Anthropic Subscription Adapter

[davidste]

Summary

Implement the Anthropic subscription adapter path on top of the shared subscription auth foundation.

This issue covers Anthropic-specific runtime behavior when Loomkin uses subscription OAuth credentials instead of standard API keys.

Depends On

• #105 — Subscription Auth Foundation (OAuth, Token Lifecycle, Config)

Scope

Adapter behavior

• Add Anthropic subscription auth mode selection at runtime.
• Route requests through the correct Anthropic endpoint path for this mode.
• Apply Anthropic subscription identity/header behavior required by this auth mode.
• Keep standard Anthropic API-key flow as fallback.

Request shaping

• Implement any required tool-name/system-context transformations for compatibility in subscription mode.
• Ensure tool-call and streaming behavior remain compatible with Loomkin’s current agent loop.

Risk controls

• Explicit user opt-in before enabling Anthropic subscription mode.
• Clear warning copy about policy/risk tradeoffs.
• Safe fallback behavior when subscription auth is invalid/expired/revoked.

Observability

• Add adapter-level telemetry for mode selection, auth failures, and fallback activation.
• Keep secrets redacted across all error/log surfaces.

Out of Scope

• Shared OAuth lifecycle implementation.
• Codex/Gemini adapter behavior.
• Coding-plan provider integrations.

Acceptance Criteria

• Anthropic subscription mode works end-to-end with valid auth.
• Required Anthropic subscription headers/identity behavior are applied correctly.
• Streaming and tool-call paths work in subscription mode.
• Invalid/expired auth triggers deterministic fallback and user-visible status.
• API-key Anthropic flow remains backward compatible.
• Integration tests cover happy path, expired auth, revoked auth, and fallback path.

Implementation Touchpoints

• lib/loomkin/agent_loop.ex
• lib/loomkin/session/architect.ex
• lib/loomkin/teams/agent.ex
• lib/loomkin/models.ex
• lib/loomkin_web/live/model_selector_component.ex

Related

• Umbrella: #103 — Subscription-Backed Model Support (Umbrella)
• Adaptive Agent Roles & Dynamic Team Composition #67 (Adaptive Agent Roles & Dynamic Team Composition) — model/backend routing intersects role execution behavior.