Drum Bun: an agent that knows Romania rewrote its vignette this week

This is a submission for the Sanity Challenge, Path One: Ship an Agent That Queries Real Content

TL;DR: Drum Bun tells a driver what their car needs between Romania and Germany or Austria, computed from dated, structured content in Sanity; the model never computes a price. On 18 questions in four languages: agent 18 / 18, semantic search over the same documents 16, keyword search 13, the same model without the content 4. Try it live, no login.

What I Built

Every Christmas, Romanians who live in Germany and Austria drive home through Hungary: over the 2019 holidays about 941,000 people crossed Romania's western border, 361,000 at Nădlac II alone (Romanian Border Police). The questions before the drive are always the same: which vignettes, for which days, bought where, and what else gets you fined on the way? The answers are spread over four toll operators, four languages and a lot of outdated blog posts.

This year they changed under everyone's feet:

• Romania replaced its rovinietă on 1 October 2026: new seller (TollRo), prices in lei by Euro class, and a car whose class cannot be shown pays the Euro 0 rate. It went live at midnight, as planned.
• Hungary added an M1 regional vignette in 2026 that can make a yearly crossing cost less than half the national one, if you know that the Pest and Komárom-Esztergom county vignettes leave a gap on the M1 that only Fejér covers.
• Austria sells only digital vignettes for validity from 1 December 2026, raised the on-the-spot penalty to €200, and its 2027 prices are not published yet, so a Christmas trip cannot be priced exactly.

Drum Bun ("have a good road", what Romanians say before a journey) tells you what your car needs for your trip:

• the cheapest set of products per country for your dates and vehicle, with the price valid on each travel day (and a flag when it is not published yet);
• the rules that apply on those dates (winter tyres, emission zones at the destination, border checks);
• the outdated claims you probably read, each linked to the fact that corrects it;
• an agent you can ask in Romanian, German, Hungarian or English, which shows every Knowledge Base entry and query it used.

Demo

Live: https://drum-bun-agent.vercel.app (no login; the planner works without the model, the chat is rate-limited)

The route as a strip map drawn from the data: tolled sections red with a yellow core, free sections hollow, borders dashed.

Every answer shows its steps: planner run, Knowledge Base entries opened, GROQ queries.

Code

danielbutnar / drum-bun

Road-trip agent on Sanity Context: vignettes, tolls and rules between Romania and Germany/Austria, priced for your dates

Drum Bun

What your car needs on the road between Romania and Germany or Austria: vignettes and tolls for your dates (the cheapest combination), winter-tyre and emission-zone rules, and which claims you read online are out of date. Every answer is traced to an official source.

Live: https://drum-bun-agent.vercel.app · Demo video (2:52): https://youtu.be/X2qOuYowQro · Sanity project pd5e7gez, dataset production (public) · Built for the DEV Sanity Challenge, Path One: the post.

"Drum bun!" is what Romanians say before a journey, and what the sign says when you leave a town.

Why this needs structure

"What does Brașov → Munich on 20 December, back 3 January, cost in a Euro 5 diesel?" has no page that answers it. The answer is computed from:

• the route: which road sections, in which Hungarian counties, which are tolled (the Salzburg Nord → Walserberg stretch is free, the M1 between…

View on GitHub

How I Used Sanity

1. Structured content that computes

"Brașov to Munich, 20 December, back 3 January, Euro 5 diesel" has no page that answers it. So the content is modelled as the pieces the answer is computed from:

• route → ordered legs → roadSection references. A section has tolled, coveredBy[] (the products that make it legal, any one is enough), counties[] and exemptVehicles[].
• tollProduct with validity (days, months, calendarYear with overlap windows) and dated prices[]: each price has validFrom/validTo and an optional emission band (euroMin, euroMax, electric, appliesWhenUnknown).
• rule with a yearly season window, conditional + condition, effectiveFrom/To and severity; zone with dieselMinEuro and status.
• claim: a statement found online, its verdict (outdated, wrong, misleading), the source it was seen on, and correctedBy[] references to the facts that are true now.
• source with trust (official, club, press, blog, forum), language and checkedAt. Every fact references at least one.

Two of the stored prices of the 12-month rovinietă, as the planner reads them:

{"amount": 292, "currency": "RON", "validFrom": "2026-10-01", "validTo": "2026-12-31",
 "band": {"label": "Euro IV–V", "euroMin": 4, "euroMax": 5}}
{"amount": 330, "currency": "RON", "validFrom": "2026-10-01", "validTo": "2026-12-31",
 "band": {"label": "Euro 0–III or unknown", "euroMin": 0, "euroMax": 3, "appliesWhenUnknown": true}}

A pure planner with 21 unit tests walks that structure: it picks the price valid on each date, runs a small dynamic program for the cheapest cover (two 1-day vignettes beat one 2-month; a 2026 Austrian annual vignette still covers 3 January 2027), solves an exact set cover over Hungarian county vignettes and the M1 regional one, and applies Austria's 18-day rule for online purchases. The agent calls it as a tool. The model never computes a price.

