Update: parked HITL writes. Cheap Flash for a read-only analytics agent — dates, bilingual routing, and Gemini cache at 0%

Thanks for the replies on the last post (read-only POS copilot, route → fetch → narrate → ground, Node/TS + Vercel AI SDK). The write-path comments were consistent: preview ≠ confirm in the same loop, idempotency + optimistic lock, fail closed near mutations. That’s enough for me to hold HITL. I’m not adding mutate tools until the read loop is tighter. What I did take: honor pins (no more “computed but not registered”), keep CORE-first schemas, eval on traces / fetch / step count / $/% ⊆ DTO. I did not split into a two-call “CORE then pins” router. Model. Still Gemini 2.5/3.5 Flash Lite in dev. It’s cheap, and this job is “pick a tool, read a small JSON, say it in English or French.” I don’t want a high-thinking model in the loop. Dev is on their free tier. If that’s a trap (cache, tool-calling, bilingual), I’m open to another LLM — same constraint: low cost, good at tools + short narration, not a reasoner. Cost, typical ask (50 intent turns, one store, Redis miss, Flash Lite): Metrics mean median input tokens 4,840 4,718 Gemini cached input 0 0 output tokens 123 107 LLM steps (round trips) 2.0 2 tools called 1.0 1 wall time 2.3s 2.0s registered tools 12.2 12 Shape is almost always: step 0 pick one tool (~2.3k in) → fetch slim DTO → step 1 narrate (~2.6k in). Wider log (n=229): Gemini implicit cache 2.2% overall, 0/96 on current CORE-12, 0/51 on pinned. The only hits were an older CORE-10 prefix (~40% of that request’s input). So the prefix can cache; it isn’t right now. Pins aren’t proven as the breaker — CORE-12 alone is cold too. That’s why I didn’t add a second model call. Caveat: local eval + one store, short sessions. Redis exact-match is only for first-turn how-to, not analytics. Different cache. I’m optimizing the read agent next (Canada EN+FR). Two asks: Dates. Portal always sends a visible dateRange. A phrase table in our code may override it. The model never sets tool from/to — generateObject invented windows last time. When the table misses (hier, “this month vs last month”), do you pause with chips (Claude/OpenClaw-style, but as a UI interrupt, not a Gemini tool), or keep the bar default and name the window in the first sentence? I don’t want to ask on every “what’s our revenue?” Bilingual routing. Gemini can write French. Keyword pins / how-to terms are English, so « préparation cuisine » never loads get_fulfillment. I’m leaning EN+FR synonym tables on the same regexes, not translate-for-routing (mangles $/%) and not htt p 400 for other languages. Anyone run a bilingual keyword router that didn’t rot? Is request locale enough for answer language? Not selling anything. Happy to go into comments.