feat(prompt): implement prompt injection slice 2

pi-extension.ts

@@ -11,6 +11,8 @@ import {
 	buildPreInitHint,
 	modeAllowsPreInitHint,
 	modeAllowsInjection,
+	discoverContextWindow,
+	buildInjectionPayload,
 } from "./src/index.js";
 import { loadConfig } from "./src/config.js";
 import { createLLMClient } from "./src/llm/llm-client.js";
@@ -367,17 +369,18 @@ export default function (pi: ExtensionAPI) {
 		}
 
 		// Maps exist but advisory mode does not permit automatic artifact injection yet.
-		// Full root-pair injection with canonical markers comes in later slices.
 		if (!modeAllowsInjection(config.promptInjectionMode)) {
 			return {};
 		}
 
+		// Slice 2: post-init root-pair preload + budgeted expansion
+		const contextWindow = discoverContextWindow(_ctx);
+		const payload = buildInjectionPayload(_ctx.cwd, config, contextWindow);
 		return {
 			message: {
 				customType: "pi-project-map-hint",
-				content:
-					"📋 Project map active: Start with the root `.pi-map.index.md`, use indexes first for routing, read the local `.pi-map.md` plus source before edits, run `project_map_patch` after source edits, and run `project_map_validate` before freshness-sensitive architectural handoff.",
-				display: false,
+				content: payload.content,
+				display: payload.display,
 			},
 		};
 	});