@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.

Lift history (#4175 Mode B daemon roadmap):

Slice	Scope	Status
PR 22a (#4295)	Skeleton + EventBus + inMemoryChannel + AcpChannel types + PermissionMediator type-only stub	✅ merged
PR 22b/1 (#4298)	Lift status + workspacePaths + bridgeErrors + bridgeTypes	✅ merged
PR 22b/2 (#4304)	Lift BridgeOptions + new DaemonStatusProvider injection seam	✅ merged
F1 (this PR)	Lift defaultSpawnChannelFactory + BridgeClient + createHttpAcpBridge factory closure + new BridgeFileSystem injection seam (22b' scope)	✅ in this PR
F3 PR 24	Implement the four PermissionMediator strategies (first-responder, designated, consensus, local-only) + pair-token revocation + audit log	F3 in the feature-cohesive plan

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 createHttpAcpBridge (now in this package) plus the channels / VSCode IDE companion's own-spawn paths consume 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 BridgeClient.requestPermission (in bridgeClient.ts after F1). F3 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,tasks} 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.) plus the DaemonStatusProvider injection seam for daemon-host env / preflight cells (production impl in cli/src/serve/daemonStatusProvider.ts) and the F1 BridgeFileSystem injection seam for the ACP fs proxy.
• spawnChannel (F1) — defaultSpawnChannelFactory + killChild + SCRUBBED_CHILD_ENV_KEYS denylist + scrubChildEnv pure env-policy helper (exported for adapter reuse + unit-test access; isolates the scrub + override + defense-in-depth ordering invariant the security argument relies on). Production spawn of the qwen --acp child with stderr prefix-and-forward, kill cascade, and env passthrough. Channels (packages/channels/base/AcpBridge.ts) and the VSCode IDE companion consume this directly instead of each reimplementing the child lifecycle.
• bridgeClient (F1) — BridgeClient class implementing the ACP Client surface: first-responder permission flow, session-update fan-out into EventBus, child-side extNotification routing, early-event buffer + tombstone bookkeeping, inline fs proxy for writeTextFile / readTextFile. Exports the supporting PendingPermission / PermissionResolutionRecord / BridgeClientSessionEntry types + MAX_RESOLVED_PERMISSION_RECORDS cap that the factory's bookkeeping maps consume.
• bridge (F1) — createHttpAcpBridge factory closure (~3000 LOC)
  • ChannelInfo / SessionEntry interfaces + factory-only helpers (withTimeout, canonicalizeExistingAncestor, verifyParentWithinWorkspace, debug log helpers, hasControlCharacter) + factory constants. Builds the bookkeeping closures (resolveEntry, registerPending, etc.) and wires them into BridgeClient.
• bridgeFileSystem (F1) — BridgeFileSystem interface for the ACP fs proxy. When wired through BridgeOptions.fileSystem, BridgeClient.readTextFile / BridgeClient.writeTextFile delegate to it instead of the inline fs.realpath / fs.writeFile / fs.readFile proxy. Production qwen serve follow-up wraps PR 18's WorkspaceFileSystem here so writes get TOCTOU + symlink + trust-gate + audit guarantees.

Imports — root vs subpaths

The package exposes both a barrel root (@qwen-code/acp-bridge) and per-module subpaths (/eventBus, /inMemoryChannel, /channel, /permission, /status, /workspacePaths, /bridgeErrors, /bridgeTypes, /bridgeOptions, /spawnChannel, /bridgeClient, /bridge, /bridgeFileSystem). 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 across the F1 lift.

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.

After F1, packages/cli/src/serve/httpAcpBridge.ts shrinks to a ~97-line re-export shim that forwards every previously-exported symbol (createHttpAcpBridge, defaultSpawnChannelFactory, BridgeClient, all the typed errors, all the type aliases) from the lifted subpaths. Every relative ./httpAcpBridge.js import in server.ts / runQwenServe.ts / workspaceAgents.ts / workspaceMemory.ts / index.ts / the bridge test suite keeps resolving without any call-site changes.

See also

• #4175 Mode B daemon roadmap (feature-cohesive F1-F5 plan targeting daemon_mode_b_main)
• #3803 Stage 1.5-prereq AcpChannel lift (chiga0's original framing)
• F3 PR 24 will replace the inline first-responder logic in BridgeClient.requestPermission with the four PermissionMediator strategies declared in permission.ts.