add missing instruction

Co-authored-by: akenra <37288280+akenra@users.noreply.github.com>

packages/core/src/plugin/agent.ts

@@ -30,15 +30,11 @@ Guidelines:
 
 Complete the user's search request efficiently and report your findings clearly.`
 
-const PROMPT_COMPACTION = `You are an anchored context summarization assistant for coding sessions.
-
-Summarize only the conversation history you are given. The newest turns may be kept verbatim outside your summary, so focus on the older context that still matters for continuing the work.
-
-If the prompt includes a <previous-summary> block, treat it as the current anchored summary. Update it with the new history by preserving still-true details, removing stale details, and merging in new facts.
+const PROMPT_COMPACTION = `You are a context summarization agent. You are given a conversation between a user and an agent. Your goal is to produce a structured summary matching the format specified so another coding agent can continue the work.
 
 Always follow the exact output structure requested by the user prompt. Keep every section, preserve exact file paths and identifiers when known, and prefer terse bullets over paragraphs.
 
-Do not answer the conversation itself. Do not mention that you are summarizing, compacting, or merging context. Respond in the same language as the conversation.`
+Do not continue the conversation. Do not respond to any questions in the conversation. Only output the structured summary in the exact format requested by the user prompt. Respond in the same language as the conversation.`
 
 const PROMPT_TITLE = `You are a title generator. You output ONLY a thread title. Nothing else.
 

packages/core/src/session/compaction.ts

@@ -44,6 +44,14 @@ Rules:
 - Use terse bullets, not prose paragraphs.
 - Preserve exact file paths, symbols, commands, error strings, URLs, and identifiers when known.
 - Do not mention the summary process or that context was compacted.`
+const SUMMARY_UPDATE_INSTRUCTIONS = `Update the existing anchored summary with the new information.
+
+When updating:
+- Preserve all information from the <prior-summary> unless the new conversation shows that it is inaccurate, superseded, or no longer applicable.
+- Add new progress, decisions, constraints, and context from the conversation.
+- Move completed work from "Active" to "Completed".
+- If a blocker has been resolved, update the summary to reflect that while keeping any details still needed to continue the work.
+- Update "Objective" and "Next Move" to reflect the current work state.`
 
 type Entry = {
   readonly seq: number
@@ -158,14 +166,22 @@ const select = (
   }
 }
 
-export const buildPrompt = (input: { readonly previousSummary?: string; readonly context: readonly string[] }) =>
-  [
-    input.previousSummary
-      ? `Update the anchored summary below using the conversation history above.\nPreserve still-true details, remove stale details, and merge in the new facts.\n<previous-summary>\n${input.previousSummary}\n</previous-summary>`
-      : "Create a new anchored summary from the conversation history.",
+export const buildPrompt = (input: { readonly previousSummary?: string; readonly context: readonly string[] }) => {
+  const conversation = `Here is the conversation so far:\n\n<conversation>\n${input.context.join("\n\n")}\n</conversation>`
+  if (!input.previousSummary)
+    return [
+      conversation,
+      "Create a new anchored summary from the conversation history in the <conversation> tags above so another coding agent can continue the work.",
+      SUMMARY_TEMPLATE,
+    ].join("\n\n")
+  return [
+    conversation,
+    `Here is the previous summary:\n\n<prior-summary>\n${input.previousSummary}\n</prior-summary>`,
+    "The <conversation> tags above contain new conversation history to incorporate into the existing summary in the <prior-summary> tags.",
+    SUMMARY_UPDATE_INSTRUCTIONS,
     SUMMARY_TEMPLATE,
-    ...input.context,
   ].join("\n\n")
+}
 
 export const make = (dependencies: Dependencies) => {
   const config = settings(dependencies.config)

packages/core/test/session-compaction.test.ts

@@ -4,12 +4,33 @@ import { SessionCompaction } from "@opencode-ai/core/session/compaction"
 test("compaction prompt preserves detailed work state and relevant files", () => {
   const prompt = SessionCompaction.buildPrompt({ context: ["conversation history"] })
 
