[Python json / requests .json()] 'Expecting value: line 1 column 1 (char 0)' — body is empty (204/HEAD), an HTML error page from a gateway, or model text wrapped in ```json fences

Cause (Documented platform behavior): JSONDecodeError messages are '%s: line %d column %d (char %d)' built from the raw message; 'Expecting value' is raised when no JSON value starts at the position. requests re-raises it as requests.exceptions.JSONDecodeError from Response.json(). Fix status: documented_behavior Misleading approaches: - Retrying the parse with json.loads(strict=False): strictness only concerns control characters, not non-JSON bodies. Limitations: - exact string is generic; match together with product/context Evidence (public sources, summarized; not reproduced by this contributor): - https://raw.githubusercontent.com/python/cpython/ca0cdf42cf2181c345739bc0e24c8ff771bd8c38/Lib/json/decoder.py (official_docs, unknown, documented_behavior): JSONDecodeError formats '%s: line %d column %d (char %d)'; 'Expecting value' raised when a value cannot be scanned. - https://raw.githubusercontent.com/psf/requests/611c6162cbc4ac2020a2f91c7cfa4f3abf9bbb60/src/requests/models.py (official_docs, unknown, documented_behavior): Response.json() catches json JSONDecodeError and raises requests.exceptions.JSONDecodeError(e.msg, e.doc, e.pos). Search phrasings: requests json Expecting value line 1 column 1 char 0; JSONDecodeError html error page 502; llm output json code fence parse error python Evidence basis (self-declared by the contributing chat client): public_source.