(output: str) -> tuple[str, str]:
         stripped = line.lstrip()
         if stripped.startswith("rg: ") or stripped.startswith("grep: "):
             diagnostics.append(line)
+            # rg's "regex parse error:" header is followed by several
+            # continuation lines with no tool prefix (an indented echo of the
+            # offending pattern + a caret, then a bare "error: <summary>").
+            # Track that we're inside such a block so those continuations are
+            # classified as diagnostics — but only there.
+            in_rg_parse_error = "regex parse error" in stripped
+            continue
+        if output_mode == "files_only":
+            # files_only output is one bare path per line and may legitimately
+            # contain spaces ("My Document.md") or even start with "error:".
+            # The content-mode shape regex forbids whitespace, so using it here
+            # would misclassify valid paths as diagnostics and silently drop
+            # them. The ONLY non-path lines in this mode are the continuation
+            # of an rg regex-parse-error block, and a parse error aborts the
+            # search (no matches are interleaved with it). So strip a line only
+            # when it is a continuation INSIDE an active parse-error block;
+            # every other line is a real path and is preserved verbatim.
+            if in_rg_parse_error and (line[:1].isspace() or stripped.startswith("error: ")):
+                diagnostics.append(line)
+            else:
+                in_rg_parse_error = False
+                payload.append(line)
             continue
         # Otherwise classify by output shape. rg's regex-parse-error block
         # also emits an indented caret line and a trailing "error: ..." line
@@ -2306,7 +2329,7 @@ def _search_with_rg(self, pattern: str, path: str, file_glob: Optional[str],
         # diagnostic lines ("rg: <file>: <error>", "rg: regex parse error:")
         # are interleaved with match output. Split them out: diagnostics must
         # not be parsed as matches, and on a hard error they ARE the message.
-        diagnostics, payload = _split_tool_diagnostics(stdout)
+        diagnostics, payload = _split_tool_diagnostics(stdout, output_mode)
 
         # rg exit codes: 0=matches found, 1=no matches, 2=error. rg returns 2
         # even on partial errors (e.g. one unreadable file in a tree that
@@ -2434,7 +2457,7 @@ def _search_with_grep(self, pattern: str, path: str, file_glob: Optional[str],
         # ("grep: <file>: <error>") are interleaved with matches. Split them
         # out so they're never parsed as matches and so a hard error has a
         # clean message.
-        diagnostics, payload = _split_tool_diagnostics(stdout)
+        diagnostics, payload = _split_tool_diagnostics(stdout, output_mode)
 
         # grep exit codes: 0=matches found, 1=no matches, 2=error. grep
         # returns 2 on partial errors (e.g. an unreadable file) even when