wanderbooks/docs/testing.md

Testing strategy

How wanderbooks knows its books are right. Strongest oracle first: a test's worth is where its idea of "correct" comes from, not what it runs. Formal proofs are in docs/verification.md; the authorities every rule comes from are in docs/spec/. Every crate is covered: ledger-core, the store, import, config, and MCP in full; the GUI where it computes and writes numbers (its view model and formatting) and in its read-only promise.

Layers

Layer	Oracle (rank)	Where	Command	Runtime	Gates
Spec-derived examples	written specs with sources (1)	tests/spec_*.rs, invariants.rs, statements.rs, assets.rs, ...; the store's tests/spec_store.rs (written blind, from its specs only)	just check	seconds	every change
Regressions	the bug, named (1)	beside the code they cover, *_regression/named for the defect	just check	seconds	every change
Compatibility contracts	journals written under older rules must open, and replay to the figures their version computed (1)	ledger-store/tests/store.rs (books_written_under_older_rules_still_open; books_an_earlier_version_wrote_open_to_its_figures over tests/fixtures/old-books: books main 188c90ea wrote, with main's own figures in expected.json, in the writer and the viewer; every_figure_over_old_books_is_computed_or_refused); ledger-mcp/tests/hostile_args.rs old_books_answer_every_tool; ledger-gui/tests/old_books.rs	just check	~30s	every change
Properties	laws over all inputs (2)	properties.rs, spec_*.rs, kernel_bridge.rs	just check	seconds	every change
Metamorphic	scaling, reversal, ordering invariance (2)	spec_reports.rs	just check	seconds	every change
Refusal law (store)	a refused command never reaches the journal, an accepted one always does; the live ledger equals its journal's replay in every part, and the books reopen to it (2, 3)	store.rs refused_commands_never_reach_the_journal	just check (STORE_CASES=5000 deeper)	~20s	every change
Fault injection (store)	a full disk or a cut-off append leaves whole, openable books (1)	ledger-store/tests/faults.rs, store.rs (power_loss_at_any_byte_of_the_last_append_is_recovered)	just check	~5s	every change
Concurrency (store)	a viewer reading while the books are written sees only whole books, never a false "differs" (2)	ledger-store/tests/concurrency.rs	just check	<1s	every change
Model-based stateful	the Lean state machine, transcribed (3)	tests/model.rs	just check	~3s	every change
Differential: Decimal vs i64	the kernel at two types (3)	kernel_bridge.rs	just check	<1s	every change
Differential: GnuCash	another implementation, adjudicated (3)	tests/oracle_gnucash.rs, oracle/gnucash/	just oracle	~2 min	weekly
Formal proofs	Kani (bounded) and Lean (unbounded)	src/proofs.rs, verify/lean/	just prove	~3 min	weekly
Fuzzing	crash, hang, broken books (4); for fuzz_store_replay (validly chained journals with fuzz-chosen events): books that open must verify, and the viewer must accept exactly what the writer does	fuzz/fuzz_targets/, corpora in fuzz/corpus/	just fuzz <target> <secs>	10 min each	weekly
Miri	undefined behavior in our use of dependencies (4)	the core's unit, bridge, invariant tests	just miri	~2 min	on demand
