add-provider— agent skill

Context

Providers implement interfaces defined in core. They are selected at runtime via config (e.g., STORAGE_PROVIDER_TYPE). Tier 3 providers lazy-load their dependencies to keep the core bundle small.

Providers live inside the package source tree — import the interface via relative path (e.g., import type { IStorageProvider } from '../core/IStorageProvider.js'), not via the package subpath exports (those are for consumers).

Provider interfaces

Read the relevant interface fully before implementing — each has distinct required members. ISpeechProvider in particular requires readonly name, readonly supportsTTS, readonly supportsSTT, and healthCheck() in addition to the capability methods; these flags drive routing in SpeechService.

File conventions

Provider file location and naming differ by domain:

• Storage — nested subdirectory, camelCase directory name, PascalCase-suffixed provider file.

Each provider gets its own subdirectory for the provider file plus any co-located types: src/storage/providers/{{providerName}}/{{providerName}}Provider.ts (e.g., src/storage/providers/inMemory/inMemoryProvider.ts, src/storage/providers/supabase/supabaseProvider.ts + supabase.types.ts)

• LLM / Speech — flat directory, kebab-case with .provider.ts suffix:

src/services/llm/providers/{{provider-name}}.provider.ts src/services/speech/providers/{{provider-name}}.provider.ts (e.g., src/services/llm/providers/openrouter.provider.ts, src/services/speech/providers/elevenlabs.provider.ts)

Steps

1. Identify the provider interface — read the interface file for the target domain

(see table above).

1. Create the provider file following the file convention for its domain (see above).
2. Implement the interface — all methods must be implemented. Storage providers build

on src/storage/core/providerHelpers.ts rather than re-deriving what the existing providers share:

• serializeValue / encodeEntries — the JSON guard every provider runs before it

writes. serializeValue returns the value's JSON text and throws McpError(SerializationError) for a bigint, a cyclic reference, or a top-level undefined, function, or symbol. encodeEntries encodes a whole setMany batch first, so one bad value rejects the batch before anything is written. Store and read back the JSON form; never keep the caller's object.

• getManyViaGet / setManyViaSet / deleteManyViaDelete — the batch methods as a

parallel fan-out of single-key operations, for backends with no native batch API. Pass setManyViaSet the output of encodeEntries and a private per-key write. Calling this.set per entry would let a bad entry fail after the others have landed.

• encodeEnvelope / decodeEnvelope — the TTL envelope for backends with no TTL of their

own (R2, filesystem). encodeEnvelope takes the JSON text from serializeValue and returns the stored document. decodeEnvelope returns { kind: 'expired' } so the provider can delete on read, returns pre-envelope JSON as a plain value, and throws SyntaxError on invalid JSON so the provider can attach the key to the error it raises.

• paginateSortedKeys — one list() page over an already-sorted key set, with the cursor

for the page that follows.

• escapeLikePattern — escapes %, _, and \ in a prefix before a SQL LIKE.

1. Lazy-load dependencies if Tier 3:

   let _client: SomeClient | undefined;
   async function getClient(): Promise<SomeClient> {
     if (!_client) {
       const { SomeClient } = await import('some-package');
       _client = new SomeClient(/* config */);
     }
     return _client;
   }

1. Register the provider — the registration point differs by domain:

• Storage — two changes required:

1. Add the new provider string to the z.enum for STORAGE_PROVIDER_TYPE in

src/config/index.ts — without this, the config schema rejects the env var at runtime.

1. Add a case to the switch in src/storage/core/storageFactory.ts

inside createStorageProvider(). Import the new provider class at the top of that file.

• Speech — two changes required:

1. Add the new provider string literal to the provider union in

SpeechProviderConfig (src/services/speech/types.ts, field provider).

1. Add a case to the switch in createSpeechProvider()

(src/services/speech/core/SpeechService.ts). Import the new provider class at the top of that file.

• LLM — currently only one provider exists (OpenRouterProvider); it is

instantiated directly in src/core/app.ts rather than through a factory switch. There is no factory pattern yet — adding a second provider requires introducing one (a selector env var, a factory function, and a conditional in app.ts). Read src/core/app.ts to understand the current instantiation site before designing the wiring.

1. Update the Worker-compatible provider list if the new storage provider runs in

Cloudflare Workers. The list is an inline array in storageFactory.ts at the isServerless() guard:

   // src/storage/core/storageFactory.ts
   !['in-memory', 'cloudflare-r2', 'cloudflare-kv', 'cloudflare-d1'].includes(providerType)

Add the new provider string to this array. Non-storage providers have no equivalent gate.

1. Add the dependency if Tier 3: add to both peerDependencies and

peerDependenciesMeta (with { "optional": true }) in package.json. Without the peerDependenciesMeta entry, the dep appears required rather than optional.

1. Run `bun run rebuild` — since this is package source, verify the build output compiles.
2. Run `bun run devcheck` to verify.

Checklist

• [ ] Provider file created with JSDoc @fileoverview + @module header
• [ ] Interface fully implemented (including name, supportsTTS/supportsSTT for speech)
• [ ] Tier 3 dependencies lazy-loaded (not top-level imports)
• [ ] Registered in the correct factory for the domain (see Step 5)
• [ ] Storage: provider string added to z.enum in src/config/index.ts
• [ ] Storage: Worker-compatible array in storageFactory.ts updated if applicable
• [ ] Storage: value encoding, batch, TTL envelope, paging, and LIKE escaping come from providerHelpers.ts, not a local copy
• [ ] Storage: the shared compliance suite (tests/compliance/storage-provider.ts) runs against the provider
• [ ] Speech: provider literal added to SpeechProviderConfig union in types.ts
• [ ] LLM: src/core/app.ts instantiation logic updated if adding a second LLM provider
• [ ] Optional peer dependency added to both peerDependencies and peerDependenciesMeta in package.json if Tier 3
• [ ] bun run rebuild succeeds
• [ ] bun run devcheck passes
• [ ] Tests added under tests/unit/storage/providers/{{providerName}}/ (storage) or tests/unit/services/{{domain}}/providers/{{provider-name}}.provider.test.ts (LLM / speech), and bun run test passes