Replace deprecated Dictionary with ConfigStore and SecretStore in context.env

[trieloff]

Background

PR #77 introduced unified environment/geo/device APIs. Comment #77 (comment) identified that context.env uses the deprecated Dictionary API.

Current Implementation

src/template/fastly-adapter.js:74 creates context.env using:

context.env: new Proxy(new Dictionary('secrets'), {
  get: (target, prop) => {
    try {
      return target.get(prop);
    } catch {
      // fallback to package params fetch
    }
  }
})

Required Changes

Replace Dictionary with modern Fastly APIs:

For secrets:

import { SecretStore } from 'fastly:secret-store';
const secrets = new SecretStore('secrets');
const value = await secrets.get('key');
const plaintext = value.plaintext();

For config:

import { ConfigStore } from 'fastly:config-store';
const config = new ConfigStore('config');
const value = config.get('key');

Implementation Notes

• SecretStore.get() is async, returns object with plaintext() method
• ConfigStore.get() is sync, returns string directly
• Update Proxy handler to handle async secret retrieval
• Both require resource link names matching Fastly service config
• Only available during request processing, not at build-time

References

• https://js-compute-reference-docs.edgecompute.app/docs/fastly:secret-store/SecretStore/
• https://js-compute-reference-docs.edgecompute.app/docs/fastly:config-store/ConfigStore/
• docs/api-unification/environment-geo.md