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_subagent.h

@@ -0,0 +1,65 @@
+#ifndef CST_SUBAGENT_H
+#define CST_SUBAGENT_H
+
+/*
+ * Sub-agents: the task(description, prompt, agent?) tool runs one turn of a
+ * child agent with its own context and returns its final report.
+ *
+ * Roles: built-in general / explore / plan, plus Markdown files in
+ * <ws>/.agent/agents/ and <config>/agents/ (the workspace wins, both win
+ * over built-ins). Frontmatter: name, description, model, tools (allowlist),
+ * max_steps, readonly; the body is the role's instructions.
+ *
+ * Transcripts: <ws>/.agent/sessions/<parent-id>/sub-<n>.jsonl, with a
+ * sub-<n>.json summary next to each (not listed as sessions).
+ */
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define CST_ROLES_MAX 32
+
+typedef struct {
+  char name[64];
+  char desc[256];
+  char source[16]; /* "builtin" | "workspace" | "user" */
+  char model[128]; /* empty = the parent's */
+  char tools[1024]; /* ",a,b," allowlist; empty = all but task */
+  int max_steps;    /* 0 = default */
+  int read_only;
+  char *prompt; /* role instructions (malloc'd) */
+} cst_agent_role_t;
+
+/* Roles sorted built-ins first, then by name. Free with cst_roles_free. */
+int cst_roles_list(const char *workspace, cst_agent_role_t *out, int max);
+void cst_roles_free(cst_agent_role_t *v, int n);
+/* System prompt section listing the roles (malloc'd), or NULL. */
+char *cst_subagent_index(const char *workspace);
+/* Register the task tool (owner "builtin:task") for workspace. */
+int cst_subagent_register_tool(const char *workspace);
+
+typedef struct {
+  char file[64]; /* "sub-3" */
+  char role[64];
+  char desc[160];
+  char status[32]; /* "done" | "error" | "cancelled" | "running" */
+  int steps, tools;
+  double ms;
+  long long mtime;
+} cst_subagent_rec_t;
+
+/* This parent session's sub-agent runs, newest first. */
+int cst_subagent_list(const char *workspace, const char *parent_id,
+                      cst_subagent_rec_t *out, int max);
+/* Full path of a transcript (sub-<n>.jsonl). */
+int cst_subagent_path(const char *workspace, const char *parent_id,
+                      const char *file, char *out, size_t out_sz);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif