feat(tools): native MCP client — mount stdio MCP servers as Correx tools

Adds an MCP host layer so external MCP servers (AST/LSP code-intelligence,
package resolvers, etc.) can be mounted at startup and surface their tools/list
as first-class Correx tools named mcp__<server>__<tool>. Each MCP tool is a
Tool+ToolExecutor, so it rides the normal ToolExecutor path and inherits tier
gating, receipts, and event-recorded execution (#5) with zero special-casing;
replay reads the recorded receipt rather than re-calling the server (#8/#9).

- McpProtocol/McpStdioClient/McpTool/McpMounter in infrastructure:tools
  (stdio JSON-RPC 2.0, tools/* slice only). Capabilities empty; safety via
  default T2 tier since external side effects are opaque.
- [[mcp]] config (id/command/env/tier) + array-of-tables parsing.
- Main wires mounted servers into extraTools (main + per-workspace paths) with
  a shutdown hook; a server that fails to start is logged and skipped.
- Tests: in-process fake transport (handshake/list/call/error + tool mapping),
  [[mcp]] parser.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

core/config/src/main/kotlin/com/correx/core/config/ConfigLoader.kt

@@ -265,9 +265,11 @@ object ConfigLoader {
         val providers = mutableListOf<MutableMap<String, Any>>()
         val models = mutableListOf<MutableMap<String, Any>>()
         val artifacts = mutableListOf<MutableMap<String, Any>>()
+        val mcpServers = mutableListOf<MutableMap<String, Any>>()
         var currentProvider: MutableMap<String, Any>? = null
         var currentModel: MutableMap<String, Any>? = null
         var currentArtifact: MutableMap<String, Any>? = null
+        var currentMcp: MutableMap<String, Any>? = null
 
         // Flush any open array-of-table entry into its list. Called whenever a new
         // table header (array or section) starts, so the previous entry is committed.
@@ -275,9 +277,11 @@ object ConfigLoader {
             currentProvider?.let { providers.add(it) }
             currentModel?.let { models.add(it) }
             currentArtifact?.let { artifacts.add(it) }
+            currentMcp?.let { mcpServers.add(it) }
             currentProvider = null
             currentModel = null
             currentArtifact = null
+            currentMcp = null
         }
 
         for ((lineNum, line) in lines.withIndex()) {
@@ -302,6 +306,11 @@ object ConfigLoader {
                     currentArtifact = mutableMapOf()
                     currentSection = ""
                 }
+                trimmed == "[[mcp]]" -> {
+                    flushTables()
+                    currentMcp = mutableMapOf()
+                    currentSection = ""
+                }
                 trimmed.startsWith("[") && !trimmed.startsWith("[[") && trimmed.endsWith("]") -> {
                     // Parse section headers like [server] or [tools.shell]
                     flushTables()
@@ -320,10 +329,12 @@ object ConfigLoader {
                         val provider = currentProvider
                         val model = currentModel
                         val artifact = currentArtifact
+                        val mcp = currentMcp
                         when {
                             provider != null -> provider[key] = parsedValue
                             model != null -> model[key] = parsedValue
                             artifact != null -> artifact[key] = parsedValue
+                            mcp != null -> mcp[key] = parsedValue
                             currentSection.isNotEmpty() -> sections[currentSection]?.put(key, parsedValue)
                         }
                     }
@@ -334,7 +345,7 @@ object ConfigLoader {
         // Don't forget the last array-of-table entry if file ends with one
         flushTables()
 
-        return buildConfig(sections, providers, models, artifacts)
+        return buildConfig(sections, providers, models, artifacts, mcpServers)
     }
 
     private fun parseValue(valueStr: String, lineNum: Int): Any {
@@ -452,6 +463,7 @@ object ConfigLoader {
         providersList: List<Map<String, Any>> = emptyList(),
         modelsList: List<Map<String, Any>> = emptyList(),
         artifactsList: List<Map<String, Any>> = emptyList(),
+        mcpList: List<Map<String, Any>> = emptyList(),
     ): CorrexConfig {
         val serverSection = sections["server"] ?: emptyMap()
         val tuiSection = sections["tui"] ?: emptyMap()
@@ -735,6 +747,20 @@ object ConfigLoader {
             repeatPenalty = samplingSection["repeat_penalty"]?.let { asDouble(it) },
         )
 
+        val mcp = mcpList.mapNotNull { mcpMap ->
+            val id = asStringOrNull(mcpMap["id"]) ?: return@mapNotNull null
+            val command = asStringList(mcpMap["command"])
+            if (command.isEmpty()) return@mapNotNull null
+            @Suppress("UNCHECKED_CAST")
+            val env = (mcpMap["env"] as? Map<String, Any>)?.mapValues { it.value.toString() } ?: emptyMap()
+            McpServerConfig(
+                id = id,
+                command = command,
+                env = env,
+                tier = asString(mcpMap["tier"], "T2"),
+            )
+        }
+
         val gitSection = sections["git"] ?: emptyMap()
         val git = GitConfig(
             enabled = asBoolean(gitSection["enabled"], false),
@@ -758,6 +784,7 @@ object ConfigLoader {
             orchestration = orchestration,
             sampling = sampling,
             git = git,
+            mcp = mcp,
         )
     }
 

core/config/src/main/kotlin/com/correx/core/config/CorrexConfig.kt

@@ -19,6 +19,19 @@ data class CorrexConfig(
     val sampling: SamplingConfig = SamplingConfig(),
     val health: HealthConfig = HealthConfig(),
     val git: GitConfig = GitConfig(),
+    val mcp: List<McpServerConfig> = emptyList(),
+)
+
+/**
+ * An MCP server to mount at startup. Its `tools/list` becomes Correx tools (`mcp__<id>__<name>`),
+ * gated at [tier] (default T2 = approval) since an external tool's side effects are opaque.
+ */
+@Serializable
+data class McpServerConfig(
+    val id: String,
+    val command: List<String>,
+    val env: Map<String, String> = emptyMap(),
+    val tier: String = "T2",
 )
 
 /**

core/config/src/test/kotlin/com/correx/core/config/ConfigLoaderTest.kt

@@ -390,6 +390,31 @@ class ConfigLoaderTest {
         assertEquals(10001, result.modelsSettings.port)
     }
 
+    @Test
+    fun `parseToml parses mcp array-of-tables with command list and env`() {
+        val toml = """
+            [[mcp]]
+            id = "codebase-memory"
+            command = ["codebase-memory-mcp", "serve"]
+            env = { RUST_LOG = "info" }
+
+            [[mcp]]
+            id = "other"
+            command = ["other-server"]
+        """.trimIndent()
+
+        val parseTomlMethod = ConfigLoader::class.java.getDeclaredMethod("parseToml", String::class.java)
+        parseTomlMethod.isAccessible = true
+        val result = parseTomlMethod.invoke(ConfigLoader, toml) as CorrexConfig
+
+        assertEquals(2, result.mcp.size)
+        assertEquals("codebase-memory", result.mcp[0].id)
+        assertEquals(listOf("codebase-memory-mcp", "serve"), result.mcp[0].command)
+        assertEquals("info", result.mcp[0].env["RUST_LOG"])
+        assertEquals("T2", result.mcp[0].tier)
+        assertEquals(listOf("other-server"), result.mcp[1].command)
+    }
+
     @Test
     fun `parseToml returns empty models list and default modelsSettings when sections absent`() {
         val toml = """