feat(monitor): focus on pstack sessions and show what each agent is doing

[thisguymartin]

What changed

• pstack only. The monitor marks a spawn tree as pstack work when any member shows pstack evidence: Claude attribution fields, a pstack: skill, agent, or command, a Codex prompt or runner call naming pstack, or any runner lane. The page shows those trees by default. Show all in the session list, or pstack-monitor start --all, shows every session.
• Running versus doing something. Sessions group into Working, Open (process alive, waiting for input), and Earlier. Claude sessions without a process record and Claude subagents follow turn boundaries, so a subagent reads done when its own turn ends. A turn-only run silent for 15 minutes reads as stalled instead of running forever.
• What each agent is doing. Each agent carries its latest prompt and the tool call awaiting a result. Cards, session rows, and the panel's Task and Now lines show them. The lane journal now records the first 300 characters of a lane's prompt.
• Wider panel. Drag the panel edge or use the widen button; the width persists, and a double-click resets it.
• Shorter prose. The monitor skill, usage guide, reference, changelog, README entries, CLI help, and page copy are rewritten shorter.

Verification

• Bun tests, strict typecheck, static invariants, and plugin validation pass.
• The exact candidate is installed in every affected harness.
• The changed behavior passes from each real user surface.
• The installed version, action, and observed result appear below.

Gate: 325 tests pass, bun run typecheck is clean, the four manifests parse, and PSTACK_STATIC_ONLY=1 bash tests/skill-collision-repro.sh passes.

Live evidence:

Checkout build 1.5.0+2322e9d9ab, not an installed plugin. Monitor started from the checkout with pstack-monitor start --parent claude and driven in headless Chrome:

• Only the three pstack sessions are listed. This Claude Code session sits under Working with its pending Bash call; two killed-mid-turn SDK sessions read stalled under Earlier. Show all lists 16 sessions.
• Lanes run through pstack-runner from this session attach under it. A Codex lane showed working · 14s with its pending sleep 25 call, then done. MiniMax and DeepSeek lanes (no API keys here) and a Grok lane (CLI not installed) showed failed with the receipt's reason.
• Dragging the panel edge set it to 905px, the width survived a reload, and a double-click reset it to 460px. At 800px wide the layout collapses to one column.

Still needed before this leaves draft: the installed candidate tested from the Claude Code and Codex surfaces, and a successful MiniMax, DeepSeek, and Grok lane.

A pull request without live evidence remains a draft. Do not merge, tag, release, or roll it out.