v2.1.0

Three additive, backward-compatible honesty improvements over 2.0.0. No config change
needed; opt out of the whole contract engine with GROUNDTRUTH_CONTRACT=0 as before.

Added — multi-turn deferral persistence (spec §6)

A deferred claim declared on an earlier turn now stays visible on later turns' cards
until verified work closes it, reconstructed from the transcript (the unforgeable record)
rather than a forgeable ledger — so a declared set-aside can't silently vanish by being
omitted next turn. Closure uses only verify-grounded channels and a distinctive key.

Added — prose class-1 fallback for contract-unaware turns (warn-only)

A session whose agent never emits a groundtruth-claims block now still gets a bare prose
"tests pass" lie caught (warn), reinstating v1's _passClaim shape (a test/build noun +
a pass-verdict verb, with negation/modal/reported-speech guards). Never fires when a valid
block exists, abstains with no transcript, and doesn't fire on honest closings like
"Done — fixed the typo."

Changed — no_change contradiction is now block-eligible

A no_change claim may no longer coexist with any other claim (schema-invalid → NC), and
a sole no_change claim on a turn that authored non-excluded changes is now a block-tier
CA self-contradiction (naming up to 3 paths), with the redundant per-file UC warns
suppressed. An empty authored set or an all-excluded diff stays silent (the honest case).

Added — tree-state stamping for tests_pass/build_pass staleness

The green-run staleness check previously relied on within-session event ordering (the
last green run's position vs the last source edit). Its blind spot, surfaced by
community review: an edit made through the bash channel (sed -i, a heredoc,
> f) never updates the edit position — it tracks only Write/Edit tool ops — so a
green predating such an edit passed clean.

This is closed by recording the repo's code fingerprint independently at command time
and comparing it at claim time — grounded in code state rather than event ordering, so it
sees a bash-channel edit directly:

• Stamp — a new PostToolUse[Bash] hook (--stamp) records { head, tree } after
  every TEST_BUILD_RE command, appending one JSON line to
  .claude/groundtruth/<session>-stamps.jsonl. tree is a hash of the repo's normalized
  code — the CODE_EXT_RE source files (comments and whitespace stripped, the same scope
  and normalization the event-ordering anchor already treats as "staling"), read straight
  from disk. So it does not fire on a docs/config edit, a comment-only or whitespace-only
  edit, a harness-written settings file, or a commit of the tested code (the fingerprint is
  absolute content — HEAD identity is not compared); a real code change through any channel
  does. Groundtruth's own .claude/groundtruth/ state is excluded. Non-mutating git only
  (--no-optional-locks); fail-open (not a repo / git error / non-matching command → writes
  nothing).
• Sensor — a stale-by-tree check runs ahead of the event-ordering check in the
  at-most-one-fires chain: when the stamp for the last matching green run differs in code
  fingerprint from the value computed now, it emits a warn-tier CA ("the working tree has
  changed since that run — the green is STALE"). Every uncertainty abstains (no stamps,
  malformed line, ambiguous stamp↔run mapping, failed current-tree computation), falling back
  to the unchanged event-ordering check — a false "stale" on an honest green is the fatal FP
  this must never emit. Because the stamp log is agent-writable on-disk state, the sensor can
  only add a stale warn; a fresh verdict never suppresses the transcript-anchored
  event-ordering warn.
• Tamper surface — the stamp log is in the referee-tamper perimeter: an agent-authored
  Write/Edit to it is flagged. A deleted or missing log is treated as absence (abstain),
  never as evidence.

Scope note: stamps are per-session (<session>-stamps.jsonl); a claim citing a command
with no matching run in this session is already intercepted by the "no such command ran
this session" check, so the sensor's reach is within a session (including a resumed one).

Design credit to community review for identifying the blind spot and the
record-at-command-time / compare-at-claim-time approach, and for the review pass that
rescoped the fingerprint from the whole tree to normalized code (avoiding a false-stale on
every honest post-green docs/comment/commit turn).

Full symptom → root-cause → fix → regression-test in FIXES.md.