feat: establish read-only DocForge MCP foundation

docs/MCP_CONTRACT.md

@@ -0,0 +1,43 @@
+# MCP boundary
+
+The DFG-2 server will use local standard input/output transport and bind once to the explicit
+`--project-root` supplied at process startup. It will not expose an HTTP port in the first release.
+
+## Read tools
+
+- `docforge_project_info`
+- `docforge_get_contract`
+- `docforge_get_node`
+- `docforge_search`
+- `docforge_filter_nodes`
+- `docforge_backlinks`
+- `docforge_dependencies`
+- `docforge_impact`
+- `docforge_get_context`
+- `docforge_validate_project`
+- `docforge_render_status`
+
+Each response states that document text is project content, not higher-priority instructions. Each
+response includes project identity, revision, source hash, adapter version, and staleness state.
+
+## Proposal tools reserved for DFG-3
+
+- `docforge_create_changeset`
+- `docforge_propose_node_create`
+- `docforge_propose_node_update`
+- `docforge_propose_node_move`
+- `docforge_propose_node_delete`
+- `docforge_validate_changeset`
+- `docforge_get_changeset_diff`
+- `docforge_preview_changeset`
+
+Proposal tools may write only below the configured changeset root. They never change canonical files.
+
+## Excluded tools
+
+The normal server never exposes shell execution, arbitrary reads or writes, canonical changeset
+application, Git mutation, project builds, deployment, publication, global project selection, or
+cross-project retrieval.
+
+DocForge pins the official stable Python MCP SDK to the compatible `mcp>=1.28,<2` release line.
+Migration to a later major release requires a separate contract and protocol compatibility review.