feat(tui): load conversation and session history

[ryanwyler]

Summary

Adds on-demand message loading UI to the TUI, enabling users to access message history beyond the initial 100-message window.

Depends on: #8996 (adds ts_before and breakpoint API parameters)

Problem

Users cannot access message history beyond the initial 100 messages loaded on session init:

• Resolves Cannot scroll to beginning of long conversations (message limit hardcoded to 100) (#6138) #6137 - Cannot scroll to beginning of long conversations
• Resolves feature request: pagination for messages & sessions #4918 - Feature request: pagination for messages & sessions
• Resolves old messages disappear #7380 - Old messages disappear
• Related to feat: virtualized scrolling + paginated message loading for long sessions (#8535) #6548

Solution

Two loading modes accessed via a "Load more messages" banner when 100+ messages are present:

1. Load conversation history - Loads messages up to the next compaction summary, providing relevant context without overwhelming the UI
2. Load full session history - Loads all remaining messages for complete session reconstruction

Key features:

• Only pulls missing messages (uses ts_before timestamp anchoring)
• Zero breaking changes - all parameters optional
• Message roll-off maintained - works with existing 100-message pruning
• Toast notifications show message counts

Why Two PRs?

This PR was split from the original #8627 to separate concerns:

1. feat(session): add ts_before and breakpoint params to Session.messages API #8996 (API foundation) - Adds ts_before and breakpoint params to Session.messages(). This is a foundational capability that benefits:

   • This TUI implementation
   • Web client (currently reloads all messages)
   • SDK consumers building custom integrations
   • Other pagination approaches (feat(session): bi-directional cursor-based pagination (#6548) #8535, session: paginate message loading #6656)

2. This PR (TUI consumer) - Implements the user-facing feature using the API

This separation allows the API enhancement to merge independently and unblock multiple consumers.

Implementation

Client (sync.tsx):

• loadConversationHistory() - calls API with breakpoint: true
• loadFullSessionHistory() - calls API without breakpoint

UI (routes/session/index.tsx):

• Synthetic __load_more__ message prepended when 100+ messages
• Clickable options with hover states
• Loading state prevents duplicate requests

Screenshots

From original PR #8627:

Option to load conversation or full session:

Loading conversation history:

Loading full session history:

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one highly related PR that appears to be the original version of the current PR:

Related PR

PR #8627 - feat(tui): load conversation and session history

• feat(tui): load conversation and session history #8627
• This is the original PR from which the current PR (feat(tui): load conversation and session history #8999) was split. According to the description in the current PR, feat(tui): load conversation and session history #8627 was split into two separate PRs (feat(session): add ts_before and breakpoint params to Session.messages API #8996 for API foundation and feat(tui): load conversation and session history #8999 for TUI consumer implementation).

Additional Context

The search also found:

• PR feat(session): add ts_before and breakpoint params to Session.messages API #8996 - feat(session): add ts_before and breakpoint params to Session.messages API (the dependency PR mentioned in feat(tui): load conversation and session history #8999)
• PR feat(tui): add session_list_limit for session picker (#6137) #6138 - feat(tui): add configurable message_limit for session history
• PR session: paginate message loading #6656 - session: paginate message loading
• PR feat(session): bi-directional cursor-based pagination (#6548) #8535 - feat(session): bi-directional cursor-based pagination

However, #8627 is the most directly related as it represents the original work that was intentionally refactored and split into the current PR (#8999).