feat(mcp): books.write_off_invoice (P4b S7)

One tool for the bad debt (rules.md B-41): it writes off an invoice that
will not be collected, Dr 6990 Bad Debt Expense / Cr 1200 Accounts
Receivable, the receivable line tagged with the invoice so the document
reads written_off and its figures stay derived (B-38).

The evidence is the point, and the tool takes exactly one of
upload_id (an upload, filed with the write-off) and
existing_attachment_id (one already filed, linked to the write-off's
entry and the invoice); neither or both is refused. amount defaults to
what the invoice owes and may be partial.

Without confirmed it is a preview: the engine runs on a clone (every
refusal the post would give) and the answer is the figures the write-off
would leave, entry_id 0, nothing journaled.

The tool lives in its own group file, tools/write_offs.rs (plan U0a), so
S4.4's document tools and this one land apart; it is destructive, needs
books:write to preview and books:post to post (scopes.rs), and is
documented under "Tools — A/R and A/P". The destructive-tool count, the
tool tables and the journey test's tool count each move by one.

Tests over the wire: write_off_then_recovery, write_off_needs_evidence.
This commit is contained in:
swaits committed 2026-10-27 12:44:45 -06:00
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//! Documents over the wire (plan P4b S4 to S7; this file starts with S7's
//! bad debts). One test per behavior the tools promise, through the
//! books server exactly as an agent reaches it: `common::Books` on a data
//! root of the test's own, a session, and `books.*` calls.
//!
//! ```text
//! GOAL: a bad debt is written off with its evidence in one call, reads
//! written off, and a same-year recovery is the reversal D-49
//! records; a write-off with no evidence is refused.
//! SOURCE: docs/spec/rules.md B-41; plan P4b S7; IRC §166(a), §111;
//! Treas. Reg. §1.166-1(e), -2(a), -3(a).
//! ```
mod common;
use serde_json::{Value, json};
/// A call's structured result, or a panic naming the tool and the refusal.
fn ok(wire: &mut common::Wire, tool: &str, args: Value) -> Value {
common::answer_of(&wire.call(tool, args)).unwrap_or_else(|e| panic!("{tool}: {e}"))
}
/// A call's refusal, or a panic naming the tool.
fn refused(wire: &mut common::Wire, tool: &str, args: Value) -> String {
match common::answer_of(&wire.call(tool, args)) {
Err(e) => e,
Ok(v) => panic!("{tool} accepted: {v}"),
}
}
/// The books of every test here: a bank account 1000, a customer, and one
/// invoice for 100.00 dated 2026-01-05, due 2026-02-04.
fn invoice(wire: &mut common::Wire) -> u64 {
ok(
wire,
"books.add_account",
json!({
"code": "1000",
"name": "Checking",
"account_type": "asset",
"parent": null,
"placeholder": null,
}),
);
let customer = ok(
wire,
"books.add_customer",
json!({ "name": "Fernhill Labs" }),
)["id"]
.as_u64()
.unwrap();
ok(
wire,
"books.create_invoice",
json!({
"party_id": customer,
"date": "2026-01-05",
"due_date": "2026-02-04",
"lines": [{ "description": "Design", "amount": "100.00" }],
}),
)["id"]
.as_u64()
.unwrap()
}
/// A collection letter, the evidence of worthlessness.
const LETTER: &[u8] = b"%PDF-1.4\nFinal demand, unpaid\n%%EOF\n";
/// P4b S7: an invoice half paid is written off for the rest with its
/// evidence in the same call, reads written off, and the same-year
/// recovery D-49 records (reverse the write-off, then a payment) reopens
/// and settles it.
#[test]
fn write_off_then_recovery() {
let books = common::Books::new("s7-recovery");
let mut wire = books.wire();
wire.initialize("s7-recovery");
let inv = invoice(&mut wire);
ok(
&mut wire,
"books.receive_payment",
json!({
"document_id": inv,
"date": "2026-01-20",
"amount": "40.00",
"cash_account": "1000",
}),
);
// The write-off's evidence, uploaded as an agent uploads it (D-46).
let upload = wire.upload(LETTER, "collection-letter.pdf", "application/pdf", "document");
let out = ok(
&mut wire,
"books.write_off_invoice",
json!({
"invoice": inv,
"date": "2026-01-31",
"reason": "collection exhausted",
"upload_id": upload,
"confirmed": true,
}),
);
let entry = out["entry_id"].as_u64().unwrap();
assert!(entry > 0, "{out}");
assert_eq!(out["document"]["ref"], json!(format!("invoice:{inv}")));
assert_eq!(out["document"]["status"], json!("written_off"));
