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sandbox-agent/research/acp/ts-client.md
Nathan Flurry 94353f7696 chore: fix bad merge
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TypeScript Client Rewrite Spec (ACP HTTP Client + Sandbox Agent SDK)

Status

  • Draft.
  • Captures confirmed decisions and server-verified contracts before implementation.

Goals

  • Split TypeScript clients into:
  1. acp-http-client: protocol-pure ACP-over-HTTP transport/client.
  2. sandbox-agent SDK: Sandbox Agent wrapper that hides ACP terminology and applies Sandbox-specific metadata/extensions.
  • Make the Sandbox Agent SDK API as simple as creating a client and connecting once.
  • Remove ACP-facing API from sandbox-agent public surface.

Confirmed Product Decisions

  • Dedicated protocol package name: acp-http-client.
  • acp-http-client must implement ACP HTTP protocol "to the T" and include no Sandbox-specific metadata/extensions.
  • Sandbox SDK public constructor pattern: new SandboxAgentClient(...).
  • Sandbox SDK auto-connects by default, but supports disabling auto-connect.
  • ACP-related SDK calls must fail if .connect() has not been called.
  • After .disconnect(), ACP-related SDK calls must fail until reconnected.
  • A SandboxAgentClient instance can hold at most one active ACP connection.
  • No API for creating multiple ACP clients per wrapper instance.
  • ACP terminology should not appear in Sandbox SDK public API/docs.
  • Sandbox SDK should be a thin conversion layer on top of ACP protocol, mainly for metadata/event conversion.
  • Existing ACP-facing methods in sandbox-agent are removed (full rewrite).
  • Non-ACP HTTP helpers remain in sandbox-agent (health/agents/install/fs/etc).

Server-Verified v1 ACP Contract

HTTP endpoints and headers

  • Endpoints:
  1. POST /v1/rpc
  2. GET /v1/rpc (SSE)
  3. DELETE /v1/rpc
  • Headers:
  1. No connection-id header.
  2. Last-Event-ID for SSE replay.
  3. Agent selection is in payload metadata: params._meta["sandboxagent.dev"].agent.
  • Sources:
  1. server/packages/sandbox-agent/src/router.rs:862
  2. server/packages/sandbox-agent/src/router.rs:913
  3. server/packages/sandbox-agent/src/router.rs:948
  4. server/packages/sandbox-agent/src/acp_runtime/mod.rs:26
  5. server/packages/sandbox-agent/src/acp_runtime/mod.rs:27

Custom _sandboxagent/* methods/events currently implemented

  • Request methods handled in runtime:
  1. _sandboxagent/session/detach
  2. _sandboxagent/session/terminate
  3. _sandboxagent/session/list_models
  4. _sandboxagent/session/set_metadata
  • Notification methods handled in runtime:
  1. _sandboxagent/session/detach
  2. _sandboxagent/session/terminate
  3. _sandboxagent/session/set_metadata
  • Runtime notifications:
  1. _sandboxagent/session/ended
  2. _sandboxagent/agent/unparsed
  • Sources:
  1. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:3
  2. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:4
  3. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:5
  4. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:6
  5. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:7
  6. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:8
  7. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:11
  8. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:30
  9. server/packages/sandbox-agent/src/acp_runtime/mod.rs:1496
  10. server/packages/sandbox-agent/src/acp_runtime/backend.rs:95

Custom extension capability advertisement

  • Injected into initialize response at:
  • result.agentCapabilities._meta["sandboxagent.dev"].extensions
  • Includes booleans and methods array for extension availability.
  • Source:
  1. server/packages/sandbox-agent/src/acp_runtime/ext_meta.rs:32
  2. server/packages/sandbox-agent/src/acp_runtime/ext_meta.rs:55
  3. server/packages/sandbox-agent/tests/v1_api/acp_extensions.rs:3

Server-Verified _meta["sandboxagent.dev"] Behavior

Namespace definition

  • Canonical metadata namespace key: sandboxagent.dev.
  • Source:
  1. server/packages/sandbox-agent/src/acp_runtime/ext_meta.rs:4

