Serve a request by the revision its _meta declares, not by the carrier

[HackTuah]

Closes the ping defect live in published 0.1.0: the _meta clause refused ping with -32601 for every revision reaching it, including 2025-11-25, where ping exists. Its own comment named 2026-07-28; the code named no revision.

Red first

$ mix test test/beam_mcp/negotiation_test.exs
12 tests, 2 failures
exit=2

Nine pre-existing tests passed. Full output at slices/001b-ping-guard/logs/red.txt, written by the command.

Two halves of one defect

The same version-blind cond also stamped resultType and modern _meta serverInfo onto results answering 2025-11-25 requests — two fields 2026-07-28 introduced and 2025-11-25 does not define. Fixing only ping would have left the clause version-blind.

The clause now branches on the declared version. 2026-07-28 refuses ping and modernises; 2025-11-25 answers ping and does not; anything else is -32022.

Decided against the fetched specification rather than the issue text. Refusing a _meta naming 2025-11-25 would contradict this server's own advertisement — it returns that revision from server/discover and lists it in the -32022 supported payload, and the spec tells a client receiving -32022 to select from that list and retry the request, which produces exactly this message. The three specification pages quoted are archived under logs/, fetched by curl, and the sweep re-fetches and diffs them against upstream.

Verification

./tools/gate.sh    format / compile / test / credo  pass
                   reuse  pass (19 commentable files)
                   licence files  pass
                   Gate OK.  exit=0
mix test           39 tests, 0 failures

Three tests added for state threading through the new branches; two are mutation-killed with raw captures at logs/mutation-a.txt and logs/mutation-b.txt, the third guards a write that does not exist and is not scored — stated rather than claimed.

Review

Six rounds, two independent lanes, each on a git archive checkout of the index; both lanes printed the tree hash they read and both matched git write-tree. Twelve reports, each written by its own lane, are in logs/. Both approved tree d9b0c01e.

lib/ and test/ have not changed since round 2 — both lanes cleared the substance early, and every round after was evidence integrity. What that caught, three times running, was an archive whose bytes were not its command's, where each fix introduced the next instance. It stopped when the population was derived rather than the instance patched; tools/archive_sweep.sh now classifies every file and exits 1 if the population and the classifications disagree, scored by mutation rather than asserted.

Release note — needs a decision before publish

This removes resultType and _meta serverInfo from results for every method on the legacy-declared path, not just ping. A 0.1.0 client reading result.resultType there gets nil after what is numbered a patch. The removal is labelled under its own ### Changed heading; whether 0.2.0 is the honester number is left open deliberately. 0.1.1 reached main and was never published — its documentation fix ships inside 0.1.2.

Known, filed rather than folded in

tools/list omits ttlMs/cacheScope and server/discover carries no resultType, both required by 2026-07-28 (SCR-261). Two gaps in tools/gate.sh's own honesty (SCR-262). A conditional defect in the sweep's exit status, harmless today and blocking the moment it is wired into CI, is filed separately.