fix: render valid TOML when a command body contains backslashes (#3135)

render_toml_command() emitted the body inside a multiline *basic* TOML
string ("""..."""), which processes backslash escape sequences. A command
body containing a backslash — e.g. a Windows path like C:\Users\... whose
\U reads as an invalid unicode escape — therefore produced unparseable TOML
("Invalid hex value"), so the generated Gemini/Tabnine command file failed
to load. A body ending in a backslash also silently ate the closing newline
via TOML line-continuation.

Route bodies containing a backslash to the multiline *literal* form
('''...'''), which does not process escapes, or to the escaped basic string
when both triple-quote styles are present. Mirrors the escaping already done
by base.py's TomlIntegration.

Add tests covering a Windows path, a trailing backslash, and the
backslash + both-triple-quote-styles fallback.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/specify_cli/agents.py

@@ -236,9 +236,14 @@ class CommandRegistrar:
         toml_lines.append(f"# Source: {source_id}")
         toml_lines.append("")
 
-        # Keep TOML output valid even when body contains triple-quote delimiters.
-        # Prefer multiline forms, then fall back to escaped basic string.
-        if '"""' not in body:
+        # Keep TOML output valid even when body contains triple-quote delimiters
+        # or backslashes. Prefer multiline forms, then fall back to escaped basic
+        # string. A multiline *basic* string ("""...""") processes backslash escape
+        # sequences, so a body containing a backslash (e.g. a Windows path
+        # ``C:\\Users\\...`` whose ``\\U`` reads as an invalid unicode escape) would
+        # produce unparseable TOML — route those to the *literal* form ('''...'''),
+        # which does not process escapes, or to the escaped basic string.
+        if '"""' not in body and "\\" not in body:
             toml_lines.append('prompt = """')
             toml_lines.append(body)
             toml_lines.append('"""')