Cortex-Inara/documentation/ARCH__BACKENDS.md

Architecture: LLM Backends

How Cortex selects and talks to AI models. Last updated: 2026-05-06

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Providers

Cortex supports four model types, each dispatched differently:

Type	Auth	Use
claude_cli	OAuth token from ~/.claude/.credentials.json	Chat, persona responses
gemini_cli	Gemini CLI credentials	Chat fallback / explicit selection
gemini_api	API key from registry account or .env	Orchestrator tool loop
local_openai	API key per host in model registry	Open WebUI, Ollama, OpenRouter, LiteLLM, etc.

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Backend Selection

Default: Role-Based Routing (Auto)

When no explicit backend is selected, Cortex routes to the model configured for the request's role in the user's model registry. Roles: chat, orchestrator, distill, coder, research (extensible via DEFINED_ROLES in .env).

Resolution order for a role:

1. User registry: roles[role].primary → backup_1 → backup_2 → backup_3 → backup_4
2. .env role default: ROLE_CHAT=claude_cli, ROLE_DISTILL=claude_cli, etc.
3. Hardcoded last-resort: chat/distill/coder → claude_cli, orchestrator/research → gemini_api

Explicit Override

The Role toggle in the Context & Memory panel cycles through configured role slots for the chat role: Primary → Backup 1 → Backup 2 → auto.

• Each slot shows the configured model label
• auto uses the Primary without forcing a specific backend type
• The ⚡ Tools toggle is independent — it routes to the orchestrator role regardless of the chat role selection

Fallback chain (automatic, only when no explicit registry entry exists):

claude  → gemini
gemini  → claude
local   → claude

When a model is explicitly configured in the registry, errors surface immediately — no silent fallback.

Each response shows a model tag (bottom-right of the message bubble) with the model label and host.

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Model Registry — V2 Schema

Per-user configuration stored in home/{user}/model_registry.json.

Managed at Settings → Models (/settings/models). Full provider UI coming in Phase 2.

{
  "version": 2,

  "providers": {
    "anthropic": {
      "credentials": [
        {"id": "cli", "label": "Claude CLI (OAuth)", "type": "cli"}
      ]
    },
    "google": {
      "accounts": [
        {"id": "a1b2", "label": "One Sky IT", "api_key": "AIza..."}
      ]
    }
  },

  "hosts": [
    {
      "id": "abc123",
      "label": "Gaming Laptop",
      "api_url": "http://192.168.x.x:3000",
      "api_key": "",
      "host_type": "openwebui"
    }
  ],

  "models": [
    {
      "id": "m1",
      "type": "claude_cli",
      "label": "Sonnet 4.6 (CLI)",
      "model_name": "claude-sonnet-4-6",
      "provider": "anthropic",
      "credential_id": "cli",
      "context_k": 200,
      "tags": ["chat", "persona"]
    },
    {
      "id": "m2",
      "type": "gemini_api",
      "label": "Gemini 2.5 Flash (OSIT)",
      "model_name": "gemini-2.5-flash",
      "provider": "google",
      "account_id": "a1b2",
      "context_k": 1000,
      "tags": ["orchestrator", "research"]
    },
    {
      "id": "m3",
      "type": "local_openai",
      "label": "Gemma 4 E4B",
      "model_name": "gemma4:e4b",
      "provider": "local",
      "host_id": "abc123",
      "context_k": 72,
      "max_rounds": 5,
      "tools": true,
      "tags": ["fast", "local"]
    }
  ],

  "roles": {
    "chat":         {"primary": "m1", "backup_1": "m2", "backup_2": "m3"},
    "orchestrator": {"primary": "m2", "backup_1": "m3"},
    "distill":      {"primary": "m1"}
  }
}

Optional model fields

Field	Type	Default	Meaning
context_k	int	32	Context window in thousands of tokens. Used for compaction budget (75% of window).
max_rounds	int | null	null	Per-model tool loop cap. null = use global orchestrator_max_rounds. Effective limit = min(per_model, global).
tools	bool	true	Whether this model supports tool calling. false = skip tool loop entirely; model gets a plain chat request.

host_type (local hosts)

host_type	Chat endpoint	Models endpoint	Use for
openwebui (default)	POST {url}/api/chat/completions	GET {url}/api/models	Open WebUI, Ollama
openai	POST {url}/chat/completions	GET {url}/models	OpenRouter, LiteLLM, Anthropic-compat

Set api_url to the base path before /chat/completions:

• OpenRouter: https://openrouter.ai/api/v1

Built-in model IDs

Always resolvable without a user-created registry entry. Used as role defaults.

ID	Type	Notes
claude_cli	claude_cli	Model from DEFAULT_MODEL in .env
gemini_cli	gemini_cli	Gemini CLI subprocess
gemini_api	gemini_api	Model from ORCHESTRATOR_MODEL in .env; key from GEMINI_API_KEY

V1 → V2 migration

Automatic on first load. Changes:

• Adds providers section (Anthropic CLI credential + empty Google accounts)
• Migrates gemini_api_key from auth.json → providers.google.accounts[0]
• All existing hosts, models, and role assignments are preserved

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Claude Backend (_claude())

Runs claude --print --no-session-persistence --output-format text as a subprocess.

• System prompt passed via --system-prompt
• Conversation history formatted as <conversation> block
• Token read live from ~/.claude/.credentials.json on every call — never uses the env var, which goes stale after claude auth login
• Model override via --model flag when model_name is set in the registry entry

Timeout: TIMEOUT_CLAUDE=60 seconds (.env)

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Gemini CLI Backend (_gemini())

Runs gemini --output-format text --extensions "" -p <prompt> as a subprocess.

• --extensions "" disables all MCP extensions — prevents child processes keeping pipes open
• start_new_session=True puts the process in its own group for clean os.killpg on timeout
• Output is cleaned to strip CLI noise (loading messages, retry notices, quota warnings)

Timeout: TIMEOUT_GEMINI=120 seconds (.env)

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Local Backend (_local())

HTTP POST to an OpenAI-compatible endpoint. Model config is resolved via the model registry.

# host_type "openwebui":  POST {api_url}/api/chat/completions
# host_type "openai":     POST {api_url}/chat/completions

Timeout: TIMEOUT_LOCAL=300 seconds (.env) — local models may need to load from disk.

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Gemini API (Orchestrator)

Used by orchestrator_engine.py for the ReAct tool loop. Not used for general chat.

API key resolution order:

1. api_key embedded in the resolved orchestrator model config (V2 registry with account_id)
2. get_user_gemini_key(user) — reads from auth.json (legacy, kept for compat)
3. GEMINI_API_KEY in .env (server default)

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Distillation

Memory distillation uses role="distill". Configure via Model Registry → Role Assignments.

.env override: ROLE_DISTILL=claude_cli (default).

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Code locations

File	Responsibility
cortex/llm_client.py	complete() — routing, dispatch, fallback
cortex/model_registry.py	Per-user registry CRUD and resolution (V2)
cortex/routers/local_llm.py	Settings UI routes + /api/models/role AJAX
cortex/routers/chat.py	_backend_label(), fallback_used flag
cortex/routers/orchestrator.py	Engine selection, Gemini API key resolution
cortex/config.py	ROLE_* env defaults, DEFINED_ROLES, PRIMARY_BACKEND