Eric Allam 9f64bf404b docs(ai-chat): slim-wire HITL continuations + field-level merge contract (#3721)
## 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`)
2026-05-23 17:27:15 +01:00
2025-12-23 18:37:19 +00:00

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