Inbound metadata ingestion

  • session/new reads _meta["sandboxagent.dev"] as map and stores it.
  • Source:
  1. server/packages/sandbox-agent/src/acp_runtime/mod.rs:610
  2. server/packages/sandbox-agent/src/acp_runtime/ext_meta.rs:21

Metadata mutation extension

  • _sandboxagent/session/set_metadata accepts either:
  1. params.metadata object, or
  2. params._meta["sandboxagent.dev"] object.
  • Source:
  1. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:163
  2. server/packages/sandbox-agent/src/acp_runtime/ext_methods.rs:182

Keys with explicit runtime behavior

  • title:
  1. Updates session.title and stored sandbox metadata.
  • model:
  1. Updates model hint and stored sandbox metadata.
  • mode:
  1. Updates mode hint and stored sandbox metadata.
  • Source:
  1. server/packages/sandbox-agent/src/acp_runtime/mod.rs:1355
  2. server/packages/sandbox-agent/src/acp_runtime/mod.rs:1369
  3. server/packages/sandbox-agent/src/acp_runtime/mod.rs:1374
  4. server/packages/sandbox-agent/src/acp_runtime/mod.rs:1377

Keys injected/derived by runtime in session/list

  • Runtime always injects these keys under _meta["sandboxagent.dev"]:
  1. agent
  2. createdAt
  3. updatedAt
  4. ended
  5. eventCount
  6. model (if model hint exists)
  • Source:
  1. server/packages/sandbox-agent/src/acp_runtime/mod.rs:817

Known pass-through keys (stored and returned, not strongly typed in runtime)

  • Observed in tests/docs as pass-through metadata:
  1. variant
  2. requestedSessionId
  3. permissionMode
  4. skills
  5. agentVersionRequested
  • Sources:
  1. server/packages/sandbox-agent/tests/v1_api/acp_extensions.rs:145
  2. research/acp/v1-schema-to-acp-mapping.md:73
  3. research/acp/v1-schema-to-acp-mapping.md:80

Package Split

Package A: acp-http-client

  • Scope:
  1. ACP JSON-RPC over streamable HTTP only (/v1/rpc, headers, SSE replay, close).
  2. Generic envelope send/receive and connection lifecycle.
  3. No _sandboxagent/* helpers.
  4. No _meta["sandboxagent.dev"] helpers.
  5. No Sandbox-specific type aliases.
  • API intent:
  1. Low-level, minimal, protocol-faithful.
  2. Usable by any ACP-compatible server.

Package B: sandbox-agent (SandboxAgentClient)

  • Scope:
  1. Control-plane and host APIs: health, agents, install, filesystem, etc.
  2. Single ACP-backed session client lifecycle hidden behind sandbox naming.
  3. Metadata conversion in/out of _meta["sandboxagent.dev"].
  4. Sandbox extension conversion for _sandboxagent/* methods/events.
  • Lifecycle rules:
  1. Constructor: new SandboxAgentClient(options).
  2. Auto-connect by default (configurable opt-out).
  3. .connect(...) creates/activates one ACP connection.
  4. .connect(...) throws if already connected.
  5. .disconnect(...) closes current ACP connection.
  6. ACP-related methods throw a not-connected error when disconnected.

ACP-Shaped vs Sandbox API Names

ACP-shaped names are method names that mirror ACP primitives directly (or current SDK wrappers around them), such as initialize, newSession, prompt, extMethod.

Naming rule: for stable ACP methods, Sandbox Agent SDK method names stay ACP-aligned; only extension/unstable helpers may use Sandbox-specific naming.

ACP-shaped name ACP protocol message Sandbox-facing name (candidate) Notes
initialize() {\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\",\"params\":{...}} connect() First request must include params._meta[\"sandboxagent.dev\"].agent when no connection id exists.
newSession() {\"jsonrpc\":\"2.0\",\"id\":2,\"method\":\"session/new\",\"params\":{...}} newSession() Stable ACP method name preserved.
loadSession() {\"jsonrpc\":\"2.0\",\"id\":3,\"method\":\"session/load\",\"params\":{\"sessionId\":\"...\",...}} loadSession() Stable ACP method name preserved.
prompt() {\"jsonrpc\":\"2.0\",\"id\":4,\"method\":\"session/prompt\",\"params\":{...}} prompt() Stable ACP method name preserved.
cancel() / session/cancel {\"jsonrpc\":\"2.0\",\"method\":\"session/cancel\",\"params\":{\"sessionId\":\"...\"}} cancel() Stable ACP method name preserved.
setSessionMode() {\"jsonrpc\":\"2.0\",\"id\":5,\"method\":\"session/set_mode\",\"params\":{\"sessionId\":\"...\",\"modeId\":\"...\"}} setSessionMode() Stable ACP method name preserved.
setSessionConfigOption() {\"jsonrpc\":\"2.0\",\"id\":6,\"method\":\"session/set_config_option\",\"params\":{...}} setSessionConfigOption() Stable ACP method name preserved.
unstableListSessions() or session/list {\"jsonrpc\":\"2.0\",\"id\":7,\"method\":\"session/list\",\"params\":{...}} listSessions() Wrapper chooses best server method.
unstableForkSession() {\"jsonrpc\":\"2.0\",\"id\":8,\"method\":\"session/fork\",\"params\":{...}} forkSession() Preserve capability if exposed.
unstableResumeSession() {\"jsonrpc\":\"2.0\",\"id\":9,\"method\":\"session/resume\",\"params\":{...}} resumeSession() Preserve capability if exposed.
unstableSetSessionModel() / session/set_model {\"jsonrpc\":\"2.0\",\"id\":10,\"method\":\"session/set_model\",\"params\":{\"sessionId\":\"...\",\"modelId\":\"...\"}} setSessionModel() ACP-aligned naming when exposed.
extMethod(\"_sandboxagent/session/list_models\") {\"jsonrpc\":\"2.0\",\"id\":11,\"method\":\"_sandboxagent/session/list_models\",\"params\":{...}} listModels() Native wrapper method.
extMethod(\"_sandboxagent/session/set_metadata\") {\"jsonrpc\":\"2.0\",\"id\":12,\"method\":\"_sandboxagent/session/set_metadata\",\"params\":{...}} setMetadata() Native wrapper method.
extMethod(\"_sandboxagent/session/detach\") {\"jsonrpc\":\"2.0\",\"id\":13,\"method\":\"_sandboxagent/session/detach\",\"params\":{\"sessionId\":\"...\"}} detachSession() Native wrapper method.
extMethod(\"_sandboxagent/session/terminate\") {\"jsonrpc\":\"2.0\",\"id\":14,\"method\":\"_sandboxagent/session/terminate\",\"params\":{\"sessionId\":\"...\"}} terminateSession() Native wrapper method.
close ACP connection DELETE /v1/rpc disconnect() Transport-level close, not a JSON-RPC envelope.

Conversion Layer Requirements

  • Request conversion (sandbox -> ACP):
  1. Map sandbox method names to ACP methods.
  2. Inject/merge _meta["sandboxagent.dev"] where needed.
  • Response/event conversion (ACP -> sandbox):
  1. Convert _sandboxagent/session/ended to sandbox lifecycle event.
  2. Convert _sandboxagent/agent/unparsed to sandbox parse-error event.
  3. Surface metadata fields from _meta["sandboxagent.dev"] as first-class sandbox fields where appropriate.

Error Model

  • Shared HTTP error type for non-2xx (application/problem+json) remains in sandbox SDK.
  • Additional wrapper errors:
  1. NotConnectedError for ACP-related calls before .connect().
  2. AlreadyConnectedError when calling .connect() while connected.

Rewrite Impact (expected)

  • Remove from sandbox-agent public API:
  1. createAcpClient
  2. postAcpEnvelope
  3. closeAcpClient
  4. ACP type re-exports from @agentclientprotocol/sdk
  5. ACP-named classes (SandboxAgentAcpClient)
  • Replace with sandbox-facing API on SandboxAgentClient.

Testing Requirements

  • Continue integration tests against real server/runtime over real /v1 HTTP APIs.
  • Add integration coverage for:
  1. Auto-connect on constructor.
  2. autoConnect: false behavior.
  3. Not-connected error gates.
  4. Single-connection guard (connect() twice).
  5. Metadata injection/extraction parity.
  6. Extension event conversion parity (_sandboxagent/session/ended, _sandboxagent/agent/unparsed).