Golden	tests/golden/fixture_company.json (5)	invariants.rs	just check	<1s	every change
Benchmarks	a baseline (6)	ledger-core/benches/books.rs, ledger-store/benches/store.rs	just bench	~2 min	none (no budget, by decision)
Mutation	can the tests fail?	ledger-core (2026-10-13: 1,011 caught + 13 timeouts of 1,024 viable, 0 missed)	just mutants	~3 h	weekly
Mutation (store)	can the tests fail?	ledger-store (2026-10-13: 357 caught + 1 timeout of 365 viable, from 82%; three of its seven survivors then killed; four equivalent left: sort_value's two arms, OpenFlags `	vs^`, the long form of a sweepless close)	just mutants-store	~12 min
Mutation (import)	can the tests fail?	ledger-import (2026-10-13: from 91 of 171 (53%) to 208 of 239 viable on the full run; the 31 survivors (XLSX layout, borders, alignment, exact-text grouping, IIF transliteration, tax-summary optional sections, day-equals-month dates) then killed by targeted tests, re-run clean but one: a blank amount cell written unbordered on an unruled row, invisible, so equivalent)	just mutants-import	~1 h	weekly
Mutation (roles, reload)	can the tests fail?	control roles and settings reload (2026-10-15, targeted: the role paths in ledger-core 30 caught of 30 viable; ledger-store's journaling and replay of role.assigned 20 of 20; ledger-mcp settings, reload, roles, digest 28 of 28)	cargo mutants -F on those functions (see the commit)	~15 min	with the crate's weekly run
Mutation (config)	can the tests fail?	ledger-config (2026-10-14: 55 caught of 55 viable)	just mutants-config	minutes	weekly
Mutation (MCP)	can the tests fail?	ledger-mcp (2026-10-14: from 197 caught + 5 timeouts of 328 viable (62%) to 314 caught + 2 timeouts of 331; of its 15 survivors, five then killed by targeted tests (the settings file beside the books, year earnings with an open period and with last year's partial close, year 1, a failed flush), one dead guard removed (profit_and_loss_by_class skipping placeholders, which never take postings), nine equivalent: money rescaling an amount already at two places, the lock wait's deadline instant, year_earnings starting the day the year starts either way, the bank import's rehearsal sides (a line's side can't make a draft refuse) and its zero-amount side (zero rows are dropped by the parser), a disposal's zero gain adding zero, and the CPA package index summing debits instead of credits (entries balance))	just mutants-mcp	~1 h	weekly
Mutation (GUI)	can the tests fail?	ledger-gui view model and formatting (2026-10-14: 140 caught of 176 viable on the full run, then 92 of 99 on a targeted rerun of the money paths after new tests; of its 7 survivors, one then killed by a test (burn over exactly one month, confirmed by a rerun of compute_kpis's 48 mutants), two dead arms removed (parties' bill arms: the ledger tags bill entries with their vendor, which wins), four equivalent: an entry's debits vs its credits (they balance), the three-month burn boundary (both paths give 3), burn over zero covered months (only when the first entry is after the window, which then holds no loss), and compact's sign test at zero (zero prints "$0" unsigned either way))	just mutants-gui	~2 h	weekly

