fix(keyword-detector): skip keyword detection for background task sessions

Skip all keyword detection for background task sessions to prevent mode
injection (e.g., [analyze-mode], [search-mode]) which incorrectly triggers
Prometheus planner restrictions on Sisyphus sessions.

This aligns with the existing pattern used in:
- sisyphus-orchestrator (line 504)
- todo-continuation-enforcer (line 303)
- session-notification (line 278)

Closes #713

src/hooks/keyword-detector/index.ts

@@ -2,7 +2,7 @@ import type { PluginInput } from "@opencode-ai/plugin"
 import { detectKeywordsWithType, extractPromptText, removeCodeBlocks } from "./detector"
 import { log } from "../../shared"
 import { isSystemDirective } from "../../shared/system-directive"
-import { getMainSessionID, getSessionAgent } from "../../features/claude-code-session-state"
+import { getMainSessionID, getSessionAgent, subagentSessions } from "../../features/claude-code-session-state"
 import type { ContextCollector } from "../../features/context-injector"
 
 export * from "./detector"
@@ -37,6 +37,13 @@ export function createKeywordDetectorHook(ctx: PluginInput, collector?: ContextC
         return
       }
 
+      // Skip keyword detection for background task sessions to prevent mode injection
+      // (e.g., [analyze-mode]) which incorrectly triggers Prometheus restrictions
+      const isBackgroundTaskSession = subagentSessions.has(input.sessionID)
+      if (isBackgroundTaskSession) {
+        return
+      }
+
       const mainSessionID = getMainSessionID()
       const isNonMainSession = mainSessionID && input.sessionID !== mainSessionID