2. A Knowledge Base from official pages in four languages

The Knowledge Base "Drum Bun road rules" is built from the dataset (a GROQ query that flattens each document into readable fields) plus 20 web pages: the toll operators, ministries and cities in Romanian, Hungarian, German and English, and the blogs drivers actually read. The first build filed 14 issues; after all fixes and a full rebuild the Knowledge Base has 22 entries from 103 dataset documents and 20 web pages, 21 decided issues and 9 standing instructions. I resolved them with @sanity/client's context API instead of clicking through the Dashboard, so every decision is in the repo with its reason (decisions.md):

• Two of the four conflicts came from my own vocabulary: the build read my enum value carTrailer as "a trailer" and concluded trailers must carry warning triangles. One standing instruction fixed the vocabulary for every future build. Of the other two, one was true for different dates (Austria's substitute toll was €120 before 2026, €200 since), so an instruction now makes entries state the date; the other was a Hungarian motorcycle price that is right once you know motorcycles buy the car's annual vignette.
• It invented Hungarian purchase points (post offices, the automobile club) that no source names. An instruction limits entries to the channels the sources name.
• It missed one: an entry quoted the Romanian Interior Ministry page's winter-tyre fine, computed with an old penalty-point value. I wrote an instruction scoped to that page; the background contradiction check then filed an issue against the stale entry by itself, and applying it fixed the number. That loop, human instruction → automatic check → issue → rebuild, is the part I would not want to build myself.
• It keeps up. On 1 October, the day Romania switched, I updated the dataset and ran a refresh: it re-checked every source and filed four issues, all about pages it had imported but never cited (CNAIR's own TollRo announcement, and four more pages with outdated prices or the German car-toll myth). I applied them and rebuilt the two entries that still mentioned the postponement bill.

One of the conflicts the build filed, with the decision and the reason.

The public How it knows page shows every issue with both sides, what was kept, the standing instructions and the outline, from a snapshot the script writes into the dataset.

3. Sanity Context MCP, two endpoints

One endpoint serves one mode, so there are two: drum-bun-kb (Knowledge Base mode: outline + knowledge_base_read/knowledge_base_search) and drum-bun-rules (GROQ mode over the dataset, embeddings enabled). The agent (AI SDK 7, AI Gateway) fetches both initial contexts once, inlines them, and gets the planner as a third tool. Conversations are saved with Sanity Context Insights; a daily cron classifies them.

4. Does structure beat search?

Eighteen questions in Romanian, German, Hungarian and English, each with facts an answer must contain and outdated facts it must not (questions). Three baselines get the same model, the same prompt and output budget, and the same fields of the same Sanity documents the Knowledge Base ingests. Only retrieval differs. (Re-run on 1 October with semantic search added, because an any-word keyword search alone is an easy opponent.)

	correct
Drum Bun agent (planner + Knowledge Base + GROQ via Sanity Context)	18 / 18
Semantic search over the same documents (embeddings, top 6)	16 / 18
Keyword search over the same documents (any word, top 6)	13 / 18
The same model with no documents	4 / 18

The model on its own gets only the facts that have not changed in years (4 / 18). Give it the structured documents and even a search box answers most single facts, because the dataset states them plainly, with dates and Euro bands: that is the first point for structured content. Search breaks where the answer has to be put together from many documents. For the Christmas trip, semantic search's six hits covered Romania and Munich and nothing on Hungary or Austria. Asked which county vignettes cover the drive from Nădlac, it named the four M1 counties and forgot the two on the M43 and M5. The planner walks the route, so it cannot forget a country or a county.

Scoring notes: the model writes non-breaking hyphens ("1‑day", "Bács‑Kiskun") that my patterns did not match, so the scorer now reads them as plain hyphens for every system (before that fix: 16, 15, 12, 4). One of the new Hungarian questions turned out lenient: keyword search passes it by naming the counties without the cheapest combination. Every run, with every answer, is in evals/runs; the method is in RESULTS.md. The first version of this post reported the 29 September run: 15 / 16 against keyword search's 11 / 16.

Honest notes: the first run, on 29 September, scored the agent 6 / 16 against keyword search's 9. It asked "which city?" for general questions, answered an English question in Romanian, returned empty answers when reasoning tokens ate the output budget, and hit the free model tier's 5-requests-a-minute limit. The fixes were a tool for single-product prices, language detection in code, a bigger output budget and a paced runner. That moment, from the failing answers to the paced re-run:

Building Drum Bun with Claude Code claude-opus-5-5

Agent

The repo is public at https://github.com/danielbutnar/drum-bun with everything committed so far. Checking the evaluation:

Agent

▸ Bash node -e " const r=JSON.parse(require('fs').readFileSync('evals/runs/2026-09-2...

