PERRY_JSON_TAPE=1: extreme-exponent numbers keep their source text instead of round-tripping through f64

[proggeramlug]

With the tape path forced on, three number literals survive JSON.parse as their source text rather than as the double they denote:

JSON.parse("[1e308]")    →  perry: [1e308]     node: [1e+308]
JSON.parse("[-1e308]")   →  perry: [-1e308]    node: [-1e+308]
JSON.parse("[1e-400]")   →  perry: [1e-400]    node: [0]

The third is the substantive one: 1e-400 is below the smallest subnormal double, so it is 0, and Node prints 0. Perry answering 1e-400 means the value never went through an f64 — the tape appears to carry the literal's bytes and re-emit them on stringify. The first two are the same mechanism showing up as a formatting difference (1e+308 is what Number.prototype.toString produces; 1e308 is the source spelling).

Scope — not the default path

• Default (TapeMode::Auto): unaffected. All 64 cases of my JSON accept/reject battery match Node, and a 4001-element document containing 1e308, -1e308, 1e-400, 1.25e2 and 5e-324 round-trips identically.
• PERRY_JSON_TAPE=1 (ForceOn): diverges on the three cases above. The same large document is also identical under ForceOn, so the trigger is the small/simple-document shape that ForceOn routes to the tape and Auto does not.

So this is an opt-in-mode bug rather than a live one. It still matters, because the knob exists to A/B the tape and anyone measuring with it — as I was, while investigating #9184 — gets wrong values back rather than a warning.

Suggested check

Whatever the tape stores for a number entry, the value handed back to JS should be the result of the same decimal→f64 conversion the direct parser performs, so that 1e-400 becomes +0 and 1e308 becomes the double whose toString is 1e+308. A round-trip assertion over exponent extremes (1e308, 1e-400, 5e-324, 1.7976931348623157e308, 2**53+1) would pin it.

Found with the 64-case accept/reject battery from #9184, run against the new one-pass parser from #9224 — which, for the record, passes all 64 on the default path. That work is solid; this is the tape path beside it.

https://claude.ai/code/session_012Ys25ni6VwDKE71o1NTYAT