feat(cli): add areno runs command to list active/recent runs

[wtbdev]

Closes #250

Summary

Add areno runs — a lightweight CLI command that lists active and recent AReno train/serve runs from the existing ~/.areno/dashboard-jobs.json registry. No database, no new dependencies, no GPU imports.

Usage

areno runs               # terminal table (default)
areno runs --json        # machine-readable JSON
areno runs --limit 10    # show last 10 entries
areno runs --all         # show all entries

Output (table mode)

STATUS     KIND    NAME                  PID    AGE        DURATION
rollout    train   gspo Qwen/Qwen3-0.6B  12345  3m 12s ago 3m 12s
exited     serve   serve my-model        12344  1h 20m ago 1h 20m
succeeded  train   sft my-checkpoint     12300  2d 5h ago  45m 30s

What changed

File	Change
areno/cli/dashboard_registry.py	+218: public read_registry(), pid_is_running(), read_dashboard_state(), derive_status(), compute_age(), compute_duration(), format_table()
areno/cli/runs.py	New: runs_command click command
areno/cli/main.py	+1 line: register "runs" in _COMMANDS
tests/test_cli_runs_cpu.py	New: 29 CPU tests

Status derivation

Condition	Status
PID alive + stage info	Stage name (e.g. rollout, train)
PID alive, no stage	running
PID dead, dashboard state status=succeeded	succeeded
PID dead, dashboard state status=failed	failed
PID dead, dashboard state status=stopped	stopped
PID dead, no state file	exited

Status uses the status field written by the dashboard server's job watcher (not returncode, which is never persisted to disk).

Design decisions

• Zero heavy imports — the command only depends on stdlib + click; no torch/engine/GPU needed
• Shared utilities in dashboard_registry.py — PID check, age/duration formatting, status derivation, and table formatting live alongside the existing registry I/O so that future CLI commands (e.g. Compare two training runs from the CLI #255 areno diff) can reuse them without duplication
• Duration uses wall-clock time — since updated_at is initialized to created_at at registration and never updated for CLI-started jobs, compute_duration() falls back to time.time() unless updated_at > created_at

Tests (29 CPU)

• Age/duration formatting (6)
• Status derivation: running, running+stage, succeeded, failed, stopped, exited, unknown (8)
• Registry I/O: empty, malformed, missing file, PID dedup (4)
• CLI integration: --json, --limit, --all, sorting, help output, table output (9)
• Edge cases: missing pid field, wrong pid type (2)

--
🤖 Generated with Claude Code