docs: the write-off's place among the destructive tools and the tool counts (P4b S7)

docs/mcp-interface.md

@@ -350,7 +350,7 @@ Tool descriptions are at most 700 characters; eight longer ones are listed
 in `tool_descriptions_fit_700_characters`, to be shortened in P5.
 
 **Annotations.** Every tool has a `title` and a `readOnlyHint`; every tool
-that changes anything also has a `destructiveHint`, true for these 29:
+that changes anything also has a `destructiveHint`, true for these 30:
 `books.post_entry`, `books.reverse_entry`, `books.set_setting`, `books.retire_convention`, `books.unlink_receipt`,
 `books.unlink_attachment`, `books.withdraw_attachment`,
 `books.correct_asset`, `books.dispose_asset`, `books.run_depreciation`,
@@ -360,8 +360,8 @@ that changes anything also has a `destructiveHint`, true for these 29:
 `books.void_statement`, `books.void_reconciliation`, `books.set_w9`,
 `books.set_tin` (both overwrite a vault record), `books.purge_tin`,
 `books.create_invoice`, `books.create_bill`, `books.receive_payment`,
-`books.pay_bill`, `books.void_document`, `books.run_payroll`,
-`books.remit_payroll_taxes`; and an
+`books.pay_bill`, `books.void_document`, `books.write_off_invoice`,
+`books.run_payroll`, `books.remit_payroll_taxes`; and an
 `idempotentHint` on the ten that a repeat with the same arguments leaves
 the journal and the vault as they were: `books.verify`,
 `books.run_depreciation`, `books.run_schedules`, `books.run_recurring`,

docs/testing.md

@@ -2674,7 +2674,7 @@ it calls what part A proved and tested.
   check, so both output schemas are exercised on every run.
 - **The tool surface, `crates/ledger-mcp/src/server.rs`'s tests:**
   `annotations_complete` pins `books.void_document` destructive and
-  posting, `books.control_check` read-only, and counts the 29
+  posting, `books.control_check` read-only, and counts the 30
   destructive tools the doc names; `period_tools_describe_the_one_default`
   holds `books.control_check` to the one `as_of` sentence. The generic
   lints cover the rest without a change of their own:
@@ -2725,11 +2725,11 @@ strikethrough, and the test asserts the labels.
   The happy-path journey lists and reads one, so both output schemas are
   exercised on every run.
 - **The tool surface:** `annotations_complete` pins both read-only
-  (table, now 122 tools); `period_tools_describe_the_one_default` holds
+  (table, now 123 tools); `period_tools_describe_the_one_default` holds
   both to the `as_of` sentence;
   `every_tool_is_documented_and_every_documented_tool_exists` and the
   text lints cover the doc; `scopes.rs`'s table and
-  `mcp_journeys.rs::mcp_end_to_end` count 122.
+  `mcp_journeys.rs::mcp_end_to_end` count 123.
 - **The viewer, `crates/ledger-gui/tests/invoices.rs`:**
   `the_list_shows_the_ledgers_figures` (the reversed payment no longer
   counts: $580 owed, $500 of it late; "Invoice 1, Harbor Client, 14 days