fix(prometheus): prevent agent fallback to build in background tasks (#695)

src/features/claude-code-session-state/state.ts

@@ -9,3 +9,23 @@ export function setMainSession(id: string | undefined) {
 export function getMainSessionID(): string | undefined {
   return mainSessionID
 }
+
+const sessionAgentMap = new Map<string, string>()
+
+export function setSessionAgent(sessionID: string, agent: string): void {
+  if (!sessionAgentMap.has(sessionID)) {
+    sessionAgentMap.set(sessionID, agent)
+  }
+}
+
+export function updateSessionAgent(sessionID: string, agent: string): void {
+  sessionAgentMap.set(sessionID, agent)
+}
+
+export function getSessionAgent(sessionID: string): string | undefined {
+  return sessionAgentMap.get(sessionID)
+}
+
+export function clearSessionAgent(sessionID: string): void {
+  sessionAgentMap.delete(sessionID)
+}

src/features/hook-message-injector/index.ts

@@ -1,4 +1,4 @@
-export { injectHookMessage, findNearestMessageWithFields } from "./injector"
+export { injectHookMessage, findNearestMessageWithFields, findFirstMessageWithAgent } from "./injector"
 export type { StoredMessage } from "./injector"
 export type { MessageMeta, OriginalMessageContext, TextPart } from "./types"
 export { MESSAGE_STORAGE } from "./constants"

src/features/hook-message-injector/injector.ts

@@ -48,6 +48,35 @@ export function findNearestMessageWithFields(messageDir: string): StoredMessage
   return null
 }
 
+/**
+ * Finds the FIRST (oldest) message in the session with agent field.
+ * This is used to get the original agent that started the session,
+ * avoiding issues where newer messages may have a different agent
+ * due to OpenCode's internal agent switching.
+ */
+export function findFirstMessageWithAgent(messageDir: string): string | null {
+  try {
+    const files = readdirSync(messageDir)
+      .filter((f) => f.endsWith(".json"))
+      .sort() // Oldest first (no reverse)
+
+    for (const file of files) {
+      try {
+        const content = readFileSync(join(messageDir, file), "utf-8")
+        const msg = JSON.parse(content) as StoredMessage
+        if (msg.agent) {
+          return msg.agent
+        }
+      } catch {
+        continue
+      }
+    }
+  } catch {
+    return null
+  }
+  return null
+}
+
 function generateMessageId(): string {
   const timestamp = Date.now().toString(16)
   const random = Math.random().toString(36).substring(2, 14)

src/hooks/prometheus-md-only/index.ts

@@ -2,7 +2,8 @@ import type { PluginInput } from "@opencode-ai/plugin"
 import { existsSync, readdirSync } from "node:fs"
 import { join, resolve, relative, isAbsolute } from "node:path"
 import { HOOK_NAME, PROMETHEUS_AGENTS, ALLOWED_EXTENSIONS, ALLOWED_PATH_PREFIX, BLOCKED_TOOLS, PLANNING_CONSULT_WARNING } from "./constants"
-import { findNearestMessageWithFields, MESSAGE_STORAGE } from "../../features/hook-message-injector"
+import { findNearestMessageWithFields, findFirstMessageWithAgent, MESSAGE_STORAGE } from "../../features/hook-message-injector"
+import { getSessionAgent } from "../../features/claude-code-session-state"
 import { log } from "../../shared/logger"
 
 export * from "./constants"
@@ -61,10 +62,14 @@ function getMessageDir(sessionID: string): string | null {
 
 const TASK_TOOLS = ["sisyphus_task", "task", "call_omo_agent"]
 
