chore: update claude-api skill [auto-sync] (#730)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

skills/claude-api/curl/examples.md

@@ -157,6 +157,29 @@ curl https://api.anthropic.com/v1/messages \
 
 ---
 
+## Prompt Caching
+
+Put `cache_control` on the last block of the stable prefix. See `shared/prompt-caching.md` for placement patterns and the silent-invalidator audit checklist.
+
+```bash
+curl https://api.anthropic.com/v1/messages \
+  -H "Content-Type: application/json" \
+  -H "x-api-key: $ANTHROPIC_API_KEY" \
+  -H "anthropic-version: 2023-06-01" \
+  -d '{
+    "model": "claude-opus-4-6",
+    "max_tokens": 16000,
+    "system": [
+      {"type": "text", "text": "<large shared prompt...>", "cache_control": {"type": "ephemeral"}}
+    ],
+    "messages": [{"role": "user", "content": "Summarize the key points"}]
+  }'
+```
+
+For 1-hour TTL: `"cache_control": {"type": "ephemeral", "ttl": "1h"}`. Top-level `"cache_control"` on the request body auto-places on the last cacheable block. Verify hits via the response `usage.cache_creation_input_tokens` / `usage.cache_read_input_tokens` fields.
+
+---
+
 ## Extended Thinking
 
 > **Opus 4.6 and Sonnet 4.6:** Use adaptive thinking. `budget_tokens` is deprecated on both Opus 4.6 and Sonnet 4.6.