[FEATURE]: Show message/run start and completion timestamps with millisecond precision #35348

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

OpenCode already shows how long a turn/run took, and the TUI has a /timestamps toggle for message creation times. I would like an option to show the exact start and completion timestamps for a turn/run directly in the TUI and/or web UI.

Desired display:

• Start timestamp with full date and local time down to milliseconds
• Completion timestamp when the run finishes, also down to milliseconds
• Existing duration can remain, but should be paired with the explicit start/end times

Example:

Started:   2026-07-04 14:32:18.427
Completed: 2026-07-04 14:35:02.913
Duration:  2m 44.486s

Why this would be useful

When reviewing sessions later, it is helpful to know not just how long something took, but exactly when it started and when it completed. This is especially useful for:

1. Tracking when work was completed from the UI/front-end side
2. Correlating OpenCode activity with git commits, CI logs, deploys, terminal output, and external incidents
3. Reviewing long sessions where several runs happen close together
4. Auditing/debugging tool calls and assistant turns with precise wall-clock timing

Related but narrower issues

• [FEATURE]: Add timestamp next to messages in chat (both agent and user messages) #8634 asks for timestamps next to messages
• [FEATURE]: Add seconds to message timestamp display #20406 asks for seconds in message timestamps
• [FEATURE]: Show timestamp and duration on tool execution blocks #22144 asks for timestamp + duration on tool execution blocks
• [FEATURE]: TUI: timestamp gutter mode for messages #29399 asks for a timestamp gutter mode
• /timestamps command has no visible effect and /exit missing from autocomplete #26625 reports /timestamps not visibly rendering in some TUI cases

This request is specifically for visible start and completion timestamps with millisecond precision, not only creation time or duration.

Implementation notes

The message data already appears to include millisecond-level timing fields such as created/completed times, since OpenCode can calculate durations. This may primarily be a display/configuration feature rather than a new data model requirement.

Possible UI approaches:

• Add an expanded timestamp mode behind /timestamps
• Add a config option for timestamp precision/format
• Show full details on hover/focus/expanded message metadata
• Add a compact line under each completed assistant turn: 2026-07-04 14:32:18.427 → 14:35:02.913 · 2m44.486s