Greptile Summary

This PR extracts the compaction delegation logic from LegacyContextEngine.compact() into a standalone delegateCompactionToRuntime(...) helper, exports it from openclaw/plugin-sdk, refactors the legacy engine to call it, and tightens documentation around ownsCompaction semantics.

Key changes:

• src/context-engine/delegate.ts — new file containing the extracted bridge; logic is an exact copy of the removed LegacyContextEngine.compact() body, so behavior is unchanged
• src/context-engine/legacy.ts — 40-line inline impl replaced with a single delegateCompactionToRuntime(params) call
• src/plugin-sdk/core.ts and src/plugin-sdk/index.ts — export the new helper on both SDK entrypoints
• Docs (compaction.md, context-engine.md, context.md, plugin.md) — clarify that ownsCompaction: false is not an automatic fallback and that non-owning engines must still implement compact() by delegating explicitly
• Tests — new focused test verifies the helper and the existing legacy test still passes

One minor point to consider: params.compactionTarget ("budget" | "threshold") is received by delegateCompactionToRuntime as part of the ContextEngine.compact() signature but is silently not forwarded to compactEmbeddedPiSessionDirect (which has no such field in CompactEmbeddedPiSessionParams). This is correct and preserves pre-existing LegacyContextEngine behavior, but since delegateCompactionToRuntime is now a public API, a brief JSDoc note would prevent confusion for third-party plugin authors who pass compactionTarget and expect it to be honored.

Confidence Score: 5/5

• Safe to merge — the refactoring is a faithful extraction with no behavior changes, the tests pass, and the documentation improvements are accurate.
• The entire delegate.ts implementation is a verbatim copy of the removed LegacyContextEngine.compact() body, so there is zero risk of behavioral regression. Export paths are correctly wired in both SDK entrypoints, tests cover the new helper directly, and the documentation changes close a real semantic gap around ownsCompaction. The only note is a missing JSDoc clarification about compactionTarget not being forwarded, which is a documentation suggestion rather than a correctness concern.
• No files require special attention.

This is a comment left during a code review.
Path: src/context-engine/delegate.ts
Line: 31-40

Comment:
**`compactionTarget` silently dropped without documentation**

`params.compactionTarget` is part of the `ContextEngine.compact()` interface (as `"budget" | "threshold"`), but it is not forwarded to `compactEmbeddedPiSessionDirect` — which doesn't have that field in `CompactEmbeddedPiSessionParams`. This is intentional and consistent with the original `LegacyContextEngine` behavior.

However, since `delegateCompactionToRuntime` is now a **public API** for third-party plugin authors, the silent discard of `compactionTarget` is not obvious. A caller who passes `compactionTarget` via their `compact()` params would reasonably expect it to be honored.

Consider adding a note to the JSDoc to make this explicit:

```ts
/**
 * ...
 *
 * Note: `compactionTarget` from the compact params is not forwarded to the
 * runtime bridge — the underlying runtime does not expose this knob via this
 * path. If you need compaction-target control, implement your own `compact()`
 * algorithm.
 */
```

How can I resolve this? If you propose a fix, please make it concise.

_{Last reviewed commit: 18f3de8}

Hi @jalehman ,

Thanks for taking the time to clarify the semantics of ownsCompaction: false and for providing an official compaction delegation path.

I think this is a very meaningful improvement to the contextEngine plugin model. It removes a lot of ambiguity for plugin authors and makes the non-owning / delegating mode much more practical for plugins that want to focus on long-term memory, retrieval augmentation, or other context-management behavior without having to implement their own compaction algorithm.

I believe this will help the OpenClaw context-engine ecosystem become both more mature and more vibrant over time.