Summary

• Replace the hand-rolled pkg/acpserver package (~590-line custom JSON-RPC/SSE server) with the upstream github.com/coder/acp-go-sdk, eliminating ~2,000 lines of bespoke protocol code that duplicated what the SDK provides
• Decompose the monolithic ACP infrastructure layer into focused adapters: Agent (session lifecycle), Emitter (SDK event dispatch), PermissionClient (tool-approval requests), and a simplified Renderer that writes directly to SDK streams
• Fix session lifecycle bugs discovered during migration: Shutdown now permanently tears down session context rather than only interrupting the current run, and NewSession correctly validates the type assertion on the session ID field
• Add a full functional test suite (acp_serve_functional_test.go) and architecture enforcement tests that were previously absent

Changes

Removed — custom ACP server package

• pkg/acpserver/server.go: Deleted (~590 lines of custom JSON-RPC/SSE server)
• pkg/acpserver/protocol.go: Deleted (custom framing protocol)
• pkg/acpserver/types.go: Deleted (custom request/response types)
• pkg/acpserver/doc.go: Deleted
• pkg/acpserver/architecture_test.go: Deleted
• pkg/acpserver/goroutine_leak_test.go: Deleted
• pkg/acpserver/protocol_test.go: Deleted
• pkg/acpserver/server_test.go: Deleted
• pkg/acpserver/types_test.go: Deleted
• pkg/acpserver/writeframe_internal_test.go: Deleted
• internal/infrastructure/acp/message.go: Deleted (custom message DTOs replaced by SDK types)
• internal/infrastructure/acp/message_test.go: Deleted

Infrastructure — new SDK adapters

• internal/infrastructure/acp/agent.go: New Agent handler implementing session create/resume/run against the SDK
• internal/infrastructure/acp/agent_test.go: Unit tests for Agent covering success, validation errors, and type assertion edge cases
• internal/infrastructure/acp/emitter.go: New Emitter wrapping SDK connection to dispatch SessionUpdate events; extracted sessionUpdater interface for testability
• internal/infrastructure/acp/emitter_internal_test.go: Internal tests for Emitter internals
• internal/infrastructure/acp/emitter_test.go: Behavioural tests for Emitter with fake connection
• internal/infrastructure/acp/errors.go: Centralized ACPHandlerError transport-neutral error type
• internal/infrastructure/acp/errors_test.go: Tests for error construction and unwrapping
• internal/infrastructure/acp/permission.go: New PermissionClient handling tool-approval round-trips via the SDK
• internal/infrastructure/acp/permission_test.go: Tests for PermissionClient including error propagation
• internal/infrastructure/acp/architecture_test.go: New architecture enforcement tests (SDK import confinement, documentation drift detection)
• internal/infrastructure/acp/doc_test.go: Public surface and documentation coverage tests
• internal/infrastructure/acp/event_projector.go: Updated to consume SDK event types instead of custom message structs
• internal/infrastructure/acp/event_projector_test.go: Revised to match new SDK-based projector
• internal/infrastructure/acp/renderer.go: Simplified to emit directly to SDK streams; added concurrency invariant documentation
• internal/infrastructure/acp/renderer_test.go: Substantially refactored to match simplified renderer surface
• internal/infrastructure/acp/doc.go: Rewritten to document new component decomposition and SDK integration contract

Application — session service fixes

• internal/application/acp_session.go: Updated session lifecycle; Shutdown permanently tears down context
• internal/application/acp_session_service.go: Wired new SDK-backed adapters; improved NewSession result validation
• internal/application/acp_session_service_parking_test.go: New parking/prompt-routing test coverage
• internal/application/acp_session_service_test.go: Expanded to cover NewSession error paths and session ID validation
• internal/application/acp_session_service_concurrency_test.go: Minor updates for renamed types
• internal/application/acp_audit_fixes_test.go: Minor updates

CLI wiring

• internal/interfaces/cli/acp_serve.go: Updated serve command to wire SDK server instead of custom server; fixed signal-watch goroutine lifetime
• internal/interfaces/cli/acp_serve_lifecycle_test.go: New lifecycle tests for server startup/shutdown sequence
• internal/interfaces/cli/acp_serve_test.go: Revised to match new wiring surface
• internal/interfaces/cli/acp_wiring.go: Simplified; removed pkg-acpserver dependency, wires SDK components directly
• internal/interfaces/cli/acp_wiring_test.go: Updated with sync/atomic import for streamFlaggingEmitter tests

Architecture & configuration

• .go-arch-lint.yml: Removed pkg-acpserver component; added go-sdk-acp vendor; updated infra-acp dependency rules
• go.mod / go.sum: Added github.com/coder/acp-go-sdk dependency

Tests — integration

• tests/integration/acp/acp_serve_functional_test.go: New end-to-end functional suite covering session create, run, streaming, and shutdown flows
• tests/integration/acp/acp_jsonrpc_e2e_test.go: Updated to use SDK-based server
• tests/integration/acp/acp_goroutine_leak_test.go: Updated for SDK lifecycle
• tests/integration/acp/testhelpers_test.go: Refactored test helpers for SDK server setup

Documentation

• docs/ADR/020-acp-server-migration-to-coder-sdk.md: New ADR documenting the migration rationale, tradeoffs, and SDK adoption decision
• docs/ADR/018-acp-transparent-agent-server-protocol.md: Minor update to reference ADR-020
• docs/ADR/README.md: Added entry for ADR-020
• CHANGELOG.md: Release entry for F105
• README.md: Updated feature status

ZPM knowledge base

• .zpm/kb/pr_feature_f105_acp_server_migration_to_coderacp_go_s/journal.wal: PR tracking journal
• .zpm/kb/pr_feature_f105_acp_server_migration_to_coderacp_go_s/knowledge.pl: Prolog knowledge facts for this PR

Test plan

• make build produces a clean binary with no compilation errors
• make test passes including the new acp_serve_functional_test.go functional suite and all unit tests for Agent, Emitter, PermissionClient, and Renderer
• make lint reports zero violations; architecture lint confirms infra-acp no longer imports pkg-acpserver and only the SDK vendor is used
• awf acp-serve starts an ACP server, accepts a session, processes a prompt, and streams events correctly end-to-end

Closes #367

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