## Summary
`chat.headStart` (the warm step-1 fast path) previously handed its
response over only to `chat.agent`. This extends handover to the other
two backends: `chat.customAgent` consumes it with
`conversation.consumeHandover({ payload })` on turn 0, and
`chat.createSession` surfaces it as `turn.handover` (call
`turn.complete()` with no source to finalize a pure-text handover). The
low-level `chat.waitForHandover()` and `accumulator.applyHandover()` are
exported for hand-rolled loops.
It also adds `triggerConfig` to `chat.headStart()` and
`chat.openSession()`, so the auto-triggered handover-prepare run
inherits tags, queue, machine, and the other session run options the
same way `chat.createStartSessionAction()` does. The `chat:{chatId}` tag
is prepended automatically. Because the session is created once on the
first head-start turn (idempotent on the chat id), this is the only
place those options can be set for a head-start chat's lifetime.
## Fix: tool-call resume
When the warm step-1 hands over a pending tool call (rather than pure
text), the agent loop resumes that tool round. For it to merge cleanly
the pipe threads the spliced partial as `originalMessages`, so the
resumed tool-output chunk attaches to the handed-over tool-call instead
of throwing `No tool invocation found`. `MessageAccumulator.addResponse`
now also dedups by id (replace-in-place), so the persisted history
doesn't carry a duplicate assistant message when the resumed response
reuses the partial's id.
Incorporates the `triggerConfig` work from
[#3933](https://github.com/triggerdotdev/trigger.dev/pull/3933) by
@saasjesus, with `createStartSessionAction` extended to also forward
`maxDuration`, `region`, and `lockToVersion` so the two session entry
points stay consistent.
Verified end-to-end against a local environment: handover (pure-text and
tool-call) on both new backends, a `chat.agent` regression pass, and
`triggerConfig` tags and queue landing on the run.
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Co-authored-by: saasjesus <armin@chatarmin.com>
Eric Allam
17482c0577