feat(agentic-server): make canonical package the OpenAI-compatible gateway

[pyramation]

Summary

Part of the agentic-server de-duplication in constructive-planning#1337: there are two divergent agentic-server implementations (this repo's published threads service vs. constructive-db's private OpenAI-compatible gateway). This makes the published agentic-server the one source of truth = the gateway, and relocates the legacy threads surface into graphql/server so nothing deployed breaks.

Two moves, no behavior loss:

1. agentic-server becomes the gateway (ported from constructive-db).
Stateless multi-provider proxy (/v1/chat/completions, /v1/embeddings, /v1/usage, /v1/providers, /healthz) with provider resolution + request/response transforms for OpenAI / Anthropic / Ollama. Crucially it is backend-agnostic — metering is injected, the package imports no concrete telemetry/billing backend:

export interface InferenceSink {
  logInference(entry: InferenceEntry): void; // fire-and-forget; must not throw
}

createAgenticServer({ providerType, providerBaseUrl, inferenceSink });

So the gateway carries none of constructive-db's compute_log/ModuleLoader/pg code — a future constructive-db change injects createComputeLogSink(pool, platformDatabaseId) and deletes its private fork. X-Database-Id is required (400 otherwise); isPublic strips identity headers so untrusted requests fail loud rather than being mis-attributed. Package deps shrink to just @pgpmjs/logger.

2. The legacy threads router moves into graphql/server unchanged.
graphql/server was the only consumer of the old published package (dashboard / diligence-app-demo don't use it — verified). Rather than delete /v1/threads + /v1/embed, the router (express-context auth, billing, thread persistence, SSE) is relocated verbatim to graphql/server/src/agentic/ and mounted locally:

- import { createAgenticRouter } from 'agentic-server';
+ import { createAgenticRouter } from './agentic';

graphql/server drops the agentic-server dependency and picks up the threads router's own deps (@agentic-kit/ollama, @constructive-io/llm-env). The relocated router and its test are byte-identical to the originals (only the test's import path changed).

Verification

• agentic/agentic-server: pnpm build + pnpm test → gateway suite 10/10 pass.
• graphql/server: relocated threads suite 20/20 pass; lint clean.
• No remaining importers of the old agentic-server package (grep-verified across repo).

Publish

This bundles the canonical agentic-server package version to publish once merged; the follow-up constructive-db PR will then consume the published dep and delete its private fork.

Link to Devin session: https://app.devin.ai/sessions/9d694c4be37a41719809d7e740343fc6
Requested by: @pyramation

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