fix(openrouter): allow DeepSeek cache-ttl eligibility

docs/reference/prompt-caching.md

@@ -123,7 +123,7 @@ Per-agent heartbeat is supported at `agents.list[].heartbeat`.
 - Anthropic Claude model refs (`amazon-bedrock/*anthropic.claude*`) support explicit `cacheRetention` pass-through.
 - Non-Anthropic Bedrock models are forced to `cacheRetention: "none"` at runtime.
 
-### OpenRouter Anthropic models
+### OpenRouter models
 
 For `openrouter/anthropic/*` model refs, OpenClaw injects Anthropic
 `cache_control` on system/developer prompt blocks to improve prompt-cache
@@ -131,6 +131,11 @@ reuse only when the request is still targeting a verified OpenRouter route
 (`openrouter` on its default endpoint, or any provider/base URL that resolves
 to `openrouter.ai`).
 
+For `openrouter/deepseek/*`, `openrouter/moonshot*/*`, and `openrouter/zai/*`
+model refs, `contextPruning.mode: "cache-ttl"` is allowed because OpenRouter
+handles provider-side prompt caching automatically. OpenClaw does not inject
+Anthropic `cache_control` markers into those requests.
+
 If you repoint the model at an arbitrary OpenAI-compatible proxy URL, OpenClaw
 stops injecting those OpenRouter-specific Anthropic cache markers.