test(agent): scripted evals follow only next_steps; the surface over the wire (P5)

Agent reason: the envelope is only worth having if an agent can do its work
by following it. crates/ledger-cli/tests/agent_evals/ holds six scripted
transcripts, no model: onboarding to a first post, a receipt-backed post, a
draft that waits for its receipt and posts when it arrives, a reversal, a
reconciliation, a month-end close. agent_evals_follow_only_next_steps plays
each against a real books server: after books.start a step may call only a
tool (or fetch only a prompt) the previous result's next_steps named, with
the arguments the step gave and the ones the agent decides; setup calls (the
chart and the books an agent finds) are not the agent's moves.

agent_surface.rs holds the over-the-wire tests of the rest: the journal in
words (order, subject and type filters, paging, a bad subject refused),
source corrections through the three tools, the prompts rendered against
their files and refused when malformed, the resource templates advertised
and read, books.start v2 whole and under 8 KiB with the self-report in the
access log only, a new book told to onboard, and a mutating call answering
with the head the journal has and a refusal naming its remedy.

Docs: testing.md's P5 section (every test, and the For-P12 paragraph naming
what a mutant would flip), parity.md (no feature moved; one row), and
architecture.md (the envelope and the guards); mcp-interface.md's overview
sections now describe the surface as built.

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

crates/ledger-cli/tests/agent_evals/reconciliation.json

@@ -0,0 +1,148 @@
+{
+  "description": "A cash account reconciled to its statement: record it, mark the lines, reconcile.",
+  "settings": "[company]\nname = \"Eval Co\"\nfiscal_year_start = \"01-01\"\n[books]\ncash_accounts = [\"1000\"]\n",
+  "setup": [
+    {
+      "call": "books.add_account",
+      "args": {
+        "code": "1000",
+        "name": "Cash",
+        "account_type": "asset"
+      }
+    },
+    {
+      "call": "books.add_account",
+      "args": {
+        "code": "3000",
+        "name": "Capital",
+        "account_type": "equity"
+      }
+    },
+    {
+      "call": "books.add_account",
+      "args": {
+        "code": "6000",
+        "name": "Rent",
+        "account_type": "expense"
+      }
+    },
+    {
+      "call": "books.draft_entry",
+      "args": {
+        "date": "2026-01-05",
+        "description": "Opening capital",
+        "no_party_reason": "opening balance"
+      },
+      "save": {
+        "entry": "/entry_id"
+      }
+    },
+    {
+      "call": "books.add_line",
+      "args": {
+        "entry_id": {
+          "$var": "entry"
+        },
+        "account": "1000",
+        "side": "debit",
+        "amount": "10.00"
+      }
+    },
+    {
+      "call": "books.add_line",
+      "args": {
+        "entry_id": {
+          "$var": "entry"
+        },
+        "account": "3000",
+        "side": "credit",
+        "amount": "10.00"
+      }
+    },
+    {
+      "call": "books.post_entry",
+      "args": {
+        "entry_id": {
+          "$var": "entry"
+        },
+        "confirmed": true
+      }
+    },
+    {
+      "call": "books.file_document",
+      "args": {
+        "category": "statement",
+        "file_name": "jan.pdf",
+        "mime_type": "application/pdf",
+        "upload_id": {
+          "$upload": {
+            "name": "jan.pdf",
+            "mime": "application/pdf",
+            "text": "%PDF-1.4 January statement",
+            "purpose": "document"
+          }
+        }
+      },
+      "save": {
+        "statement": "/attachment_id"
+      }
+    }
+  ],
+  "steps": [
+    {
+      "call": "books.start",
+      "args": {}
+    },
+    {
+      "expect_next_steps_contains": "books.record_statement"
+    },
+    {
+      "follow": "books.record_statement",
+      "with": {
+        "attachment_id": {
+          "$var": "statement"
+        },
+        "account": "1000",
+        "period_start": "2026-01-01",
+        "period_end": "2026-01-31",
+        "opening_balance": "0.00",
+        "closing_balance": "10.00"
+      }
+    },
+    {
+      "follow": "books.mark_cleared",
+      "with": {
+        "entry_id": {
+          "$var": "entry"
+        },
+        "line_index": 0,
+        "cleared": true
+      }
+    },
+    {
+      "follow": "books.reconcile",
+      "with": {
+        "account": "1000",
+        "statement_date": "2026-01-31",
+        "statement_balance": "10.00",
+        "statement_attachment": {
+          "$var": "statement"
+        }
+      }
+    },
+    {
+      "expect": {
+        "/status": "preview"
+      }
+    },
+    {
+      "follow": "books.reconcile",
+      "with": {}
+    },
+    {
+      "expect": {
+        "/status": "reconciled"
+      }
+    }
+  ]
+}