config, mcp, gui: specs from sources, spec-blind suites, and the bugs they found

ledger-config: parse gets a sourced spec. A fiscal year starts on the
first of a month (IRS Pub. 538); tax_classification is read by whole
words (Treas. Reg. 301.7701-3, Schedule C instructions; "business corp"
no longer reads as an S corp, "corporation or S corporation" is refused);
duplicate or blank members and shared capital accounts are refused; a
negative or non-grammatical receipt threshold is refused; codes trimmed.
tests/spec_config.rs (65 spec-blind tests, 14 properties), fuzz target
fuzz_config_parse (weekly). Mutation: 55 of 55 viable caught (from 25/38).

The receipt policy moves to ledger-config, with one loader
(effective_receipt_policy) and one decimal grammar, so the server and
the viewer enforce and show the same rule (the viewer had its own: only
expense-like debits, a silent $25 default, and no config.json).

ledger-mcp: a module spec (MCP 2025-06-18 tools, JSON-RPC 2.0, the
operating contract). Amounts in are exactly -?digits[.digits]; a number
that is one account's code and another's id (vendors, classes alike) is
refused, not guessed; the threshold is validated at startup. Fixed:
add_line with a bad class journaled the line before refusing;
profit_and_loss_by_class ignored `class`; aging buckets said "0". A wire
in front of rmcp answers malformed JSON with -32700 and invalid requests
with -32600 and their id (rmcp dropped the first, omitted the id).
tests/spec_mcp.rs (26 spec-blind tests: every tool's result against its
own outputSchema, a random-call state machine checking the journal is
untouched by every refusal, amount grammar, previews, the receipt policy).

ledger-gui: money, accounting, and dollars never round (they rounded to
cents, banker's style); export file names avoid Windows device names,
trailing dots and spaces, empty names, and 255-byte overflow; specs on
attention, history, fuzzy search, and axis ticks.

ledger-core: the lifetime profit_and_loss is renamed unclosed_earnings
(docs/testing.md #3).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

docs/spec/sources/mcp-tools.md

@@ -0,0 +1,47 @@
+# Model Context Protocol: tools (specification 2025-06-18)
+
+Governs `ledger-mcp`'s tool results and errors. Source:
+https://github.com/modelcontextprotocol/modelcontextprotocol,
+docs/specification/2025-06-18/server/tools.mdx (MIT). Fetched 2026-10-14.
+
+**Structured Content**
+
+> **Structured** content is returned as a JSON object in the
+> `structuredContent` field of a result.
+>
+> For backwards compatibility, a tool that returns structured content
+> SHOULD also return the serialized JSON in a TextContent block.
+
+**Output Schema**
+
+> Tools may also provide an output schema for validation of structured
+> results. If an output schema is provided:
+>
+> - Servers **MUST** provide structured results that conform to this schema.
+> - Clients **SHOULD** validate structured results against this schema.
+
+**Error Handling**
+
+> Tools use two error reporting mechanisms:
+>
+> 1. **Protocol Errors**: Standard JSON-RPC errors for issues like:
+>    - Unknown tools
+>    - Invalid arguments
+>    - Server errors
+>
+> 2. **Tool Execution Errors**: Reported in tool results with `isError: true`:
+>    - API failures
+>    - Invalid input data
+>    - Business logic errors
+
+**Security Considerations**
+
+> 1. Servers **MUST**:
+>    - Validate all tool inputs
+>    - Implement proper access controls
+>    - Rate limit tool invocations
+>    - Sanitize tool outputs
+
+(A local stdio server for one bookkeeper: access control is the file
+system's, and rate limiting has no one to limit; wanderbooks takes
+"validate all tool inputs" and "sanitize tool outputs" as binding.)