Fuse upstream JSON parsing, scalar packing, heap admission, and value assembly into synchronous token stages while retaining asynchronous file reads and existing capacity, cancellation, decoding, identity, and typed-error semantics. Declare stream-chain 4.2.6 directly.
Validation: 30 focused tests; check:fast, Knip and formatting; actual Flameox paired full-content oracles; real Linux evidence replay and Windows source-built package/Ghidra snapshot recovery; final-head CI 31/31 success.
Refs #1065, #1680.