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Model the orchestrator in Quint, and reproduce its counterexamples
specs/orchestrator.qnt models control.py: states, gate, pending
questions, comment cursors, publish intents and the worker queue, with
operator messages, Gitea comments, work outcomes (exceptions included)
and a crash at any point interleaving freely. Eight properties.

Seven counterexamples, each written out as a trace in
specs/orchestrator_scenarios.qnt and reproduced against the real code in
nisse-dev/tests/test_quint_counterexamples.py (xfail, strict, until
fixed):

1-4 an approval or feedback lands on a plan the operator had not seen:
    a double 'approve', 'approve rev-1' meant for the architecture,
    approving on both channels, and 'approve' plus an afterthought;
5   a crash after the PR opens but before PR_OPEN publishes again and
    cannot get back to PR_OPEN;
6   a crash while answering a review comment loses it silently;
7   'project complete' leaves the plan issue open.

no_stranding, await_input_has_a_question and execution_needs_approval
held over 200,000 random traces of 40 steps, and under Apalache's
exhaustive check to depth 8, which does find counterexample 1 at that
depth. No behaviour changes here.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPQ14L3LikyefCMFBqEbKE
2026-09-29 18:51:59 +00:00

1.7 KiB

Formal models

Quint models of designs where interleavings matter more than any single code path. A model is a hand-written reading of the code: it finds flaws the design and the code share, not places where the code strays from the design. So every counterexample is also reproduced as a failing test against the real code before anything is changed.

orchestrator.qnt: nisse-dev's control loop

Models nisse-dev/src/nisse_dev/control.py: the states, the gate, pending questions, Gitea comment cursors, publish intents, and the worker queue. Operator messages, Gitea comments, planner/executor/publisher outcomes (exceptions included) and a crash at any point all interleave freely. Each pure function is named after the method it mirrors.

The properties are at the end of the file (all_properties is their conjunction). Counterexamples are written out as short traces in orchestrator_scenarios.qnt, and replayed against the real code in nisse-dev/tests/test_quint_counterexamples.py.

npm install -g @informalsystems/quint     # 0.33 or later

# Random simulation, one property at a time:
quint run specs/orchestrator.qnt --invariant=no_stranding \
    --max-steps=40 --max-samples=200000

# The counterexample traces (each expects its property to break):
quint test specs/orchestrator_scenarios.qnt

Exhaustive bounded checking (quint verify) uses Apalache and needs Java 17.

Keeping it true. When control.py changes how a state is entered or left, change the matching function here in the same PR. When a counterexample's fix lands, flip its scenario's expect to the property holding, and drop the xfail from its Python reproduction.