feat: contract-driven runtime HTTP server with a pluggable MEOS engine

[estebanzimanyi]

What

Adds server/ + serve.py: the projection that executes. It builds routing, request validation and dispatch from the enriched catalog (network / wire) — the same single source the OpenAPI and MCP generators consume; the server is just the consumer that runs the algebra.

python run.py                                 # enriched catalog
python serve.py                               # 127.0.0.1:8080 (StubEngine)
MEOS_LIBRARY_PATH=/path/libmeos.so python serve.py 0.0.0.0 9000

How

POST /{function} per stateless-exposable function: validate the JSON body → decode each serialized string to an opaque handle → invoke → encode the result → {"result": …} (204 void, 400 {"error","code"} on a MEOS/validation error, 404 unknown). All MEOS work is behind an Engine:

• CtypesEngine — dlopen a built libmeos, call by symbol. Every opaque value is an anonymous void *; no struct layout is ever needed, because the catalog already reduced every exposable function to scalars + decode/encode of opaque pointers. Selected via MEOS_LIBRARY_PATH.
• StubEngine — no MEOS build: routing/validation/error-mapping run; calls return deterministic placeholders. Default; makes the server runnable and testable without a compiled MEOS.

Stdlib http.server only — no new dependencies.

Validation (and its honest boundary)

• Generation / routing / validation / dispatch / error mapping: fully validated — built from the live MobilityDB master catalog and exercised end-to-end over real HTTP sockets.
• CtypesEngine arg/return ctype mapping and the decode→invoke→encode flow: unit-tested against a fake shared library.
• Not validated here: linkage against a real libmeos.so — no compiled MEOS exists in this environment (only headers + the catalog). That is the integration step; CtypesEngine is the seam for it, stated plainly in docs/server.md.

The server is a correct-by-construction reference implementation, not a tuned production stack — concurrency, auth, and ASGI are intentionally out of scope. tests/test_server.py and tests/test_engine_integration.py hold the worked examples.