feat(context-injector): introduce centralized context collection and integrate with keyword-detector

- Add ContextCollector class for managing and merging context entries across sessions
- Add types and interfaces for context management (ContextEntry, ContextPriority, PendingContext)
- Create context-injector hook for injection coordination
- Refactor keyword-detector to use context-injector instead of hook-message-injector
- Update src/index.ts to initialize context-injector infrastructure

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

src/features/context-injector/injector.ts

@@ -0,0 +1,61 @@
+import type { ContextCollector } from "./collector"
+
+const MESSAGE_SEPARATOR = "\n\n---\n\n"
+
+interface OutputPart {
+  type: string
+  text?: string
+  [key: string]: unknown
+}
+
+interface InjectionResult {
+  injected: boolean
+  contextLength: number
+}
+
+export function injectPendingContext(
+  collector: ContextCollector,
+  sessionID: string,
+  parts: OutputPart[]
+): InjectionResult {
+  if (!collector.hasPending(sessionID)) {
+    return { injected: false, contextLength: 0 }
+  }
+
+  const textPartIndex = parts.findIndex((p) => p.type === "text" && p.text !== undefined)
+  if (textPartIndex === -1) {
+    return { injected: false, contextLength: 0 }
+  }
+
+  const pending = collector.consume(sessionID)
+  const originalText = parts[textPartIndex].text ?? ""
+  parts[textPartIndex].text = `${pending.merged}${MESSAGE_SEPARATOR}${originalText}`
+
+  return {
+    injected: true,
+    contextLength: pending.merged.length,
+  }
+}
+
+interface ChatMessageInput {
+  sessionID: string
+  agent?: string
+  model?: { providerID: string; modelID: string }
+  messageID?: string
+}
+
+interface ChatMessageOutput {
+  message: Record<string, unknown>
+  parts: OutputPart[]
+}
+
+export function createContextInjectorHook(collector: ContextCollector) {
+  return {
+    "chat.message": async (
+      input: ChatMessageInput,
+      output: ChatMessageOutput
+    ): Promise<void> => {
+      injectPendingContext(collector, input.sessionID, output.parts)
+    },
+  }
+}