XERK-130: active sessions no longer read idle on narrow panes

[xerhab]

What

The ticket: session working/idle accuracy — "more often than not active sessions are marked as idle".

Reviewing the live sessions on the fleet host found the cause. tmux keeps a window at its smallest-ever attached client width; a session once viewed from a phone renders ~54 columns. At that width the Claude Code TUI ellipsizes the footer's · esc to interrupt hint to · esc to inte…, and both busy detectors key on the full string:

• _busy_from_capture in hub-agent.py — the heartbeat's paneBusy, which drives every status surface (fleet dots, session cards, glasses glyph, Android list) and the turn-finished notification;
• parsePaneLiveTurn's gate in tunnel-agent.js — the live chat's working bar / Stop button.

So every working session on a narrowed pane read idle for its entire turn. Four of five live sessions on the host were on 54-col panes.

Fix

Both detectors now accept two additional shapes (same shapes on both sides, per the existing parity contract):

• the width-truncated hint remnant on the mode footer line: mode-glyph (⏸/⏵) anchored line whose last ·-segment is any prefix of esc to interrupt ending in the TUI's own …. Character-class prefix matching covers every cut point; middle segments vary across sessions ((shift+tab to cycle) comes and goes, a · PR #98 chip can sit before the hint) so the anchor is the glyph + tail, not fixed wording. The idle suffix · ← for agents can never match (doesn't start with e). This is the only visible signal while text streams on a narrow pane (no spinner painted then) or while the pane is scrolled up.
• the column-0 spinner line (✢ Determining… (12m 19s · ↓ 44.2k tokens), · Perusing… (54m 38s · still thinking)): glyph-agnostic but excluding the assistant ● bullet and ❯ prompt, requiring the gerund's ellipsis — the completed-turn line an idle pane keeps on screen (✻ Brewed for 9s) has none, and echoed pane captures in tool output are indented, so neither fakes busy.

Both fail toward idle (today's behaviour) if the TUI wording shifts, and stay off when TURMA_PANE_BUSY_MARKERS is emptied.

How it was verified

• Empirically diagnosed and verified against the real fleet: captured live panes of 5 running sessions; a probe claude TUI at 200 and 54 columns captured the exact idle footer (· ← for agents, no hint), busy footer (full hint), truncated busy footer, and completed-turn line.
• Ran the new _busy_from_capture against all 5 live panes: the two working sessions flipped idle→busy (the defect), the idle/dialog ones stayed idle — before/after comparison in the session transcript.
• python3 -m unittest agent.tests.test_hub_agent: 737 tests OK (10 new narrow-pane cases in TestPaneBusy).
• node --test agent/tests/tunnel-agent.test.js: 62 tests pass (4 new parsePaneLiveTurn fixtures).

Agent-side only — no web UI change, so no Android parity work.