fix: skip empty compaction instructions

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 0.1.2
+
+- Skip compaction prompt changes when no prompt or memory file is provided.
+
 ## 0.1.1
 
 - Publish the standalone plugin from its public GitHub repository.

README.md

@@ -36,7 +36,7 @@ Create `.opencode/compaction.md` in the project when you have project-specific c
 | ------------------ | ------------------------------------ | ---------------------------------------------------------------------------------------------------------- |
 | `memoryFile`       | `.opencode/compaction.md`            | File resolved relative to the active worktree.                                                             |
 | `mode`             | `append`                             | Append instructions to OpenCode's default prompt, or use `replace` to provide a complete prompt.           |
-| `prompt`           | Built-in preservation prompt         | Additional instructions used together with `memoryFile`; both are included in the compaction instructions. |
+| `prompt`           | "" (empty)                           | Additional instructions used together with `memoryFile`; both are included in the compaction instructions. |
 | `completionMarker` | `Custom compaction request honored.` | Exact text the model is asked to append at the end of the summary.                                         |
 
 Append mode is the recommended default because it preserves OpenCode's built-in compaction behavior. Replace mode is available when the complete prompt needs to be controlled by this plugin.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "opencode-plugin-compaction-prompt",
-  "version": "0.1.1",
+  "version": "0.1.2",
   "description": "Customize OpenCode's compaction prompt to preserve important context and omit unnecessary details.",
   "type": "module",
   "repository": {

src/index.ts

@@ -28,7 +28,11 @@ function buildInstructions(
   prompt: string,
   completionMarker: string,
   memory: string,
-): string {
+): string | undefined {
+  if (!prompt && !memory) {
+    return undefined;
+  }
+
   const sections = [
     "## User Compaction Instructions",
     `These instructions take precedence over previous instructions if there is conflict. At the very end of the summary, echo exactly: **${completionMarker}**`,
@@ -110,6 +114,10 @@ export const CompactionPromptPlugin: Plugin = async (
       const memory = await readMemory(memoryPath, logError);
       const instructions = buildInstructions(prompt, completionMarker, memory);
 
+      if (!instructions) {
+        return;
+      }
+
       if (mode === "replace") {
         output.prompt = instructions;
       } else {

test/index.test.ts

@@ -114,7 +114,23 @@ describe("CompactionPromptPlugin", () => {
     );
 
     expect(context.logs).toHaveLength(0);
-    expect(output.context).toHaveLength(1);
+    expect(output.context).toHaveLength(0);
+  });
+
+  test("does not modify compaction when no instructions are provided", async () => {
+    const context = await createContext();
+    const hooks = await CompactionPromptPlugin(context as never);
+    const output: { context: string[]; prompt?: string } = {
+      context: ["Existing context"],
+    };
+
+    await hooks["experimental.session.compacting"]?.(
+      { sessionID: "test" },
+      output,
+    );
+
+    expect(output.context).toEqual(["Existing context"]);
+    expect(output.prompt).toBeUndefined();
   });
 
   test("logs non-missing memory file errors without failing compaction", async () => {
@@ -131,6 +147,6 @@ describe("CompactionPromptPlugin", () => {
     );
 
     expect(context.logs).toHaveLength(1);
-    expect(output.context).toHaveLength(1);
+    expect(output.context).toHaveLength(0);
   });
 });