t3 thread: add archive, settle, and delete subcommands

[andydoucet]

t3 thread can list/start/send/show, so scripts and outside orchestrators can create threads but can't clean them up. Bots that run many jobs leave dozens of finished threads behind (see also #27117, one auth session per call).

cli/thread.ts already opens an MCP session to /mcp, and t3_thread_organize supports settle | archive | unarchive (and pin/snooze). Proposal:

t3 thread settle <thread-id> [--json]
t3 thread archive <thread-id> [--json]
t3 thread unarchive <thread-id>
t3 thread delete <thread-id> [--yes]

The first three map directly to t3_thread_organize. Delete currently has no MCP tool (only the thread.delete orchestration command), so this needs either a t3_thread_delete tool (or a delete action) requiring orchestration:operate, or delete stays out of scope. Exit non-zero on active turns, consistent with #23451. Settle/archive of an active thread should error instead of breaking the turn (#15135).

[dmitryrechkin]

We built this (and a bit past it) on a fork, so consolidating here rather than in a second thread — I opened #27972 a day after this one before finding it.

Branch: https://github.com/dmitryrechkin/t3code/tree/feat/plat-240-cli-commands (on top of 80a2351f), live-tested against a running server.

What it does, and how it maps to the tools that already exist:

• thread organize <id> <action> — pin | unpin | snooze [--snoozed-until] | unsnooze | settle | unsettle | archive | unarchive | mark_unread via t3_thread_organize, so settle/archive/unarchive land without the checks already in that tool.
• thread stop <id> — t3_thread_interrupt with stop: true (the Stop button: interrupt, hold the queue, end PR watches, stop delegated tasks), plus thread interrupt <id> for the plain case.
• thread configure <id> [--provider --model] — t3_thread_configure, read-only when no flags are passed.
• thread wait <id> [--run] [--timeout] — t3_thread_wait in slices, exit 0 completed / 1 failed / 2 waiting for an answer / 3 deadline.
• thread prs <id>, thread rename <id> <title>, models [--search], project list [--json] — PR list, t3_thread_update, orchestrator_capabilities, and the project-id lookup scripts keep reimplementing.
• t3 mcp list | describe | call <tool> — the escape hatch so the long tail (t3_queue, t3_pending_request, t3_thread_transfer, scheduled tasks, PR linking) needs no dedicated command.

On delete: I left it out for the reason you give — no MCP tool exposes thread.delete, and adding one is an access-model decision (orchestration:operate), not a wrapper. Settle (settled: true), archive (archived: true, disappears from thread list) and stop are all verified live.

One small server change came with it: OrchestratorMcpThreadListItem now carries branch and worktreePath (optional on the wire), so thread list --branch no longer costs one read per thread; older servers fall back to reading.

Focused tests: 34 in cli/{thread,project,models}.test.ts plus 5 for the mcp commands; contracts and MCP/orchestration suites green; tsc and lint clean.

Not upstreamed yet — waiting on approval, per CONTRIBUTING.