assert_eq!(out["document"]["paid"], json!("40.00"));
assert_eq!(out["document"]["written_off"], json!("60.00"));
assert_eq!(out["document"]["outstanding"], json!("0.00"));
// The evidence is on the write-off's entry, as a receipt, and on the
// invoice: get_entry shows the one, the document's timeline the other.
let got = ok(&mut wire, "books.get_entry", json!({ "entry_id": entry }));
assert_eq!(got["receipts"].as_array().map(Vec::len), Some(1), "{got}");
assert_eq!(got["receipts"][0]["file_name"], json!("collection-letter.pdf"));
let doc = ok(
&mut wire,
"books.document",
json!({ "ref": format!("invoice:{inv}"), "as_of": "2026-02-01" }),
);
assert_eq!(doc["status"], json!("written_off"));
assert_eq!(doc["written_off"], json!("60.00"));
let write_off_lines: Vec<&Value> = doc["timeline"]
.as_array()
.unwrap()
.iter()
.filter(|t| t["kind"] == json!("write_off"))
.collect();
assert_eq!(write_off_lines.len(), 1, "{doc}");
// The same tax year: reverse the write-off; the invoice reopens.
ok(
&mut wire,
"books.reverse_entry",
json!({
"entry_id": entry,
"date": "2026-03-01",
"description": "Paid after all",
"confirmed": true,
}),
);
let doc = ok(
&mut wire,
"books.document",
json!({ "ref": format!("invoice:{inv}"), "as_of": "2026-03-02" }),
);
assert_eq!(doc["status"], json!("partial"));
assert_eq!(doc["outstanding"], json!("60.00"));
ok(
&mut wire,
"books.receive_payment",
json!({
"document_id": inv,
"date": "2026-03-02",
"amount": "60.00",
"cash_account": "1000",
}),
);
let doc = ok(
&mut wire,
"books.document",
json!({ "ref": format!("invoice:{inv}"), "as_of": "2026-03-03" }),
);
assert_eq!(doc["status"], json!("paid"));
assert_eq!(doc["outstanding"], json!("0.00"));
// The control accounts still equal their documents.
let check = ok(
&mut wire,
"books.control_check",
json!({ "as_of": "2026-03-31" }),
);
assert_eq!(check["agrees"], json!(true), "{check}");
}
/// P4b S7: no evidence, no write-off (B-41 INVARIANT 1): the tool refuses
/// with neither or both, and an attachment already filed is linked
/// instead of a new file.
#[test]
fn write_off_needs_evidence() {
let books = common::Books::new("s7-evidence");
let mut wire = books.wire();
wire.initialize("s7-evidence");
let inv = invoice(&mut wire);
let args = |extra: Value| {
let mut v = json!({
"invoice": inv,
"date": "2026-01-31",
"reason": "uncollectible",
"confirmed": true,
});
v.as_object_mut()
.unwrap()
.extend(extra.as_object().unwrap().clone());
v
};
let why = refused(&mut wire, "books.write_off_invoice", args(json!({})));
assert!(why.contains("upload_id"), "{why}");
assert!(why.contains("existing_attachment_id"), "{why}");
let why = refused(
&mut wire,
"books.write_off_invoice",
args(json!({ "upload_id": "up_nope", "existing_attachment_id": 1 })),
);
assert!(why.contains("exactly one"), "{why}");
// A filed attachment (not linked to an entry) is linked to the
// write-off's entry and the invoice.
let upload = wire.upload(LETTER, "letter.pdf", "application/pdf", "document");
let filed = ok(
&mut wire,
"books.file_document",
json!({
"category": "other",
"upload_id": upload,
"description": "Collection attempts",
}),
);
let attachment = filed["attachment_id"].as_u64().unwrap();
let out = ok(
&mut wire,
"books.write_off_invoice",
args(json!({ "existing_attachment_id": attachment })),
);
assert_eq!(out["document"]["status"], json!("written_off"));
assert_eq!(out["document"]["written_off"], json!("100.00"));
let receipt = ok(
&mut wire,
"books.get_receipt",
json!({ "attachment_id": attachment }),
);
let links = receipt["links"].as_array().cloned().unwrap_or_default();
assert!(links.iter().any(|l| l["kind"] == json!("invoice")), "{receipt}");
assert!(links.iter().any(|l| l["kind"] == json!("entry")), "{receipt}");
}
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@@ -125,7 +125,7 @@ fn mcp_end_to_end() {
// Tool listing: the narrow tools; chart is read-only.
let list = mcp.request("tools/list", json!({}));
let tools = list["result"]["tools"].as_array().unwrap();
assert_eq!(tools.len(), 122, "expected 122 tools, got {}", tools.len());
assert_eq!(tools.len(), 123, "expected 123 tools, got {}", tools.len());
// Files come in as tool input: books.begin_upload, never a local path.
assert!(tools.iter().any(|t| t["name"] == "books.begin_upload"));
assert!(!tools.iter().any(|t| t["name"] == "books.import_local_file"));