feat(mcp): books.start v2 and the agent's self-report (P5)

Agent reason: the first call of a session should say who is asking, what is
waiting and what to do, in under 8 KiB, from the same lists the viewer
draws. books.start now carries book.id and book.url (the book's path on the
server, never a path on a disk), you {principal, kind, scopes, client_id},
drafts {building, awaiting_evidence}, reconciliation {tracked,
never_reconciled, behind}, backup {last_at, through_seq, stale}, the
prompts, and needs_attention (the twelve most urgent items, problems first,
with every item counted by kind), beside next_steps now in the envelope's
shape (tool or prompt, why, required; attention problems are required). A
new book is told to run the onboard prompt first, then to record the
company's facts and set up the chart; an active one is offered a draft
entry. The tool carries _meta anthropic/alwaysLoad, so a client that defers
tools loads it up front. The size fit shortens attention items and waiting
drafts after the convention summaries and before the lists, as before.

agent {model, reasoning_effort, harness} is accepted and written to the
call's access record (the access log shows it as agent), self-reported and
never checked, and used for nothing else: not in the answer, not in any
decision. Who asked is the request's alone: it is cleared when the request
ends, so a later resource read on the same thread cannot see it.

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

crates/ledger-mcp/src/access.rs

@@ -86,6 +86,7 @@ pub(crate) struct Call {
     action: &'static str,
     subject: String,
     args_digest: Option<String>,
+    agent: Option<ledger_store::access::Agent>,
 }
 
 /// Why a call wasn't run, for its record and its answer.
@@ -124,6 +125,7 @@ impl Call {
             action,
             subject: subject.to_string(),
             args_digest: None,
+            agent: None,
         }
     }
 
@@ -140,6 +142,16 @@ impl Call {
         self.args_digest = args_digest;
     }
 
+    /// This call, with what the agent said about itself (`books.start`).
+    pub(crate) fn with_agent(&mut self, agent: Option<ledger_store::access::Agent>) {
+        self.agent = agent;
+    }
+
+    /// The client program's name, as it named itself at `initialize`.
+    pub(crate) fn client_name(&self) -> Option<String> {
+        self.client.as_ref().map(|c| c.name.clone())
+    }
+
     /// The call's caller, if the door named one.
     pub(crate) fn caller(&self) -> Option<&Caller> {
         self.caller.as_ref()
@@ -172,6 +184,7 @@ impl Call {
             args_digest: self.args_digest.clone(),
             result,
             head_after,
+            agent: self.agent.clone(),
         };
         match self.log.record(&access) {
             Ok(_) => Ok(()),