feat(pi-cursor-agent): Inject pi context as cursor rules (#12)

Author: sudosubin

pi-cursor-agent/package-lock.json

@@ -37,7 +37,8 @@
   "dependencies": {
     "@bufbuild/protobuf": "1.10.0",
     "@connectrpc/connect": "^1.7.0",
-    "@connectrpc/connect-node": "^1.7.0"
+    "@connectrpc/connect-node": "^1.7.0",
+    "yaml": "^2.8.0"
   },
   "devDependencies": {
     "@biomejs/biome": "^2.4.2",

pi-cursor-agent/package.json

@@ -1,4 +1,5 @@
 import os from "node:os";
+import type { CursorRule } from "../../../__generated__/agent/v1/cursor_rules_pb";
 import type { McpToolDefinition } from "../../../__generated__/agent/v1/mcp_pb";
 import { GitRepoInfo } from "../../../__generated__/agent/v1/repo_pb";
 import type { RequestContextArgs } from "../../../__generated__/agent/v1/request_context_exec_pb";
@@ -23,11 +24,17 @@ export class LocalRequestContextExecutor
 {
   private readonly tools: McpToolDefinition[];
   private readonly workspacePaths: string[];
+  private readonly rules: CursorRule[];
   private readonly gitExecutor: LocalGitExecutor;
 
-  constructor(tools: McpToolDefinition[], workspacePaths: string[]) {
+  constructor(
+    tools: McpToolDefinition[],
+    workspacePaths: string[],
+    rules: CursorRule[] = [],
+  ) {
     this.tools = tools;
     this.workspacePaths = workspacePaths;
+    this.rules = rules;
     this.gitExecutor = new LocalGitExecutor();
   }
 
@@ -42,7 +49,7 @@ export class LocalRequestContextExecutor
       ]);
 
       const requestContext = new RequestContext({
-        rules: [],
+        rules: this.rules,
         env,
         repositoryInfo: [],
         tools: this.tools,

pi-cursor-agent/src/bridge/cursor-to-pi/executors/request-context.ts

@@ -1,3 +1,4 @@
+import type { CursorRule } from "../../../__generated__/agent/v1/cursor_rules_pb";
 import type { McpToolDefinition } from "../../../__generated__/agent/v1/mcp_pb";
 import {
   backgroundShellResource,
@@ -46,6 +47,7 @@ interface LocalResourceProviderOptions {
   ctx: PiToolContext;
   requestContextTools?: McpToolDefinition[];
   workspacePaths?: string[];
+  cursorRules?: CursorRule[];
 }
 
 export class LocalResourceProvider extends RegistryResourceAccessor {
@@ -63,6 +65,7 @@ export class LocalResourceProvider extends RegistryResourceAccessor {
       new LocalRequestContextExecutor(
         requestContextTools,
         resolvedWorkspacePaths,
+        options.cursorRules ?? [],
       ),
     );
 

pi-cursor-agent/src/bridge/cursor-to-pi/local-resource-provider/provider.ts

@@ -0,0 +1,16 @@
+import type { CursorRule } from "../../__generated__/agent/v1/cursor_rules_pb";
+import { parsePiSystemPrompt } from "./parser";
+import { buildCursorRules } from "./rules-builder";
+
+export interface PreparedPiContext {
+  rules: CursorRule[];
+  cleanedPrompt: string;
+}
+
+export async function preparePiContext(
+  systemPrompt: string,
+): Promise<PreparedPiContext> {
+  const parsed = parsePiSystemPrompt(systemPrompt);
+  const rules = await buildCursorRules(parsed);
+  return { rules, cleanedPrompt: parsed.cleanedPrompt };
+}

