refactor: use ContextCollector for hook injection and remove unused background tools

Split changes:
- Replace injectHookMessage with ContextCollector.register() pattern for improved hook content injection
- Remove unused background task tools infrastructure (createBackgroundOutput, createBackgroundCancel)

🤖 Generated with assistance of OhMyOpenCode (https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/claude-code-hooks/index.ts

@@ -27,14 +27,18 @@ import { cacheToolInput, getToolInput } from "./tool-input-cache"
 import { recordToolUse, recordToolResult, getTranscriptPath, recordUserMessage } from "./transcript"
 import type { PluginConfig } from "./types"
 import { log, isHookDisabled } from "../../shared"
-import { injectHookMessage } from "../../features/hook-message-injector"
 import { detectKeywordsWithType, removeCodeBlocks } from "../keyword-detector"
+import type { ContextCollector } from "../../features/context-injector"
 
 const sessionFirstMessageProcessed = new Set<string>()
 const sessionErrorState = new Map<string, { hasError: boolean; errorMessage?: string }>()
 const sessionInterruptState = new Map<string, { interrupted: boolean }>()
 
-export function createClaudeCodeHooksHook(ctx: PluginInput, config: PluginConfig = {}) {
+export function createClaudeCodeHooksHook(
+  ctx: PluginInput,
+  config: PluginConfig = {},
+  contextCollector?: ContextCollector
+) {
   return {
     "experimental.session.compacting": async (
       input: { sessionID: string },
@@ -164,24 +168,26 @@ export function createClaudeCodeHooksHook(ctx: PluginInput, config: PluginConfig
               output.parts[idx].text = `${hookContent}\n\n${output.parts[idx].text ?? ""}`
               log("UserPromptSubmit hooks prepended to first message parts directly", { sessionID: input.sessionID })
             }
-          } else {
-            const message = output.message as {
-              agent?: string
-              model?: { modelID?: string; providerID?: string }
-              path?: { cwd?: string; root?: string }
-              tools?: Record<string, boolean>
-            }
-
-            const success = injectHookMessage(input.sessionID, hookContent, {
-              agent: message.agent,
-              model: message.model,
-              path: message.path ?? { cwd: ctx.directory, root: "/" },
-              tools: message.tools,
+          } else if (contextCollector) {
+            contextCollector.register(input.sessionID, {
+              id: "hook-context",
+              source: "custom",
+              content: hookContent,
+              priority: "high",
             })
 
-            log(success ? "Hook message injected via file system" : "File injection failed", {
+            log("Hook content registered for synthetic message injection", {
               sessionID: input.sessionID,
+              contentLength: hookContent.length,
             })
+          } else {
+            const idx = output.parts.findIndex((p) => p.type === "text" && p.text)
+            if (idx >= 0) {
+              output.parts[idx].text = `${hookContent}\n\n${output.parts[idx].text ?? ""}`
+              log("Hook content prepended to message (fallback)", {
+                sessionID: input.sessionID,
+              })
+            }
           }
         }
       }