Extensions: skills, plugins, MCP, sub-agents; configurable keys

- Skills (SKILL.md discovery, skill tool, /skills /skill)
- plugin.json exec tools with permission prompts, timeouts and workspace trust (/plugins)
- MCP stdio client: JSON-RPC initialize/tools/list/tools/call, mcp__server__tool, /mcp and sidebar status
- task tool with general/explore/plan and .agent/agents/*.md roles, parallel read-only runs, cancel propagation, /agents
- Keymap with Ctrl+X leader, keybinds.json overrides and /keys panel
- Collapsed thinking, throttled streaming Markdown, leaner tool output, parallel read-only tools
- Spawn: close-on-exec pipes and a process-wide fork lock
- Tests for keymap, skills, plugins, MCP, sub-agents, shell compaction; docs/plugins.md

include/cst_mcp.h

@@ -0,0 +1,66 @@
+#ifndef CST_MCP_H
+#define CST_MCP_H
+
+/*
+ * MCP (Model Context Protocol) client over stdio: newline-delimited
+ * JSON-RPC 2.0. Each server is spawned with its command/args/env, gets
+ * initialize + notifications/initialized + tools/list, and every tool is
+ * registered as mcp__<server>__<tool> (approved like network tools).
+ *
+ * Config, merged in this order (first name wins):
+ *   <ws>/.agent/mcp.json (trusted workspaces only), <config>/mcp.json,
+ *   plugin "mcpServers". Format: {"mcpServers": {"name": {"command": "npx",
+ *   "args": ["-y", "pkg"], "env": {"K": "V"}, "cwd": "...",
+ *   "disabled": false}}}
+ */
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define CST_MCP_MAX 16
+
+typedef enum {
+  CST_MCP_OFF = 0,
+  CST_MCP_STARTING,
+  CST_MCP_READY,
+  CST_MCP_FAILED,
+  CST_MCP_EXITED
+} cst_mcp_state_t;
+
+typedef struct {
+  char name[64];
+  char source[48]; /* "workspace" | "user" | "plugin:<name>" */
+  char command[256];
+  int state; /* cst_mcp_state_t */
+  int ntools;
+  char error[200];
+} cst_mcp_info_t;
+
+/* One server from a JSON object text ({"command":..., "args":[...], ...}).
+ * cwd: default working directory (NULL = workspace). Returns 0, or -1 when
+ * the name exists / the config is invalid. */
+int cst_mcp_add_config_json(const char *name, const char *server_json,
+                            const char *cwd, const char *source);
+/* Read the mcp.json files for workspace (the workspace one only when
+ * trusted). Returns servers added; *untrusted counts skipped ones. */
+int cst_mcp_load_configs(const char *workspace, int ws_trusted,
+                         int *untrusted);
+/* Start every configured server in the background; tools appear as each
+ * one finishes its handshake. */
+void cst_mcp_start_all(const char *workspace);
+/* Wait up to ms for servers still starting (headless runs). */
+void cst_mcp_wait_ready(int ms);
+/* Stop servers, unregister their tools and forget the configs. */
+void cst_mcp_stop_all(void);
+int cst_mcp_info(cst_mcp_info_t *out, int max);
+/* Ready / configured counts (for the sidebar). */
+void cst_mcp_counts(int *ready, int *total);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif