Summary

Adds a grouped media-block UX improvement for Slack Block Kit messages by deriving meaningful fallback text from block content.

• add shared fallback extractor for Block Kit blocks (header, section, context, image, video, file)
• use derived fallback text in sendMessageSlack when content is empty and blocks are present
• use derived fallback text in editSlackMessage when content is empty and blocks are present
• add targeted tests for standalone image, video, and file block behavior across send/edit paths

Scope

• src/slack/blocks-fallback.ts
• src/slack/blocks-fallback.test.ts
• src/slack/send.ts
• src/slack/send.blocks.test.ts
• src/slack/actions.ts
• src/slack/actions.blocks.test.ts

Validation

• pnpm test src/slack/blocks-fallback.test.ts src/slack/send.blocks.test.ts src/slack/actions.blocks.test.ts
• pnpm check

Dependency

Depends on:

• Slack: improve Block Kit interaction handling (foundation) #18180 Slack: improve Block Kit interaction handling (foundation)
• feat(slack): capture Block Kit view_closed lifecycle events #18234 feat(slack): capture Block Kit view_closed lifecycle events
• feat(slack): use static_select for large slash arg menus #18242 feat(slack): use static_select for large slash arg menus
• feat(slack): route modal interactions with private metadata #18252 feat(slack): route modal interactions with private metadata
• feat(slack): support Block Kit blocks in sendMessage #18257 feat(slack): support Block Kit blocks in sendMessage
• feat(slack): support Block Kit blocks in editMessage #18262 feat(slack): support Block Kit blocks in editMessage
• feat(slack): support blocks in plugin send action #18268 feat(slack): support blocks in plugin send action
• feat(slack): support blocks in plugin edit action #18278 feat(slack): support blocks in plugin edit action
• feat(slack): centralize Block Kit input validation #18284 feat(slack): centralize Block Kit input validation
• fix(slack): add blocks+media send guardrails #18290 fix(slack): add blocks+media send guardrails
• test(slack): cover sendMessage Block Kit paths #18372 test(slack): cover sendMessage Block Kit paths
• refactor(slack): centralize modal private_metadata utilities #18409 refactor(slack): centralize modal private_metadata utilities
• Slack: expand interaction payload normalization coverage #18413 Slack: expand interaction payload normalization coverage
• Slack: validate runtime blocks in send and edit paths #18416 Slack: validate runtime blocks in send and edit paths
• Slack: dedupe normalized interaction selections #18423 Slack: dedupe normalized interaction selections
• Slack: enrich block action context payloads #18431 Slack: enrich block action context payloads
• Slack: add overflow menus for slash arg choices #18439 Slack: add overflow menus for slash arg choices
• Slack: update action rows for select interactions #18448 Slack: update action rows for select interactions
• Slack: enrich modal input payload normalization #18455 Slack: enrich modal input payload normalization
• Slack: add header and context blocks to arg menus #18458 Slack: add header and context blocks to arg menus
• Slack: show picker values in interaction confirmations #18465 Slack: show picker values in interaction confirmations
• Slack: expand advanced modal controls payloads and confirms #18467 Slack: expand advanced modal controls payloads and confirms
• Slack: add rich text previews for modal inputs #18472 Slack: add rich text previews for modal inputs
• Slack: attribute interaction confirmations and structured selects #18474 Slack: attribute interaction confirmations and structured selects

If reviewing before dependencies merge, review tip commit: b33de4c6d.