feat(client): add the API client for the postcode gateway

.changeset/first-client-release.md

@@ -0,0 +1,5 @@
+---
+'@gatepost/client': minor
+---
+
+Add the client package. It looks up postcodes, finds the postcode of a place and completes a typed postcode through NIPOST's gateway, with the retries, waits and limits of spec 0.2.0.

.github/workflows/live.yml

@@ -0,0 +1,44 @@
+# SPDX-FileCopyrightText: 2026 The Gatepost authors
+# SPDX-License-Identifier: Apache-2.0
+name: live
+
+# Each night, the client makes three calls to NIPOST's staging gateway with the test key: a
+# lookup of a test code from NIPOST's docs, an autocomplete and a reverse geocode at sea. The
+# contract scenarios cannot run there, because they need the scripted answers of the mock server.
+# A failure means that the gateway changed. The job prints no response.
+on:
+  schedule:
+    - cron: '30 2 * * *'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  staging:
+    # A fork has no secrets and makes no call, so it need not run the job.
+    if: github.repository == 'gatepost-dev/js'
+    runs-on: ubuntu-24.04
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          submodules: true
+          persist-credentials: false
+      - uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
+        with:
+          node-version: 24
+      - run: corepack enable
+      - run: pnpm install --frozen-lockfile
+      - name: Call the staging gateway
+        env:
+          GATEPOST_LIVE_URL: ${{ secrets.NIPOST_STAGING_URL }}
+          GATEPOST_LIVE_KEY: ${{ secrets.NIPOST_TEST_SECRET_KEY }}
+          # A test code from NIPOST's docs. The gateway knew it on 2 Oct 2026.
+          GATEPOST_LIVE_CODE: FC-03-B06-AG-12
+        run: |
+          if [ -z "$GATEPOST_LIVE_URL" ]; then
+            echo "::notice::NIPOST has not given a staging URL yet, so the job makes no call."
+            exit 0
+          fi
+          pnpm --filter @gatepost/client exec vitest run test/live.test.ts

AGENTS.md

@@ -1,6 +1,6 @@
 # AGENTS.md
 
-This repo is part of Gatepost, unofficial open-source developer tools for Nigeria's National Digital Postcode. This repo holds the TypeScript packages. Today it has `@gatepost/core` and the private `@gatepost/mock-server`.
+This repo is part of Gatepost, unofficial open-source developer tools for Nigeria's National Digital Postcode. This repo holds the TypeScript packages. Today it has `@gatepost/core`, `@gatepost/client` and the private `@gatepost/mock-server`.
 
 ## Read first
 

README.md

@@ -12,6 +12,7 @@ TypeScript packages for Nigeria's National Digital Postcode.
 | Package                                         | What it does                                        |
 | ----------------------------------------------- | --------------------------------------------------- |
 | [`@gatepost/core`](packages/core)               | Parse, check and format postcodes offline.          |
+| [`@gatepost/client`](packages/client)           | Call NIPOST's gateway, with retries and limits.     |
 | [`@gatepost/mock-server`](packages/mock-server) | Mock NIPOST's gateway for client tests. Not on npm. |
 
 ## Develop
@@ -22,12 +23,12 @@ You need Node 24, `corepack enable`, Python 3.11 or later and `uv`.
     pnpm install
     pnpm check
 
-`pnpm check` also builds the package. Then it runs publint, attw, size-limit and API Extractor on
-the result, and it starts the built package once. It checks the licence of each dependency and of
+`pnpm check` also builds the packages. Then it runs publint, attw, size-limit and API Extractor on
+the result, and it starts each built package once. It checks the licence of each dependency and of
 each file, and it checks the workflows with zizmor. It starts REUSE and zizmor with `uvx` at pinned
 versions. REUSE needs an encoding detector, and `uvx` installs REUSE without one, so the script pins
-`charset-normalizer` as well. Renovate updates the three pins. After a change to the public API, run
-`pnpm --filter @gatepost/core run api:update` and commit `packages/core/etc/core.api.md`. For each
+`charset-normalizer` as well. Renovate updates the three pins. After a change to the public API of a
+package, run `pnpm --filter <package> run api:update` and commit its `etc/<name>.api.md`. For each
 change to a package, add a change file with `pnpm changeset`, or with `pnpm changeset --empty` when
 the change needs no release. The pull request job fails without a change file.
 

docs/adr/0001-client-depends-on-core.md

@@ -0,0 +1,24 @@
+# 1. The client depends on the core
+
+Date: 3 Oct 2026
+
+## Context
+
+`@gatepost/client` must parse each postcode before it sends a lookup, so that a bad code sends no request. It also returns parsed postcodes in its results, and it builds the partial postcode of each autocomplete offer. `@gatepost/core` holds the only parser, with the state table and the segment rules from the spec data.
+
+The client was first planned with no runtime dependencies. DEP-3 asks for a record of each new runtime dependency.
+
+## Decision
+
+The client lists `@gatepost/core` as its one dependency, with a caret range on the same release line. It has no other dependency. Its size limit of 5 KB counts the core too, because size-limit bundles the dependencies.
+
+## Reasons
+
+- A copy of the parser in the client would be a second place for the spec data, which CS-4 forbids, and an app that uses both packages would ship the parser twice.
+- The core is a Gatepost package with no dependencies of its own, so the client still pulls in no third-party code.
+- The client's types name the core's `Postcode` and `Precision`, so a caller can pass a parsed postcode to `lookup`.
+
+## Consequences
+
+- A breaking release of the core needs a release of the client.
+- The client's tests and type check read the core's source, so they need no build of the core first. The published package reads the core's built files.

package.json

@@ -22,7 +22,7 @@
     "tells": "python3 spec/scripts/check-tells",
     "context:check": "cmp CONTEXT.md spec/CONTEXT.md",
     "licences:check": "node scripts/check-licences.mjs",
-    "licence-files:check": "cmp LICENSE packages/core/LICENSE && cmp NOTICE packages/core/NOTICE",
+    "licence-files:check": "pnpm -r run licence-files:check",
     "reuse:check": "uvx --with charset-normalizer==3.5.2 reuse@6.2.0 lint",
     "workflows:check": "uvx zizmor@1.30.1 --offline .github/workflows",
     "generate": "node scripts/generate-spec-data.mjs",

packages/client/LICENSE

@@ -0,0 +1,202 @@
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packages/client/NOTICE

@@ -0,0 +1,5 @@
+Gatepost
+Copyright 2026 The Gatepost authors
+
+This product is unofficial. The Nigerian Postal Service (NIPOST) did not make it and does not endorse it.
+Gatepost uses the name NIPOST only to describe compatibility with NIPOST's National Digital Postcode.