feat(date-time): standardize time context and tool timestamps

docs/date-time.md

@@ -0,0 +1,85 @@
+---
+summary: "Date and time handling across envelopes, prompts, tools, and connectors"
+read_when:
+  - You are changing how timestamps are shown to the model or users
+  - You are debugging time formatting in messages or system prompt output
+---
+
+# Date & Time
+
+Clawdbot uses **UTC for transport timestamps** and **user-local time only in the system prompt**.
+We avoid rewriting provider timestamps so tools keep their native semantics.
+
+## Message envelopes (UTC)
+
+Inbound messages are wrapped with a UTC timestamp (minute precision):
+
+```
+[Provider ... 2026-01-05T21:26Z] message text
+```
+
+This envelope timestamp is **always UTC**, regardless of the host timezone.
+
+## System prompt: Current Date & Time
+
+If the user timezone or local time is known, the system prompt includes a dedicated
+**Current Date & Time** section:
+
+```
+Thursday, January 15th, 2026 — 3:07 PM (America/Chicago)
+Time format: 12-hour
+```
+
+If only the timezone is known, we still include the section and instruct the model
+to assume UTC for unknown time references.
+
+## System event lines (UTC)
+
+Queued system events inserted into agent context are prefixed with a UTC timestamp:
+
+```
+System: [2026-01-12T20:19:17Z] Model switched.
+```
+
+### Configure user timezone + format
+
+```json5
+{
+  agents: {
+    defaults: {
+      userTimezone: "America/Chicago",
+      timeFormat: "auto" // auto | 12 | 24
+    }
+  }
+}
+```
+
+- `userTimezone` sets the **user-local timezone** for prompt context.
+- `timeFormat` controls **12h/24h display** in the prompt. `auto` follows OS prefs.
+
+## Time format detection (auto)
+
+When `timeFormat: "auto"`, Clawdbot inspects the OS preference (macOS/Windows)
+and falls back to locale formatting. The detected value is **cached per process**
+to avoid repeated system calls.
+
+## Tool payloads + connectors (raw provider time + normalized fields)
+
+Channel tools return **provider-native timestamps** and add normalized fields for consistency:
+
+- `timestampMs`: epoch milliseconds (UTC)
+- `timestampUtc`: ISO 8601 UTC string
+
+Raw provider fields are preserved so nothing is lost.
+
+- Slack: epoch-like strings from the API
+- Discord: UTC ISO timestamps
+- Telegram/WhatsApp: provider-specific numeric/ISO timestamps
+
+If you need local time, convert it downstream using the known timezone.
+
+## Related docs
+
+- [System Prompt](/concepts/system-prompt)
+- [Timezones](/concepts/timezone)
+- [Messages](/concepts/messages)