`StrictJsonValue` removed `undefined`, but the type cannot express the rest of
the gap: TypeScript has one `number`, and JSON has no encoding for `NaN` or
`±Infinity`, so `JSON.stringify` rewrites them to `null`.
This is reachable from ordinary input, not a careless caller.
`JSON.parse('{"a":1e400}')` returns `Infinity` on overflow — so text a user
types parses cleanly, satisfies the type, and reaches the server as `null`
while the editor still shows `1e400`.
`isSerializableJson` in `core/json` is the runtime half of `StrictJsonValue`,
applied at both boundaries that turn text into metadata:
- the editor's draft parser, which now reports "Numbers must be finite" inline
and withholds the value rather than emitting one it cannot send;
- the CLI's `--metadata` / `--tool-metadata` parser, which throws. Silently
sending `null` would be wrong, and so would falling back to the literal
string — neither is what was asked for.
Tests cover the validator directly (including that `JSON.stringify` really does
write `null`, which is the reason it matters), the editor parser, and the CLI
flag.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0177mPHAdECD18nLLCTwR5rh
Signed-off-by: cliffhall <cliff@futurescale.com>
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