Input

$ node -e "
const r=JSON.parse(require('fs').readFileSync('evals/runs/2026-09-29T18-29-39-078Z.json','utf8'));
for(const x of r.results){if(x.agent.pass)continue;console.log('=== '+x.id+' missing:'+JSON.stringify(x.agent.missing)+' wrong:'+JSON.stringify(x.agent.wrong));console.log(x.agent.text.slice(0,500).replace(/\n+/g,' | '))}"

Output

=== christmas-munich missing:["1-day|one-day|1 day"] wrong:[]
Pe scurt — ca să nu fiți amendat: | - România: rovinietă 1 zi pentru 20.12.2026 și pentru 03.01.2027 — 26 RON/zi (2×26 = 52 RON). [CNAIR (RO)](https://portal.etoll.ro/) / [Ordin MTI 888/2026 (RO)](https://lege5.ro/Gratuit/ge4tqnzthazti/ordinul-nr-888-2026-pentru-aprobarea-categoriilor-de-vehicule-si-a-nivelului-rovinietei)   | - Ungaria: e‑vignette D1 (daily) pentru 20.12.2026 și 03.01.2027 — 5.550 HUF/zi (2×5.550 = 11.100 HUF). Cumpărați înainte de a intra pe autostradă, introduceți corect numărul
=== at-18-days missing:["18","(point of sale|petrol station|sales point|toll station|vending machine|10-day)"] wrong:[]
Which Romanian start city are you leaving from — Brașov, Bucharest, Cluj‑Napoca or Timișoara?
=== ro-unknown-euro missing:["39"] wrong:[]
Which exact travel date do you mean? (give one YYYY‑MM‑DD date after 2026-10-01)
=== ro-7-day missing:["(nu|no)","10 zile|10 days"] wrong:[]
Te referi la rovinieta pentru România? Pot presupune că ești cu o mașină privată (car) sau vrei să-mi spui alt tip de vehicul?
=== de-ms-tyres missing:["(Alpine|Schneeflocke|3PMSF|Bergpiktogramm)","2024"] wrong:[]
Kurzfrage: Von welcher rumänischen Stadt starten Sie, welches Ziel in Deutschland und an welchen Datum(en) fahren Sie?
=== euro5-cities missing:["Munich.{0,200}(yes|allowed|may enter|can)","Stuttgart.{0,300}(not|banned|no)"] wrong:[]
What date will you travel (YYYY-MM-DD)?
=== hu-surcharge missing:["27,?790|27 790","60"] wrong:[]
I can check that precisely, but I need your trip details first. What is your Romanian start city (Brașov, Bucharest, Cluj-Napoca or Timișoara), destination (Vienna, Munich, Stuttgart, Frankfurt or Berlin) and travel date(s)?
=== at-ersatzmaut missing:["200"] wrong:[]
Für welches Datum 2026 soll ich die Ersatzmaut prüfen?
=== hu-buy-after missing:["60 minutes"] wrong:[]

=== ro-winter-dates missing:["(snow|ice|conditions)"] wrong:[]

Agent

▸ Bash cd ~/code/danielbutnar/drum-bun/web && node - <<'JS' const fs=require('fs') l...

Input

$ cd ~/code/danielbutnar/drum-bun/web && node - <<'JS'
const fs=require('fs')
let s=fs.readFileSync('lib/agent.ts','utf8')
const rep=(a,b)=>{if(!s.includes(a))throw new Error('missing '+a.slice(0,60));s=s.replace(a,b)}
rep(`- If the trip is missing details the planner needs (start city, destination, dates, vehicle), ask one short question, or assume a car and say so. Unknown fuel or Euro class is fine: the planner prices the worst case and says so.`,
`- Most questions are general (a rule, one product's price, a fine, a claim someone read). Answer those directly from the Knowledge Base or GROQ. Never ask for a start city, destination or dates unless the user wants a full trip plan.
- For a full trip plan, call plan_trip with what you have: assume a car if the vehicle is missing and say so. Unknown fuel or Euro class is fine: the planner prices the worst case and says so. Ask one short question only when the start city, the destination or the departure date is missing.
- A question about a price or rule "after" or "from" a date means that date: do not ask which date.`)
rep(`- Answer in the user's language (Romanian, German, Hungarian or English).`, `- Answer in the language of the user's latest message (Romanian, German, Hungarian or English), even if the trip is in Romania.`)
rep(`      maxOutputTokens: 1400,`, `      // Reasoning tokens come out of the same budget: too low and the answer is empty.
      maxOutputTokens: 5000,`)
fs.writeFileSync('lib/agent.ts',s)
JS
sleep 3; npx tsx ../evals/run.mts http://localhost:3000 at-18-days,ro-unknown-euro,ro-7-day,de-ms-tyres,euro5-cities,hu-surcharge,at-ersatzmaut,hu-buy-after,ro-winter-dates,christmas-munich 2>&1 | grep -v "Assertion\|^\s*at "

Output

christmas-munich   agent fail  baseline fail  tools: plan_trip
at-18-days         agent PASS  baseline PASS  tools: plan_trip,knowledge_base_read
ro-unknown-euro    agent fail  baseline PASS  tools: 
ro-7-day           agent PASS  baseline fail  tools: knowledge_base_read
de-ms-tyres        agent PASS  baseline PASS  tools: knowledge_base_search,knowledge_base_read
euro5-cities       agent fail  baseline fail  tools: knowledge_base_search
hu-surcharge       agent fail  baseline fail  tools: knowledge_base_read
at-ersatzmaut      agent PASS  baseline PASS  tools: knowledge_base_read
hu-buy-after       agent PASS  baseline PASS  tools: knowledge_base_search,knowledge_base_read
ro-winter-dates    agent fail  baseline PASS  tools: knowledge_base_search,knowledge_base_read

agent 5/10, keyword baseline 6/10
written /~/code/danielbutnar/drum-bun/evals/runs/2026-09-29T18-34-09-725Z.json

Agent

▸ Bash cd ~/code/danielbutnar/drum-bun && node -e " const r=JSON.parse(require('fs')...

