feat(prompt): implement prompt injection slice 3

pi-extension.ts

@@ -13,6 +13,9 @@ import {
 	modeAllowsInjection,
 	discoverContextWindow,
 	buildInjectionPayload,
+	shouldReinjectForEvent,
+	getRootPairMtimes,
+	rootPairChanged,
 } from "./src/index.js";
 import { loadConfig } from "./src/config.js";
 import { createLLMClient } from "./src/llm/llm-client.js";
@@ -76,6 +79,7 @@ function renderProgressBar(
 }
 
 export default function (pi: ExtensionAPI) {
+	let lastRootPairMtimes: import("./src/index.js").RootPairMtimes = {};
 	pi.registerTool({
 		name: "project_map_init",
 		label: "Project Map Init",
@@ -373,6 +377,28 @@ export default function (pi: ExtensionAPI) {
 			return {};
 		}
 
+		// Slice 3b: detect root-pair artifact changes
+		const currentMtimes = getRootPairMtimes(_ctx.cwd);
+		const hasPrevious =
+			lastRootPairMtimes.mapMtime !== undefined ||
+			lastRootPairMtimes.indexMtime !== undefined;
+		const artifactChanged =
+			hasPrevious && rootPairChanged(currentMtimes, lastRootPairMtimes);
+		lastRootPairMtimes = currentMtimes;
+
+		// Slice 3a/3b: avoid redundant reinjection by scanning outgoing context
+		const eventType = artifactChanged ? "artifact_change" : "agent_start";
+		const decision = shouldReinjectForEvent(
+			{
+				messages: _event?.messages,
+				type: eventType,
+			},
+			config.promptInjectionMode,
+		);
+		if (!decision.needed) {
+			return {};
+		}
+
 		// Slice 2: post-init root-pair preload + budgeted expansion
 		const contextWindow = discoverContextWindow(_ctx);
 		const payload = buildInjectionPayload(_ctx.cwd, config, contextWindow);
@@ -384,4 +410,51 @@ export default function (pi: ExtensionAPI) {
 			},
 		};
 	});
+
+	// Per-turn context scanning for reinjection in strong/strict modes
+	pi.on("context", async (event: any, ctx: any) => {
+		const config = loadConfig(ctx.cwd);
+		const mapFiles = findPiMapFiles(ctx.cwd);
+
+		if (mapFiles.length === 0) {
+			return {};
+		}
+
+		if (!modeAllowsInjection(config.promptInjectionMode)) {
+			return {};
+		}
+
+		// Slice 3b: detect root-pair artifact changes
+		const currentMtimes = getRootPairMtimes(ctx.cwd);
+		const hasPrevious =
+			lastRootPairMtimes.mapMtime !== undefined ||
+			lastRootPairMtimes.indexMtime !== undefined;
+		const artifactChanged =
+			hasPrevious && rootPairChanged(currentMtimes, lastRootPairMtimes);
+		lastRootPairMtimes = currentMtimes;
+
+		const eventType = artifactChanged ? "artifact_change" : event?.type;
+
+		const decision = shouldReinjectForEvent(
+			{
+				messages: event?.messages,
+				type: eventType,
+				payload: event?.payload,
+			},
+			config.promptInjectionMode,
+		);
+		if (!decision.needed) {
+			return {};
+		}
+
+		const contextWindow = discoverContextWindow(ctx);
+		const payload = buildInjectionPayload(ctx.cwd, config, contextWindow);
+		return {
+			message: {
+				customType: "pi-project-map-hint",
+				content: payload.content,
+				display: payload.display,
+			},
+		};
+	});
 }