feat(drafts): the drafts tools, the preview digest on every confirm, the digest tool (P4)

Accounting reason: a confirm must act on the thing that was previewed.
Every tool with confirmed (post_entry, reverse_entry, run_schedules,
dispose_asset, reconcile, close_period, create_invoice, create_bill,
write_off_invoice, purge_tin, consolidate_duplicates, and the S6
settlement tools receive_payment and pay_bill, which gain confirmed and
preview on a clone of the ledger) returns preview (SHA-256 of the
canonical preview) and refuses a confirm whose preview is missing or
stale (stale_preview, before anything is written). A draft's digest is
its own state and the settings seq; an operation's is the tool, its
arguments as sent, the settings seq and the journal head seq, so another
session's write forces a re-preview (D-50).

New tools books.list_drafts, books.set_draft_state, books.discard_draft,
books.preview_entry; reports carry as_of_status (drafts open on or before
their end, unreconciled accounts, settings problems) and take strict; the
CPA package is refused while a draft dated in it is open unless
allow_open_drafts gives a reason, journaled as a decision;
books.digest takes since_seq (what was posted since a journal line,
backdated entries included: defect 6) and lists zero_net_accounts,
drafts_by_state and the reconciliation split. Needs attention gains
'draft awaiting receipt' beside 'draft not posted'; the drafts handbook
is rewritten. Every over-the-wire harness confirms the way an agent does.

Docs: mcp-interface, rules B-43, parity, testing (with the For-P12
paragraph), architecture, and the unit's As-built block.

Tests: drafts.rs (a_draft_waits_for_its_receipt_and_posts,
the_gate_moved_and_the_mcp_error_is_unchanged,
a_reversal_needs_no_receipt_of_its_own, discard_unblocks_the_close_over_the_wire,
report_warns_on_draft_before_as_of, cpa_package_refuses_open_draft,
stale_preview_refused, every_confirm_tool_takes_a_preview,
digest_since_seq_is_posting_time, legacy_reversed_replays_identically,
gui_and_server_gate_agree), attention_parity.rs, format_upgrade.rs.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

crates/ledger-mcp/src/server_tests.rs

@@ -42,7 +42,7 @@ fn annotations_complete() {
     const D: Hints = (Some(false), Some(true), None);
     const WI: Hints = (Some(false), Some(false), Some(true));
     const DI: Hints = (Some(false), Some(true), Some(true));
-    let table: [(&str, Hints); 129] = [
+    let table: [(&str, Hints); 133] = [
         ("books.handbook", R),
         ("books.start", R),
         ("books.set_setting", DI),
@@ -174,6 +174,11 @@ fn annotations_complete() {
         ("books.back_up_now", WI),
         // P4b S7: a bad-debt write-off.
         ("books.write_off_invoice", D),
+        // P4: drafts.
+        ("books.list_drafts", R),
+        ("books.set_draft_state", W),
+        ("books.discard_draft", D),
+        ("books.preview_entry", R),
     ];
     let tools = BooksServer::tool_router().list_all();
     assert_eq!(tools.len(), table.len());
@@ -213,8 +218,8 @@ fn annotations_complete() {
             "{name}: openWorldHint"
         );
     }
-    // docs/mcp-interface.md names the 31 destructive tools.
-    assert_eq!(table.iter().filter(|(_, h)| h.1 == Some(true)).count(), 31);
+    // docs/mcp-interface.md names the 32 destructive tools.
+    assert_eq!(table.iter().filter(|(_, h)| h.1 == Some(true)).count(), 32);
 }
 
 /// Every refusal an agent can be given whose text is fixed here, or