compaction: extract buildIdentityReinforcement helper

ESRE-dev · ESRE-dev · commit 49700133b6bb · 2026-04-23T14:43:27.000+02:00
* Extract inline system-reminder ternary into a
      named, exported buildIdentityReinforcement()
      function that constructs identity reinforcement
      XML from agent name and definition
    * Include agent description (or "a specialized
      agent" fallback) and behavioral constraints in
      the reminder to strengthen post-compaction role
      anchoring beyond the previous generic message
    * Add 7 unit tests covering Properties 1-5 and 10:
      custom agent with description, fallback for
      missing/empty description, native agent exclusion,
      undefined source safety, no-prompt agent, and
      return type verification
    * Bead opencode-x10.1 — passed all 3 judges on
      first review cycle
diff --git a/packages/opencode/src/session/compaction.ts b/packages/opencode/src/session/compaction.ts
@@ -56,6 +56,12 @@ export interface Interface {
 
 export class Service extends Context.Service<Service, Interface>()("@opencode/SessionCompaction") {}
 
+export function buildIdentityReinforcement(agentName: string, source: Agent.Info | undefined): string | undefined {
+  if (!source?.prompt || source?.native) return undefined
+  const description = source?.description || "a specialized agent"
+  return `<system-reminder>\nYou are the "${agentName}" agent.\nRole: ${description}\nYour role and constraints from your system prompt still apply after this compaction.\nContinue performing your designated role. Do not switch to code implementation or deviate from your assigned responsibilities.\n</system-reminder>`
+}
+
 export const layer: Layer.Layer<
   Service,
   never,
@@ -222,8 +228,7 @@ When constructing the summary, try to stick to this template:
       const system: string[] = []
       if (source?.prompt) {
         const max = 4000
-        const truncated =
-          source.prompt.length > max ? source.prompt.slice(0, max) + "\n[...truncated]" : source.prompt
+        const truncated = source.prompt.length > max ? source.prompt.slice(0, max) + "\n[...truncated]" : source.prompt
         system.push(truncated)
       }
       const msgs = structuredClone(messages)
@@ -314,10 +319,7 @@ When constructing the summary, try to stick to this template:
 
       if (result === "continue" && input.auto) {
         // Inject post-compaction agent identity reminder for specialized agents
-        const reminder =
-          source?.prompt && !source?.native
-            ? `<system-reminder>You are the "${userMessage.agent}" agent. Your role and constraints from your system prompt still apply after this compaction. Do not deviate from your assigned role.</system-reminder>`
-            : undefined
+        const reminder = buildIdentityReinforcement(userMessage.agent, source)
         if (replay) {
           const original = replay.info
           const replayMsg = yield* session.updateMessage({
diff --git a/packages/opencode/test/session/compaction.test.ts b/packages/opencode/test/session/compaction.test.ts
@@ -7,7 +7,7 @@ import { Bus } from "../../src/bus"
 import { Config } from "../../src/config"
 import { Agent } from "../../src/agent/agent"
 import { LLM } from "../../src/session/llm"
-import { SessionCompaction } from "../../src/session/compaction"
+import { SessionCompaction, buildIdentityReinforcement } from "../../src/session/compaction"
 import { Token } from "../../src/util"
 import { Instance } from "../../src/project/instance"
 import { Log } from "../../src/util"
@@ -1828,3 +1828,63 @@ describe("session.compaction.agentAware", () => {
     })
   })
 })
+
+describe("buildIdentityReinforcement", () => {
+  function makeAgent(overrides: Partial<Agent.Info> = {}): Agent.Info {
+    return {
+      name: "test-agent",
+      mode: "primary",
+      permission: [],
+      options: {},
+      ...overrides,
+    }
+  }
+
+  test("custom agent with description returns reinforcement containing name and description", () => {
+    const source = makeAgent({ prompt: "You are a reviewer", description: "a code review specialist", native: false })
+    const result = buildIdentityReinforcement("reviewer", source)
+    expect(result).toBeDefined()
+    expect(result).toContain("reviewer")
+    expect(result).toContain("a code review specialist")
+    expect(result).toContain("<system-reminder>")
+    expect(result).toContain("</system-reminder>")
+  })
+
+  test("custom agent without description falls back to generic description", () => {
+    const source = makeAgent({ prompt: "You are a reviewer", native: false })
+    const result = buildIdentityReinforcement("reviewer", source)
+    expect(result).toBeDefined()
+    expect(result).toContain("reviewer")
+    expect(result).toContain("a specialized agent")
+  })
+
+  test("custom agent with empty description falls back to generic description", () => {
+    const source = makeAgent({ prompt: "You are a reviewer", description: "", native: false })
+    const result = buildIdentityReinforcement("reviewer", source)
+    expect(result).toBeDefined()
+    expect(result).toContain("a specialized agent")
+  })
+
+  test("native agent returns undefined", () => {
+    const source = makeAgent({ prompt: "Built-in prompt", native: true })
+    const result = buildIdentityReinforcement("build", source)
+    expect(result).toBeUndefined()
+  })
+
+  test("undefined source returns undefined without throwing", () => {
+    const result = buildIdentityReinforcement("ghost", undefined)
+    expect(result).toBeUndefined()
+  })
+
+  test("agent without prompt returns undefined", () => {
+    const source = makeAgent({ native: false })
+    const result = buildIdentityReinforcement("reviewer", source)
+    expect(result).toBeUndefined()
+  })
+
+  test("returns plain string, not modifying system prompt inputs", () => {
+    const source = makeAgent({ prompt: "You are a reviewer", description: "reviewer role", native: false })
+    const result = buildIdentityReinforcement("reviewer", source)
+    expect(typeof result).toBe("string")
+  })
+})
