Add Opus 4.8 migration guide and model updates to claude-api skill (#1216)

* Add Managed Agents self-hosted sandboxes + mid-session agent updates + MCP tool-output offload to claude-api skill

Self-hosted sandboxes: new shared/managed-agents-self-hosted-sandboxes.md for config:{type:"self_hosted"} — agent loop on Anthropic's orchestration, tool execution on customer infra via outbound-polling worker. Covers EnvironmentWorker.run()/.run_one() (Py/TS), ant beta:worker poll/run, mid-level work.poller()/WorkPoller (Py/TS/Go only; Go has no auto_stop opt-out), AgentToolContext/beta_agent_toolset/tool_runner(), monitoring (environments.work.stats/stop — x-api-key, call from outside worker host), runtime deps, cloud-vs-self_hosted delta table, credentials, security ownership split. Cross-refs in environments.md, overview.md (Reading Guide + rewrote cloud-only pitfall), api-reference.md (SDK row + naming-quirks + schema + work REST rows), tools.md (Who-runs-it carve-out), onboarding.md, live-sources.md.

Mid-session agent updates: sessions.update(session_id, agent={tools, mcp_servers}, vault_ids=[...]) — session-local override (doesn't bump agent version), full-replacement semantics, session must be idle. New core.md section + pointers in tools.md, api-reference.md (UpdateSession row), overview.md.

Large MCP tool outputs → files: >100K tokens → automatic offload to sandbox file; agent gets truncated preview + path. Plus: invalid vault credentials don't block sessions.create() — session.error event fires, auth retries on next idle→running. Both in tools.md.

* Point ant CLI install ref to live-sources.md (OSS has no anthropic-cli.md)

* Add Opus 4.8 model migration guide to claude-api skill

* Add prescriptive tool-description guidance for Opus 4.8 to claude-api skill

skills/claude-api/curl/examples.md

@@ -18,7 +18,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-7",
+    "model": "claude-opus-4-8",
     "max_tokens": 16000,
     "messages": [
       {"role": "user", "content": "What is the capital of France?"}
@@ -38,7 +38,7 @@ response=$(curl -s 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-4-7","max_tokens":16000,"messages":[{"role":"user","content":"Hello"}]}')
+  -d '{"model":"claude-opus-4-8","max_tokens":16000,"messages":[{"role":"user","content":"Hello"}]}')
 
 # Print the first text block (-r strips the JSON quotes)
 echo "$response" | jq -r '.content[0].text'
@@ -65,7 +65,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-7",
+    "model": "claude-opus-4-8",
     "max_tokens": 64000,
     "stream": true,
     "messages": [{"role": "user", "content": "Write a haiku"}]
@@ -104,7 +104,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-7",
+    "model": "claude-opus-4-8",
     "max_tokens": 16000,
     "tools": [{
       "name": "get_weather",
@@ -129,7 +129,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-7",
+    "model": "claude-opus-4-8",
     "max_tokens": 16000,
     "tools": [{
       "name": "get_weather",
@@ -167,7 +167,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-7",
+    "model": "claude-opus-4-8",
     "max_tokens": 16000,
     "system": [
       {"type": "text", "text": "<large shared prompt...>", "cache_control": {"type": "ephemeral"}}
@@ -182,17 +182,17 @@ For 1-hour TTL: `"cache_control": {"type": "ephemeral", "ttl": "1h"}`. Top-level
 
 ## Extended Thinking
 
-> **Opus 4.7, Opus 4.6, and Sonnet 4.6:** Use adaptive thinking. `budget_tokens` is removed on Opus 4.7 (400 if sent); deprecated on Opus 4.6 and Sonnet 4.6.
+> **Opus 4.8, Opus 4.7, Opus 4.6, and Sonnet 4.6:** Use adaptive thinking. `budget_tokens` is removed on Opus 4.8 and 4.7 (400 if sent); deprecated on Opus 4.6 and Sonnet 4.6.
 > **Older models:** Use `"type": "enabled"` with `"budget_tokens": N` (must be < `max_tokens`, min 1024).
 
 ```bash
-# Opus 4.7 / 4.6: adaptive thinking (recommended)
+# Opus 4.8 / 4.7 / 4.6: adaptive thinking (recommended)
 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-4-7",
+    "model": "claude-opus-4-8",
     "max_tokens": 16000,
     "thinking": {
       "type": "adaptive"