v1.13.0 — AI-native authoring

The AI-first release: agents write plans without doing coordinate arithmetic, and fix them mechanically.

• Placement sugar — door|window|opening on <wall> at <pos> attachment, swing into <room>, hinge near start|end, furniture in <room> centered | anchor <corner> [inset N], and strip room rows. Attached openings cannot be off-wall by construction.
• Machine-applicable fixes — Diagnostic.fixes (rustc-style 4-tier applicability), arch fix (piece-table applier, bounded self-checking fixpoint), arch suggest (candidate doors/windows for unreachable rooms as data, never auto-applied), LSP quick-fixes in the VS Code extension.
• Structured I/O — Plan JSON in/out (compile --from-json, arch ast) aligned to the academic LLM floor-plan schema, validate --graph intent checking, arch complete, generated schemas/plan.schema.json.
• Constrained decoding — generated grammars/archlang.gbnf so llama.cpp / vLLM-class stacks can hard-guarantee valid .arch.
• Zero-dep perception — arch compile -f txt / preview --ascii renders a box-drawing floor plan any sandboxed agent can read.
• Eval — live authorability eval (OpenAI provider, cost-guarded), corpus 18→22, recorded baseline + delta reporting.
• MCP — new optional @chanmeng666/archlang-mcp stdio shim (ADR 0012); the CLI stays the primary agent interface and the core stays zero-dependency.

See CHANGELOG.md for the full tranche-by-tranche detail.