Input

$ cd ~/code/danielbutnar/drum-bun && node -e "
const r=JSON.parse(require('fs').readFileSync('evals/runs/2026-09-29T18-34-09-725Z.json','utf8'));
for(const x of r.results){if(x.agent.pass)continue;console.log('=== '+x.id+' missing:'+JSON.stringify(x.agent.missing)+' wrong:'+JSON.stringify(x.agent.wrong));console.log(x.agent.text.slice(0,900).replace(/\n+/g,' | '))}"

Output

=== christmas-munich missing:["1-day|one-day|1 day"] wrong:[]
Pe scurt — ca să nu fiți amendat: 1) rovinietă valabilă pentru fiecare zi când circulați pe drumurile naţionale din RO; 2) e‑vigneta maghiară înainte de a intra pe autostradă (plata / număr de înmatriculare corect); 3) vigneta austriacă pentru zilele pe A‑utostrăzi; 4) WWF‑sticker (Umweltplakette verde) lipită înainte de intrarea în zona low‑emission a Münchenului. Mașina Euro 5 diesel este permisă în München. | Ce cumpărați (cheapest combo sugerat) și costuri estimate: | - România: 2 × Rovinietă 1 zi (26 RON / zi) — 52 RON total. Cumpărați prin TollRo (CNAIR). [CNAIR / TollRo](https://portal.etoll.ro/)   | - Ungaria: 2 × e‑vigneta D1 (napi) — 5.550 HUF / zi → 11.100 HUF total. Cumpărați înainte pe ematrica.nemzetiutdij.hu; introduceți corect plăcuţa și codul RO. [Nemzeti Útdíj](https://ematrica.nemzetiutdij.hu/)   | - Austria: 2 × vigneta 1‑day (auto) — 9.60 EUR / zi → 19.20 EUR total. Cumpăra
=== ro-unknown-euro missing:["39"] wrong:[]
I can fetch the official price — I just need one short detail: which of these start cities is your trip from: Brașov, Bucharest, Cluj‑Napoca or Timișoara?
=== euro5-cities missing:["Munich.{0,200}(yes|allowed|may enter|can)","Stuttgart.{0,300}(not|banned|no)"] wrong:[]

=== hu-surcharge missing:["27,?790|27 790","60"] wrong:[]

=== ro-winter-dates missing:["(snow|ice|conditions)"] wrong:[]

Agent

▸ Bash grep -n "\[agent\]" -A 6 "~/.claude/projects/C--Users-danie-code-danielbutnar...

Input

$ grep -n "\[agent\]" -A 6 "~/.claude/projects/C--Users-danie-code-danielbutnar/1d3dd969-55b7-437f-822b-82660f6f0d7c/tool-results/mcp-Claude_Browser-preview_logs-1790706873153.txt" | grep -v "^\s*$" | cut -c1-300 | head -40

