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(workflowScript, 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:

• one-child workflowScript execution
• async: true
• context: "fresh"
• control: { enabled: false } on the outer workflow and its child

The bridge does not send the removed public clarify field.

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. Version 1 remains available on plan-exec:bridge:v1:request with replies on plan-exec:bridge:v1:reply:<requestId>.

Version 2 uses plan-exec:bridge:v2:request and plan-exec:bridge:v2:reply:<requestId>. It keeps the same ping, spawn, operation, status, result, stop, and adopt methods while adding durable launch identity and native process-terminal proof.

• ping verifies the live pi-subagents RPC before advertising workflowScriptSpawn, durableOperationLookup, and processTerminalProof capabilities.
• spawn requires operationId, cwd when needed, params.agent, params.task, and an owner { kind: "pi-plan-exec", runId, key, requestDigest }. The digest is SHA-256 over canonical { cwd, params }. The bridge rejects mismatches before dispatch.
• The durable journal is written before the native spawn is emitted. A bound operation survives a full Pi restart. A dispatch with no durable native reply becomes unknown; the bridge never launches it again automatically.
• operation never starts work. Version 2 returns operationId, requestDigest, and absent, pending, found, or unknown binding state.
• status and adopt include a validated native processTerminal value when pi-subagents returns one. Only an observed proof with the matching run ID proves process termination.
• result uses the native status RPC because pi-subagents has no separate result RPC. stop delegates to the native stop RPC.
• adopt is observational. It does not silently transfer session ownership.

The journal defaults to ~/.pi/pi-subagents-bridge/plan-exec-operations.sqlite. SQLite transactions provide crash recovery and cross-process serialization without a stale application lock. Version 1 clients retain their existing response shape and also benefit from durable bound-operation lookup. Operation identity rows are retained as idempotency records; automatic pruning could make an old operation ID dispatch again. Remove the database only after all referenced plan runs are permanently retired and duplicate-launch protection is no longer needed. Existing v1 accepted-run rows migrate fail-closed with no session identity; they require explicit manual recovery rather than unsafe cross-session delivery.

Failures use { success: false, error: { code, message } }. operation_capacity means the in-process bridge has 128 unresolved active operation IDs and will not evict one 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 one live request are coalesced only after their session and request digest match. The request ID is also journaled before native dispatch, so replay after the in-memory reply cache expires returns the existing run or fails closed as unknown instead of dispatching again. Transient persistence failures for known accepted runs and launch bindings are retried while the bridge process remains active.

Accepted run IDs are tied to the originating Pi session ID and a leased process owner. A foreign Pi session cannot claim or delete them. The same resumed session can reclaim them after the owner exits or its heartbeat lease expires; the lease covers PID reuse. The owner renews its fence before emitting completion, and failed reconciliation is retried periodically. If another session wins ownership, the bridge stops polling and emits subagents:warning with code accepted_run_ownership_lost instead of silently dropping the run.

The legacy pi-tasks spawn request does not contain task ID, list ID, or attempt generation. Therefore the bridge cannot recover a task binding after a crash that occurs after native dispatch but before the run ID is received. The durable request becomes unknown and is not launched again automatically. The bridge does not use prompt matching.

If the native run ID is known but local accepted-run persistence fails, the bridge acknowledges that known run instead of returning an error that could trigger a duplicate launch. It keeps completion ownership for the current process and logs the durability loss; a subsequent process restart then requires manual completion recovery.

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