pi-cursor-agent/src/bridge/pi-context/index.ts

@@ -0,0 +1,115 @@
+/** Parse Pi system prompt into structured components for Cursor's RequestContext.rules. */
+
+export interface PiContextFile {
+  path: string;
+  content: string;
+}
+
+export interface PiSkillRef {
+  name: string;
+  description: string;
+  location: string;
+}
+
+export interface ParsedPiContext {
+  contextFiles: PiContextFile[];
+  skills: PiSkillRef[];
+  cleanedPrompt: string;
+}
+
+// Stable structural markers only — no description text that may change across Pi versions.
+const CONTEXT_HEADING = "# Project Context";
+const SKILLS_OPEN = "<available_skills>";
+const SKILLS_CLOSE = "</available_skills>";
+
+const SKILL_RE =
+  /<skill>\s*<name>([\s\S]*?)<\/name>\s*<description>([\s\S]*?)<\/description>\s*<location>([\s\S]*?)<\/location>\s*<\/skill>/g;
+
+function unescapeXml(s: string): string {
+  return s
+    .replace(/&amp;/g, "&")
+    .replace(/&lt;/g, "<")
+    .replace(/&gt;/g, ">")
+    .replace(/&quot;/g, '"')
+    .replace(/&apos;/g, "'");
+}
+
+function extractContextFiles(prompt: string): PiContextFile[] {
+  const start = prompt.indexOf(CONTEXT_HEADING);
+  if (start === -1) return [];
+
+  let end = prompt.length;
+  for (const marker of [SKILLS_OPEN, "\nCurrent date: "]) {
+    const idx = prompt.indexOf(marker, start);
+    if (idx !== -1 && idx < end) end = idx;
+  }
+
+  return prompt
+    .slice(start, end)
+    .split(/^(?=## \/)/m)
+    .slice(1)
+    .flatMap((block) => {
+      const nl = block.indexOf("\n");
+      if (nl === -1) return [];
+      const path = block.slice(3, nl).trim();
+      const content = block.slice(nl + 1).trim();
+      return path && content ? [{ path, content }] : [];
+    });
+}
+
+function extractSkills(prompt: string): PiSkillRef[] {
+  const openIdx = prompt.indexOf(SKILLS_OPEN);
+  if (openIdx === -1) return [];
+
+  const closeIdx = prompt.indexOf(SKILLS_CLOSE, openIdx);
+  if (closeIdx === -1) return [];
+
+  const xml = prompt.slice(openIdx, closeIdx + SKILLS_CLOSE.length);
+  const skills: PiSkillRef[] = [];
+
+  for (const m of xml.matchAll(SKILL_RE)) {
+    if (!m[1] || !m[2] || !m[3]) continue;
+    const name = unescapeXml(m[1].trim());
+    const description = unescapeXml(m[2].trim());
+    const location = unescapeXml(m[3].trim());
+    if (name && description && location) {
+      skills.push({ name, description, location });
+    }
+  }
+
+  return skills;
+}
+
+const PRESERVED_PATTERNS = [
+  /^Pi documentation[^\n]*(?:\n- [^\n]*)*/m,
+  /^Current date: .+$/m,
+  /^Current working directory: .+$/m,
+];
+
+function buildCleanedPrompt(original: string, hasExtracted: boolean): string {
+  const lines = PRESERVED_PATTERNS.map((re) => original.match(re)?.[0]).filter(
+    (s): s is string => s != null,
+  );
+
+  return lines.length === 0 && !hasExtracted ? original : lines.join("\n");
+}
+
+export function parsePiSystemPrompt(systemPrompt: string): ParsedPiContext {
+  if (!systemPrompt) {
+    return { contextFiles: [], skills: [], cleanedPrompt: "" };
+  }
+
+  try {
+    const contextFiles = extractContextFiles(systemPrompt);
+    const skills = extractSkills(systemPrompt);
+    const hasExtracted = contextFiles.length > 0 || skills.length > 0;
+
+    return {
+      contextFiles,
+      skills,
+      cleanedPrompt: buildCleanedPrompt(systemPrompt, hasExtracted),
+    };
+  } catch {
+    return { contextFiles: [], skills: [], cleanedPrompt: systemPrompt };
+  }
+}

