fix(client): add system text to compaction and generate requests

CHANGELOG.md

@@ -6,6 +6,16 @@ All notable changes to this project are documented here. The format follows
 
 ## [Unreleased]
 
+### Fixed
+
+- **Compaction and warming keep the prompt cache on OpenCode 2.** Review, Shell and Trail added
+  their system text to the conversation's requests only, through the session `context` hook.
+  OpenCode 2 builds compaction and `generate` (warming) requests through their own hooks, so those
+  went out with a shorter system block — 4 parts where the conversation had 9 — and the provider
+  wrote the whole conversation to its cache again instead of reading it. The same text is now added
+  on all three hooks; a compaction's system block matches the conversation's exactly. Reported in
+  #53.
+
 ## [0.11.1] - 2026-10-17
 
 ### Added

packages/client/src/opencode/server/index.ts

@@ -309,9 +309,14 @@ export function dualServer(id: string, start: ServerStart) {
       }
       if (parts.system) {
         const system = parts.system
-        await ctx.session.hook("context", async (event) => {
+        /**
+         * Every request kind gets the same text: a compaction or warming request whose system part
+         * differs from the conversation's misses the provider's prompt cache and prefills it again.
+         */
+        const add = async (event: { sessionID: string; system: unknown[] }) => {
           for (const text of await system(event.sessionID)) event.system.push({ type: "text", text })
-        })
+        }
+        for (const kind of ["context", "compaction", "generate"] as const) await ctx.session.hook(kind, add)
       }
       const stop = new AbortController()
       if (parts.sessionDeleted || parts.event) {

packages/client/src/opencode/server/v2.ts

@@ -39,7 +39,11 @@ export interface V2ServerContext {
     prompt?(input: { sessionID: string; text: string; delivery?: "steer" | "queue" }): Promise<unknown>
     /** A session's messages as the model is given them (2.0.15). */
     context?(input: { sessionID: string }): Promise<unknown[]>
-    hook(name: "context", run: (event: { sessionID: string; system: unknown[] }) => unknown): Promise<unknown>
+    /** One hook per request kind: `context` is the primary request only, not compaction or `generate`. */
+    hook(
+      name: "context" | "compaction" | "generate",
+      run: (event: { sessionID: string; system: unknown[] }) => unknown,
+    ): Promise<unknown>
   }
   event: { subscribe(options: { signal: AbortSignal }): AsyncIterable<V2Event> }
 }

packages/client/test/server.test.ts

@@ -179,7 +179,7 @@ function fakeV2(events: { type: string; data?: { sessionID?: string } }[] = [],
   const skills: { id: string; path: string }[] = []
   const commands: { name: string; execute(input: unknown): Promise<void> }[] = []
   const prompts: unknown[] = []
-  let context: ((event: { sessionID: string; system: unknown[] }) => unknown) | undefined
+  const runs = new Map<string, (event: { sessionID: string; system: unknown[] }) => unknown>()
   const ctx = {
     options: {},
     location: { directory },
@@ -205,9 +205,9 @@ function fakeV2(events: { type: string; data?: { sessionID?: string } }[] = [],
       get: async () => undefined,
       synthetic: async () => undefined,
       prompt: async (input: unknown) => void prompts.push(input),
-      hook: async (name: string, run: typeof context) => {
+      hook: async (name: string, run: (event: { sessionID: string; system: unknown[] }) => unknown) => {
         hooks.push(name)
-        context = run
+        runs.set(name, run)
       },
     },
     event: {
@@ -216,7 +216,7 @@ function fakeV2(events: { type: string; data?: { sessionID?: string } }[] = [],
       },
     },
   }
-  return { ctx, added, hooks, skills, commands, prompts, system: () => context }
+  return { ctx, added, hooks, skills, commands, prompts, system: (kind = "context") => runs.get(kind) }
 }
 
 describe("one entry for both", () => {
@@ -231,7 +231,7 @@ describe("one entry for both", () => {
     expect(started).toBe(false)
   })
 
-  test("v2's setup registers the tools, the context hook, and follows deleted sessions", async () => {
+  test("v2's setup registers the tools, the request hooks, and follows deleted sessions", async () => {
     const deleted: string[] = []
     let disposed = false
     const fake = fakeV2([{ type: "session.idle" }, { type: "session.deleted", data: { sessionID: "ses_9" } }])
@@ -249,10 +249,13 @@ describe("one entry for both", () => {
     })
     const cleanup = await entry.setup(fake.ctx as never)
     expect(fake.added).toContain("echo")
-    expect(fake.hooks).toEqual(["context"])
-    const event = { sessionID: "ses_1", system: [] as unknown[] }
-    await fake.system()?.(event)
-    expect(event.system).toEqual([{ type: "text", text: "guidance for ses_1" }])
+    /** Compaction and warming carry the same system text, or they miss the prompt cache. */
+    expect(fake.hooks).toEqual(["context", "compaction", "generate"])
+    for (const kind of fake.hooks) {
+      const event = { sessionID: "ses_1", system: [] as unknown[] }
+      await fake.system(kind)?.(event)
+      expect(event.system).toEqual([{ type: "text", text: "guidance for ses_1" }])
+    }
     await Bun.sleep(0)
     expect(deleted).toEqual(["ses_9"])
     await cleanup?.()