fix(providers): correct Anthropic prompt caching + add datetime tool

- Move cache_control from request root (ignored by API) to per-block
  placement on last system block and last tool definition
- Change system prompt time format to date-only for better cache stability
- Add builtin datetime tool for precise timestamps (cron, memory, etc.)
- Add atMs past-time validation in cron handleUpdate (was only in handleAdd)
- Update cron description to guide model to use datetime tool first

cmd/gateway.go

@@ -165,6 +165,9 @@ func runGateway() {
 	skillsLoader, skillSearchTool, globalSkillsDir := setupSkillsSystem(cfg, workspace, dataDir, pgStores, toolsReg, providerRegistry, msgBus)
 	_ = skillSearchTool // used via wireExtras → skillsLoader; kept for type clarity
 
+	// DateTime tool (precise time for cron scheduling, memory timestamps, etc.)
+	toolsReg.Register(tools.NewDateTimeTool())
+
 	// Cron tool (agent-facing, matching TS cron-tool.ts)
 	toolsReg.Register(tools.NewCronTool(pgStores.Cron))
 	slog.Info("cron tool registered")

internal/agent/systemprompt.go

@@ -67,6 +67,7 @@ var coreToolSummaries = map[string]string{
 	"spawn":         "Spawn a self-clone subagent to handle a task in the background",
 	"web_search":    "Search the web",
 	"web_fetch":     "Fetch and extract content from a URL",
+	"datetime":      "Get current date/time with timezone support — use before creating cron jobs or time-sensitive operations",
 	"cron":          "Manage scheduled jobs and reminders",
 	"skill_search":     "Search available skills by keyword (weather, translate, github, etc.)",
 	"use_skill":        "Invoke a skill by name and follow its instructions",

internal/agent/systemprompt_sections.go

@@ -86,7 +86,7 @@ func buildUserIdentitySection(ownerIDs []string) []string {
 func buildTimeSection() []string {
 	now := time.Now()
 	return []string{
-		fmt.Sprintf("Current time: %s (UTC)", now.UTC().Format("2006-01-02 15:04 Monday")),
+		fmt.Sprintf("Current date: %s (UTC)", now.UTC().Format("2006-01-02 Monday")),
 		"",
 	}
 }

internal/providers/anthropic_request.go

@@ -145,11 +145,15 @@ func (p *AnthropicProvider) buildRequestBody(model string, req ChatRequest, stre
 		}
 	}
 
+	// Add cache_control breakpoint to the last system block (caches system prompt prefix).
+	if len(systemBlocks) > 0 {
+		systemBlocks[len(systemBlocks)-1]["cache_control"] = map[string]any{"type": "ephemeral"}
+	}
+
 	body := map[string]any{
-		"model":         model,
-		"max_tokens":    4096,
-		"messages":      messages,
-		"cache_control": map[string]any{"type": "ephemeral"},
+		"model":      model,
+		"max_tokens": 4096,
+		"messages":   messages,
 	}
 
 	if stream {
@@ -172,6 +176,10 @@ func (p *AnthropicProvider) buildRequestBody(model string, req ChatRequest, stre
 			}
 			tools = append(tools, tool)
 		}
+		// Add cache_control breakpoint to the last tool (caches tool definitions prefix).
+		if len(tools) > 0 {
+			tools[len(tools)-1]["cache_control"] = map[string]any{"type": "ephemeral"}
+		}
 		body["tools"] = tools
 	}
 

internal/tools/cron.go

@@ -64,6 +64,7 @@ CRITICAL CONSTRAINTS:
 - message is required for add action
 - schedule is required for add action
 - Default: jobs run as isolated agent turns with the specified message
+- Before creating or updating a scheduled job, call the datetime tool first to get the precise current time and unix_ms timestamp. Do NOT guess or estimate timestamps.
 
 Use jobId as the canonical identifier; id is accepted for compatibility.`
 }
@@ -309,6 +310,13 @@ func (t *CronTool) handleUpdate(args map[string]any, agentID, userID string) *Re
 	patchJSON, _ := json.Marshal(patchObj)
 	json.Unmarshal(patchJSON, &patch)
 
+	// Validate atMs not in the past when updating schedule
+	if patch.Schedule != nil && patch.Schedule.Kind == "at" && patch.Schedule.AtMS != nil {
+		if *patch.Schedule.AtMS <= time.Now().UnixMilli() {
+			return ErrorResult(fmt.Sprintf("schedule.atMs is in the past (%d). Use the datetime tool to get current time, then set a future timestamp. Current time is %d ms", *patch.Schedule.AtMS, time.Now().UnixMilli()))
+		}
+	}
+
 	job, err := t.cronStore.UpdateJob(jobID, patch)
 	if err != nil {
 		return ErrorResult(fmt.Sprintf("failed to update cron job: %v", err))

internal/tools/datetime.go

@@ -0,0 +1,56 @@
+package tools
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+// DateTimeTool provides precise current date/time with timezone support.
+// Models use this before creating cron jobs or any time-sensitive operation
+// instead of guessing timestamps from the system prompt's date-only field.
+type DateTimeTool struct{}
+
+func NewDateTimeTool() *DateTimeTool { return &DateTimeTool{} }
+
+func (t *DateTimeTool) Name() string { return "datetime" }
+
+func (t *DateTimeTool) Description() string {
+	return `Get the current date and time. Use this when you need precise timestamps for scheduling (cron jobs), logging, or any time-sensitive operation.
+
+Returns current time in both UTC and the requested timezone.
+If no timezone is provided, returns UTC only.`
+}
+
+func (t *DateTimeTool) Parameters() map[string]any {
+	return map[string]any{
+		"type": "object",
+		"properties": map[string]any{
+			"timezone": map[string]any{
+				"type":        "string",
+				"description": "IANA timezone name (e.g. 'Asia/Ho_Chi_Minh', 'America/New_York'). If omitted, returns UTC only.",
+			},
+		},
+	}
+}
+
+func (t *DateTimeTool) Execute(_ context.Context, args map[string]any) *Result {
+	now := time.Now()
+	result := map[string]any{
+		"utc":     now.UTC().Format(time.RFC3339),
+		"unix_ms": now.UnixMilli(),
+	}
+
+	if tz, ok := args["timezone"].(string); ok && tz != "" {
+		loc, err := time.LoadLocation(tz)
+		if err != nil {
+			return ErrorResult(fmt.Sprintf("invalid timezone '%s': use IANA names like 'Asia/Ho_Chi_Minh', 'America/New_York'", tz))
+		}
+		result["local"] = now.In(loc).Format(time.RFC3339)
+		result["timezone"] = tz
+	}
+
+	data, _ := json.MarshalIndent(result, "", "  ")
+	return NewResult(string(data))
+}