fix(tui): preserve agent state after compaction

[ndarilek]

Track lastUserMessage().id changes instead of session ID changes when
syncing agent state. Previously, compaction would create a new user
message with the current agent mode (e.g., "plan"), but since the
session ID stayed the same, the agent state was never synced from it.

Fixes #8349

[github-actions]

Hey! Your PR title preserve agent state doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

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

Based on my search, I found some potentially related PRs:

Most Relevant:

• feat(compaction): Hybrid compaction pipeline with deterministic extraction + LLM #7104: feat(compaction): Hybrid compaction pipeline with deterministic extraction + LLM - Related to compaction which is mentioned in your fix
• feat(tui): fire-and-forget async subagent tasks #7206: feat(tui): fire-and-forget async subagent tasks - Related to TUI agent state management

Windows/Path Related:

• fix (desktop): menu behavior in the desktop app on windows/linux #9872: fix (desktop): menu behavior in the desktop app on windows/linux - Windows-specific fixes
• fix(tui): fix Ctrl+V paste on Windows/WSL2 (#6560 and #8209) #8626: fix(tui): fix Ctrl+V paste on Windows/WSL2 - Windows path/clipboard handling
• fix(core): normalize file paths in read tool output #7015: fix(core): normalize file paths in read tool output - Path normalization

These PRs could be related to your changes around agent state preservation and Windows path handling. However, none appear to be direct duplicates of PR #10101. The closest related work seems to be PR #7104 on compaction and PR #7206 on TUI agent tasks.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.