+  expect(prompt).toStartWith(
+    "Here is the conversation so far:\n\n<conversation>\nconversation history\n</conversation>",
+  )
+  expect(prompt.indexOf("</conversation>")).toBeLessThan(prompt.indexOf("Create a new anchored summary"))
+  expect(prompt).toContain("conversation history in the <conversation> tags above")
   expect(prompt).toContain("## Work State\n### Completed")
   expect(prompt).toContain("### Active")
   expect(prompt).toContain("### Blocked")
   expect(prompt).toContain("## Relevant Files")
 })
 
+test("compaction prompt gives explicit update instructions for a prior summary", () => {
+  const prompt = SessionCompaction.buildPrompt({
+    context: ["new conversation"],
+    previousSummary: "existing summary",
+  })
+
+  expect(prompt.indexOf("<conversation>")).toBeLessThan(prompt.indexOf("<prior-summary>"))
+  expect(prompt.indexOf("<prior-summary>")).toBeLessThan(prompt.indexOf("When updating:"))
+  expect(prompt).toContain(
+    "Preserve all information from the <prior-summary> unless the new conversation shows that it is inaccurate, superseded, or no longer applicable.",
+  )
+  expect(prompt).toContain(
+    "If a blocker has been resolved, update the summary to reflect that while keeping any details still needed to continue the work.",
+  )
+})
+
 test("compaction describes tool media without embedding base64", () => {
   const base64 = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAAB"
   const serialized = SessionCompaction.serializeToolContent([

packages/core/test/session-runner.test.ts

@@ -1135,7 +1135,7 @@ describe("SessionRunnerLLM", () => {
 
       expect(requests).toHaveLength(2)
       expect(userTexts(requests[0])[0]).toContain(
-        "<previous-summary>\n## Objective\n- Preserve the task\n</previous-summary>",
+        "<prior-summary>\n## Objective\n- Preserve the task\n</prior-summary>",
       )
       expect(userTexts(requests[0])[0]).toContain("Recent exact request")
       expect((yield* (yield* SessionStore.Service).context(sessionID))[0]).toMatchObject({

packages/opencode/src/agent/prompt/compaction.txt

@@ -1,9 +1,5 @@
-You are an anchored context summarization assistant for coding sessions.
-
-Summarize only the conversation history you are given. The newest turns may be kept verbatim outside your summary, so focus on the older context that still matters for continuing the work.
-
-If the prompt includes a <previous-summary> block, treat it as the current anchored summary. Update it with the new history by preserving still-true details, removing stale details, and merging in new facts.
+You are a context summarization agent. You are given a conversation between a user and an agent. Your goal is to produce a structured summary matching the format specified so another coding agent can continue the work.
 
 Always follow the exact output structure requested by the user prompt. Keep every section, preserve exact file paths and identifiers when known, and prefer terse bullets over paragraphs.
 
-Do not answer the conversation itself. Do not mention that you are summarizing, compacting, or merging context. Respond in the same language as the conversation.
+Do not continue the conversation. Do not respond to any questions in the conversation. Only output the structured summary in the exact format requested by the user prompt. Respond in the same language as the conversation.

packages/opencode/src/session/compaction.ts

@@ -381,10 +381,20 @@ const layer = Layer.effect(
         { sessionID: input.sessionID },
         { context: [], prompt: undefined },
       )
-      const nextPrompt = compacting.prompt ?? buildPrompt({ previousSummary, context: compacting.context })
       const msgs = structuredClone(selected.head)
       yield* plugin.trigger("experimental.chat.messages.transform", {}, { messages: msgs })
       const conversation = msgs.map(serialize).filter(Boolean).join("\n\n")
+      const nextPrompt =
+        compacting.prompt ??
+        [
+          buildPrompt({
+            previousSummary,
+            context: [conversation],
+          }),
+          ...compacting.context,
+        ]
+          .filter(Boolean)
+          .join("\n\n")
       const ctx = yield* InstanceState.context
       const msg: SessionV1.Assistant = {
         id: MessageID.ascending(),
@@ -430,7 +440,10 @@ const layer = Layer.effect(
             content: [
               {
                 type: "text",
-                text: [nextPrompt, "The following is the conversation history:", conversation]
+                text: [
+                  nextPrompt,
+                  ...(compacting.prompt ? ["The following is the conversation history:", conversation] : []),
+                ]
                   .filter(Boolean)
                   .join("\n\n"),
               },