-function getAgentFromSession(sessionID: string): string | undefined {
+function getAgentFromMessageFiles(sessionID: string): string | undefined {
   const messageDir = getMessageDir(sessionID)
   if (!messageDir) return undefined
-  return findNearestMessageWithFields(messageDir)?.agent
+  return findFirstMessageWithAgent(messageDir) ?? findNearestMessageWithFields(messageDir)?.agent
+}
+
+function getAgentFromSession(sessionID: string): string | undefined {
+  return getSessionAgent(sessionID) ?? getAgentFromMessageFiles(sessionID)
 }
 
 export function createPrometheusMdOnlyHook(ctx: PluginInput) {

src/index.ts

@@ -49,6 +49,8 @@ import { getSystemMcpServerNames } from "./features/claude-code-mcp-loader";
 import {
   setMainSession,
   getMainSessionID,
+  setSessionAgent,
+  clearSessionAgent,
 } from "./features/claude-code-session-state";
 import {
   builtinTools,
@@ -428,11 +430,22 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
           setMainSession(undefined);
         }
         if (sessionInfo?.id) {
+          clearSessionAgent(sessionInfo.id);
           await skillMcpManager.disconnectSession(sessionInfo.id);
           await lspManager.cleanupTempDirectoryClients();
         }
       }
 
+      if (event.type === "message.updated") {
+        const info = props?.info as Record<string, unknown> | undefined;
+        const sessionID = info?.sessionID as string | undefined;
+        const agent = info?.agent as string | undefined;
+        const role = info?.role as string | undefined;
+        if (sessionID && agent && role === "user") {
+          setSessionAgent(sessionID, agent);
+        }
+      }
+
       if (event.type === "session.error") {
         const sessionID = props?.sessionID as string | undefined;
         const error = props?.error;

src/tools/background-task/tools.ts

@@ -4,7 +4,9 @@ import { join } from "node:path"
 import type { BackgroundManager, BackgroundTask } from "../../features/background-agent"
 import type { BackgroundTaskArgs, BackgroundOutputArgs, BackgroundCancelArgs } from "./types"
 import { BACKGROUND_TASK_DESCRIPTION, BACKGROUND_OUTPUT_DESCRIPTION, BACKGROUND_CANCEL_DESCRIPTION } from "./constants"
-import { findNearestMessageWithFields, MESSAGE_STORAGE } from "../../features/hook-message-injector"
+import { findNearestMessageWithFields, findFirstMessageWithAgent, MESSAGE_STORAGE } from "../../features/hook-message-injector"
+import { getSessionAgent } from "../../features/claude-code-session-state"
+import { log } from "../../shared/logger"
 
 type OpencodeClient = PluginInput["client"]
 
@@ -63,6 +65,19 @@ export function createBackgroundTask(manager: BackgroundManager): ToolDefinition
       try {
         const messageDir = getMessageDir(ctx.sessionID)
         const prevMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+        const firstMessageAgent = messageDir ? findFirstMessageWithAgent(messageDir) : null
+        const sessionAgent = getSessionAgent(ctx.sessionID)
+        const parentAgent = ctx.agent ?? sessionAgent ?? firstMessageAgent ?? prevMessage?.agent
+        
+        log("[background_task] parentAgent resolution", {
+          sessionID: ctx.sessionID,
+          ctxAgent: ctx.agent,
+          sessionAgent,
+          firstMessageAgent,
+          prevMessageAgent: prevMessage?.agent,
+          resolvedParentAgent: parentAgent,
+        })
+        
         const parentModel = prevMessage?.model?.providerID && prevMessage?.model?.modelID
           ? { providerID: prevMessage.model.providerID, modelID: prevMessage.model.modelID }
           : undefined
@@ -74,7 +89,7 @@ export function createBackgroundTask(manager: BackgroundManager): ToolDefinition
           parentSessionID: ctx.sessionID,
           parentMessageID: ctx.messageID,
           parentModel,
-          parentAgent: ctx.agent ?? prevMessage?.agent,
+          parentAgent,
         })
 
         ctx.metadata?.({

src/tools/call-omo-agent/tools.ts

@@ -1,8 +1,26 @@
 import { tool, type PluginInput, type ToolDefinition } from "@opencode-ai/plugin"
+import { existsSync, readdirSync } from "node:fs"
+import { join } from "node:path"
 import { ALLOWED_AGENTS, CALL_OMO_AGENT_DESCRIPTION } from "./constants"
 import type { CallOmoAgentArgs } from "./types"
 import type { BackgroundManager } from "../../features/background-agent"
 import { log } from "../../shared/logger"
+import { findFirstMessageWithAgent, findNearestMessageWithFields, MESSAGE_STORAGE } from "../../features/hook-message-injector"
+import { getSessionAgent } from "../../features/claude-code-session-state"
+
+function getMessageDir(sessionID: string): string | null {
+  if (!existsSync(MESSAGE_STORAGE)) return null
+
+  const directPath = join(MESSAGE_STORAGE, sessionID)
+  if (existsSync(directPath)) return directPath
+
+  for (const dir of readdirSync(MESSAGE_STORAGE)) {
+    const sessionPath = join(MESSAGE_STORAGE, dir, sessionID)
+    if (existsSync(sessionPath)) return sessionPath
+  }
+
+  return null
+}
 
