fix: reject non-finite numbers before they reach _meta

`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>

clients/web/src/utils/jsonObjectDraft.ts

@@ -1,4 +1,5 @@
 import type { StrictJsonObject } from "@inspector/core/json/jsonUtils.js";
+import { isSerializableJson } from "@inspector/core/json/jsonUtils.js";
 
 /**
  * What a JSON-object editor's draft text currently means: the object to emit,
@@ -49,5 +50,15 @@ export function parseJsonObjectDraft(text: string): JsonObjectDraft {
       error: "Must be a JSON object (`{ … }`) — changes are not applied",
     };
   }
+  // `JSON.parse` accepts numeric literals it cannot represent: `1e400` parses
+  // to `Infinity`, which `JSON.stringify` then writes as `null`. Accepting it
+  // here would show the user one value and send another.
+  if (!isSerializableJson(parsed)) {
+    return {
+      ok: false,
+      error:
+        "Numbers must be finite — a value like `1e400` overflows and would be sent as null",
+    };
+  }
   return { ok: true, value: parsed };
 }