v0.3.2 — leaf-mode bypass observable end-to-end on real MCP traffic
The Codec leaf-mode bypass — the architectural target the entire v0.3 contract was designed for — fires end-to-end. `[Codec][leaf]` log line confirms the gateway is a transparent ID pipe; the tokenizer sits at the leaf where it belongs.
The Codec v0.3 leaf-mode contract — the architectural target where the tool tokenizes once, the gateway forwards IDs verbatim — landed on real lab traffic for the first time today. The proof is one log line:
[INFO] [Codec][leaf] downstream tool returned pre-tokenized result
for vocab sha256:9db56ff6… — gateway shim bypassed.Two coordinated fixes shipped in v0.3.2:
1. Wire shape change — @codecai/mcp-leaf now annotates each text content block with a per-block _meta['ai.codec/leaf-tokenization'] payload instead of pushing a sibling _codec_meta content block. The sibling form crashed the MCP SDK’s validator on the server side (-32602 Invalid tools/call result) before the result ever left the leaf process — _codec_meta isn’t in the SDK’s discriminated content-block union. The per-block _meta slot is a first-class MCP spec field that the SDK passes through unchanged. Bonus side-effect: the per-block representation is ~4.6× more compact than the sibling form (a 4.6 KB JSON baseline collapsed to 990 B).
2. Gateway detector — codec-metamcp’s hasExistingCodecMeta now checks both shapes (per-block _meta first, legacy sibling-block as back-compat). When it finds either, the shim bypasses, the [Codec][leaf] log fires, and the gateway acts as a transparent ID pipe for that hop.
Bench numbers from the v0.3.2 run (2026-05-09T12-17-48Z):
| Workload | json | msgpack-both+gzip+map (leaf) |
|---|---|---|
codec-time-leaf__get_current_time | 990 B | 931 B |
codec-time-leaf__convert_time | 1.0 KB | 972 B |
tools/list (40 tools) | 21.4 KB | 5.9 KB |
Wire bytes between variant 4 (gzip with shim) and variant 5 (gzip with leaf-bypass) are now identical because gzip already collapses redundant content. The leaf-bypass benefit on this hop is CPU on the gateway (no tokenizer runs) and KV-cache safety (the engine receives the exact IDs the leaf produced) — the [Codec][leaf] log is the right observability target, not a smaller number.
tools/list holds at 3.6× wire reduction across the 40-tool namespace.
Status of the v0.3 release: spec, polyglot clients, MCP integration, website + RSS, bench methodology, and now the leaf-mode end-to-end demo all live.