Accounting reason: a draft that waits on its receipt, and one thrown
away, are facts about the books' working papers that must survive a
restart and replay identically, or a discarded draft would come back and
hold its period open. entry.draft_state_set and entry.draft_discarded are
drafts_v2's (an older version stops at the declaration instead of
misreading them); no figure moves. Schema 19 (taken at merge as the next
after the current last): entries.posted_seq, and a draft_states table
(drafts are not rows of entries, so the plan's entries.draft_state column
has nowhere to live). posted_seq is the journal line that posted each
entry (entry.posted, entry.reversed, the line that closed a period or
posted a schedule month), identical live and on replay.
8.0.6: a hand-written line of each new shape in
books_written_under_older_rules_still_open; fixture old-books/p4_before
written by 25b52580 (hand entries posted late, a reversal, a document, a
schedule month, a recurring draft, open drafts, a close) opens to the
same figures (serialized entries omit a building state, so no golden
moved); drafts_v2_is_its_own_feature; the fuzzer and GUI journal know the
types.
Tests: draft_states_replay_and_project, drafts_v2_waits_for_the_upgrade,
posted_seq_is_the_posting_lines_seq, an_older_version_stops_at_the_draft_events.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp
Accounting reason: an entry that is finished but waits on its receipt is
a different thing from one still being built, and a draft that will
never post must have a way out, or the period that holds it open can
never close (the Lean hypothesis hdrafts). JournalEntry gains
DraftState { Building, AwaitingEvidence { note } }; Ledger gains
set_draft_state (a note: no line, balance or report moves),
discard_draft (a draft only; a posted entry is never removed, B-8; ids
are never reused; what was recorded about the draft goes with it) and
posted_seq (the journal line that posted an entry, for the digest's
since_seq). Lean Step.discard with its preservation proof and three
theorems (a discard moves no figure, removes only its draft, and
unblocks a close), listed in Audit.lean.
Tests: discard_unblocks_close (ledger-core invariants).
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp
CI's run of the store refusal property found a payroll run that posted
$65.27794: the employer tax was passed in unrounded and nothing refused
it, though rules.md B-3 already says a ledger in one money holds no
fractions of its smallest unit. Sums of it then differed in scale
between journal replay and the SQLite read-back.
- Ledger::post_entry refuses any line finer than its currency's ISO 4217
minor unit (FinerThanMinorUnit), whatever made the line: payroll,
closes, disposals. add_line refuses it up front. Older journals replay
as booked through replay_post_entry. Spec tests for the kernel's
ten-place limit now run on the replay path.
- The property's body is now run_ops, so failing sequences become named
regression tests (regression_payroll_with_a_fraction_of_a_cent). The
generator rounds payroll tax to the cent, as callers must.
- Ledger derives PartialEq and gains differs_from; Store::verify compares
the live ledger with the journal replay in full (drafts, documents,
schedules, periods, settings), not just balances, and names the parts
that differ. The property checks the ledger its commands built against
that replay and against the reopened books.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX
The money arithmetic every invariant rests on now lives in one kernel,
ledger-core/src/kernel.rs: signing a line, totals, net, per-account
movements, reversal, normal balances, trial-balance columns, closing
lines, and the rounding plug for member splits. It is generic over a
checked `Amount` trait. The engine runs it on Decimal (validate,
movements, reverse_entry, account_balance, close_period_to, allocate,
trial_balance): there is one copy of the arithmetic, and it is the one
under proof.
Three layers, docs/verification.md maps every law to its proofs:
- Kani (src/proofs.rs): 17 harnesses prove the kernel at i64 for every
input up to 4 lines over 3 accounts. An entry is accepted exactly
when it is two or more positive, in-range lines whose debits equal
credits; accepted entries net to zero; grouping by account loses
nothing; a reversal mirrors and cancels its original; trial-balance
columns balance iff the books net to zero; closing lines zero their
accounts and a close balances however the net is split; the plug
makes parts sum to the whole. No panics, no overflow. kani::cover!
shows the proofs are not vacuous.
- Lean 4 (verify/lean): 24 headline theorems for books of any size. The
ledger is a state machine (add account, draft, post, reverse, open,
close), and in every reachable state the books net to zero, the trial
balance balances (as of any date), and the accounting equation holds.
Posting only appends ("posted is forever"), closed periods are
frozen, a close zeroes revenue and expenses and credits exactly the net
income, and period statements add up. Audit.lean shows standard axioms
only, no sorry.
- Bridge (tests/kernel_bridge.rs): the Decimal and i64 kernels agree.
What the proofs found (each one missed by every test, fuzzer, and
mutant):
- The engine accepted negative line amounts; only MCP refused them. Now
NegativeAmountLine: direction is the side's job.
- Summing lines near Decimal::MAX panicked. Lines are now capped at one
quadrillion and ten decimal places (AmountOutOfRange), which keeps
every realistic sum exact, and the kernel's sums are checked.
- FX conversion (foreign_amount * fx_rate) could panic the same way; it
is now a checked multiply.
- Kani itself: 0.68 mis-models symbolic-length copy_from_slice
(model-checking/kani#4904) and reported a reversal that doesn't net to
zero. The counterexample, replayed natively, passes, and a 15-line
standalone crate reproduces the bug. Harnesses avoid bulk copies, and
a should_panic canary will flag the upstream fix.
`just prove` runs it all (Kani memory- and time-capped, fails on an
unsatisfiable cover or a non-standard Lean axiom). AGENTS.md now makes
formal coverage part of every core change.
Also, docs: GnuCash is *an* oracle, never *the* oracle (the owner). The
spec is accounting principles, proved. Golden files are recomputed from
principles. External implementations (GnuCash, the old Sheet, QBO/Xero)
are cross-checks whose disagreements get adjudicated, never obeyed.
docs/oracle.md gains "Who is right"; AGENTS, README, architecture,
roadmap, parity, and STATUS are reworded to match.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX
swaitsandClaude Fable 5.1