Agent Plugins 0.14.9

Trials become measurable: their prompts live in the repository, and each run is scored against a
committed baseline, so a drop in quality fails instead of waiting to be noticed.

• trials/<name>/trial.yaml defines each trial (prompt, fixture, setup, measures, expected
  outputs); task trial:run TRIAL=<name> builds the sandbox, prepares the fixture and runs it. Seven
  trials: ESS new spec, retrofit, pipeline and full package; aep backlog planning; worktree
  onboarding; upgrade from a seeded install. The gate checks the definitions.
• New trial ess-full-package: every ESS output (JSON Schema, OpenAPI, AsyncAPI, docs and site,
  Rust and Go type libraries, the Go conformance suite), then an in-memory Go implementation run
  with go test against the generated suite. Sandboxes get go.
• agentplugins-check trial-report measures a run: tool calls, the last validate verdict,
  synthesis scenarios and refusals, UNMAPPED: markers read from the files written, which outputs
  exist, and go test passed/failed/skipped. With --baseline trials/baseline.json it exits 1 when
  a measure gets worse; --write-baseline records an accepted run. trial:run calls it after the
  isolation check.