Add agent-shell-restore-context defcustom

[nhojb]

Currently when restoring a session you can choose a minimal resume or a full load via agent-shell-prefer-session-resume.

This PR adds a summary option via a new agent-shell-restore-context defcustom. The options are:

• minimal: Equivalent to agent-shell-prefer-session-resume: t
• full: Equivalent to agent-shell-prefer-session-resume: nil
• summary: Loads the full session (when available), but renders only the first prompt and last text response.

The idea is that summary gives you enough context about the session, without needing to restore the entire conversation and tool calls.

Here's an example:

Checklist

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[xenodium]

Thanks for the PR!

Left a couple of minor comments.

The more significant request I'd ask is that you commit to landing the feature, if that's ok with you? If there are related bugs raised, I'd cc ya for visibility.

[xenodium]

How about naming this agent-shell-session-restore-strategy, it's its more about restoring sessions than context-centric?

[xenodium]

Can we reserve summary for a different feature please?

I've been contemplating pairing resume request with an automaric prompt sent to agent asking to summarize the resumed session.

Maybe name it 'first-last?

[xenodium]

nit: search "Initial prompt", replace with "First prompt".

[nhojb]

Thanks for the review. Just pushed the suggested fixes.

The more significant request I'd ask is that you commit to landing the feature, if that's ok with you? If there are related bugs raised, I'd cc ya for visibility.

Yes, I'm quite happy to tackle any related bugs and own the feature 😅