feat(agent): add durable agent invocations and spawning

[dcramer]

Adds durable agent invocations and a spawnAgent tool so a parent agent can schedule named or one-off child work through Junior's existing conversation mailbox and lease worker. Unnamed invocations use isolated child conversations; named agents reuse their child conversation and prior agent history. Different named agents can run concurrently, repeated tool calls are idempotent, overlapping work for one name is rejected, and one child's failure does not affect its siblings.

The model supplies only the task, optional name, and optional reasoning level. The runtime keeps parent identity, actor, credentials, routing, and idempotency bound to the active run, and the tool returns only a durable invocation handle. Child creation shares the root conversation mutation lock with retention purge, and bindings and invocations are deleted with the conversation tree.

Child work uses the existing provider-neutral mailbox worker. Local chat processes child wakes in-process, while production continues to use Vercel Queues. The rebased schema change is generated as migration 0012_sour_vargas after the newer conversation-history and reporting migrations on main.

SQL-backed regression coverage exercises isolated and named agents, history and reasoning reuse, concurrent replay, overlap rejection, sibling failure isolation, validation failure, recovery, and retention cleanup. This slice returns invocation handles; parent result delivery, deterministic result recovery, cancellation, and recursive children remain follow-up work on #880.

Fixes #879
Refs #880

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Project	Deployment	Actions	Updated (UTC)
junior-docs	Ready	Preview	Jul 30, 2026 5:50pm

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Stranded child never terminates

High Severity

recoverRunningSession throws when a stranded running child has no model or no resumable boundary, but empty resume wakes set isFinalAttempt to false, so the catch rethrows instead of failing the invocation. The worker then re-wakes forever while status stays running, which also keeps a named agent permanently busy.

Additional Locations (2)

• packages/junior/src/chat/agent-invocations/work.ts#L245-L267
• packages/junior/src/chat/task-execution/worker.ts#L499-L502

 

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