refactor(rules): delegate injectors to rules-core

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/directory-agents-injector/injector.ts

@@ -1,4 +1,5 @@
 import type { PluginInput } from "@opencode-ai/plugin";
+import type { AgentsMdCache } from "@oh-my-opencode/rules-core";
 import { promises as fsPromises } from "node:fs";
 import { dirname } from "node:path";
 
@@ -15,13 +16,18 @@ function getSessionCache(
   if (!sessionCaches.has(sessionID)) {
     sessionCaches.set(sessionID, loadInjectedPaths(sessionID));
   }
-  return sessionCaches.get(sessionID)!;
+  const cache = sessionCaches.get(sessionID);
+  if (cache) return cache;
+  const loaded = loadInjectedPaths(sessionID);
+  sessionCaches.set(sessionID, loaded);
+  return loaded;
 }
 
 export async function processFilePathForAgentsInjection(input: {
   ctx: PluginInput;
   truncator: DynamicTruncator;
   sessionCaches: Map<string, Set<string>>;
+  agentsMdCache?: AgentsMdCache;
   filePath: string;
   sessionID: string;
   output: { title: string; output: string; metadata: unknown };
@@ -35,26 +41,29 @@ export async function processFilePathForAgentsInjection(input: {
 
   const dir = dirname(resolved);
   const cache = getSessionCache(input.sessionCaches, input.sessionID);
-  const agentsPaths = await findAgentsMdUp({ startDir: dir, rootDir: input.ctx.directory });
+  const agentsPaths = await findAgentsMdUp({
+    startDir: dir,
+    rootDir: input.ctx.directory,
+    cache: input.agentsMdCache,
+  });
 
   let dirty = false;
   for (const agentsPath of agentsPaths) {
     const agentsDir = dirname(agentsPath);
     if (cache.has(agentsDir)) continue;
 
-    try {
-      const content = await fsPromises.readFile(agentsPath, "utf-8");
-      cache.add(agentsDir);
-      const { result, truncated } = await input.truncator.truncate(
-        input.sessionID,
-        content,
-      );
-      const truncationNotice = truncated
-        ? `\n\n[Note: Content was truncated to save context window space. For full context, please read the file directly: ${agentsPath}]`
-        : "";
-      input.output.output += `\n\n[Directory Context: ${agentsPath}]\n${result}${truncationNotice}`;
-      dirty = true;
-    } catch {}
+    const content = await fsPromises.readFile(agentsPath, "utf-8").catch(() => null);
+    if (content === null) continue;
+    cache.add(agentsDir);
+    const { result, truncated } = await input.truncator.truncate(
+      input.sessionID,
+      content,
+    );
+    const truncationNotice = truncated
+      ? `\n\n[Note: Content was truncated to save context window space. For full context, please read the file directly: ${agentsPath}]`
+      : "";
+    input.output.output += `\n\n[Directory Context: ${agentsPath}]\n${result}${truncationNotice}`;
+    dirty = true;
   }
 
   if (dirty) {