Output

1:[agent] stream error Error [GatewayInternalServerError]: AI Gateway requires a valid credit card on file to service requests. Please visit https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dadd-credit-card to add a card and unlock your free credits.
2-    at [3mignore-listed frames[23m {
3-  statusCode: [33m403[39m,
4-  generationId: [90mundefined[39m,
5-  isRetryable: [33mfalse[39m,
6-  type: [32m'internal_server_error'[39m,
7-  [cause]: Error [AI_APICallError]: {"error":{"message":"AI Gateway requires a valid credit card on file to service requests. Please visit https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dadd-credit-card to add a card and unlock your free credits.","type":"customer_verification_required"
--
47:[agent] ui stream error Error [GatewayInternalServerError]: AI Gateway requires a valid credit card on file to service requests. Please visit https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dadd-credit-card to add a card and unlock your free credits.
48-    at [3mignore-listed frames[23m {
49-  statusCode: [33m403[39m,
50-  generationId: [90mundefined[39m,
51-  isRetryable: [33mfalse[39m,
52-  type: [32m'internal_server_error'[39m,
53-  [cause]: Error [AI_APICallError]: {"error":{"message":"AI Gateway requires a valid credit card on file to service requests. Please visit https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dadd-credit-card to add a card and unlock your free credits.","type":"customer_verification_required
--
93:[agent] stream error Error [GatewayInternalServerError]: Free tier users do not have access to this model. Upgrade to paid credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up for unrestricted access.
94-    at [3mignore-listed frames[23m {
95-  statusCode: [33m403[39m,
96-  generationId: [90mundefined[39m,
97-  isRetryable: [33mfalse[39m,
98-  type: [32m'internal_server_error'[39m,
99-  [cause]: Error [AI_APICallError]: {"error":{"message":"Free tier users do not have access to this model. Upgrade to paid credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up for unrestricted access.","type":"no_providers_available","param":{"error":"Free tier users do no
--
140:[agent] ui stream error Error [GatewayInternalServerError]: Free tier users do not have access to this model. Upgrade to paid credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up for unrestricted access.
141-    at [3mignore-listed frames[23m {
142-  statusCode: [33m403[39m,
143-  generationId: [90mundefined[39m,
144-  isRetryable: [33mfalse[39m,
145-  type: [32m'internal_server_error'[39m,
146-  [cause]: Error [AI_APICallError]: {"error":{"message":"Free tier users do not have access to this model. Upgrade to paid credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up for unrestricted access.","type":"no_providers_available","param":{"error":"Free tier users do n
--
187:[agent] stream error Error [AI_RetryError]: Failed after 3 attempts. Last error: GatewayRateLimitError: Rate limit exceeded for openai/gpt-5-mini for provider azure: this team's limit of 5 requests per minute (across all regions) was reached. Retry after 60s.
188-    at [3mignore-listed frames[23m {
189-  cause: [90mundefined[39m,
190-  reason: [32m'maxRetriesExceeded'[39m,
191-  errors: [
192-    Error [GatewayRateLimitError]: Rate limit exceeded for openai/gpt-5-mini for provider azure: this team's limit of 5 requests per minute (across all regions) was reached. Retry after 60s.
193-        at [3mignore-listed frames[23m {
--

Agent

▸ Bash cd ~/code/danielbutnar/drum-bun/web && cat >> lib/plan-tool.ts <<'EOF' expor...

Input

$ cd ~/code/danielbutnar/drum-bun/web && cat >> lib/plan-tool.ts <<'EOF'

export const COUNTRIES = ['RO', 'HU', 'AT', 'DE'] as const

const PRODUCTS_QUERY = `*[_type == "tollProduct" && country->code == $country && $vehicle in vehicles] | order(kind asc, name.en asc){
  _id, name, kind, vehicles, localCategory, county, validity, prices[]{amount, currency, validFrom, validTo, status, band},
  activation, purchase[]{channel, label, url}, summary, penalty,
  pendingChanges[]{summary, wouldTakeEffect, checkAgainBy, "source": source->{title, url}},
  "sources": sources[]->{title, url, publisher, language, trust}
}`

// One country's products with the price valid on a date, for questions about
// a single product ("what does X cost after 1 October?"). Deterministic, one
// round trip, no trip details needed.
export const countryProductsTool = tool({
  description:
    'List every toll product of one country (RO, HU, AT) for a vehicle, with the official price valid on a given date, validity rule, online-purchase delay, penalty and sources. Use it for questions about one product, a price on a date, a Euro-class price, or a penalty, when no full trip is involved.',
  inputSchema: z.object({
    country: z.enum(COUNTRIES),
    date: z.string().regex(/^\d{4}-\d{2}-\d{2}$/).describe('The date the price should be valid on. Use today if the user gave none.'),
    vehicle: z.enum(['car', 'carTrailer', 'camper', 'motorcycle']),
    fuel: z.enum(['petrol', 'diesel', 'hybrid', 'electric', 'lpg']).nullable(),
    euroNorm: z.number().int().min(0).max(6).nullable(),
  }),
  execute: async ({country, date, vehicle, fuel, euroNorm}) => {
    const products = await sanity.fetch<TollProduct[]>(PRODUCTS_QUERY, {country, vehicle})
    return products.map((p) => {
      const hit = priceOn(p.prices ?? [], p.validity.unit === 'calendarYear' ? `${date.slice(0, 4)}-07-01` : date, {fuel, euroNorm})
      return {
        name: p.name.en,
        localName: p.name.ro ?? p.name.hu ?? p.name.de ?? null,
        kind: p.kind,
        county: p.county ?? null,
        validity: p.validity.wording,
        priceOnDate: hit
          ? {amount: hit.price.amount, currency: hit.price.currency, band: hit.price.band?.label ?? null, estimate: hit.estimate, bandNote: hit.bandNote}
          : null,
        onlineDelayDays: p.activation?.onlineDelayDays ?? 0,
        immediateOptions: p.activation?.immediateOptions ?? null,
        penalty: p.penalty?.note ?? null,
        buy: (p.purchase ?? []).filter((c) => c.url).map((c) => ({label: c.label, url: c.url})),
        pendingChanges: p.pendingChanges ?? [],
        sources: p.sources,
      }
    })
  },
})
EOF
node - <<'JS'
const fs=require('fs')
let s=fs.readFileSync('lib/plan-tool.ts','utf8')
s=s.replace("import {planTrip} from './planner'\nimport {fetchPlannerData} from './queries'", "import {planTrip, priceOn} from './planner'\nimport {fetchPlannerData, sanity} from './queries'\nimport type {TollProduct} from './types'")
fs.writeFileSync('lib/plan-tool.ts',s)

let a=fs.readFileSync('lib/agent.ts','utf8')
const rep=(x,y)=>{if(!a.includes(x))throw new Error('missing '+x.slice(0,60));a=a.replace(x,y)}
rep("import {planTripTool, today} from './plan-tool'", "import {countryProductsTool, planTripTool, today} from './plan-tool'")
rep(`function instructions(date: string) {`, `const LANGUAGE_NAMES = {ro: 'Romanian', de: 'German', hu: 'Hungarian', en: 'English'} as const

