0.16.0

Added

• An authored scenario can claim a length of time. ess-scenario/1 could say what happened and
  in what order, and nothing about how long anything took: at: ordered the file and reached no
  runner. A migration of forty-five ACD scenarios into the format reported that as its one class of
  loss, and enumerated it — a twenty-second hold that is an experiment's independent variable, two
  wrap-up windows, a one-second queue-exit threshold, a one-minute callback TTL and a five-second
  teardown margin, all of them gaps between two instants and enforced by nothing. A system that
  fires every timer the moment it is armed passed every check ESS could write.

• Three bounds, each on an anchor somebody wrote. An act names its instant with mark:, and a
  later act states what must be true of the gap: not_before: is the hold, within: is the
  deadline, and quiet: {for: …, events: […]} is the bounded negative. Every window names the
  instant it opens at, and there is no implicit anchor anywhere — the suite this was built for had
  negatives whose window opened wherever the preceding block happened to end, so inserting one
  arrangement step moved five assertions and no diff showed it.

• at: is load-bearing at last. It still reaches no runner, and it is now what a duration claim
  is held against: not_before: PT20S in a file whose two instants are five seconds apart is a
  document saying two things, and it is refused rather than compiled into whichever one the compiler
  read first.

• Six refusals, ESS-AUTHOR-028 to ESS-AUTHOR-033: a window measured from an instant nothing
  marked, one name for two instants, a window of no seconds, a bounded negative that forbids no
  event, a claim the timeline contradicts, and a window stating other than exactly one bound. The
  format now numbers thirty-three, and tests/authored.rs still holds a case per code and a case
  asserting the numbering and the documents agree.

• Four steps and two target methods. mark_instant, expect_not_before, expect_within and
  expect_quiet join the closed vocabulary, which now has seventeen words. ConformanceTarget
  gains mark_instant and observe_elapsed, both with default bodies answering Unsupported, so a
  target written against the earlier interface compiles unchanged; the emitted Go runner asks for an
  optional Clock interface for the same reason. A target that implements neither reports the
  scenario unsupported, which §28 makes a failing run. There is no path on which an unheld
  window passes.

• The clock stays the target's. A duration claim could have been built on wall-clock waiting,
  which makes every suite slow and flaky; on a logical clock, which most systems have none of; or on
  an observation reported after the fact, which on its own cannot make twenty seconds happen. This
  asks for the third and permits the first two to produce it: the suite states a length and the
  instant it is measured from, observe_elapsed says how much of the window to let close before
  answering, and the target reports a reading in milliseconds it stands behind. An end-to-end target
  waits; an in-memory target advances a clock it owns and answers instantly; the runner compares the
  reading with the claim and will not round towards it.

Changed

• ess-conformance/3. The step vocabulary grew, which is a change to the shape of the persisted
  document, and that shape is exactly what a suite format versions. The reader this number is for is
  the one that would otherwise be worst off: an old Rust reader parses a closed tagged enum, so a
  3-shaped suite labelled 2 fails with unknown variant — a message blaming the document for
  the age of the tool. An old Go runner does not return a wrong verdict here; its step switch
  abandons a scenario whose first word it does not know and reports it skipped, which is the right
  answer reached by accident. SUPPORTED_SUITE_FORMATS keeps 1 and 2, because a 2 suite means
  in 3 exactly what it meant in 2. The committed suites under suites/generated/ are
  regenerated at the new number and are otherwise byte-identical.

Releases 0.16.0.