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-store/src/error.rs

@@ -38,20 +38,10 @@ pub enum StoreError {
     /// The receipt policy covers the entry and it has no receipt (plan P4,
     /// I-5; rules.md B-43): refused before anything is journaled.
     #[error(
-        "entry {entry_id} needs a receipt before it posts: {reason} ({policy}); attach one with books.attach_receipt"
+        "entry {} needs a receipt before it posts: {} ({}); attach one with books.attach_receipt",
+        .0.entry_id, .0.reason, .0.policy
     )]
-    ReceiptRequired {
-        /// The entry that needs the receipt.
-        entry_id: u64,
-        /// Its total debits, `None` when they pass exact arithmetic.
-        debits: Option<rust_decimal::Decimal>,
-        /// The policy that triggered, in words.
-        policy: String,
-        /// Why this entry is covered.
-        reason: String,
-        /// The posted entries it appears to split (anti-splitting).
-        split_group: Vec<u64>,
-    },
+    ReceiptRequired(Box<ReceiptRequiredInfo>),
 
     /// Filesystem error.
     #[error("io error: {0}")]
@@ -217,3 +207,18 @@ fn newer_journal_text(seq: u64, event_type: &str, need: &str, verified: bool) ->
         )
     }
 }
+
+/// What a refused post tells (boxed in [`StoreError::ReceiptRequired`]).
+#[derive(Debug)]
+pub struct ReceiptRequiredInfo {
+    /// The entry that needs the receipt.
+    pub entry_id: u64,
+    /// Its total debits, `None` when they pass exact arithmetic.
+    pub debits: Option<rust_decimal::Decimal>,
+    /// The policy that triggered, in words.
+    pub policy: String,
+    /// Why this entry is covered.
+    pub reason: String,
+    /// The posted entries it appears to split (anti-splitting).
+    pub split_group: Vec<u64>,
+}