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-cli/tests/local_server.rs

@@ -1179,8 +1179,8 @@ async fn a_token_does_only_what_its_scopes_allow() {
         "it may preview"
     );
     assert!(
-        !tools.contains(&"books.receive_payment".to_string()),
-        "it may preview an invoice, but not post a payment"
+        !tools.contains(&"books.void_document".to_string()),
+        "it may preview an invoice, but not void one"
     );
     let preview = call(&writer, "books.post_entry", json!({"entry_id": entry})).await;
     if let Err(e) = &preview {
@@ -1273,7 +1273,8 @@ async fn every_call_is_recorded_once_refusals_included() {
     assert_eq!(by("books.get_entry"), 1);
     assert_eq!(by("books.draft_entry"), 1);
     assert_eq!(by("books.add_line"), 2);
-    assert_eq!(by("books.post_entry"), 1);
+    // The preview, then the confirm (plan P4: each is a call, each recorded).
+    assert_eq!(by("books.post_entry"), 2);
     assert_eq!(by("books.access_log"), 0, "recorded once answered");
     let refused: Vec<&&Value> = tools
         .iter()