pi-subagents-bridge

pi-subagents-bridge is a protocol adapter between two Pi extensions:

• @tintinweb/pi-tasks
• pi-subagents

It makes TaskExecute work with pi-subagents by translating the pi-tasks subagent RPC into the RPC and completion events that pi-subagents exposes. It also exposes a separate, generic plan-exec RPC for direct execution clients.

What it does

@tintinweb/pi-tasks expects a v2 subagent protocol. pi-subagents exposes a v1 RPC plus async completion events. This bridge sits between them and handles the mismatch.

Specifically, it:

• answers the pi-tasks v2 ping handshake
• forwards spawn and stop requests to pi-subagents
• translates pi-subagents completion events back into pi-tasks task updates
• falls back to polling pi-subagents run status if an async completion event is missed
• keeps the generic plan-exec RPC separate from all pi-tasks channels

Request and completion flow

sequenceDiagram
  autonumber
  participant Tasks as @tintinweb/pi-tasks
  participant Bridge as pi-subagents-bridge
  participant Subs as pi-subagents

  Tasks->>Bridge: ping (v2)
  Bridge-->>Tasks: version 2

  Tasks->>Bridge: spawn(type, prompt, options)
  Bridge->>Subs: spawn(agent, task, async: true)
  Subs-->>Bridge: runId
  Bridge-->>Tasks: id = runId

  Subs-->>Bridge: subagent:async-complete
  Bridge-->>Tasks: subagents:completed / subagents:failed

  alt async completion event is missed
    Bridge->>Subs: status(runId)
    Subs-->>Bridge: state + result path
    Bridge-->>Tasks: subagents:completed / subagents:failed
  end

Install

Install the two extensions being bridged, then install the bridge:

pi install npm:@tintinweb/pi-tasks
pi install npm:pi-subagents
pi install npm:@alexeiled/pi-subagents-bridge

Requirements:

• Node >= 22.19.0
• Pi with extension loading enabled

Usage

Create tasks with TaskCreate, then execute them with TaskExecute.

TaskCreate(subject="Write a short plan", agentType="general-purpose", ...)
TaskExecute(task_ids=["1"])

Agent type mapping

The bridge preserves task agent names except for the compatibility aliases that pi-tasks examples commonly use.

| TaskCreate(..., agentType=...) | pi-subagents agent | | -------------------------------- | ------------------------ | | general-purpose | delegate | | Explore | scout | | explore | scout | | anything else | passed through unchanged |

Use an execution-capable agent for tasks that need shell commands, builds, or tests. A read-only agent can still be useful for read-only tasks such as review or metadata inspection.

Bridge behavior

Request flow

| pi-tasks input | Bridge behavior | | --------------------- | ------------------------------------------------- | | subagents:rpc:ping | replies locally with protocol version 2 | | subagents:rpc:spawn | sends a pi-subagents v1 spawn request | | subagents:rpc:stop | sends a best-effort pi-subagents stop request |

Spawned runs are always forwarded as:

• async: true
• clarify: false
• context: "fresh"

The bridge returns the spawned run ID back to pi-tasks and tracks that run as bridge-owned state. It runs at most two bridge-owned tasks at once. A task without an explicit maxTurns receives a 12-turn budget.

Completion flow

For runs the bridge spawned itself, it converts pi-subagents outcomes into pi-tasks events:

• success → subagents:completed
• failure → subagents:failed
• stopped or paused run → subagents:failed with status: "stopped"

If subagent:async-complete does not arrive, the bridge polls pi-subagents status, reads the result file path from that status output, and emits the same completion event that pi-tasks expects. If a terminal status arrives before its result file is readable, the bridge retries for up to five seconds instead of silently dropping the result.

Generic plan-exec RPC

This protocol is independent of pi-tasks. Send { version: 1, requestId, method, ... } on plan-exec:bridge:v1:request; replies use plan-exec:bridge:v1:reply:<requestId>.

Supported methods are ping, spawn, operation, status, result, stop, and adopt.

• spawn requires a durable top-level operationId, top-level cwd when needed, and params.agent plus params.task. It forwards supported execution fields (async, clarify, context, model, turnBudget, control, acceptance, and timeout) to pi-subagents. It accepts timeout or timeoutMs and rejects mismatched values; either maps to pi-subagents timeoutMs. It returns { runId, asyncDir? }. A repeated operation ID reuses the original reply for this Pi process lifetime.
• operation requires operationId and never starts a child. It returns { state: "absent" }, { state: "pending" }, { state: "found", runId, asyncDir? }, or { state: "unknown", error }. Its lookup map survives bridge re-registration in one Pi process but is not durable across a full Pi restart. It retains at most 127 completed outcomes and never evicts active operations. Clients must use it after an unknown spawn outcome and must not blindly launch a second child.
• status and result return normalized observations from the pi-subagents status RPC. result uses status because pi-subagents has no separate result RPC.
• stop delegates to the pi-subagents stop RPC.
• adopt validates and observes a run but does not transfer ownership or promise cross-session stop support.

Failures use { success: false, error: { code, message } }. operation_capacity means the bridge has 128 unresolved active operation IDs and will not evict any to accept another spawn.

TaskExecute-specific safeguards

TaskExecute is queue-style orchestration, not direct subagent supervision. Because of that, the bridge also applies two execution defaults to bridge-spawned runs:

• disables pi-subagents acceptance gating
• disables pi-subagents live control nudges

This avoids false pauses on missing acceptance reports and avoids misleading background needs attention notices for normal task runs. Repeated copies of the same spawn request are coalesced, so retries cannot launch duplicate bridge-owned agents.

Scope and limits

This package is intentionally narrow.

It does:

• bridge TaskExecute task launches to pi-subagents
• track only runs spawned through this bridge
• ignore unrelated pi-subagents runs

It does not:

• replace pi-tasks task orchestration
• act as a generic adapter for pi-subagents methods beyond the documented plan-exec protocol
• support loading @tintinweb/pi-subagents alongside this bridge

Do not load @tintinweb/pi-subagents at the same time as this package.

More detail

• docs/design.md — bridge behavior and maintenance rules
• docs/protocol-research.md — upstream protocol notes
• DEVELOPMENT.md — local validation and release workflow
• CHANGELOG.md — release history and RPC compatibility changes