/** Cheap language detection for the reply: the model drifts into Romanian when a trip starts in Romania. */
export function detectLanguage(text: string): keyof typeof LANGUAGE_NAMES {
  const t = \` \${text.toLowerCase()} \`
  const score = (re: RegExp) => (t.match(re) ?? []).length
  const ro = score(/[ăâîșşțţ]|\\s(și|să|pentru|cu|ce|care|este|mașin\\w*|rovinieta|pot|trebuie|nu)\\s/g)
  const de = score(/[äöüß]|\\s(ich|und|der|die|das|nicht|mit|für|reichen|wie|ist|mein\\w*|brauche)\\s/g)
  const hu = score(/[őű]|\\s(és|hogy|nem|kell|autópálya|mennyi|megyei|vagy)\\s/g)
  const best = Math.max(ro, de, hu)
  if (best === 0) return 'en'
  return best === ro ? 'ro' : best === de ? 'de' : 'hu'
}

function instructions(date: string) {`)
rep(`1. plan_trip: the deterministic planner`, `1. plan_trip and country_products: the deterministic planner and price lookup`)
rep(`For any question about what a trip needs or costs, call it first. Never compute prices, validity or coverage yourself.`, `For any question about what a trip needs or costs, call plan_trip first. For one product's price on a date (e.g. by Euro class) or a penalty, call country_products. Never compute prices, validity or coverage yourself.`)
rep(`    const system = [
      instructions(today()),`, `    const lastUser = [...messages].reverse().find((m) => m.role === 'user')
    const lang = detectLanguage(lastUser?.parts.map((p) => (p.type === 'text' ? p.text : '')).join(' ') ?? '')
    const system = [
      instructions(today()),
      \`The user's latest message is in \${LANGUAGE_NA
[… 1299 characters trimmed]

Output

ok
TSC-DONE

Agent

The code typechecks. Pulling the new Insights token into local env, adding a language-detection test, and pacing the evaluation to stay under 5 requests a minute:

Agent

▸ Bash cat > web/lib/agent.test.ts <<'EOF' import {describe, expect, it} from 'vites...

Input

$ cat > web/lib/agent.test.ts <<'EOF'
import {describe, expect, it} from 'vitest'

import {detectLanguage} from './agent'

describe('detectLanguage', () => {
  it('recognises the four languages of the route', () => {
    expect(detectLanguage('Cât costă rovinieta de 12 luni pentru un diesel Euro 5?')).toBe('ro')
    expect(detectLanguage('Reichen M+S-Reifen im Winter in Deutschland?')).toBe('de')
    expect(detectLanguage('Mennyi a megyei matrica és hogy kell megvenni?')).toBe('hu')
    expect(detectLanguage('I drive from Brașov to Munich on 20 December. What do I need?')).toBe('en')
  })
})
EOF
node - <<'JS'
const fs=require('fs')
let s=fs.readFileSync('evals/run.mts','utf8')
s=s.replace("  const [agent, baseline] = await Promise.allSettled([askAgent(q.q), askBaseline(q.q)])",
"  // The free AI Gateway tier allows 5 requests a minute: run one system at a\n  // time and pause, so a rate limit never counts as a wrong answer.\n  const [agent] = await Promise.allSettled([askAgent(q.q)])\n  await sleep(PAUSE_MS)\n  const [baseline] = await Promise.allSettled([askBaseline(q.q)])\n  await sleep(PAUSE_MS / 3)")
s=s.replace("const only = process.argv[3]?.split(',')", "const only = process.argv[3]?.split(',')\nconst PAUSE_MS = Number(process.env.EVAL_PAUSE_MS ?? 45_000)\nconst sleep = (ms: number) => new Promise((r) => setTimeout(r, ms))")
s=s.replace("      if (ev.type === 'tool-input-available') tools.push(ev.toolName)", "      if (ev.type === 'tool-input-available') tools.push(ev.toolName)\n      if (ev.type === 'error') text += `\\n[ERROR] ${ev.errorText}`")
fs.writeFileSync('evals/run.mts',s)
JS
cd web && npx vitest run lib 2>&1 | tail -3

Output

[2m   Start at [22m 21:36:03
[2m   Duration [22m 2.72s[2m (transform 396ms, setup 0ms, collect 1.68s, tests 32ms, environment 1ms, prepare 911ms)[22m

