bug: reject non-finite numbers in JSON and NDJSON contracts

[codeforester]

Problem

The public JSON serializers use Python's permissive NaN/Infinity defaults. They can report successful output containing tokens rejected by strict JSON consumers such as JavaScript JSON.parse, undermining the advertised cross-language machine boundary.

Verified evidence

Reviewed on 2026-09-12 at 7faf347a5b90969e169c88f3ac18e7202d142dd0; the local checkout matches GitHub main.

stream = io.StringIO()
base_cli.NdjsonWriter(stream).write({"value": float("nan")})
print(stream.getvalue())
# {"schema_version":1,"schema":"base-cli.record","record":{"value":NaN}}

render_records(..., requested_format="json") and dumps_envelope(success_envelope(run_id=None, details={"value":float("inf")})) have the same permissive serialization path. Python json.loads accepts these extensions, so round-trip tests using only Python miss the violation.

Sources:

• lib/python/base_cli/output.py
• lib/python/base_cli/json_contracts.py
• scripts/validate_contract_fixtures.mjs

Acceptance criteria

• Choose and document strict handling for NaN and positive/negative infinity (prefer rejecting with a clear error rather than silently changing data).
• Serialize a full record before writing it so an invalid record does not leave a partial NDJSON line.
• Test all public JSON/envelope/NDJSON emitters with nested non-finite values.
• Use a strict parser, including the Node contract path, to reject nonstandard output.

Project fields

• Status: Backlog
• Priority: P2
• Area: CLI
• Initiative: v1.0 Readiness
• Size: S
• Assignee: @codeforester
• Milestone: v1.0.0
• Target date: unscheduled