add chat timeline navigation with message timestamps

[Artawower]

Small UX improvements that allow you to quickly find user messages, navigate to them in the chat, and quickly paste them back into the prompt input field, similar to what opencode does.

[Copilot]

Pull Request Overview

This PR adds chat timeline navigation features to the ECA chat interface, enabling users to quickly locate and reuse previous messages through a completion-based interface with timestamp metadata.

Key Changes:

• Adds timestamp tracking to user messages via overlays
• Implements three new interactive commands for message navigation and reuse: eca-chat-timeline, eca-chat-repeat-prompt, and eca-chat-clear-prompt
• Updates the transient menu with new keybindings and corrected menu labels

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
eca-util.el	Updates transient menu with new navigation commands and fixes menu label typo
eca-chat.el	Implements core timeline functionality including timestamp tracking, message extraction, and navigation commands

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[ericdallo]

That looks nice! I will take a closer look soon
Did you try C-<up> to cycle message history? I know it doesn't show timestamp, but it's what I use since day 1

[Artawower]

Yes, I often use this feature, but during long conversations, scrolling through messages can take quite a long time. Completion helps me quickly filter messages by history using fuzzy search and then copy/go to them.

Of course, I could have searched using a regular search, but during long conversations there’s also quite a lot of noise from the agent’s responses

[ericdallo]

Sounds convenient enough, and given considerably small changes, I'm happy to accept that, will take a look soon, thank you!

[ericdallo]

looks and works great, thank you!