Agent

▸ Bash npx vitest run lib 2>&1 | grep -E "Tests|FAIL|passed|failed" | head -5

Input

$ npx vitest run lib 2>&1 | grep -E "Tests|FAIL|passed|failed" | head -5

Output

 [31m❯[39m lib/agent.test.ts [2m([22m[2m1 test[22m[2m | [22m[31m1 failed[39m[2m)[22m[32m 12[2mms[22m[39m
[31m⎯⎯⎯⎯⎯⎯⎯[39m[1m[41m Failed Tests 1 [49m[22m[31m⎯⎯⎯⎯⎯⎯⎯[39m
[41m[1m FAIL [22m[49m lib/agent.test.ts[2m > [22mdetectLanguage[2m > [22mrecognises the four languages of the route
[2m Test Files [22m [1m[31m1 failed[39m[22m[2m | [22m[1m[32m1 passed[39m[22m[90m (2)[39m
[2m      Tests [22m [1m[31m1 failed[39m[22m[2m | [22m[1m[32m21 passed[39m[22m[90m (22)[39m

Agent

The English question with "Brașov" in it was detected as Romanian, the exact failure the check is meant to catch. The fix: ignore place names, and count English words too.

Agent

▸ Bash node - <<'JS' const fs=require('fs') let a=fs.readFileSync('lib/agent.ts','ut...

Input

$ node - <<'JS'
const fs=require('fs')
let a=fs.readFileSync('lib/agent.ts','utf8')
const start=a.indexOf('export function detectLanguage')
const end=a.indexOf('\n}\n', start)+3
a=a.slice(0,start)+`export function detectLanguage(text: string): keyof typeof LANGUAGE_NAMES {
  // Place names carry diacritics in every language here (Brașov, München), so
  // they must not decide the language.
  const t = \` \${text.toLowerCase()} \`.replace(/brașov|brasov|timișoara|bucurești|cluj-napoca|nădlac|borș|münchen|wien|győr|hegyeshalom/g, ' ')
  const score = (re: RegExp) => (t.match(re) ?? []).length
  const ro = score(/[ăâîșşțţ]|\\s(și|să|pentru|cu|ce|care|este|mașin\\w*|rovinieta|pot|trebuie|nu|cât|costă)\\s/g)
  const de = score(/[äöüß]|\\s(ich|und|der|die|das|nicht|mit|für|reichen|wie|ist|mein\\w*|brauche|im|in der)\\s/g)
  const hu = score(/[őű]|\\s(és|hogy|nem|kell|autópálya|mennyi|megyei|vagy|matrica)\\s/g)
  const en = score(/\\s(the|and|what|do|does|i|to|from|on|is|my|need|cost|can|which|are)\\s/g)
  const best = Math.max(ro, de, hu, en)
  if (best === 0 || best === en) return 'en'
  return best === ro ? 'ro' : best === de ? 'de' : 'hu'
}
`+a.slice(end)
fs.writeFileSync('lib/agent.ts',a)
JS
npx vitest run lib 2>&1 | grep -E "Tests |FAIL" | head -3

Output

[31m⎯⎯⎯⎯⎯⎯⎯[39m[1m[41m Failed Tests 1 [49m[22m[31m⎯⎯⎯⎯⎯⎯⎯[39m
[41m[1m FAIL [22m[49m lib/agent.test.ts[2m > [22mdetectLanguage[2m > [22mrecognises the four languages of the route
[2m      Tests [22m [1m[31m1 failed[39m[22m[2m | [22m[1m[32m21 passed[39m[22m[90m (22)[39m

Agent

▸ Bash npx vitest run lib/agent.test.ts 2>&1 | grep -E "Expected|Received|toBe|❯ lib...

Input

$ npx vitest run lib/agent.test.ts 2>&1 | grep -E "Expected|Received|toBe|❯ lib" | head -6

Output

Expected: [32m"[7md[27me"[39m
Received: [31m"e[7mn[27m"[39m

Agent

▸ Bash cat > /tmp/lang.test.ts <<'EOF' EOF node -e " const t=' reichen m+s-reifen im...

Input

$ cat > /tmp/lang.test.ts <<'EOF'
EOF
node -e "
const t=' reichen m+s-reifen im winter in deutschland? ';
const sc=(re)=>(t.match(re)??[]).length;
console.log('de',sc(/[äöüß]|\s(ich|und|der|die|das|nicht|mit|für|reichen|wie|ist|mein\w*|brauche|im|in der)\s/g),'en',sc(/\s(the|and|what|do|does|i|to|from|on|is|my|need|cost|can|which|are)\s/g))"; grep -n "reichen" lib/agent.ts

Output

de 2 en 0
29:  const de = score(/[äöüß]|s(ich|und|der|die|das|nicht|mit|für|reichen|wie|ist|meinw*|brauche|im|in der)s/g)

Agent

My scripted edit lost the regex backslashes (\s became s). Rewriting the function directly:

