feat: avoid duplicate project-map hint injection by checking context

The before_agent_start handler now inspects the current session context
and skips injection if a pi-project-map-hint custom message is already
present in the active branch. This prevents duplicate hints on every
prompt while still re-injecting after compaction or tree navigation.

Also removes the unused hooks/on-prompt.ts prompt-text injector.

pi-extension.ts

@@ -50,6 +50,25 @@ function isDirty(content: string): boolean {
 	return content.includes("## dirty") && !content.includes("## dirty\n-");
 }
 
+const HINT_CUSTOM_TYPE = "pi-project-map-hint";
+
+function hintAlreadyInContext(ctx: any): boolean {
+	const manager = ctx?.sessionManager;
+	if (!manager || typeof manager.buildSessionContext !== "function") {
+		return false;
+	}
+
+	const { messages } = manager.buildSessionContext();
+	if (!Array.isArray(messages)) return false;
+
+	return messages.some(
+		(m: any) =>
+			m &&
+			m.role === "custom" &&
+			m.customType === HINT_CUSTOM_TYPE,
+	);
+}
+
 export default function (pi: ExtensionAPI) {
 	pi.registerTool({
 		name: "project_map_init",
@@ -236,14 +255,17 @@ export default function (pi: ExtensionAPI) {
 		}
 	});
 
-	// Inject maintenance instructions before agent starts
+	// Inject maintenance instructions before agent starts, but only once
+	// within the current branch of context. Re-inject after compaction or
+	// tree navigation removes the hint from the active path.
 	pi.on("before_agent_start", async (_event, _ctx) => {
 		const mapFiles = findPiMapFiles(_ctx.cwd);
 		if (mapFiles.length === 0) return {};
+		if (hintAlreadyInContext(_ctx)) return {};
 
 		return {
 			message: {
-				customType: "pi-project-map-hint",
+				customType: HINT_CUSTOM_TYPE,
 				content:
 					"📋 Project map active: If you modify any source file, run `project_map_patch` with the file path. If you suspect staleness, run `project_map_validate`.",
 				display: false,