Agent Client Protocol bridge over JSON-RPC stdio. Editors can create or resume agents, stream their events, answer questions and approvals, and render tool calls. One connection supports multiple isolated sessions; Zed is the primary compatibility target.
It is a **client-driver / UI plugin**, the structured analogue of the readline `stdio-chat` plugin — NOT a loop change and NOT a [capability seam](../../../docs/rfc/implemented/architecture/2026-06-13-capability-seams.md). It consumes the existing `agent/*` event taxonomy, the `dsh-agent` create/resume factory, and `dsh-session-persistence`.
`apply(ctx, config)` — wires an `AgentSideConnection` (from `@agentclientprotocol/sdk`) to `process.stdin`/`process.stdout` and implements the ACP `Agent` method surface.
The plugin injects `agents`, `sessions`, `sessionPersistence`, `tools`, and `userInteraction`, never the concrete loop. Persistence backs `session/load`; tool definitions own presentation; user interaction maps agent questions to ACP forms.
(No persona key: `dsh-system-prompt`'s own `persona` config supplies the global default section, so ACP-created agents render it without the bridge carrying prompt text. An agent-scoped same-name section may still shadow that default.)
The `initialize` handshake reports a fixed server identity (`agentInfo: { name: 'deepseek-harness-acp', version: '0.0.1' }`) — branding is a literal at the `initialize` site, not config.
| `initialize` | static | negotiate `protocolVersion`; advertise baseline prompt capabilities (`text`, plus `resource_link` rendered as text) and `loadSession: true` |
| `session/new` | `ctx.agents.create({ sessionId, meta:{cwd} })` | creates a new session/agent; N concurrent sessions are allowed, keyed by id; `cwd` must be absolute (it becomes the session's workspace — see Per-session cwd); non-empty `additionalDirectories` and `mcpServers` rejected |
| `session/prompt` | `agent.send()` | supports ACP `text` and `resource_link` blocks; rejects image/audio/embedded resource and empty prompts; one in-flight prompt PER session (independent); settles on the OWNING turn's end (a turn that ends in `error` rejects the RPC) |
| `session/cancel` | `agent.cancel()` | the queue-aware cancel: aborts a running step, clears queued + steering work, and drops a turn about to start, then settles the prompt `cancelled` — for ONLY that session (a cancel never touches another session's stream or prompt) |
| `elicitation/create` | `ctx.userInteraction.ask()` | maps `ask_user_question` questions to ACP form elicitations; option descriptions are shown in enum titles, `multi_select` uses ACP array enums, optionless requests use a required `custom` field, and a non-empty custom answer overrides any selected choice |
Forward and reverse indexes route every event, prompt, cancel, and approval to one session. Each session permits one in-flight prompt; teardown drains all sessions in parallel. See the [multi-session RFC](../../../docs/rfc/implemented/feature/2026-06-14-acp-multi-session.md).
The bridge advertises `sandbox-mode` and `approval-policy` only when their services are composed. Current values fold from each session's log over the composition default, so load restores overrides directly. `session/set_config_option` validates against the closed vocabulary, calls the domain writer, and returns refreshed state. Changes inside an open turn append immediately; idle changes are coalesced in memory and anchored at the next `agent/prompt-submit`, preserving turn enclosure and event order. A crash before anchoring discards the pending change, and load reports durable log truth. See the [sandbox RFC](../../../docs/rfc/implemented/feature/2026-07-06-sandbox.md).
Background bash tasks use the session id as an opaque owner token, so one session cannot inspect or stop another's task. That contract belongs to [`dsh-tool-bash`](../../bash/tool-bash/).
`session/new` records the request's absolute cwd in the session header. `session/load` requires an absolute request cwd matching persisted metadata and rejects missing or mismatched metadata before constructing an agent. Bash defaults to that workspace; an explicit relative workdir resolves against it. `additionalDirectories` remains unsupported.
Tools return provider-neutral `generic`, `terminal`, or `diff` render intents from `presentCall()` and `presentResult()`. The bridge maps the discriminator to ACP without special-casing tool names and falls back to a generic card. Per-session call-id state supplies result events with their omitted name and arguments during live streaming and replay. See [`dsh-tools`](../../core/tools/README.md#tool-owned-ui-presentation).
When the client advertises `_meta.terminal_output`, terminal intents map to Zed's terminal info, output, and exit metadata; result text is omitted because ACP updates replace call content. Other clients receive a generic card and fenced console fallback. Session creation snapshots the capability so call and result agree. The command still executes through the harness, not ACP terminal creation. See the [terminal-rendering RFC](../../../docs/rfc/implemented/feature/2026-06-18-acp-terminal-and-tool-rendering.md).
A prompt captures its owning turn and settles exactly once from the matching durable `turn/end`, even if presentation failed. Turn correlation excludes stale endings. Error turns reject with an ACP internal error; empty prompts reject before enqueue.
For a bridge-owned call, the [approval seam](../user-approval/README.md) maps `ask` to an editor prompt with one-shot allow/reject options. Foreign or call-less requests delegate; unknown choices never grant, cancellation stays cancellation, and transport failure becomes fail-closed unavailability. Whether a tool asks remains policy outside the bridge.
Disposal and client disconnect share one memoized teardown. It cancels pending prompts and disposes all owned agent handles in parallel, waiting for loop exit and final flush before registry removal. Mid-turn teardown records `disposed`; `session/cancel` records `aborted`.
- **`additionalDirectories`** — rejected. A session operates in its single `cwd` (see Per-session cwd); widening the tool/filesystem scope to extra roots is a separate sandbox concern, not yet implemented.
The JSON-RPC frames go on stdout, so this plugin MUST run in an example that loads **no stdout logger** (the console logger writes to stdout and would corrupt the frames). The guarantee is config-only — see `examples/acp-agent` (no console logger) and [ACP support risks](../../../docs/rfc/implemented/feature/2026-06-14-acp-agent-client-protocol.md#risks). A stderr exporter is fine for logging.
`pnpm --dir /path/to/deepseek-harness run demo:acp` boots `examples/acp-agent` (needs `DEEPSEEK_API_KEY`). Point an ACP client at it; for Zed, add to `agent_servers`:
