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Provider architecture

For maintainers. Using T3 Code? See docs/user.

A provider is the agent runtime that does the actual work. T3 Code supports several, and the orchestration layer does not know which one is behind a thread.

Built-in drivers

builtInDrivers.ts exports BUILT_IN_DRIVERS with five entries:

Driver kind Driver source
codex Drivers/CodexDriver.ts
claudeAgent Drivers/ClaudeDriver.ts
cursor Drivers/CursorDriver.ts
grok Drivers/GrokDriver.ts
opencode Drivers/OpenCodeDriver.ts

Each driver declares its driverKind, a configSchema, and a create function that builds an adapter in a child scope. Adapter implementations live beside them in apps/server/src/provider/Layers/ (CodexAdapter.ts, ClaudeAdapter.ts, and so on) and conform to ProviderAdapter.ts. Read the driver plus its adapter to see how a specific agent's transport, config, and event shapes are mapped.

Registry and routing

Two registries separate configuration from live processes:

  • ProviderInstanceRegistry keys configured instances by ProviderInstanceId. Creating one looks up the driver by driverKind, decodes entry.config with that driver's schema, opens a child scope, and calls driver.create.
  • ProviderAdapterRegistry resolves an instance ID to its live adapter via getByInstance.

ProviderService sits on top. It combines the adapter registry with the provider session directory to route session and turn operations for a thread, so callers name a thread, not an agent.

Adding a driver means writing the driver plus adapter and adding it to BUILT_IN_DRIVERS. No orchestration, contract, or client change is required for the common case.

OpenCode server ownership and catalog

Each OpenCode provider instance owns one lazy local server for catalog discovery and text-generation helpers through OpenCodeServerOwner.ts. Concurrent borrowers share startup. The server closes 30 seconds after the last borrower releases it, or when the provider instance closes. A failed or exited process can be started again on the next use. An externally configured OpenCode server remains externally owned.

The local server and its SDK clients use one resolved password. An explicit provider password overrides OPENCODE_SERVER_PASSWORD in the spawned environment. Without an explicit password, the client uses the password from the environment that the process inherits. External servers use only their explicit provider password and never inherit the host's local password.

Every server connection must pass the authenticated /global/health check before inventory or session operations start. The response must contain a valid version at or above 1.14.19. Local owners cache this result for the lifetime of the spawned process. External actions check once when they create their server connection, not for each model or SDK request.

Chat adapters keep their own server per thread. They register a thread-specific t3-code MCP connection, while OpenCode stores MCP connections by directory. Sharing these chat servers without changing MCP routing would let two threads in one directory replace each other's connection.

OpenCode loads its catalog through the HTTP API when an enabled provider instance starts. The provider registry keeps the snapshot in memory and persists it in the existing per-instance cache. Each subscribeServerConfig connection refreshes all providers, so a client reconnect reloads the OpenCode catalog from the current helper. The serverRefreshProviders request also refreshes it. Periodic OpenCode probes remain disabled. OpenCode reads credentials for each inventory request, but its native configuration files can remain cached for the lifetime of the helper process. The helper closes 30 seconds after its last inventory or text-generation borrower releases it. A refresh after that idle period starts a new helper and reads file changes. Repeated refreshes and active text-generation work can extend process reuse. Changes to the provider configuration or environment replace the instance and start a new discovery. Changes to unrelated settings only update snapshot enrichment. Other providers retain their existing refresh policy.

T3 Code does not own an external OpenCode process. Native configuration changes there can require an external reload or restart before T3 Code's next refresh sees them.

The shared server's idle shutdown does not clear the catalog. Failed discovery keeps the last known models, slash commands, and skills through the registry's existing merge rules. A successful empty inventory is authoritative. Existing threads keep their explicit model identifier and options when catalog metadata is missing; the catalog is not permission to choose a different model for a thread.

Model manifest

The model picker's legacy section is driven by apps/server/src/provider/model-manifest.json, which lists the current (non-legacy) model slugs per driver kind. The ModelManifest service (apps/server/src/provider/ModelManifest.ts) refreshes that data from the same file on main via raw.githubusercontent.com, so moving a model in or out of the legacy section is a commit, not a release. Preference order is remote fetch, then the on-disk copy of the last successful fetch (in the state directory), then the bundled copy. Fetches are TTL-gated, run concurrently with provider probes, respect the enableProviderUpdateChecks setting, and never fail a provider check. The Codex and Claude drivers apply the classification to every snapshot with applyModelManifest; driver kinds absent from the manifest have no legacy concept.

Attachment access

The server stores uploaded attachments in its attachment directory, outside the project workspace. ProviderService adds the absolute path of each attachment to the turn text, then passes every attachment to the provider adapter. Each adapter decides what its provider ingests natively:

  • Codex, Claude, Cursor, and Grok send images as native image inputs and skip generic files. For these providers, generic files reach the agent only as file paths in the turn text.
  • OpenCode sends PNG/JPEG/GIF/WebP images, text files, and PDFs up to 20 MB as native file parts with their real mime type. Everything else (ZIP and other binaries, image formats model APIs reject, oversized files) falls back to the file path in the turn text, like the other providers.

Claude receives the attachment directory as an allowed additional directory. Codex keeps its configured sandbox policy, so access depends on that policy and the selected runtime mode. OpenCode allows all paths in full-access mode and requests approval for directories outside the workspace in restricted modes. Cursor and Grok use their own provider permission rules.

The server does not copy attachments into a project or bypass provider approval rules. If an agent cannot read an attachment, the user must approve the access or select a runtime mode that permits it.

Updated attachment schemas tolerate unknown attachment members, but old image-only clients still cannot decode messages that contain file attachments. Client file-picking rollouts must account for this limit.

Do not run an old image-only server against state that contains file attachments. Replay decodes each persisted event before projection. A file-bearing event can make ProjectionPipeline bootstrap and OrchestrationEngine startup fail for the entire environment, not only the affected thread.

How provider work is requested

Clients never call a provider directly. They dispatch orchestration commands over the RPC method orchestration.dispatchCommand, defined with the rest of the orchestration surface in orchestration.ts. The client-dispatchable provider-facing commands are thread.turn.start, thread.turn.interrupt, thread.approval.respond, thread.user-input.respond, thread.checkpoint.revert, and thread.session.stop, plus the mode setters thread.runtime-mode.set and thread.interaction-mode.set.

The engine persists an event for the command, and a server-side reactor performs the provider call. Provider output comes back as internal commands such as thread.message.assistant.delta and thread.session.set, which clients observe through orchestration.subscribeThread. See overview.md for the command/event loop.

Server-side workers

Provider work flows through three queue-backed workers. All three are built with makeDrainableWorker from DrainableWorker.ts and expose drain for deterministic test synchronization.

  1. ProviderRuntimeIngestion consumes provider runtime streams and emits orchestration commands.
  2. ProviderCommandReactor reacts to orchestration intent events and dispatches provider calls.
  3. CheckpointReactor captures workspace checkpoints on turn start and completion, and performs reverts.

Buffered assistant delivery

A thread in buffered assistant delivery mode accumulates assistant text instead of streaming each delta. The buffer is not held until turn completion. In ProviderRuntimeIngestion, MAX_BUFFERED_ASSISTANT_CHARS is 24,000: the append that would exceed it invalidates the buffer and spills the whole accumulated text as one delta. The buffer also flushes at interaction boundaries, when a request opens (approval) or user input is requested, via flushBufferedAssistantMessagesForTurn.