CVE-2026-63470: fastapi-code-generator: Call-time RCE via operation summary -> unescaped route-handler docstring

### Summary fastapi-code-generator (koxudaxi) emits an operation's `summary` as the generated route handler's docstring, using a triple-quoted string without escaping `"""`. A `"""` in the summary closes the docstring and, via concatenation, injects a live expression that becomes an expression statement in the handler body -- which runs when the route handler is CALLED (the endpoint is hit). The summary is a pure data field. Verified on fastapi-code-generator 0.8.0 / Python 3 / FastAPI. ### Details ```python def get_thing() -> None: ( """ x""" + (__import__("os").system('…') or "") + """y """ ) pass ``` The generator post-processes with black/isort, so a syntax-breaking payload aborts generation; a valid-Python breakout (`"""+expr+"""`, kept valid with `(… or "")`) is written and executes at call time. info.description, tags, parameter defaults are escaped; operation description is not emitted into the function body; the summary in the handler docstring is the unescaped sink. Models come from datamodel-code-generator (repr-escaped, no RCE). Not a duplicate: distinct product from OpenAPI Generator's python-fastapi; and distinct field/sink from the route path -> @app.get('…') decorator (import-time) in the same product -- this is the operation summary in the handler docstring (call-time). ### PoC `reproduce.sh` (+ `make_spec.py`) attached: generates the app and calls the route handler; the injected expression runs and writes a marker. Verified on 0.8.0. ### Impact Code execution on the server when the affected endpoint is invoked, in any app generated with fastapi-code-generator from an attacker-controlled or attacker-influenced spec. ### Suggested fix Escape the summary for the docstring context (escape `"""`/backslashes via repr, or strip triple-quotes) before emitting it as the handler docstring; apply the same to any free-text field rendered into a docstring. [maintainer-report.txt](https://github.com/user-attachments/files/29534450/maintainer-report.txt) [make_spec.py](https://github.com/user-attachments/files/29534452/make_spec.py) [reproduce.sh](https://github.com/user-attachments/files/29534453/reproduce.sh)