 type ToolContextWithMetadata = {
   sessionID: string
@@ -60,12 +78,29 @@ async function executeBackground(
   manager: BackgroundManager
 ): Promise<string> {
   try {
+    const messageDir = getMessageDir(toolContext.sessionID)
+    const prevMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
+    const firstMessageAgent = messageDir ? findFirstMessageWithAgent(messageDir) : null
+    const sessionAgent = getSessionAgent(toolContext.sessionID)
+    const parentAgent = toolContext.agent ?? sessionAgent ?? firstMessageAgent ?? prevMessage?.agent
+    
+    log("[call_omo_agent] parentAgent resolution", {
+      sessionID: toolContext.sessionID,
+      messageDir,
+      ctxAgent: toolContext.agent,
+      sessionAgent,
+      firstMessageAgent,
+      prevMessageAgent: prevMessage?.agent,
+      resolvedParentAgent: parentAgent,
+    })
+
     const task = await manager.launch({
       description: args.description,
       prompt: args.prompt,
       agent: args.subagent_type,
       parentSessionID: toolContext.sessionID,
       parentMessageID: toolContext.messageID,
+      parentAgent,
     })
 
     toolContext.metadata?.({

src/tools/sisyphus-task/tools.ts

@@ -5,11 +5,12 @@ import type { BackgroundManager } from "../../features/background-agent"
 import type { SisyphusTaskArgs } from "./types"
 import type { CategoryConfig, CategoriesConfig, GitMasterConfig } from "../../config/schema"
 import { SISYPHUS_TASK_DESCRIPTION, DEFAULT_CATEGORIES, CATEGORY_PROMPT_APPENDS } from "./constants"
-import { findNearestMessageWithFields, MESSAGE_STORAGE } from "../../features/hook-message-injector"
+import { findNearestMessageWithFields, findFirstMessageWithAgent, MESSAGE_STORAGE } from "../../features/hook-message-injector"
 import { resolveMultipleSkills } from "../../features/opencode-skill-loader/skill-content"
 import { createBuiltinSkills } from "../../features/builtin-skills/skills"
 import { getTaskToastManager } from "../../features/task-toast-manager"
-import { subagentSessions } from "../../features/claude-code-session-state"
+import { subagentSessions, getSessionAgent } from "../../features/claude-code-session-state"
+import { log } from "../../shared/logger"
 
 type OpencodeClient = PluginInput["client"]
 
@@ -147,7 +148,19 @@ export function createSisyphusTask(options: SisyphusTaskToolOptions): ToolDefini
 
       const messageDir = getMessageDir(ctx.sessionID)
       const prevMessage = messageDir ? findNearestMessageWithFields(messageDir) : null
-      const parentAgent = ctx.agent ?? prevMessage?.agent
+      const firstMessageAgent = messageDir ? findFirstMessageWithAgent(messageDir) : null
+      const sessionAgent = getSessionAgent(ctx.sessionID)
+      const parentAgent = ctx.agent ?? sessionAgent ?? firstMessageAgent ?? prevMessage?.agent
+      
+      log("[sisyphus_task] parentAgent resolution", {
+        sessionID: ctx.sessionID,
+        messageDir,
+        ctxAgent: ctx.agent,
+        sessionAgent,
+        firstMessageAgent,
+        prevMessageAgent: prevMessage?.agent,
+        resolvedParentAgent: parentAgent,
+      })
       const parentModel = prevMessage?.model?.providerID && prevMessage?.model?.modelID
         ? { providerID: prevMessage.model.providerID, modelID: prevMessage.model.modelID }
         : undefined