ACP resume does not replay history and session list titles stay generic

[i-oliva]

What happened?

When OpenCode is used through an ACP client like agent-shell, reopening an existing session via ACP resume can restore the session id/config without replaying the prior conversation, so the client opens the session but does not show the earlier messages.

In the same ACP workflow, session/list can surface generic titles like New session - ... even when the first real user prompt would be a much better label for session pickers.

Expected behavior

• ACP resume should replay the existing session history so ACP clients can render the earlier conversation.
• ACP session lists should expose a readable fallback title when the persisted session title is still the default placeholder.

Reproduction

1. Open an OpenCode session from an ACP client such as agent-shell.
2. Have a short conversation and close the client.
3. Reopen that same session through ACP resume.
4. Notice that the prior conversation is not replayed.
5. Look at ACP session lists for untitled sessions and notice generic New session - ... labels.

[github-actions]

This issue might be a duplicate of an existing issue for part of its scope. Please check:

• [FEATURE]: ACP sessions should get auto-generated titles instead of "ACP Session <UUID>" #13139: Covers the same "generic session titles" problem for ACP sessions (sessions showing ACP Session <UUID> or placeholder titles instead of meaningful labels).

If the session title concern in this issue is the same as #13139, consider whether it should be tracked there instead. The ACP resume history-replay aspect appears to be distinct and not covered by existing issues.