CI: .github/workflows/check.yml runs just check on every push; scheduled.yml runs proofs, the oracle, fuzzing, and mutation weekly.

Seeds and failure databases: proptest's *.proptest-regressions files are checked in and replay on every run. The GnuCash oracle's books come from fixed seeds (SEED in oracle_gnucash.rs). Fuzz corpora live in fuzz/corpus/<target>.

Golden review: fixture_company.json is hand-verified (docs/oracle.md, Layer 1). The van depreciation golden was replaced on 2026-10-13 by a hand computation (van_schedule_is_the_hand_computed_one) after every row was checked against it.

P0 guard rails (2026-10-16)

Laws added with P0 (plan/served.md) and its review, each with the test that would fail if it broke:

Law	Test
Books from a newer wanderbooks are "newer", never "corrupt", from the writer, the viewer and the server; damage stays corruption (rules.md B-27)	ledger-store tests/format.rs (old_reader_gets_newer_journal, damaged_journals_are_still_corrupt); ledger-gui tests/newer_journal.rs; ledger-mcp tests/startup.rs
A line the gate refuses is called newer only once the next line's prev checks its hash; a last line is "newer or damaged"	a_damaged_line_that_looks_newer_is_corrupt_when_the_next_line_checks_it, an_unreadable_last_line_is_reported_as_newer_or_damaged, a_newer_line_the_next_line_chains_onto_is_newer_and_intact (the message vouches for that line only)
The envelope and its hash are frozen across formats: a next line in a newer format (a float, a string seq, keys of its own) settles by its prev alone, never as corrupt; a key beside the envelope is newer, never dropped, and still checked through; a refused line followed by an unreadable one is "newer or damaged"	format.rs a_newer_format_frames_its_lines_its_own_way, an_unknown_envelope_key_is_newer_and_checked_through, a_refused_line_followed_by_a_garbled_line_is_unverified
The writer and the viewer read bytes alike: a line that isn't UTF-8 is corrupt to both; an older version never repairs (truncates) newer books	a_line_that_is_not_utf8_is_corrupt_for_the_viewer_and_the_writer, an_old_reader_never_repairs_newer_books
A newer format is newer whatever its features look like; a blank line is damage to the viewer as to the writer	format.rs a_newer_format_is_newer_whatever_its_features_look_like; a_blank_line_is_corrupt_for_the_viewer_and_the_writer
A request that panics stops the server: every later request, on every session, is refused	server.rs a_request_that_panics_stops_the_server
No input reaches a panic (each would stop the server for every session): every tool with arguments generated from its schema and made hostile (wrong types, u64::MAX, decimals of 30+ digits or absurd exponents, dates like 0000-00-00, 99999-12-31, +262142-12-31, 2026-02-30, periods like 999999-01, control and format characters, long strings), every resource URI generated; the inputs that once panicked, pinned; after each property the server restarts and the books reopen (a call a command accepts but replay refuses would brick them); every tool and resource over every old book (rules.md B-28)	ledger-mcp tests/hostile_args.rs hostile_tool_arguments_never_stop_the_server (with a floor: most calls reach a tool, some succeed), hostile_resource_uris_never_stop_the_server, inputs_that_once_panicked_are_refused_or_answered, old_books_answer_every_tool; MCP_CASES and OLD_BOOKS_CASES (default 3 per tool per book) set the cases
Dates are in 0001-01-01 through 9999-12-31 and amounts at most a line's, for every new command; replay accepts every line an earlier version accepted (each bound has its pair: the command refuses past it, the replayed old line is accepted); a figure derived past exact arithmetic or chrono's calendar is refused, never a panic; a recurring run makes at most 1,000 drafts (rules.md B-28)	ledger-core tests/spec_bounds.rs, calendar.rs tests, plans_at_the_edges_are_computed_or_refused, intervals_reach_chronos_last_day, a_vendor_part_is_scaled_exactly_or_refused, the share_property cases; ledger-store tests/bounds.rs, tests/store.rs (the old-books tests); server.rs periods_are_a_year_and_a_month, dates_are_four_digit_years_and_real_days
Opening the books changes nothing until every complete line passes in memory (chain, gate, first line, replay); the viewer applies the writer's first-line rule (rules.md B-27)	format.rs a_bad_complete_line_before_a_torn_tail_leaves_the_journal_as_it_was, the_first_line_is_store_created_for_the_viewer_and_the_writer; fuzz_store_replay (the first line varies)
A path with a . or .. name is refused as missing before anything is looked up; a root inside the books, the data dir or the vault is refused at startup (dropped as the default)	local_files.rs a_dot_or_dotdot_name_never_tells_whether_folders_outside_exist, a_root_holding_the_books_or_the_home_folder_is_refused; startup.rs an_import_root_holding_the_books_or_the_home_folder_is_refused, a_default_download_dir_holding_the_books_is_dropped_not_fatal
UTF-16 text without a byte-order mark is scanned like any text; a refused books.set_w9 marks no file; a refused resource read never echoes a TIN	tin_files.rs (tests) utf16_text_without_a_byte_order_mark_is_scanned_either_way_round, a_refused_set_w9_never_marks_its_file, unit test only_nul_interleaved_bytes_read_as_utf16_without_a_mark; spec_vault.rs resource_refusals_never_echo_a_tin
