test(conformance): implement or retire the internal 20-scenario conformance matrix #749

Part of #710.

Summary

What reads as a 20-scenario matrix of adapters and scenarios is only a list of names, so the README overstates what is verified. Two scenario lists also invite drift.

Evidence

• tests/conformance/suite.py:20-52 declares 20 CONFORMANCE_SCENARIOS, and tests/conformance/suite.py:118-145 holds KNOWN_LIMITATIONS exemptions for adk, crewai, llamaindex and agent_framework. The exemptions use names such as gateway_identity_observed and jwt_token_refreshed, which aren't public scenarios.
• No test runs any of the 20 scenarios. Their only user, tests/conformance/test_transport_exemptions.py:53-155, checks only that the exemption table agrees with itself and with the adapter flags.
• The shipped plugin runs a different list of 4 scenarios (conformance/suite.py:196-223).
• README.md:127-140 publishes an exemptions table for scenarios that never run. CONTRIBUTING.md:290-302 presents the kit as the bar every adapter must meet.

Steps

• Pick one:
  • parametrise adapters × scenarios over the simulator using the shipped harness, with each exemption becoming a strict xfail; or
  • delete the names that have no test body.
• Unify the internal and public scenario names.
• Generate the README table from the executable suite.

Done when

• Every scenario name has an executable body, or has been removed.
• An exemption exists only for a scenario that runs for that adapter. Amended 2026-10-05: a transport-level exemption may be an asserted-inverse test (the test asserts the exempt behaviour) instead of a strict xfail.
• Every KNOWN_LIMITATIONS key is a public scenario name. Amended 2026-10-05: KNOWN_LIMITATIONS keys may be internal scenario names, provided each one is in CONFORMANCE_SCENARIOS and has an executable body. Promoting them into the public plugin is out of scope here.
• The README table is generated from, or tested against, the executable suite.

References

• Source: TEST-04, FW-05 (scenario names) (code review 2026-09-30, at commit 11b806b)
• Related: conformance: wire the Phase 2–2.8 scenario bodies as their features land #444
• Retired scenarios tracked in test(conformance): restore the 13 retired scenarios once their surfaces are verified #991.