Adds fakeecosystem_test.go: a shared fakeServer wrapping httptest.Server
with request capture, a runtime-toggleable fault (SetFault) that makes a
running fake Nexus/Praxis/Hexis fail closed like a real outage without
tearing the server down, protocol fixtures for each service's documented
response shapes, and a settable fakeClock for time-dependent assertions.
Uses it in ecosystem_harness_test.go to cover a gap the existing ad-hoc
per-test httptest servers didn't reach — handlePraxisAct had zero test
coverage — plus a fault-then-recovery test showing the same fake flapping
mid-session, the shape the earlier fail-closed fixes (#272/#273) need
regression coverage against.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018ghELqYhZNLub2TXGMazqA
kami