feat(tool-skill): teach the catalog about user-explicit skill injection

Both catalog renderings now tell the model that a directly invoked skill
arrives as an inline <skill_content> block to follow without re-loading it
through the skill tool — the seam rule that keeps the user-explicit path
and the model-autonomous path from double-injecting one skill.

examples/acp-agent/tests/snapshots/skill-load/session.jsonl

@@ -5,7 +5,7 @@
 {"type":"step/start","seq":3,"time":1785498773754,"data":{"turn":1,"step":1}}
 {"type":"user/message","seq":4,"time":1785498773754,"data":{"content":[{"type":"text","text":"Load the snapshot-skill skill with the skill tool, then reply DONE."}],"source":{"kind":"user"},"role":"user","id":"0ca31b92-27ac-451d-98d3-d1e5f605454b"},"surfaceOp":"append"}
 {"type":"user/message","seq":5,"time":1785498773755,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."}]},"role":"user","id":"3fc7e2f8-90fc-496c-b516-700cef1d86f1"},"surfaceOp":"append"}
-{"type":"user/message","seq":6,"time":1785730426818,"data":{"content":[{"type":"text","text":"<system-reminder>\nA skill is a reusable set of task-specific instructions. The following skills are available in this session:\n\n<available_skills>\n- `model-only-skill`: Prove user-disabled skills remain available to the model.\n- `snapshot-skill`: Exercise project skill discovery and loading in snapshot tests.\n</available_skills>\n\nIf the user names a skill, or the task clearly matches a skill's description, call the `skill` tool with the exact skill name before taking task actions. Load all applicable skills, then follow their full instructions. This catalog contains summaries only; do not infer or follow a skill's instructions until it has been loaded.\n</system-reminder>"}],"source":{"kind":"skill-catalog","form":"catalog","entries":[{"name":"model-only-skill","description":"Prove user-disabled skills remain available to the model."},{"name":"snapshot-skill","description":"Exercise project skill discovery and loading in snapshot tests."}]},"role":"user","id":"60880315-9799-44c8-8a99-e6fe9ee5bdc5"},"surfaceOp":"append"}
+{"type":"user/message","seq":6,"time":1785730426818,"data":{"content":[{"type":"text","text":"<system-reminder>\nA skill is a reusable set of task-specific instructions. The following skills are available in this session:\n\n<available_skills>\n- `model-only-skill`: Prove user-disabled skills remain available to the model.\n- `snapshot-skill`: Exercise project skill discovery and loading in snapshot tests.\n</available_skills>\n\nIf the user names a skill, or the task clearly matches a skill's description, call the `skill` tool with the exact skill name before taking task actions. Load all applicable skills, then follow their full instructions. This catalog contains summaries only; do not infer or follow a skill's instructions until it has been loaded.\nA user may also invoke a skill directly; its <skill_content> block then appears in this conversation. Follow it, and do not call the `skill` tool again for that skill.\n</system-reminder>"}],"source":{"kind":"skill-catalog","form":"catalog","entries":[{"name":"model-only-skill","description":"Prove user-disabled skills remain available to the model."},{"name":"snapshot-skill","description":"Exercise project skill discovery and loading in snapshot tests."}]},"role":"user","id":"60880315-9799-44c8-8a99-e6fe9ee5bdc5"},"surfaceOp":"append"}
 {"type":"session/title","seq":7,"time":1785730426818,"data":{"title":"Load the snapshot-skill skill with","messageSeqs":[4],"source":{"kind":"fallback"}}}
 {"type":"request/header","seq":8,"time":1785498773756,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":9,"time":1785730426819,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}

packages/skill/tool-skill/src/index.ts

@@ -217,6 +217,7 @@ function renderCatalogMessage(entries: SkillCatalogSource['entries']): UserMessa
         '</available_skills>',
         '',
         "If the user names a skill, or the task clearly matches a skill's description, call the `skill` tool with the exact skill name before taking task actions. Load all applicable skills, then follow their full instructions. This catalog contains summaries only; do not infer or follow a skill's instructions until it has been loaded.",
+        'A user may also invoke a skill directly; its <skill_content> block then appears in this conversation. Follow it, and do not call the `skill` tool again for that skill.',
         '</system-reminder>',
       ].join('\n'),
     }],
@@ -235,6 +236,7 @@ function renderCatalogUpdate(entries: SkillCatalogSource['entries']): UserMessag
     ]
     : [
       'Use only names in this replacement catalog. If the user names a listed skill, or the task clearly matches its description, call the `skill` tool with the exact name before acting.',
+      'A user may also invoke a skill directly; its <skill_content> block then appears in this conversation. Follow it, and do not call the `skill` tool again for that skill.',
     ]
   return createUserMessage({
     content: [{

packages/skill/tool-skill/tests/tool-skill.spec.ts

@@ -287,6 +287,7 @@ describe('dsh-tool-skill', () => {
             '</available_skills>',
             '',
             "If the user names a skill, or the task clearly matches a skill's description, call the `skill` tool with the exact skill name before taking task actions. Load all applicable skills, then follow their full instructions. This catalog contains summaries only; do not infer or follow a skill's instructions until it has been loaded.",
+            'A user may also invoke a skill directly; its <skill_content> block then appears in this conversation. Follow it, and do not call the `skill` tool again for that skill.',
             '</system-reminder>',
           ].join('\n'),
         }],