Agent

▸ Read ~\code\danielbutnar\drum-bun\web\lib\agent.ts

Input

~\code\danielbutnar\drum-bun\web\lib\agent.ts

Output

20  const LANGUAGE_NAMES = {ro: 'Romanian', de: 'German', hu: 'Hungarian', en: 'English'} as const
21  
22  /** Cheap language detection for the reply: the model drifts into Romanian when a trip starts in Romania. */
23  export function detectLanguage(text: string): keyof typeof LANGUAGE_NAMES {
24    // Place names carry diacritics in every language here (Brașov, München), so
25    // they must not decide the language.
26    const t = ` ${text.toLowerCase()} `.replace(/brașov|brasov|timișoara|bucurești|cluj-napoca|nădlac|borș|münchen|wien|győr|hegyeshalom/g, ' ')
27    const score = (re: RegExp) => (t.match(re) ?? []).length
28    const ro = score(/[ăâîșşțţ]|s(și|să|pentru|cu|ce|care|este|mașinw*|rovinieta|pot|trebuie|nu|cât|costă)s/g)
29    const de = score(/[äöüß]|s(ich|und|der|die|das|nicht|mit|für|reichen|wie|ist|meinw*|brauche|im|in der)s/g)
30    const hu = score(/[őű]|s(és|hogy|nem|kell|autópálya|mennyi|megyei|vagy|matrica)s/g)
31    const en = score(/s(the|and|what|do|does|i|to|from|on|is|my|need|cost|can|which|are)s/g)
32    const best = Math.max(ro, de, hu, en)
33    if (best === 0 || best === en) return 'en'
34    return best === ro ? 'ro' : best === de ? 'de' : 'hu'
35  }
36  
37  function instructions(date: string) {

Agent

▸ Edit ~\code\danielbutnar\drum-bun\web\lib\agent.ts

Input

~\code\danielbutnar\drum-bun\web\lib\agent.ts

Output

The file ~\code\danielbutnar\drum-bun\web\lib\agent.ts has been updated successfully.

Agent

▸ Bash npx vitest run lib 2>&1 | grep -E "Tests |FAIL" | head -3; grep -n '\\\\s\|(?...

Input

$ npx vitest run lib 2>&1 | grep -E "Tests |FAIL" | head -3; grep -n '\\\\s\|(?=' lib/agent.ts | head -3

Output

[2m      Tests [22m [1m[32m22 passed[39m[22m[90m (22)[39m
28:  const ro = score(/[ăâîșşțţ]|\s(și|să|pentru|cu|ce|care|este|mașin\w*|rovinieta|pot|trebuie|nu|cât|costă)(?=\s)/g)
29:  const de = score(/[äöüß]|\s(ich|und|der|die|das|nicht|mit|für|reichen|wie|ist|mein\w*|brauche|im)(?=\s)/g)
30:  const hu = score(/[őű]|\s(és|hogy|nem|kell|autópálya|mennyi|megyei|vagy|matrica)(?=\s)/g)

Agent

All 22 tests pass. Checking the editor's two type complaints against the real compiler:

Agent

▸ Bash npx tsc --noEmit -p . 2>&1 | grep -v "LayoutProps\|PageProps" | head -5; echo...

Input

$ npx tsc --noEmit -p . 2>&1 | grep -v "LayoutProps\|PageProps" | head -5; echo TSC-DONE; cd .. && git add -A && git commit -qm "Agent: country_products tool, language detection, rate-limit handling; eval pacing; cover image and post draft

Co-Authored-By: Claude Opus 5.5 <[e-mail]>" && git push -q origin main 2>&1 | tail -2; git log --oneline | head -1

Output

TSC-DONE
dac1675 Agent: country_products tool, language detection, rate-limit handling; eval pacing; cover image and post draft

Agent

Both were stale; the compiler is clean. Committed and pushed. Starting the full paced evaluation in the background (about 20 minutes, to respect the rate limit):

20 messages (range 332-351) of 507 total

What did not go smoothly

• A dataset source query with select() made the ingest fail with a generic server error; plain projections work.
• A website source crawls everything under the URL's path: the Munich city page pulled in 306 pages of a 150-source budget. Single deep URLs import one page.
• GROQ mode needs a deployed Studio, not only a deployed schema.
• The AI Gateway's free tier does not include Claude models and allows 5 requests a minute, so the live agent runs on gpt-5-mini, the example questions replay recorded answers (labelled as such, with an "ask it live" button), and a busy model says so instead of failing silently. The planner makes the model choice matter less.
• The first eval run lost to keyword search (above). Measuring early is what made the agent good.

Sanity Project Details

• Project ID: pd5e7gez, dataset production (public). Try one product's stored prices: *[_id=="product-ro-12month"][0]{name, prices}
• Organization ob2cyckj9, Knowledge Base kbv1SRpT2A3t, MCP endpoints drum-bun-kb and drum-bun-rules.
• Studio: https://drum-bun.sanity.studio (members only; the schema is in studio/schemaTypes).
• Read the content without a login: a route with its road sections, the M1 stretch only the Fejér vignette covers, a blog claim and the products that correct it.

Agent Session

I built Drum Bun with Claude Code. The excerpt in section 4 comes from that session: the first eval losing to keyword search, and the fixes that followed.