chore(changelog): note prompt cache stability fix

CHANGELOG.md

@@ -36,6 +36,7 @@ Docs: https://docs.openclaw.ai
 - Gateway/Daemon: forward `TMPDIR` into installed service environments so macOS LaunchAgent gateway runs can open SQLite temp/journal files reliably instead of failing with `SQLITE_CANTOPEN`. (#20512) Thanks @Clawborn.
 - Agents/Billing: include the active model that produced a billing error in user-facing billing messages (for example, `OpenAI (gpt-5.3)`) across payload, failover, and lifecycle error paths, so users can identify exactly which key needs credits. (#20510) Thanks @echoVic.
 - Gateway/TUI: honor `agents.defaults.blockStreamingDefault` for `chat.send` by removing the hardcoded block-streaming disable override, so replies can use configured block-mode delivery. (#19693) Thanks @neipor.
+- Auto-reply/Prompt caching: restore prefix-cache stability by keeping inbound system metadata session-stable and moving per-message IDs (`message_id`, `message_id_full`, `reply_to_id`, `sender_id`) into untrusted conversation context. (#20597) Thanks @anisoptera.
 - UI/Sessions: accept the canonical main session-key alias in Chat UI flows so main-session routing stays consistent. (#20311) Thanks @mbelinky.
 - OpenClawKit/Protocol: preserve JSON boolean literals (`true`/`false`) when bridging through `AnyCodable` so Apple client RPC params no longer re-encode booleans as `1`/`0`. Thanks @mbelinky.
 - Commands/Doctor: skip embedding-provider warnings when `memory.backend` is `qmd`, because QMD manages embeddings internally and does not require `memorySearch` providers. (#17263) Thanks @miloudbelarebia.