docs(memory): add comprehensive English godoc documentation

Add field-level comments to NoteMeta struct, enhance type and function
documentation across vault.go and memory tools with usage context and
behavioral details.

pkg/memory/vault.go

@@ -1,3 +1,18 @@
+// Package memory implements an Obsidian-inspired markdown vault for persistent
+// agent memory. Notes are plain markdown files with YAML frontmatter for
+// metadata (title, tags, aliases, dates). The vault is folder-agnostic:
+// organization comes from tags and [[wikilinks]], not directory structure.
+//
+// The vault generates an auto-maintained _index.md file containing a compact
+// overview of all notes, tags, and aliases. This index is injected into the
+// agent's system prompt so the LLM can efficiently query memory without
+// reading every note.
+//
+// Key design constraints:
+//   - No external dependencies (hand-rolled frontmatter parser, pure stdlib)
+//   - No in-memory caches (reads from disk on demand, <10ms for <100 notes)
+//   - No mutexes (tools are called sequentially by the agent loop)
+//   - Backward compatible with the legacy MEMORY.md format
 package memory
 
 import (
@@ -11,18 +26,20 @@ import (
 
 // NoteMeta represents parsed frontmatter metadata from a single markdown note.
 type NoteMeta struct {
-	Title   string
-	Created string
-	Updated string
-	Tags    []string
-	Aliases []string
-	RelPath string
-	Links   []string
+	Title   string   // Note title from frontmatter, or inferred from filename.
+	Created string   // Creation date in YYYY-MM-DD format.
+	Updated string   // Last modification date in YYYY-MM-DD format.
+	Tags    []string // Classification tags for search and filtering.
+	Aliases []string // Alternate names for wikilink resolution.
+	RelPath string   // Slash-separated path relative to the vault root.
+	Links   []string // Wikilink targets ([[target]]) extracted from the note body.
 }
 
 // Vault manages the memory vault: scanning, indexing, and searching notes.
+// All operations read from disk on demand with no in-memory caching, keeping
+// the implementation stateless and safe for sequential tool calls.
 type Vault struct {
-	memoryDir string
+	memoryDir string // Absolute path to the vault root directory.
 }
 
 // NewVault creates a new Vault rooted at the given memory directory.

pkg/tools/memory.go

@@ -9,6 +9,9 @@ import (
 )
 
 // MemorySaveTool saves a structured note to the memory vault with frontmatter.
+// It auto-generates YAML frontmatter (title, created, updated, tags, aliases),
+// preserves the original created date when updating an existing note, and
+// rebuilds the vault index after every write.
 type MemorySaveTool struct {
 	vault *memory.Vault
 }
@@ -102,6 +105,10 @@ func (t *MemorySaveTool) Execute(ctx context.Context, args map[string]any) *Tool
 }
 
 // MemorySearchTool searches the memory vault by tags, title, or text content.
+// Tags use AND logic (a note must match all specified tags). The text query
+// matches case-insensitively against title, tags, and aliases. Results are
+// capped at 20 entries and include metadata only — use MemoryRecallTool to
+// read full note content.
 type MemorySearchTool struct {
 	vault *memory.Vault
 }
@@ -179,7 +186,9 @@ func (t *MemorySearchTool) Execute(ctx context.Context, args map[string]any) *To
 }
 
 // MemoryRecallTool recalls specific notes from the memory vault by path or topic.
-// Unlike memory_search which returns metadata, memory_recall returns full note content.
+// Unlike MemorySearchTool which returns metadata only, MemoryRecallTool returns
+// the full note body with frontmatter stripped. When using topic-based recall,
+// it searches for matching notes and reads the top N (default 3).
 type MemoryRecallTool struct {
 	vault *memory.Vault
 }