feat(mcp): FastMCP server exposing read-only KB tools (stdio)

Implements F-14: thin FastMCP wrapper over existing codex domain modules.
Seven read-only tools: search, ask, wiki_read, wiki_list, discover_leads,
provenance_verify, synthesis_browse. All optional-feature tools degrade
gracefully to {"error": "feature not available"} instead of crashing.
Adds mcp[cli]>=1.0 dependency and codex-mcp console_script entry-point.
28 new tests across test_server, test_search, test_readonly, test_graceful,
test_http_auth — all green; 0 regressions in existing 172 tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

codex/config.py

@@ -222,6 +222,93 @@ class Settings(BaseSettings):
         ),
     )
 
+    # ------------------------------------------------------------------
+    # F-13 Synthesis / Lead-Engine
+    # ------------------------------------------------------------------
+    leads_dir: str = Field(
+        default="leads/",
+        description=(
+            "Directory where synthesis leads are written. "
+            "Grounded leads land in <leads_dir>/grounded/, conjectures in "
+            "<leads_dir>/conjectures/. INVARIANT: conjectures NEVER touch wiki/."
+        ),
+    )
+
+    synthesis_llm_model: str = Field(
+        default="qwen2.5:7b",
+        description=(
+            "Ollama model name used for synthesis (connection / gap / improvement / "
+            "conjecture). Defaults to the qwen-light profile on the Jetson."
+        ),
+    )
+
+    synthesis_llm_url: str | None = Field(
+        default=None,
+        description=(
+            "Ollama base URL for synthesis. When None, falls back to OLLAMA_BASE_URL."
+        ),
+    )
+
+    synthesis_top_k: int = Field(
+        default=20,
+        gt=0,
+        description=(
+            "Number of top chunks retrieved per synthesis probe. Higher values "
+            "improve recall at the cost of a larger LLM prompt."
+        ),
+    )
+
+    synthesis_min_grounded_ratio: float = Field(
+        default=0.5,
+        ge=0.0,
+        le=1.0,
+        description=(
+            "Minimum fraction of claims that must be grounded for a grounded lead "
+            "(connection / gap / improvement) to be emitted. Leads below this "
+            "threshold are dropped rather than written to leads/grounded/."
+        ),
+    )
+
+    synthesis_gap_min_coverage: int = Field(
+        default=2,
+        gt=0,
+        description=(
+            "A topic is considered a 'gap' candidate when it is covered by fewer "
+            "than this many distinct bibkeys in the retrieved top-K."
+        ),
+    )
+
+    # ------------------------------------------------------------------
+    # F-14 MCP Server
+    # ------------------------------------------------------------------
+    mcp_transport: str = Field(
+        default="stdio",
+        description=(
+            "Transport protocol for the MCP server. "
+            "Allowed values: 'stdio' (default) or 'http'. "
+            "HTTP transport requires MCP_AUTH_TOKEN to be set."
+        ),
+    )
+
+    mcp_host: str = Field(
+        default="127.0.0.1",
+        description="Bind host for HTTP transport (ignored for stdio).",
+    )
+
+    mcp_port: int = Field(
+        default=8765,
+        gt=0,
+        description="Bind port for HTTP transport (ignored for stdio).",
+    )
+
+    mcp_auth_token: str | None = Field(
+        default=None,
+        description=(
+            "Bearer token required when mcp_transport='http'. "
+            "If HTTP transport is requested but this is None, the server refuses to start."
+        ),
+    )
+
 
 @lru_cache(maxsize=1)
 def get_settings() -> Settings: