@qwen-code/acp-bridge

Shared ACP bridge primitives consumed by qwen serve, channels, IDE, TUI, and remote-control adapters. Lives in the monorepo, not published to npm.

This is PR 22a of the Mode B daemon roadmap (#4175 Wave 5). The full extraction is split:

Slice	Scope	Status
PR 22a (this)	Skeleton + EventBus + inMemoryChannel + AcpChannel types + PermissionMediator type-only stub	this PR
PR 22b	Lift BridgeClient + createHttpAcpBridge + defaultSpawnChannelFactory from cli/src/serve/httpAcpBridge.ts	after PR 17 (#4282) and PR 14b (#4271) merge
PR 24	Implement the four PermissionMediator strategies (first-responder, designated, consensus, local-only) + pair-token revocation + audit log	Wave 5

What's here today

• eventBus — per-session NDJSON pub/sub with bounded ring replay, Last-Event-ID reconnect, and slow-client backpressure (slow_client_warning → client_evicted).
• inMemoryChannel — paired NDJSON streams without spawning a child; used for in-process bridge tests and the parked Mode A (qwen --serve) path.
• channel — AcpChannel / AcpChannelExitInfo / ChannelFactory type contract that httpAcpBridge.ts already injects via BridgeOptions.channelFactory.
• permission — type-only PermissionMediator interface, PermissionPolicy literal union (4 strategies), and PermissionResolution discriminated union. No implementation yet — first-responder voting still lives in cli/src/serve/httpAcpBridge.ts BridgeClient.requestPermission. PR 24 will move that and add the other three policies behind this interface.
• status (PR 22b/1) — wire-contract status types for /workspace/{mcp,skills,providers,env,preflight} and /session/:id/{context,supported-commands} routes, the STATUS_SCHEMA_VERSION / SERVE_*_EXT_METHODS constants, BridgeTimeoutError / MissingCliEntryError / BridgeChannelClosedError typed exceptions, and the mapDomainErrorToErrorKind classifier (regex → instanceof after #4299 / #4300). The 27-symbol contract acp-integration/acpAgent.ts consumes lives here.
• workspacePaths (PR 22b/1) — canonicalizeWorkspace (the cross-module BX9_q contract used by config.ts / settings.ts / sandbox.ts / bridge to collapse boot-time + per-request workspace paths to one canonical key) plus MAX_WORKSPACE_PATH_LENGTH.
• bridgeErrors (PR 22b/1) — 11 typed Error subclasses the bridge throws (SessionNotFoundError, WorkspaceMismatchError, RestoreInProgressError, etc.); HTTP route layer instanceof-branches on these to map to specific status codes.
• bridgeTypes (PR 22b/1) — public bridge contract types: BridgeSpawnRequest, BridgeSession, BridgeRestoreSessionRequest, BridgeSessionState, BridgeRestoredSession, BridgeSessionSummary, SessionMetadataUpdate, BridgeClientRequestContext, BridgeHeartbeatResult, BridgeHeartbeatState, plus the HttpAcpBridge interface itself (~30-method facade).
• bridgeOptions (PR 22b/2) — BridgeOptions interface (factory construction contract: boundWorkspace, channelFactory, maxSessions, eventRingSize, permissionResponseTimeoutMs, persistence callbacks, etc.) and the new DaemonStatusProvider injection seam for daemon-host env / preflight cells (production impl in cli/src/serve/daemonStatusProvider.ts).

What's not here yet

• The bridge core itself (BridgeClient, createHttpAcpBridge, defaultSpawnChannelFactory, all the BridgeSession* types). It stays in packages/cli/src/serve/httpAcpBridge.ts until the in-flight Wave 4 PRs that touch the bridge surface (#4282 PR 17 and #4271 PR 14b) merge — moving it now would create a 3-way merge on a 4400-LOC file for no win.
• The per-session FileSystemService injection point (PR 18 #4250 introduced the boundary; PR 22b will parameterize bridge writes through it instead of the inline BridgeClient.writeTextFile).

Imports — root vs subpaths

The package exposes both a barrel root (@qwen-code/acp-bridge) and per-module subpaths (/eventBus, /inMemoryChannel, /channel, /permission). They re-export the same symbols, so either form resolves to the same module at runtime. Pick by intent:

• Root for application/test code that uses several primitives at once — concise and matches how serve/ imports landed today.
• Subpaths for client adapters (TUI / channels / IDE / future remoteControl) that only consume one slice — keeps the dependency surface explicit and lets bundlers tree-shake the rest.

Both variants are stable. PR 22b will not change either set.

Backward compatibility

packages/cli/src/serve/eventBus.ts and packages/cli/src/serve/inMemoryChannel.ts remain as one-line re-export wrappers, so every existing relative import inside serve/ and the one external import in cli/src/commands/serve.ts keeps resolving without churn.

httpAcpBridge.ts continues to export AcpChannel / AcpChannelExitInfo / ChannelFactory (now via re-export from this package) so any external consumer of those types is unaffected.

See also

• #4175 Wave 5 PR 22 row
• #3803 Stage 1.5-prereq AcpChannel lift (chiga0's original framing)
• httpAcpBridge.ts:1096-1106 (FIXME pointing at the four PermissionMediator strategies this package now declares)