## Summary
Accuracy fixes across the AI chat docs: drop the non-existent per-call
option from `transport.preload`, clarify that `onValidateMessages` only
fires on turns carrying incoming messages, soften the turn-complete
token-refresh wording (the header is optional), document the new
`onTurnComplete` `error` field and `finishReason`, and correct the
idle-timeout default to 30 seconds.
## Summary
Updates the AI chat docs to match the slim-wire + field-level merge
behavior shipped in #3719 and the precise `.in/append` cap +
CORS-readable 413 shipped in #3720. No behavior changes here — code is
correct in `main`; the docs were lagging on three patterns customers
copy out of the page.
## What changed
- **`hydrateMessages` examples upsert by id** (in `lifecycle-hooks.mdx`,
`patterns/database-persistence.mdx`, and
`patterns/persistence-and-replay.mdx`). The previous
`stored.push(newMsg)` pattern duplicated the assistant id on HITL
continuations and caused the LLM to receive a tool call with no
`arguments`. The new examples include the rationale inline.
- **`onValidateMessages` example filters to user messages**
(`lifecycle-hooks.mdx`). The previous example called
`validateUIMessages({ messages, tools })` directly, which now throws on
HITL slim wires (the AI SDK schema requires `input` on resolved tool
parts). New example shows the filter pattern, with a Warning callout
explaining why.
- **Merge contract description updated** (`lifecycle-hooks.mdx`). The
old wording said incoming messages are "auto-merged" / "replaced"; the
new description explains the actual field-level overlay (state advances
only).
- **Approval-responded wire example slimmed** (`client-protocol.mdx`).
Shows the minimum shape the agent reads — `state` + `approval` (or
`output` / `errorText` for HITL). Notes that the built-in transports
ship this slim shape by default and that fuller shapes are still
accepted.
- **`/in/append` 413 row and FAQ updated** (`client-protocol.mdx`,
`patterns/trusted-edge-signals.mdx`). Reflects the new precise S2 cap
and the CORS-readable 413.
- **New changelog entry** at the top of `changelog.mdx` covering all of
the above.
The historical `## 512 KiB ceiling removed` entry further down the
changelog is left as-is (it's a snapshot of the prior transition), and
the v4.5 upgrade-guide section is skipped — the merge contract is
backwards compatible.
## Test plan
- Mintlify dev preview renders cleanly with no broken anchors
- Linked references resolve (`/ai-chat/lifecycle-hooks#hydratemessages`,
`/ai-chat/lifecycle-hooks#onvalidatemessages`,
`/ai-chat/patterns/database-persistence#alternative-hydratemessages`,
`/ai-chat/client-protocol#step-3-send-messages-stops-and-actions`,
`/ai-chat/patterns/large-payloads`)
## Summary
Lands the full AI Agents documentation surface alongside the v4.5
release candidate of `@trigger.dev/sdk`. Covers `chat.agent` end to end
— defining agents, lifecycle hooks, the frontend transport, sub-agents,
recovery from cancel/crash/OOM, AI Prompts integration — and the
Sessions primitive that backs it.
## Coverage
- **Conceptual**: Overview, Quick Start, How it works.
- **Building agents**: Backend (`chat.agent` / `chat.createSession` /
raw primitives), Lifecycle hooks, Frontend transport, Server-side
`AgentChat`, Sessions reference, `chat.local` state primitive,
TypeScript types.
- **Features**: AI Prompts integration, Fast starts (Preload + Head
Start), Compaction, Pending Messages (steering), Background Injection
(`chat.inject` + `chat.defer`), Actions (undo / regenerate / edit),
Error handling.
- **Patterns (13)**: Sub-agents, Branching conversations, Code sandbox,
Database persistence, Persistence and replay, HITL, Tool result
auditing, Large payloads, Agent skills, OOM resilience, Recovery boot,
Trusted edge signals, Version upgrades.
- **Reference**: API Reference, Client Protocol (wire format), Testing
harness (`mockChatAgent`), MCP server tools, Upgrade guide, Changelog.
## Structure changes
- Top-level nav: AI → **Agents**, with sub-groups for *Building agents /
Features / Patterns / Reference*.
- New RC banner snippet on every page links to the supported AI SDK
versions table on the API Reference.
- All examples use Anthropic with `stopWhen: stepCountIs(15)`.
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Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Eric Allam