idempotentHint only where a repeat with the same arguments leaves the journal and the vault as they were; every tool's hints pinned in one table	spec_vault.rs idempotent_tools_change_nothing_when_repeated; annotations_complete
books.settings lists every receipt-required and exempt account, uncut; a fresh company is "a new company"; the lint catches just however it ends and where the books are	mcp_stdio.rs every_receipt_account_left_out_of_the_connect_text_is_in_books_settings; handbook.rs a_fresh_company_is_a_new_company; tool_text_lint_catches_helpers_and_locations
A local file is read only from inside an import root, never a sealed place (data dir, vault, keys, the key folders that don't hold a root), never through a swap after the check (a component walk with O_NOFOLLOW, no step onto a protected inode); a missing, dangling or outside path gets one refusal	local_files.rs import_local_file_refuses_key_and_journal, the property import_allowed_iff_regular_file_inside_a_root_outside_the_books, refusals_never_tell_what_is_there, a_file_swapped_after_the_check_is_never_read, a_folder_swapped_after_the_check_is_never_walked_through (the reviewer's race, without /proc), resolved_follows_every_link_a_dangling_one_too, sealing_a_key_never_seals_a_whole_root; through the tools, mcp_stdio.rs import_local_file_and_set_w9_refuse_the_key_vault_and_journal_inside_a_root
No import root is /, the home folder or holds it, or holds the books, data dir, vault or a key; the default is a real downloads folder or none	local_files.rs the_default_root_is_never_the_home_folder_or_the_filesystem, a_root_holding_the_books_or_the_home_folder_is_refused; startup.rs an_import_root_holding_the_books_or_the_home_folder_is_refused, a_download_dir_of_home_never_opens_the_home_folder
A file with full TINs is never written into an import root, and never filed into the books: every file the server read or wrote with TINs (from any session, after a restart, out of a CPA package), by every filing tool	mcp_stdio.rs tin_bearing_files_never_land_where_they_could_be_filed_back_in; tin_files.rs (tests) a_tin_bearing_file_is_refused_from_every_session_and_after_a_restart; unit test a_recorded_tin_file_is_refused_by_every_reader_of_the_registry
Text filed into the books is refused when it holds a TIN the vault keeps (nine digits, 3-2-4 by hyphen, space or dot, 2-7 by hyphen or space, anywhere) or a stand-alone printed SSN or EIN (123-45-6789, 12-3456789), and only then: a bank export (routing numbers, long references, a date next to an amount) and a longer number holding an SSN shape go in; a locked vault leaves the printed shapes (rules.md B-26)	tin_files.rs (tests) text_with_a_vault_tin_or_a_printed_one_is_refused_and_a_bank_export_is_not; unit tests text_holding_a_vault_tin_is_refused_in_every_rendering, a_printed_ssn_or_ein_is_refused, a_longer_number_holding_a_tin_shape_passes, an_ordinary_bank_export_passes, binary_bytes_are_not_scanned
Filing is no TIN oracle: text with more than two TIN-shaped numbers ending in a known TIN's last four (the books' TIN and W-9 facts, then the vault's own) is refused before the vault is opened, byte for byte alike whether one is the vault's TIN or none is, the vault open or locked, by every filing tool; one or two such numbers are compared against the vault, one number written many ways counts once, and other last fours never count (rules.md B-26)	tin_files.rs (tests) text_probing_for_a_tin_is_refused_alike_by_every_filing_tool; unit tests text_probing_for_a_tin_is_refused_alike_whether_or_not_it_holds_it (the vault never opened for a probe), one_or_two_candidates_are_compared_against_the_vault
The connect text fits its budgets, its lead stands alone, it states the receipt rule enforced (exact threshold in the base currency, required and exempt accounts, reversals) and the parties rule in force, and the company name can't break it (control and format characters)	handbook.rs instructions_budget, a_typical_company_gets_the_whole_connect_text, the_company_name_is_one_plain_line; receipt_policy.rs the_rule_told_is_the_rule_enforced, a_long_or_odd_account_list_stays_short_and_plain; a new session is told the settings in force: a_new_session_is_told_the_settings_in_force
No text the agent is given (whole tool JSON, resources, connect text, handbook, every error template and refusal) points at files, git, GitHub, repo docs, flags or helper commands; descriptions fit 700 characters (listed exceptions, P5)	tool_text_lint, tool_descriptions_fit_700_characters; ledger-core an_unknown_year_threshold_is_never_guessed
Every tool is annotated (openWorldHint false on all), and the read-only hint is true in behaviour (journal, every data-dir file's contents, the database's rows, the vault and the settings unchanged)	annotations_complete; spec_mcp.rs read_only_tools_change_nothing (checked on every call in Mcp::tool)
A bare (or empty-since) digest covers this month so far, on any day of it, as the server counts it (the stdio test reads the server's own month, and starts over if it turns)	a_bare_digest_covers_this_month_so_far; mcp_stdio.rs digest_resource_bare_reads
The handbook: every section, "all" in order, the schema names every id	handbook_sections_render_the_rule_in_force, the_whole_handbook_is_every_section_in_order, mcp_stdio.rs handbook_tool_and_resources_over_stdio