pi-cursor-agent/src/bridge/pi-context/parser.ts

@@ -0,0 +1,73 @@
+/** Convert parsed Pi context into CursorRule[] for Cursor's RequestContext.rules. */
+
+import { readFile } from "node:fs/promises";
+import { parse as parseYaml } from "yaml";
+import {
+  CursorRule,
+  CursorRuleType,
+  CursorRuleTypeAgentFetched,
+  CursorRuleTypeGlobal,
+} from "../../__generated__/agent/v1/cursor_rules_pb";
+import type { ParsedPiContext, PiSkillRef } from "./parser";
+
+function parseFrontmatter(content: string): {
+  frontmatter: Record<string, unknown>;
+  body: string;
+} {
+  const s = content.replace(/\r\n/g, "\n").replace(/\r/g, "\n");
+  if (!s.startsWith("---")) return { frontmatter: {}, body: s };
+
+  const end = s.indexOf("\n---", 3);
+  if (end === -1) return { frontmatter: {}, body: s };
+
+  const parsed = parseYaml(s.slice(4, end));
+  return {
+    frontmatter: (parsed ?? {}) as Record<string, unknown>,
+    body: s.slice(end + 4).trim(),
+  };
+}
+
+function globalRule(path: string, content: string): CursorRule {
+  return new CursorRule({
+    fullPath: path,
+    content,
+    type: new CursorRuleType({
+      type: { case: "global", value: new CursorRuleTypeGlobal() },
+    }),
+  });
+}
+
+function agentFetchedRuleType(description: string): CursorRuleType {
+  return new CursorRuleType({
+    type: {
+      case: "agentFetched",
+      value: new CursorRuleTypeAgentFetched({ description }),
+    },
+  });
+}
+
+async function agentFetchedRule(skill: PiSkillRef): Promise<CursorRule> {
+  try {
+    const raw = await readFile(skill.location, "utf-8");
+    const { body } = parseFrontmatter(raw);
+    return new CursorRule({
+      fullPath: skill.location,
+      content: body || raw,
+      type: agentFetchedRuleType(skill.description),
+    });
+  } catch {
+    return new CursorRule({
+      fullPath: skill.location,
+      content: skill.description,
+      type: agentFetchedRuleType(skill.description),
+    });
+  }
+}
+
+export async function buildCursorRules(
+  parsed: ParsedPiContext,
+): Promise<CursorRule[]> {
+  const globals = parsed.contextFiles.map((f) => globalRule(f.path, f.content));
+  const skills = await Promise.all(parsed.skills.map(agentFetchedRule));
+  return [...globals, ...skills];
+}

pi-cursor-agent/src/bridge/pi-context/rules-builder.ts

@@ -234,6 +234,7 @@ interface BuildRunRequestParams {
   conversationState: ConversationStateStructure | undefined;
   mcpToolDefinitions?: McpToolDefinition[];
   state?: CursorStateStore;
+  systemPromptOverride?: string;
 }
 
 interface BuildRunRequestResult {
@@ -244,9 +245,14 @@ interface BuildRunRequestResult {
 export function buildRunRequest(
   params: BuildRunRequestParams,
 ): BuildRunRequestResult {
+  const content =
+    params.systemPromptOverride ??
+    params.context.systemPrompt ??
+    "You are a helpful assistant.";
+
   const systemPromptJson = JSON.stringify({
     role: "system",
-    content: params.context.systemPrompt || "You are a helpful assistant.",
+    content: content,
   });
   const systemPromptBytes = new TextEncoder().encode(systemPromptJson);
   const systemPromptId = getBlobId(systemPromptBytes);

pi-cursor-agent/src/bridge/pi-to-cursor/request-builder.ts

@@ -28,6 +28,7 @@ import {
   rejectPendingForSession,
   type ToolExecRequest,
 } from "../bridge/cursor-to-pi/tool-bridge";
+import { preparePiContext } from "../bridge/pi-context";
 import {
   buildRunRequest,
   getContextTools,
@@ -396,9 +397,12 @@ export function streamCursorAgent(
           getChannel: () => channel,
         };
 
+        const piContext = await preparePiContext(context.systemPrompt ?? "");
+
         const resources = new LocalResourceProvider({
           ctx: piToolCtx,
           requestContextTools,
+          cursorRules: piContext.rules,
         });
 
         const blobStore = agentStore.getBlobStore();
@@ -412,6 +416,7 @@ export function streamCursorAgent(
           conversationState: agentStore.getConversationStateStructure(),
           mcpToolDefinitions: requestContextTools,
           state: overlayState,
+          systemPromptOverride: piContext.cleanedPrompt,
         });
         agentStore.conversationStateStructure = conversationState;