feat(prompt): implement prompt injection slice 1

pi-extension.ts

@@ -8,7 +8,11 @@ import {
 	validateMaps,
 	reinitPath,
 	retrieveContext,
+	buildPreInitHint,
+	modeAllowsPreInitHint,
+	modeAllowsInjection,
 } from "./src/index.js";
+import { loadConfig } from "./src/config.js";
 import { createLLMClient } from "./src/llm/llm-client.js";
 import { LLMError } from "./src/llm/llm-error.js";
 
@@ -340,8 +344,33 @@ export default function (pi: ExtensionAPI) {
 
 	// Inject maintenance instructions before agent starts
 	pi.on("before_agent_start", async (_event, _ctx) => {
+		const config = loadConfig(_ctx.cwd);
 		const mapFiles = findPiMapFiles(_ctx.cwd);
-		if (mapFiles.length === 0) return {};
+
+		// Mode is off: no injection at all
+		if (config.promptInjectionMode === "off") {
+			return {};
+		}
+
+		// No maps exist yet: show visible pre-init hint, but only if mode allows it
+		if (mapFiles.length === 0) {
+			if (!modeAllowsPreInitHint(config.promptInjectionMode)) {
+				return {};
+			}
+			return {
+				message: {
+					customType: "pi-project-map-hint",
+					content: buildPreInitHint(),
+					display: true,
+				},
+			};
+		}
+
+		// 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 {};
+		}
 
 		return {
 			message: {