feat: sharpen compaction memory extraction prompt

Wave 3 of memory quality optimization plan.

- Add good memory examples in buildCompactionPrompt()
- Add bad memory examples to skip (test counts, commit hashes, etc.)
- Add prompt assertions in tests to prevent regression
- Emphasize 'useful if a new agent opens this workspace next week'

src/plugin.ts

@@ -114,6 +114,22 @@ function buildCompactionPrompt(privateContext: string): string {
     "",
     "When unsure, skip it. Fewer high-signal memories are better than many low-value ones.",
     "",
+    "Good memory examples:",
+    "- [feedback] User prefers architecture reviews in Traditional Chinese.",
+    "- [decision] Use frozen workspace memory snapshots plus ephemeral hot state for cache stability.",
+    "- [project] The plugin should piggyback memory extraction on OpenCode compaction and avoid extra LLM calls.",
+    "- [reference] Workspace memory appears in frozen system[1]; pending memories appear in hot session state until compaction.",
+    "",
+    "Bad memory examples to skip:",
+    "- 42 tests passed.",
+    "- Wave 2 completed successfully.",
+    "- Modified 5 files.",
+    "- commit 4309cb8 contains the latest fix.",
+    "- TypeError: Cannot read properties of undefined.",
+    "- Currently running npm test.",
+    "",
+    "A memory should still be useful if a new agent opens this workspace next week.",
+    "",
     "Only extract facts that are likely to stay true across sessions.",
     "Do not extract session-specific progress like exact test counts, file counts, or phase numbers.",
     "For progress, extract the stable goal or durable milestone, not the current number.",

tests/plugin.test.ts

@@ -275,6 +275,14 @@ test("compaction hook sets output.prompt with ---free template", async () => {
     // Should contain Memory candidates format
     assert.equal(prompt!.includes("Memory candidates:"), true,
       "Prompt should include Memory candidates: label");
+    assert.equal(prompt!.includes("Good memory examples:"), true,
+      "Prompt should include concrete positive memory examples");
+    assert.equal(prompt!.includes("Bad memory examples to skip:"), true,
+      "Prompt should include concrete negative memory examples");
+    assert.equal(prompt!.includes("42 tests passed"), true,
+      "Prompt should explicitly reject test-count snapshots");
+    assert.equal(prompt!.includes("commit 4309cb8"), true,
+      "Prompt should explicitly reject commit-hash snapshots");
 
     // Should contain our context data (hot session state)
     assert.equal(prompt!.includes("Hot session state"), true,