feat(memory): add nightly vault index rebuild and agent docs

Add maybeRebuildVaultIndex() to heartbeat service for nightly full index
rebuilds during quiet hours (2-5am). Uses a date stamp file to run at
most once per day. Update AGENT.md with memory vault conventions,
note format, and tool usage guidelines.

pkg/heartbeat/service.go

@@ -17,6 +17,7 @@ import (
 	"github.com/sipeed/picoclaw/pkg/bus"
 	"github.com/sipeed/picoclaw/pkg/constants"
 	"github.com/sipeed/picoclaw/pkg/logger"
+	"github.com/sipeed/picoclaw/pkg/memory"
 	"github.com/sipeed/picoclaw/pkg/state"
 	"github.com/sipeed/picoclaw/pkg/tools"
 )
@@ -159,6 +160,9 @@ func (hs *HeartbeatService) executeHeartbeat() {
 
 	logger.DebugC("heartbeat", "Executing heartbeat")
 
+	// Nightly vault index rebuild (runs once per day between 2-5am)
+	hs.maybeRebuildVaultIndex()
+
 	prompt := hs.buildPrompt()
 	if prompt == "" {
 		logger.InfoC("heartbeat", "No heartbeat prompt (HEARTBEAT.md empty or missing)")
@@ -341,6 +345,37 @@ func (hs *HeartbeatService) parseLastChannel(lastChannel string) (platform, user
 	return platform, userID
 }
 
+// maybeRebuildVaultIndex performs a nightly full rebuild of the memory vault
+// index. It runs at most once per day, during quiet hours (2-5am local time),
+// to catch any inconsistencies from incremental updates.
+func (hs *HeartbeatService) maybeRebuildVaultIndex() {
+	memoryDir := filepath.Join(hs.workspace, "memory")
+	stampFile := filepath.Join(memoryDir, ".last_rebuild")
+	today := time.Now().Format("2006-01-02")
+
+	// Check if already rebuilt today
+	if data, err := os.ReadFile(stampFile); err == nil {
+		if strings.TrimSpace(string(data)) == today {
+			return
+		}
+	}
+
+	// Only rebuild during quiet hours (2am-5am)
+	hour := time.Now().Hour()
+	if hour < 2 || hour >= 5 {
+		return
+	}
+
+	vault := memory.NewVault(memoryDir)
+	if err := vault.RebuildIndex(); err != nil {
+		hs.logError("Vault index rebuild failed: %v", err)
+		return
+	}
+
+	os.WriteFile(stampFile, []byte(today), 0o644)
+	hs.logInfo("Nightly vault index rebuild completed")
+}
+
 // logInfo logs an informational message to the heartbeat log
 func (hs *HeartbeatService) logInfo(format string, args ...any) {
 	hs.log("INFO", format, args...)

workspace/AGENT.md

@@ -7,6 +7,39 @@ You are a helpful AI assistant. Be concise, accurate, and friendly.
 - Always explain what you're doing before taking actions
 - Ask for clarification when request is ambiguous
 - Use tools to help accomplish tasks
-- Remember important information in your memory files
+- Remember important information using the memory vault (see below)
 - Be proactive and helpful
-- Learn from user feedback
+- Learn from user feedback
+
+## Memory Vault
+
+Your memory is an Obsidian-compatible vault of markdown notes in `memory/`. Each note has YAML frontmatter for metadata.
+
+### Note Format
+
+```
+---
+title: Note Title Here
+created: 2026-02-23
+updated: 2026-02-23
+tags: [tag1, tag2]
+aliases: [alternate-name]
+---
+
+Content here. Link to other notes with [[note-title]].
+```
+
+### Tools
+
+- **memory_save** — Save knowledge with structured frontmatter and tags. Auto-generates frontmatter, preserves created dates on updates, and rebuilds the vault index.
+- **memory_search** — Search by tags (AND logic) or text query matching title/tags/aliases. Returns metadata; use memory_recall to read full content.
+- **memory_recall** — Read full note content by exact path or by topic (searches and reads top matches).
+
+### Conventions
+
+- Folders are for human convenience (e.g. `topics/`, `people/`, `projects/`), not enforced by code
+- Tags are the primary organizational mechanism
+- Daily notes (`YYYYMM/YYYYMMDD.md`) are stored alongside vault notes
+- The index at `_index.md` is auto-generated — never edit it manually
+- When you learn something new about the user or a topic, save a note
+- When answering questions, check memory first with memory_search or memory_recall