v0.32.8 — paid chat calls stream, so slow reasoning models stop 524ing after payment

Paid chat calls now stream. A non-streaming request to a slow reasoning model
(Kimi K3 with a large prompt generates for minutes) moves ZERO bytes between
"request accepted" and "body ready", so the edge in front of the gateway kills
the idle connection at ~100s and returns 524 — AFTER the x402 payment settled.
Charged, nothing delivered. Observed live 2026-07-21, twice.

• fix(chat) — paid EVM paths use SSE streaming and assemble server-side.
  All three paid call shapes (explicit model, multi-turn messages, paid
  routing tiers) switch to the SDK's chatCompletionStream and concatenate
  deltas; bytes flow from the first chunk (reasoning models emit keepalive
  chunks while thinking), so the idle timer never fires. Verified live: a
  125s kimi-k3 generation that 524'd on the old path completes. The free
  NVIDIA tier keeps the non-streaming client whose short timeout its
  deadline loop depends on; Solana clients have no streaming API and keep
  the old path (capability-checked, not assumed).
• Empty answer + finish_reason:"length" is now an explicit error.
  Reasoning tokens count toward max_tokens; a hard task with a small budget
  can burn the whole budget thinking and emit zero visible text (measured:
  kimi-k3, 8000 max_tokens, 0 chars). That surfaced as a silent empty reply —
  indistinguishable from success. It now throws with the cause and the fix
  (raise max_tokens).
• Guards that keep the stream honest: a non-SSE response (a route that ignores
  stream:true) is parsed as a plain JSON completion instead of yielding "";
  an in-band error event throws instead of returning partial text; a stream
  with no data for 120s aborts with a stall error (the SDK clears its fetch
  timeout once headers arrive, so this idle guard is the only backstop).
• x402 accounting is unchanged: the SDK's streaming method runs the same
  payment flow and increments the same spend counter the budget ledger reads.
• 234 tests (11 new pinning SSE assembly, fallbacks, stall, and the
  reasoning-exhaustion diagnosis), typecheck, build green. Server-side half
  (settle-on-success / refund on 5xx at the gateway) is tracked separately.