C wire-protocol test for the COLIEX01 framing

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What to build

A no-model C test that #includes the engine, uses a socketpair, feeds synthetic floats, and asserts byte-exact COLIEX01 framing in both directions (request: magic/version/eid/nr/input layout; response: framing echo). This proves the wire contract correct independent of any model. Mirror the discipline of JustVugg#550's test_dense_protocol.c, but for the COLIEX01 framing (the constant already exists in JustVugg#551's work).

Acceptance criteria

• Test compiles and runs under make test-c.
• Asserts byte-exact framing on both request and response paths.
• No model fixture required.
• Falsifiable: mutating a framing field (magic/version/length) fails the test.

Environment: codegraph-indexed — run codegraph explore first; refs in /home/eli/dev/_reference-docs-and-repos/colibri.