feat(cli): remove per-60-second Haiku headline ticker

[SamPlvs]

Summary

Removes the periodic Haiku headline ticker from zo build / zo continue runs. The ticker spawned claude -p --model haiku every 60 seconds throughout a session to summarise recent agent events into a one-line headline printed in the lead pane. User feedback: nobody uses it. The lead pane already shows the live task list and agent events in real time, so the Haiku summary added decoration, not signal.

Cost saved

• ~60 subprocess spawns per hour at ~$0.0001-$0.0003 each
• ~$0.06-$0.18 per 10-hour overnight run in Haiku spend
• Plus the latency / CPU churn of repeatedly spawning a Claude Code subprocess every minute

What's kept

• _generate_session_summary — single Haiku call at session end (~$0.0002 per run) that prints a 2-3 bullet wrap-up of what the team accomplished. Useful, cheap, one-shot. User explicitly confirmed keeping this.
• _headline_buffer and all the .append(...) event-capture calls in _print_status — still feed the end-of-session summary.
• --no-headlines CLI flag — preserved for backwards compatibility. Its meaning narrows to "skip the end-of-session bullet summary too" (it can no longer disable the ticker, because the ticker doesn't exist).

⚠️ Behavior change

Anyone running zo build today sees a console headline every 60s (e.g., ▸ data-engineer profiling features...). After this PR they don't. The end-of-session bullet summary is unchanged.

What was removed

Code (src/zo/cli.py):

• _maybe_print_headline() function (~30 lines)
• _last_headline_time + _headline_interval timer variables
• The _maybe_print_headline() call inside _print_status

Doc language about the ticker (rewritten or removed):

• docs/cli/build.mdx — Step 5 monitoring sentence, "Headlines" Live-monitoring Card (deleted), options table --no-headlines row, --low-token accordion text
• docs/cli/overview.mdx — shared options table --no-headlines row
• docs/quickstart.mdx — "What you'll see" bullet list + --low-token Note
• docs/COMMANDS.md — --low-token and --no-headlines lines
• docs/concepts/low-token-mode.mdx — two preset tables + Batch API forward-looking note
• docs/reference/low-token-preset.mdx — preset table + override flag entry

Pre-push verification (PR-039 protocol)

$ uv run ruff check src/
All checks passed!

$ uv run --python 3.11 pytest -q
743 passed, 7 skipped in 6.45s

$ uv run --python 3.12 pytest -q
743 passed, 7 skipped in 6.31s

$ bash scripts/validate-docs.sh
9 passed  0 failed  2 warnings  (11 checks)
Documentation is consistent with codebase.

Note: PR #92 (bypass-permissions, +17 tests) is still open and unmerged, so the test count baseline is 743 here rather than 760. This PR is independent of #92 — different files, no merge conflict either way.

Memory protocol

Per CLAUDE.md auto-protocol:

• memory/zo-platform/STATE.md — session 032 hand-off entry prepended.
• memory/zo-platform/DECISION_LOG.md — FEATURE-REMOVAL + BEHAVIOR-CHANGE entry at 2026-05-28T20:00:00Z with rationale and four alternatives considered (remove end-of-session too / remove flag entirely / non-LLM summariser / make ticker opt-in).
• No new PRIOR — this is a clean feature-removal driven by user feedback, not a failure-trace self-evolution.

Manual verification suggestion

After merge + deploy, on next zo build or zo continue run:

• ✅ Lead pane should NOT show any ▸ <one-line headline> output
• ✅ Lead pane SHOULD still show the live task list + recent agent events as before
• ✅ At session end, the 2-3 bullet Haiku summary SHOULD still print (unless --no-headlines or --low-token was passed)

🤖 Generated with Claude Code

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