feat(threads): show pending agent questions

[lastobelus]

What Changed

• Ports upstream PR #9583, including upstream commits bbd8995b3c and 9993263aee.
• Adds authenticated, thread-scoped set_thread_attention and clear_thread_attention tools to the existing t3-code MCP server.
• Shows a bare violet ? in compact sidebars and ? Question where long labels fit, across web/desktop and mobile.
• Clears the marker on the user's next reply or explicit settlement; automatic settlement waits for it to clear.
• Enforces the attention-only MCP endpoint when agent browser access is disabled and records the real question timestamp for snooze wake indicators.

LastCode Adaptations

• Preserves LastCode's action-resume MCP tools and its existing Waiting status priority.
• Preserves thread annotations, persistent threads, latest-user-message tracking, and worktree-cleanup projections.
• Uses migration 57 because LastCode already owns migrations 48–56.
• Keeps the full MCP endpoint limited to preview-capable credentials while exposing only thread-attention tools on /mcp/thread.

Why

Interview-style agent workflows can end on a blocking question while looking indistinguishable from completed threads. The explicit MCP signal is reliable and authenticated to the current thread, unlike parsing provider terminal output. A discriminated attention record keeps the initial UI narrow while allowing additional user-actionable kinds later without another persistence redesign.

UI Changes

Before: a blocking agent question fell back to the thread timestamp.

After: the row shows a bare violet ?, plus Question in layouts with long status labels. Native input continues to show Input / Awaiting Input.

Live web QA covered desktop and responsive sidebar layouts in dark mode. The visual artifact is intentionally not committed to the repository.

Validation

• 14 affected test files passed; the final MCP/snooze follow-up added 39 passing tests in its focused run.
• LastCode Quick CI passed at d3df114d24 (format, lint with no errors, and all 15 workspace typechecks).
• Live web QA passed for desktop and responsive layouts.

Implemented with GPT-5.6-Sol in the T3 Code Codex harness.