Ephemora Cell: an MCP server that runs every tool as a signed, sandboxed WASM module
MichaelS1011 · reddit · 2026-09-26
Ephemora Cell v1.0.4.3 is a dependency-free stdio MCP server where every tool is a WASM module executed in a capability sandbox: no network surface, bounded fuel/memory/time/output, 12 ms per call by default (0.5 ms pooled).
Highlights:
- Per-call module binding: under --require-signed-tools, every execution verifies the module against the digest in its signed manifest — a file swapped after signing fails closed; producers publish atomically.
- Governed dynamic loading (ADR-006): agents can only propose a tool via a .tool.request. in an operator-allowlisted dir; the server verifies signature, hash and policy before each message, installs atomically, and emits tools/listchanged. Rejections are logged.
- Speaks both the legacy handshake and the stateless 2026-07-28 revision (ttlMs, cacheScope), verified against the official MCP SDK in CI.
- Every tools/call result carries meta.execution (fuel, wall time, attested baseline), signable via DSSE/JWS envelopes.
Listed in the official MCP Registry; pip install ephemora-cell to install, with per-client configs (Claude Desktop, VS Code, Codex) in the README.
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