P0 mutation testing (2026-10-16)

Every mutant cargo-mutants makes in the final P0 diff (jj diff -r 'main..@', --in-diff), per crate, against that crate's tests (the recipes' settings: STORE_CASES=64, MCP_CASES=16, no shrinking; the viewer against its lib tests and newer_journal). Final run:

Crate	Mutants	Caught	Timeouts	Unviable	Missed
ledger-mcp	296	208	3	71	14 (equivalent, below)
ledger-store	73	58	0	12	3 (equivalent, below)
ledger-config	35	35	0	0	0
ledger-gui	9	6	0	3	0
ledger-core	1	1	0	0	0

(ledger-cli's change makes no mutant.) After the filing scan's probe bound (rules.md B-26), tin_files.rs alone was run again against the whole P0 diff: 74 mutants, 74 caught, among them every mutant of the bound (probes made true or false, > made >=, == or <, the last four's % made / or +, here and for the vault's own last fours) and of the shared tin_shaped scan. The three MCP timeouts are resolved without its hop limit (< 40 made true, the count made to go down or stay 0): a link loop then never ends, so the tests can't pass. The first run missed 36 in the MCP server, 5 in the store, 4 in config and 1 in the viewer. Each was killed by a test of the law it broke, removed by simpler code, or is equivalent:

• Killed (MCP). A section's title is its heading (a_title_is_the_heading_text; over stdio the handbook tool titles a section by its heading and "all" as the whole handbook, handbook_tool_and_resources_over_stdio). A refused default import root is dropped, never fatal (ImportRoots::explicit: a_default_download_dir_holding_the_books_is_dropped_not_fatal). A .jpg or .jpeg W-9 is taken (every_w9_file_type_is_taken). The waker wakes: a request pending until another thread wakes it completes (a_request_that_waits_is_woken_and_completes). The walk opens each folder with O_DIRECTORY | O_NOFOLLOW: a folder swapped for a link to an unprotected folder outside the roots, or for a pipe, is never walked through and never blocks (a_folder_swapped_for_a_link_or_a_pipe_is_never_walked_through). A read failure names its kind, never the path (cant_read_names_the_failure_not_the_path). resolved follows 40 links, as the kernel does, and no more (resolved_follows_forty_links_and_no_more). A file is saved only to a new file in a folder that exists, and a missing folder or a taken file is refused as such, never as a failed write (a_package_goes_only_to_a_new_file_in_a_folder_that_exists, the_w9_file_goes_to_the_vault_never_the_documents). The CPA package marks only its own TIN files: a statement it carries still goes in afterwards (a_tin_bearing_file_is_refused_from_every_session_and_after_a_restart). An unreadable TIN-file registry refuses every file (an_unreadable_registry_refuses_every_file). Text that isn't UTF-8 is scanned when its type is text/*, a JSON type (/json, +json) or its name says text (encodings in the tin_files.rs unit tests).
• Killed (store). read_journal_and_format returns every line and the format in force (read_journal_and_format_gives_every_line_and_the_format). The newline that ends a line is no part of it, so the viewer's words about a damaged line are the writer's, opening and following (the_viewer_and_the_writer_say_the_same_of_a_damaged_line; it kills snapshot.rs raw.len() - 1 → / 1).
• Killed (config). The short rule (no codes listed) counts each kind of account, whichever kinds there are, and says nothing of accounts when there are none (the_short_rule_counts_each_kind_of_account); a code of exactly 12 characters is kept whole (a_long_or_odd_account_list_stays_short_and_plain).
• Killed (viewer). The journal page tells a journal.format_set line (a_format_this_version_reads_opens_and_the_journal_page_tells_it).
• Simpler code (MCP). inspect compared canonicalize with resolved; only a race between those two calls could make them differ, and the file read was the checked one either way. It now places an existing path by canonicalize itself. read_checked refused by the file's size before reading, so its read limit (limit + 1) was only reached by a file growing during the read; the read's limit is now the one check (the 25 MiB upload test kills + 1 → * 1). openat failed on fd < 0, now on fd == -1, as openat(2) specifies.
• Equivalent (MCP, all 14 missed). ^ for | in the open flags (six: the walk's first step, each folder's two, the file's two, and openat's O_CLOEXEC): O_RDONLY is 0 and O_DIRECTORY, O_NOFOLLOW, O_NONBLOCK, O_CLOEXEC are distinct bits, so a ^ b is a | b. & for | in the first step's O_RDONLY | O_DIRECTORY: it opens / read-only either way, and / is always a folder. The off-Unix stubs (Protected::inodes, five mutants; open_walk; hard_linked) are not compiled on Linux, so their mutants change nothing here.
• Equivalent (store, all 3 missed). Snapshot::journal_format and Store::journal_format returning the default: this version reads format 1 with no features only (SUPPORTED_JOURNAL_FORMAT 1, KNOWN_FEATURES empty), and that is the default, so no journal it opens has another format in force; the first format 2 or feature makes them killable. Store::open setting aside a torn tail when complete <= raw.len(): repair_torn_tail re-reads the journal under the writer lock and does nothing when it ends in a newline.

