feat(server): skills v1 — parser, tools, /api/skills, mount

- /data/skills mount (host: /opt/skills)
- skill_find, skill_use, skill_resource added to default read-only
  tool set; opt-in for agents with explicit tools: whitelist
- AGENTS.md builtin agents drop explicit tools: arrays to inherit
  the new default (now includes skill tools)
- POST /api/chats/:id/skill_invoke for slash-command flow
- 19 SKILL.md files seeded at /opt/skills/ across 6 source groups

apps/server/src/services/tools.ts

@@ -4,6 +4,7 @@ import { z } from 'zod';
 import { pathGuard, PathScopeError } from './path_guard.js';
 import { grep as fileOpsGrep, findFiles as fileOpsFindFiles } from './file_ops.js';
 import { getGitMeta } from './git_meta.js';
+import { findSkills, getSkillBody, getSkillResource } from './skills.js';
 
 const MAX_FILE_BYTES = 5 * 1024 * 1024;
 const DEFAULT_VIEW_LINES = 200;
@@ -300,12 +301,119 @@ export const gitStatus: ToolDef<GitStatusInputT> = {
   },
 };
 
+// Batch 9.6: skill_find, skill_use, skill_resource. Lazy-loaded markdown
+// playbooks at /data/skills/. Three tools rather than one to keep each call
+// cheap — the model lists, then loads, then optionally pulls support files.
+
+const SkillFindInput = z.object({
+  query: z.string().optional(),
+});
+type SkillFindInputT = z.infer<typeof SkillFindInput>;
+
+export const skillFind: ToolDef<SkillFindInputT> = {
+  name: 'skill_find',
+  description:
+    'Find skills (markdown playbooks under /data/skills) by name or description. Returns up to 5 matches. Empty query or "*" returns all available skills. Call this first to discover what skills are available.',
+  inputSchema: SkillFindInput,
+  jsonSchema: {
+    type: 'function',
+    function: {
+      name: 'skill_find',
+      description:
+        'Find skills by name or description. Returns up to 5 matches. Empty or "*" returns all.',
+      parameters: {
+        type: 'object',
+        properties: {
+          query: { type: 'string', description: 'substring matched against skill name and description' },
+        },
+        additionalProperties: false,
+      },
+    },
+  },
+  async execute(input) {
+    return await findSkills(input.query ?? '');
+  },
+};
+
+const SkillUseInput = z.object({
+  name: z.string().min(1),
+});
+type SkillUseInputT = z.infer<typeof SkillUseInput>;
+
+export const skillUse: ToolDef<SkillUseInputT> = {
+  name: 'skill_use',
+  description:
+    "Load the full body of a skill's SKILL.md by name. Returns the markdown playbook to follow. Discover names via skill_find. Errors: unknown_skill.",
+  inputSchema: SkillUseInput,
+  jsonSchema: {
+    type: 'function',
+    function: {
+      name: 'skill_use',
+      description: "Load the full body of a skill's SKILL.md by name.",
+      parameters: {
+        type: 'object',
+        properties: {
+          name: { type: 'string', description: 'skill name from skill_find' },
+        },
+        required: ['name'],
+        additionalProperties: false,
+      },
+    },
+  },
+  async execute(input) {
+    const body = await getSkillBody(input.name);
+    if (body === null) {
+      return { error: 'unknown_skill', message: `unknown skill: ${input.name}` };
+    }
+    return { body };
+  },
+};
+
+const SkillResourceInput = z.object({
+  name: z.string().min(1),
+  path: z.string().min(1),
+});
+type SkillResourceInputT = z.infer<typeof SkillResourceInput>;
+
+export const skillResource: ToolDef<SkillResourceInputT> = {
+  name: 'skill_resource',
+  description:
+    "Read a support file inside a skill's folder (e.g. references/root-cause-tracing.md). Path is relative to the skill folder. Use skill_use to read SKILL.md itself. Errors: unknown_skill, unknown_resource, path_escape.",
+  inputSchema: SkillResourceInput,
+  jsonSchema: {
+    type: 'function',
+    function: {
+      name: 'skill_resource',
+      description: "Read a support file inside a skill's folder. Path is relative to the skill folder.",
+      parameters: {
+        type: 'object',
+        properties: {
+          name: { type: 'string', description: 'skill name' },
+          path: { type: 'string', description: 'relative path under the skill folder' },
+        },
+        required: ['name', 'path'],
+        additionalProperties: false,
+      },
+    },
+  },
+  async execute(input) {
+    const result = await getSkillResource(input.name, input.path);
+    if (!result.ok) {
+      return { error: result.code, message: result.message };
+    }
+    return { content: result.content };
+  },
+};
+
 export const ALL_TOOLS: ReadonlyArray<ToolDef<unknown>> = [
   viewFile as ToolDef<unknown>,
   listDir as ToolDef<unknown>,
   grep as ToolDef<unknown>,
   findFiles as ToolDef<unknown>,
   gitStatus as ToolDef<unknown>,
+  skillFind as ToolDef<unknown>,
+  skillUse as ToolDef<unknown>,
+  skillResource as ToolDef<unknown>,
 ];
 
 // v1.8.2: forward-compatible read-only whitelist. An agent whose `tools` is
@@ -313,12 +421,16 @@ export const ALL_TOOLS: ReadonlyArray<ToolDef<unknown>> = [
 // anything outside means the agent can mutate state and gets a tighter
 // default (10). Every tool in v1.8.2 happens to be read-only, so the
 // non-RO branch only takes effect once BooCoder lands write tools.
+// Batch 9.6: skill_* added; all still read-only.
 export const READ_ONLY_TOOL_NAMES = [
   'view_file',
   'list_dir',
   'grep',
   'find_files',
   'git_status',
+  'skill_find',
+  'skill_use',
+  'skill_resource',
 ] as const;
 
 export const TOOLS_BY_NAME: Record<string, ToolDef<unknown>> = Object.fromEntries(