feat(web-api): add blocks.validate method

[zimeg]

Summary

Adds the blocks.validate method to @slack/web-api:

await client.blocks.validate({
  blocks: [{ type: 'section', text: { type: 'plain_text', text: 'Hello world' } }],
});

Validate a Block Kit payload against the Block Kit schema by passing exactly one of:

• blocks — a typed (KnownBlock | Block)[]
• message — a { blocks, attachments } payload
• view — a View

blocks.validate is unauthenticated (no token or scopes). This brings Node to parity with the in-flight Python (slackapi/python-slack-sdk#1946) and Java (slackapi/java-slack-sdk#1622) additions.

Typed request arguments

Arguments accept typed Block Kit values (not JSON strings), matching chat.postMessage / views.open. The message shape intentionally omits text — the endpoint rejects it as an additional property (verified against the live API).

Typed errors[] response

On a failed validation the response returns errors[], each with pointer (a JSON pointer to the offending element), code, message, and a constraint. The constraint's expected/got are typed string | number | string[] because their shape is polymorphic across constraint types (a string array for enum, a number for min_length/max_length/max_items, or absent for all_of).

Testing

• npm run build (tsc) is clean.
• packages/web-api/test/types/methods/blocks.test-d.ts covers the typed blocks/message/view args and asserts the old JSON-string form is now a type error.

Note: the 6 pre-existing tsd failures in files.test-d.ts / rtm.test-d.ts (deprecated files.upload, rtm.start) are baseline on the branch and untouched by this change.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: a131e99

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@slack/web-api	Minor

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.15%. Comparing base (4322e14) to head (a131e99).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2659   +/-   ##
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  Coverage   89.15%   89.15%           
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  Files          65       65           
  Lines       10383    10393   +10     
  Branches      473      473           
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+ Hits         9257     9266    +9     
- Misses       1095     1096    +1     
  Partials       31       31           

Flag	Coverage Δ
cli-hooks	89.15% <100.00%> (+<0.01%)	⬆️
cli-test	89.15% <100.00%> (+<0.01%)	⬆️
logger	89.15% <100.00%> (+<0.01%)	⬆️
oauth	89.15% <100.00%> (+<0.01%)	⬆️
socket-mode	89.15% <100.00%> (+<0.01%)	⬆️
web-api	89.15% <100.00%> (+<0.01%)	⬆️
webhook	89.15% <100.00%> (+<0.01%)	⬆️

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[WilliamBergamin]

Nice addition, LGTM. 🚀

[zimeg]

@WilliamBergamin It's a cool method! Thanks for looking this over.