Round 3 (2026-10-17)

cargo mutants --in-diff on this round's changes (the diff from the round-2 stack to round 3), per crate, output under ~/.cache/wanderbooks/mutants/p0-r3-<crate> (MCP_CASES=16, STORE_CASES=64, PROPTEST_MAX_SHRINK_ITERS=0):

Crate	Mutants	Caught	Missed, then killed	Equivalent	Timeouts	Unviable
ledger-core (tests of core and store)	63	53	3	1	0	6
ledger-store	40	34	0	0	2	4
ledger-mcp	85	63	5	1	0	16
ledger-config (a doc comment only)	0

• Killed (core). replay_add_line_fx's size check (> to == or >=) and validate_recurring's (> to >=): a line, base or foreign, added or replayed, and a template line may be exactly the line limit (spec_bounds.rs the_bound_is_the_line_limit_itself).
• Timeouts (store, counted as caught). run_recurring's cap (> to == or <): without it, a monthly entry run through 9999-12-31 writes some 95,000 drafts, which is what the cap is for (bounds.rs a_recurring_run_has_an_end).
• Killed (MCP). text_of's byte-order-mark arms: text with a mark and no NUL byte at all (full-width digits, CJK) is still read as UTF-16 (utf16_with_a_mark_is_read_whatever_it_holds); its NUL-stripped reading (!= to ==): NULs scattered in text hide no TIN (nuls_scattered_in_text_hide_no_tin); nul_interleaved's eighth (* to +): half NUL on one side and three of sixteen on the other is not UTF-16; redact_value's array arm: a TIN inside an array of an error's data is masked (redact_error_masks_every_tin_in_the_message_and_data).
• Equivalent. k1::share_property returning early on whole <= 0 && total <= 0 instead of ||: whole is min(pool, total) with both sums of non-negative amounts, so the two differ only when whole is 0 and total positive, where the computation goes on to split 0 into zeros, the early answer. redact_value's guard has_full_tin(t) replaced by true: redact_full_tins returns its input unchanged when it finds no run, exactly when has_full_tin is false, so the guard only saves a copy.

Round 4 (2026-10-17)

cargo mutants --in-diff on this round's changes (replay restored to main's rules, derived figures checked, the old-books contracts), per crate, output under ~/.cache/wanderbooks/mutants/p0-r4-<crate> (MCP_CASES=16, OLD_BOOKS_CASES=1, STORE_CASES=64, PROPTEST_MAX_SHRINK_ITERS=0; the GUI's old-books test over the edge books only, OLD_BOOKS_ONLY=x_draft_max_lines,x_schedule_chrono_end,..., since asset_long_life alone takes three minutes a run):

Crate	Mutants	Caught	Missed, then killed	Equivalent	Timeouts	Unviable
ledger-core (tests of core and store)	176	153	6	3	0	14
ledger-store	12	11	0	0	0	1
ledger-mcp	81	13	5	1	0	62
ledger-config	7	7	0	0	0	0
ledger-gui	221	47	137	11	7	19

