feat: support user-specific memory overlays in prompt context (#995)

pkg/agent/context.go

@@ -435,6 +435,47 @@ func (cb *ContextBuilder) buildDynamicContext(channel, chatID string) string {
 	return sb.String()
 }
 
+
+func safePathSegment(v string) (string, bool) {
+	v = strings.TrimSpace(v)
+	if v == "" || v == "." || v == ".." {
+		return "", false
+	}
+	if strings.ContainsAny(v, `/\`) {
+		return "", false
+	}
+	return v, true
+}
+
+// loadUserMemoryContext loads optional per-user memory content.
+// Supported lookup order:
+// 1) <workspace>/users/<channel>/<chatID>/MEMORY.md
+// 2) <workspace>/users/<chatID>/MEMORY.md
+func (cb *ContextBuilder) loadUserMemoryContext(channel, chatID string) string {
+	channelSeg, okChannel := safePathSegment(channel)
+	chatSeg, okChat := safePathSegment(chatID)
+	if !okChat {
+		return ""
+	}
+
+	candidates := []string{}
+	if okChannel {
+		candidates = append(candidates, filepath.Join(cb.workspace, "users", channelSeg, chatSeg, "MEMORY.md"))
+	}
+	candidates = append(candidates, filepath.Join(cb.workspace, "users", chatSeg, "MEMORY.md"))
+
+	for _, p := range candidates {
+		if data, err := os.ReadFile(p); err == nil {
+			text := strings.TrimSpace(string(data))
+			if text != "" {
+				return "## User-specific Memory\n\n" + text
+			}
+		}
+	}
+
+	return ""
+}
+
 func (cb *ContextBuilder) BuildMessages(
 	history []providers.Message,
 	summary string,
@@ -457,6 +498,7 @@ func (cb *ContextBuilder) BuildMessages(
 
 	// Build short dynamic context (time, runtime, session) — changes per request
 	dynamicCtx := cb.buildDynamicContext(channel, chatID)
+	userMemoryCtx := cb.loadUserMemoryContext(channel, chatID)
 
 	// Compose a single system message: static (cached) + dynamic + optional summary.
 	// Keeping all system content in one message ensures every provider adapter can
@@ -474,6 +516,11 @@ func (cb *ContextBuilder) BuildMessages(
 		{Type: "text", Text: dynamicCtx},
 	}
 
+	if userMemoryCtx != "" {
+		stringParts = append(stringParts, userMemoryCtx)
+		contentBlocks = append(contentBlocks, providers.ContentBlock{Type: "text", Text: userMemoryCtx})
+	}
+
 	if summary != "" {
 		summaryText := fmt.Sprintf(
 			"CONTEXT_SUMMARY: The following is an approximate summary of prior conversation "+

pkg/agent/context_cache_test.go

@@ -667,3 +667,37 @@ func BenchmarkBuildMessagesWithCache(b *testing.B) {
 		_ = cb.BuildMessages(history, "summary", "new message", nil, "cli", "test")
 	}
 }
+
+func TestBuildMessages_IncludesUserSpecificMemory(t *testing.T) {
+	tmpDir := setupWorkspace(t, map[string]string{
+		"IDENTITY.md":                     "# Identity\nTest agent.",
+		"users/webchat/user123/MEMORY.md": "favorite color: blue",
+	})
+	defer os.RemoveAll(tmpDir)
+
+	cb := NewContextBuilder(tmpDir)
+	msgs := cb.BuildMessages(nil, "", "hello", nil, "webchat", "user123")
+	if len(msgs) == 0 || msgs[0].Role != "system" {
+		t.Fatalf("expected first system message")
+	}
+	if !strings.Contains(msgs[0].Content, "User-specific Memory") {
+		t.Fatalf("expected user memory section in system prompt")
+	}
+	if !strings.Contains(msgs[0].Content, "favorite color: blue") {
+		t.Fatalf("expected user memory content in system prompt")
+	}
+}
+
+func TestBuildMessages_UserSpecificMemoryIgnoredForInvalidChatID(t *testing.T) {
+	tmpDir := setupWorkspace(t, map[string]string{
+		"IDENTITY.md":             "# Identity\nTest agent.",
+		"users/webchat/u1/MEMORY.md": "secret",
+	})
+	defer os.RemoveAll(tmpDir)
+
+	cb := NewContextBuilder(tmpDir)
+	msgs := cb.BuildMessages(nil, "", "hello", nil, "webchat", "../u1")
+	if strings.Contains(msgs[0].Content, "User-specific Memory") {
+		t.Fatalf("expected no user memory section for invalid chat id")
+	}
+}