[hoangle398]

Summary

Adds LINE (Messaging API) as a new channel.

Channel

• LINE integration package: API client, channel access token issuing/refresh, webhook signature verification, inbound event mapping, reply/push sending of flow steps
• IntegrationLine table, channel registration, connect service and webhook routing; public API for LINE channels plus builder UI to connect, test the webhook and disconnect
• Honors LINE blocks via ContactInbox.channelBlockedAt; profile language as contact locale; optional ephemeral store in the SDK integration context
• LINE shown in channel options (allInboxConfigs); 1500-character alt text allowed

Flex messages

• Every button-bearing LINE message (text with buttons, card, carousel, buttons after a media step) is built as flex bubbles instead of the buttons/carousel templates (removed)
• Full card titles/subtitles, per-card buttons, up to 12 cards per carousel, bubble/carousel size budgets enforced without dropping content

Button limits and styles

• Channel flow policies state separate step (buttonCount) and card (cardButtonCount) button limits; LINE allows 5 of each, enforced at publish, in the builder and when parsing a flow spec (drafts included)
• Per-button style (primary/secondary/link) for LINE, editable in the button dialog; "(default)" clears it back to the channel default
• Card buttons over the resolved channel's limit are cut at send time with a warning; Messenger/Instagram log a warning when they drop step buttons

Docs

Design spec, channel guide (docs/line.md), flows, CLI/MCP docs, live-test results.

Notes

• Includes a DB migration for the new table — needs to be applied on deploy.
• Flex sending has not been verified against a live LINE account yet.

Test plan

• pnpm lint and pnpm check-types pass in CI
• Connect a LINE channel, verify webhook test succeeds
• Send text/buttons/card/carousel flow steps to a LINE user and confirm flex rendering
• Block/unblock the bot and confirm channelBlockedAt updates