• Killed (core). name_payroll_parties (replaced by Ok(()), and == to != in merging one employee's lines): a payroll entry names its employees, each with their net pay, live and on replay (spec_parties.rs a_payroll_entry_names_the_employees_it_paid); entry_flow's across_left -= take (+=, /=): across is used up in order (entry_flow_takes_across_in_order_until_used_up); share_target's debit filter (== to !=): an unbalanced draft moving no money splits over its debits (a_share_target_without_money_is_the_debits); resolve's capital debit sign: members' derived shares net their capital lines (derived_member_shares_net_their_capital_lines). These were in code this round touched only to make it checked; the core and store tests never reached them (the MCP tests did).
• Killed (MCP). lines_settled (whole and in parts): an empty, an unbalanced and a Decimal-overflowing draft are not settled, a balanced draft and a posted entry are (server.rs settled_lines_are_posted_or_balanced_drafts).
• Killed (GUI). The pages' display of what can't be computed and of the edges was barely asserted: new tests in tests/edges.rs and beside the pages (test_support.rs renders a page headless and reads its painted text and shapes) cover the runway and "coming up" on the cash page, the balance chart's labels and hover, an entry's totals (balanced, out of balance, too large to total), a party's span and monthly chart at chrono's edges, a split entry's part, the register's reconciliation colours, the company page's cards, the report range, prior period and column limit, and the transaction row. The rerun (p0-r4-gui-rerun) left only the equivalents.
• Equivalent (GUI, 11). party_span's < to <= (twice): they differ only at year 0, which chrono holds, so the fallback is never taken. The asset notice's > to >=: with nothing unposted both amounts are 0 and nothing is pushed. occurrences_from's five arithmetic mutants: each leaves k0 a lower bound on the first occurrence on or after from, so only the walk's length changes. The cash forecast's > to >=: a zero amount added to inflow instead of subtracted from outflow. The company page's total.is_zero() guard: a schedule's total is always positive. Its recurring total's == to !=: a template always balances, so its credits sum to its debits.
• Equivalent. entry_flow's filters v > 0 to >= 0 and v < 0 to <= 0: they only add zeros to a sum. split_first's weights.is_empty() || total.is_zero() to &&: every weight is positive (a percent above 0, a member's share checked above 0), so a non-empty list never sums to zero. lines_settled's side filter l.side == s to !=: it swaps which sum is called debits, and the comparison and the overflow refusal are symmetric.
• A real defect found while writing these tests: the depreciation true-up named its final month with chrono's %Y, which signs a year past 9999 ("+10004-03"), while the lines don't, so an asset whose life ran past 9999 never trued up and could depreciate past its salvage (spec_replayed_extremes.rs a_life_past_9999_trues_up_to_the_cent).

Benchmarks (baseline 2026-10-13)

No budget, by decision (Stephen, 2026-10-13: the books do little work and are fast enough). The numbers are a baseline to spot a regression.

40-account chart, two-line entries across a year, on the development laptop:

	1k entries	10k entries
clone the ledger (store rehearsal, per command)	56 µs	1.0 ms
post one more entry	1.0 µs	5.8 µs
trial balance	44 µs	1.07 ms
balance sheet	47 µs	1.04 ms
one month's P&L	25 µs	248 µs

The store, 10k two-line entries on the laptop's disk (every journal append is synced; benches/store.rs in ledger-store):

	10k entries
open the books (verify the chain, replay, catch the database up)	249 ms
the viewer loading them	616 ms
a full verify (replay, projection, every table)	809 ms
post one entry (create, two lines, post: four synced appends)	62 ms

Formerly assumed: checked against the standards (2026-10-13)

Stephen isn't an accountant and won't adjudicate these; each was checked against published sources instead (rank: FASB ASC via the Deloitte DART reproduction, SEC, IRS; then textbooks; software practice is evidence of convention only). Verdicts: CONFIRMED (a source supports it), CONVENTION (no standard governs; matches mainstream practice), DESIGN (not an accounting question), CHANGE (a source says otherwise; work pending).

