docs: retire cron, record MQTT/discovery/gemma4 decisions

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

DECISIONS.md

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+# POS-Automation — Decisions
+
+Format: `YYYY-MM-DD: <decision> — <why>`
+
+- **2026-06-07: On-demand trigger via MQTT bridge (lgtv pattern), not cron.** Seth
+  wants a Google Home button, not a scheduled print. Bridge `pos-briefing-mqtt.service`
+  (systemd, `User=claude`) on steel141 subscribes to `posbriefing/button/press` on
+  broker CT 301 (192.168.0.154); HA exposes a `script` to Google as a Scene (button).
+  The earlier "schedule 4:58am/3pm" was never a real cron job — that commit only
+  edited SESSION.md.
+- **2026-06-07: Printer discovered by MAC `50:57:9c:eb:0f:07`, not a fixed IP.** The
+  TM-m30's IP changes on every reboot (router DHCP, no reservation). Cache last IP
+  (`~/.cache/pos-briefing/last_ip`), verify by MAC + port, sweep the /24 on a miss.
+  A router DHCP reservation would make this belt-and-suspenders but isn't required.
+- **2026-06-07: Summaries on `gemma4:26b`; story selection stays on a fast model.**
+  Seth asked to switch summaries to gemma4. gemma4:26b under `format:json` ignores
+  the bare-array instruction and emits a reasoning object (`{"thought": ...}`), which
+  broke Phase-1 selection. Selection now uses `ollama_select_model` (default
+  `qwen2.5:1.5b`); summaries use `ollama_model` = `gemma4:26b`. Also better latency
+  for an interactive button.
+- **2026-06-07: yfinance installed on steel141** via `pip --user --break-system-packages`
+  (PEP 668). It was missing after the CT 166 → steel141 migration — the original
+  "not firing" had two causes: no cron ever installed + this missing dependency.
+- **2026-06-07: paho-mqtt v1 callbacks (`CallbackAPIVersion.VERSION1`).** paho 2.1.0
+  is installed for `claude`; matches the working lgtv bridge. One-time deprecation
+  warning at startup is harmless.
+
+## Deferred / Rejected
+- **Print latency (~1–2 min/press):** gemma4:26b summarization (+ yfinance) dominates.
+  Acceptable for v1; the button returns immediately and `posbriefing/status` tracks
+  progress. Optimize later (model keep-alive, fewer/shorter summaries) if it annoys.
+- **Router DHCP reservation for the printer:** Seth's router action; MAC discovery
+  makes it optional. Add if convenient to drop the sweep fallback.
+- **zfs/reddit/grafana dashboard fields return None on steel141** (not the tank/ZFS
+  host; `cannot open 'tank'`). Out of scope for the trigger work — track separately.