feat(compaction): re-inject workspace context files after compaction

This change ensures that USER.md, SOUL.md, and IDENTITY.md are automatically
re-injected into the compaction summary, so the agent retains persona and
user preferences after context compression.

Changes:
- Add context file re-injection in compaction-safeguard.ts
- Wire up after_compaction plugin hook with result type for additional injection
- Allow plugins to append custom text to compaction summary via after_compaction hook

Closes: context compression causing loss of user preferences

src/agents/pi-extensions/compaction-safeguard.ts

@@ -1,3 +1,6 @@
+import fs from "node:fs/promises";
+import path from "node:path";
+
 import type { AgentMessage } from "@mariozechner/pi-agent-core";
 import type { ExtensionAPI, FileOperations } from "@mariozechner/pi-coding-agent";
 import {
@@ -11,8 +14,52 @@ import {
   resolveContextWindowTokens,
   summarizeInStages,
 } from "../compaction.js";
+import { getGlobalHookRunner } from "../../plugins/hook-runner-global.js";
+import {
+  DEFAULT_USER_FILENAME,
+  DEFAULT_SOUL_FILENAME,
+  DEFAULT_IDENTITY_FILENAME,
+} from "../workspace.js";
+
 const FALLBACK_SUMMARY =
   "Summary unavailable due to context limits. Older messages were truncated.";
+
+// Context refresh settings
+const MAX_CONTEXT_FILE_SIZE = 4000; // Max chars per file to avoid bloating the summary
+const CONTEXT_FILES = [DEFAULT_USER_FILENAME, DEFAULT_SOUL_FILENAME, DEFAULT_IDENTITY_FILENAME];
+
+async function readContextFile(
+  workspaceRoot: string,
+  filename: string,
+  maxSize: number = MAX_CONTEXT_FILE_SIZE,
+): Promise<string | undefined> {
+  try {
+    const filePath = path.join(workspaceRoot, filename);
+    const content = await fs.readFile(filePath, "utf-8");
+    if (content.trim().length === 0) return undefined;
+    if (content.length > maxSize) {
+      return content.slice(0, maxSize) + "\n\n[... truncated for context limits ...]";
+    }
+    return content;
+  } catch {
+    return undefined;
+  }
+}
+
+async function buildContextRefreshSection(workspaceRoot: string | undefined): Promise<string> {
+  if (!workspaceRoot) return "";
+
+  const sections: string[] = [];
+  for (const filename of CONTEXT_FILES) {
+    const content = await readContextFile(workspaceRoot, filename);
+    if (content) {
+      sections.push(`## ${filename}\n${content}`);
+    }
+  }
+
+  if (sections.length === 0) return "";
+  return `\n\n# Workspace Context (re-injected after compaction)\n\n${sections.join("\n\n")}`;
+}
 const TURN_PREFIX_INSTRUCTIONS =
   "This summary covers the prefix of a split turn. Focus on the original request," +
   " early progress, and any details needed to understand the retained suffix.";
@@ -241,6 +288,47 @@ export default function compactionSafeguardExtension(api: ExtensionAPI): void {
       summary += toolFailureSection;
       summary += fileOpsSummary;
 
+      // Re-inject workspace context files (USER.md, SOUL.md, etc.) after compaction
+      // This ensures the agent retains persona and user preferences
+      try {
+        const contextRefresh = await buildContextRefreshSection(ctx.cwd);
+        if (contextRefresh) {
+          summary += contextRefresh;
+        }
+      } catch (contextError) {
+        console.warn(
+          `Context refresh after compaction failed: ${
+            contextError instanceof Error ? contextError.message : String(contextError)
+          }`,
+        );
+      }
+
+      // Run after_compaction hook to allow plugins to inject additional context
+      const hookRunner = getGlobalHookRunner();
+      if (hookRunner?.hasHooks("after_compaction")) {
+        try {
+          const hookResult = await hookRunner.runAfterCompaction(
+            {
+              messageCount: preparation.messagesToSummarize.length,
+              tokenCount: preparation.tokensBefore,
+              compactedCount: preparation.messagesToSummarize.length,
+              summary,
+              workspaceRoot: ctx.cwd,
+            },
+            { agentId: undefined },
+          );
+          if (hookResult?.appendToSummary) {
+            summary += `\n\n${hookResult.appendToSummary}`;
+          }
+        } catch (hookError) {
+          console.warn(
+            `after_compaction hook failed: ${
+              hookError instanceof Error ? hookError.message : String(hookError)
+            }`,
+          );
+        }
+      }
+
       return {
         compaction: {
           summary,

src/plugins/hooks.ts

@@ -8,6 +8,7 @@
 import type { PluginRegistry } from "./registry.js";
 import type {
   PluginHookAfterCompactionEvent,
+  PluginHookAfterCompactionResult,
   PluginHookAfterToolCallEvent,
   PluginHookAgentContext,
   PluginHookAgentEndEvent,
@@ -43,6 +44,7 @@ export type {
   PluginHookAgentEndEvent,
   PluginHookBeforeCompactionEvent,
   PluginHookAfterCompactionEvent,
+  PluginHookAfterCompactionResult,
   PluginHookMessageContext,
   PluginHookMessageReceivedEvent,
   PluginHookMessageSendingEvent,
@@ -218,12 +220,21 @@ export function createHookRunner(registry: PluginRegistry, options: HookRunnerOp
 
   /**
    * Run after_compaction hook.
+   * Allows plugins to return text to append to the compaction summary.
    */
   async function runAfterCompaction(
     event: PluginHookAfterCompactionEvent,
     ctx: PluginHookAgentContext,
-  ): Promise<void> {
-    return runVoidHook("after_compaction", event, ctx);
+  ): Promise<PluginHookAfterCompactionResult | undefined> {
+    return runModifyingHook<"after_compaction", PluginHookAfterCompactionResult>(
+      "after_compaction",
+      event,
+      ctx,
+      (acc, next) => ({
+        appendToSummary:
+          [acc?.appendToSummary, next.appendToSummary].filter(Boolean).join("\n\n") || undefined,
+      }),
+    );
   }
 
   // =========================================================================

src/plugins/types.ts

@@ -339,6 +339,16 @@ export type PluginHookAfterCompactionEvent = {
   messageCount: number;
   tokenCount?: number;
   compactedCount: number;
+  /** The generated summary text (read-only). */
+  summary?: string;
+  /** Agent workspace root (for reading context files). */
+  workspaceRoot?: string;
+};
+
+/** Result from after_compaction hook - allows injecting additional context into the summary. */
+export type PluginHookAfterCompactionResult = {
+  /** Additional text to append to the compaction summary. */
+  appendToSummary?: string;
 };
 
 // Message context
@@ -476,7 +486,7 @@ export type PluginHookHandlerMap = {
   after_compaction: (
     event: PluginHookAfterCompactionEvent,
     ctx: PluginHookAgentContext,
-  ) => Promise<void> | void;
+  ) => Promise<PluginHookAfterCompactionResult | void> | PluginHookAfterCompactionResult | void;
   message_received: (
     event: PluginHookMessageReceivedEvent,
     ctx: PluginHookMessageContext,