#	Behavior	Verdict	Source / note
1	A P&L whose start is after its end is refused	DESIGN	No standard governs a reversed range; refusing beats silently swapping a typo
2	A balance sheet omits zero-balance accounts	CONFIRMED	Reg. S-X 210.4-03(a): "No caption should be shown ... as to which the items and conditions are not present." A comparative statement must still show a zero beside a non-zero prior column
3	The lifetime profit_and_loss counts closing entries	CONFIRMED	Used as earnings not yet closed on the balance sheet; closed income is already in capital (OpenStax Principles of Financial Accounting 5.1). Renamed unclosed_earnings (2026-10-14)
4	Closing a period with nothing to close still locks it	CONVENTION	A close is a lock (B-12); a dormant month must still lock and count for close-in-order
5	Draws and distributions are closed into capital at period end	CONFIRMED	OpenStax 5.1: dividends "are closed to the permanent account"; drawing accounts close to owner's capital. Monthly closes mean the year's K-1 Item L withdrawals sum across months
6	Reconciliation balances	CONFIRMED	Signed by the account's normal side (a card reads as owed), as statements show it; reconciling_a_card_reads_its_normal_side_...
7	A member's ending on one equity statement may differ by a cent from the next statement's beginning	CHANGED 2026-10-13	A capital account is one running balance (Form 1065 K-1 instructions, Item L). Undistributed earnings now split cumulatively as of each date, so each member's capital chains exactly (each_members_capital_chains_across_statements; it fails on the old code); rules.md B-13
8	Cash flow nets one line per account; investing comes only from registered assets	CHANGED 2026-10-13	ASC 230-10-45-7: gross receipts and payments "more relevant" than net; 45-8 limits netting to quick-turnover items. Financing and investing are now gross; loans made and investments bought are investing (230-10-20, 45-13) via [books] investing_accounts. Owner-advanced expenses: PwC 6.9.3.1 constructive treatment via [books] financing_accounts (rules.md B-14)
9	An asset's life ends at purchase + life months, that day not held; day-count proration	CONVENTION	Exactly N months of service; day proration and the mid-month convention are both accepted book policies (ASC 360-10-35-4, read 2026-10-14: any systematic and rational allocation)
10	A payroll entry has one line per account total	CONFIRMED	The per-employee detail the IRS requires ("Amounts and dates of all wage ... payments", Employment Tax Recordkeeping) is kept in the run; a summary entry is standard
11	A period with exactly the dates of an existing one is allowed	DESIGN	Nothing governs duplicate periods; harmless (the second close locks only). Refusing exact duplicates is an option
12	Each close into members' capital rounds on its own (ties to the earlier member)	CHANGED 2026-10-13	Twelve monthly 50/50 closes could leave one member several cents ahead. A run of members closes now splits cumulatively (rules.md B-13; Lean runPart_telescopes; property each_member_stays_within_a_cent_of_their_share fails on the per-close rule); journaled "cumulative", older closes replay as booked

Questions are settled from the sources, not by any one company's CPA (wanderbooks is general software). Where the standards leave a real choice, it is a per-company setting with a sourced default, for that company's accountant to review: the cash flow account roles (rules.md B-14) are the first.

Gap list: what isn't covered, and what would bring it in

Technique	Status	Trigger
Fault injection	SKIP for the core (no I/O, clock, or network); DONE for the store's journal (full disk, cut-off append)	the first I/O or clock in ledger-core
Integration	SKIP for the core (no collaborators)	the core gains one; covered at the store and MCP layers
End-to-end	SKIP for the core (a library)	MCP stdio tests cover the journeys
Security properties	SKIP for the core (no roles, no secrets)	the first permission concept, or a secret-bearing field
Concurrency stress	SKIP for the core (no shared state); DONE for the store's writer + viewer (found the false "differs")	the first Arc, atomic, or lock in the core; the MCP server's HTTP transport shares one store across sessions (next)
Lean: apportion's sum law for any n	DONE (2026-10-14)	verify/lean/Wanderbooks/Apportion.lean: ranks are a permutation of 0..n-1 (strict total order + pigeonhole, core Lean only), so exactly u parts get a unit and one the fraction; apportion_sum and apportion_sum_of_shortfall, standard axioms only
ASC paragraphs not yet read	DONE (2026-10-14)	read in the ASC basic view (docs/spec/sources/fasb-asc.md): all confirm the rules; one citation fixed (230-10-45-14(b), not (2))
GnuCash's own close	OPEN	the oracle books closes as ordinary entries; comparing GnuCash's Close Book needs its Scheme API
Import: spec-blind suite, footing properties, mutation	DONE	sources vendored (Intuit bank CSV and IIF, ECMA-376/Excel numbers, IRS form lines); specs on every module; tests/spec_import.rs (spec-blind, footing and round-trip properties, XLSX read back from its XML, layout and styles); fuzz_import_csv; templates checked against the engine's control accounts; mutation one equivalent left
MCP, config, GUI crates	DONE (2026-10-14)	the same playbook: sourced module specs (config: Pub 538, Treas. Reg. 301.7701-3; MCP: the MCP tool spec and JSON-RPC 2.0); spec-blind suites spec_config.rs, spec_mcp.rs, spec_gui.rs; the MCP oracle oracle_mcp.rs (every export against ledger-core); startup, HTTP concurrency, and the viewer's read-only promise (read_only.rs) tested; fuzz_config_parse; mutation above