packages/opencode/test/session/compaction.test.ts

@@ -365,6 +365,20 @@ function autocontinue(enabled: boolean) {
   })
 }
 
+function compactionContext(context: string) {
+  return Layer.mock(Plugin.Service)({
+    trigger: <Name extends string, Input, Output>(name: Name, _input: Input, output: Output) => {
+      if (name !== "experimental.session.compacting") return Effect.succeed(output)
+      return Effect.sync(() => {
+        ;(output as { context: string[] }).context.push(context)
+        return output
+      })
+    },
+    list: () => Effect.succeed([]),
+    init: () => Effect.void,
+  })
+}
+
 describe("session.compaction.isOverflow", () => {
   it.live(
     "returns true when token count exceeds usable context",
@@ -1389,6 +1403,11 @@ describe("session.compaction.process", () => {
         const captured = JSON.stringify(messages)
         expect(messages).toHaveLength(1)
         expect(messages[0]?.role).toBe("user")
+        expect(captured).toContain("Here is the conversation so far:")
+        expect(captured).toContain("<conversation>")
+        expect(captured.indexOf("[User]: older context")).toBeLessThan(
+          captured.indexOf("Create a new anchored summary"),
+        )
         expect(captured).toContain("[User]: older context")
         expect(captured).not.toContain("keep this turn")
         expect(captured).not.toContain("and this one too")
@@ -1430,9 +1449,11 @@ describe("session.compaction.process", () => {
         expect(parent).toBeTruthy()
         yield* SessionCompaction.use.process({ parentID: parent!, messages: msgs, sessionID: session.id, auto: false })
 
-        expect(captured).toContain("<previous-summary>")
+        expect(captured).toContain("<prior-summary>")
         expect(captured).toContain("summary one")
         expect(captured.match(/summary one/g)?.length).toBe(1)
+        expect(captured.indexOf("latest turn")).toBeLessThan(captured.indexOf("Here is the previous summary:"))
+        expect(captured).toContain("existing summary in the <prior-summary> tags")
         expect(captured).toContain("## Important Details")
         expect(captured).toContain("## Work State")
       }).pipe(withCompaction({ llm: stub.llmLayer }))
@@ -1440,6 +1461,49 @@ describe("session.compaction.process", () => {
     { git: true },
   )
 
+  itCompaction.instance(
+    "keeps plugin context outside the serialized conversation",
+    () => {
+      const stub = llm()
+      let captured = ""
+      stub.push(
+        reply("summary", (input) => {
+          captured = JSON.stringify(input.messages)
+        }),
+      )
+
+      return Effect.gen(function* () {
+        const ssn = yield* SessionNs.Service
+        const session = yield* ssn.create({})
+        yield* createUserMessage(session.id, "older context")
+        yield* createUserMessage(session.id, "keep this turn")
+        yield* createUserMessage(session.id, "and this one too")
+        yield* createCompactionMarker(session.id)
+
+        const msgs = yield* ssn.messages({ sessionID: session.id })
+        const parent = msgs.at(-1)?.info.id
+        expect(parent).toBeTruthy()
+        yield* SessionCompaction.use.process({
+          parentID: parent!,
+          messages: msgs,
+          sessionID: session.id,
+          auto: false,
+        })
+
+        expect(captured).toContain("Prioritize unresolved migration details")
+        expect(captured.indexOf("</conversation>")).toBeLessThan(
+          captured.indexOf("Prioritize unresolved migration details"),
+        )
+      }).pipe(
+        withCompaction({
+          llm: stub.llmLayer,
+          plugin: compactionContext("Prioritize unresolved migration details"),
+        }),
+      )
+    },
+    { git: true },
+  )
+
   itCompaction.instance(
     "serializes repeated compaction history as one user message",
     () => {