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

[zimeg]

Summary

Adds the blocks.validate Web API method to the sync, async, and legacy web clients:

client.blocks_validate(blocks='[{"type":"section","text":{"type":"plain_text","text":"Hello world"}}]')

Provide exactly one of blocks, message, or view, each a JSON-encoded string, to validate a Block Kit payload against the Block Kit schema — instead of the untyped client.api_call("blocks.validate", ...) escape hatch. The method is unauthenticated (no token or scopes required) per the method reference.

This brings Python to parity with the in-flight Node (slackapi/node-slack-sdk#2659) and Java (slackapi/java-slack-sdk#1622) blocks.validate additions.

Implementation notes:

• slack_sdk/web/client.py is the source of truth; async_client.py and legacy_client.py are regenerated via python scripts/codegen.py (not hand-edited).
• blocks.validate added to the web client coverage endpoint list (count 308 → 309).

Testing

• blocks.validate is exercised by tests/slack_sdk_async/web/test_web_client_coverage.py (the endpoint-coverage test asserts every listed method is exposed on all three clients). The method's args are all optional, so it is covered by the default no-arg invocation path.
• Run: python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh

Reviewer note: I was unable to run run_validation.sh locally in my environment (test dependencies such as aiohttp/pytest were not installed, and formatting via black was unavailable). The generated files were produced by scripts/codegen.py and re-running it is idempotent; source-level checks (AST signatures, py_compile) pass. Please run the validation script before merging.

Category

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.signature (Request Signature Verifier)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.models (UI component builders)
• slack_sdk.scim (SCIM API client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.rtm_v2 (RTM client)
• /docs (Documents)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes. (See reviewer note above — could not run locally; CI covers it.)

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.18%. Comparing base (ac312d4) to head (0f86aaa).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
slack_sdk/web/async_client.py	87.50%	1 Missing ⚠️
slack_sdk/web/client.py	87.50%	1 Missing ⚠️
slack_sdk/web/legacy_client.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1946   +/-   ##
=======================================
  Coverage   84.17%   84.18%           
=======================================
  Files         118      118           
  Lines       13470    13494   +24     
=======================================
+ Hits        11339    11360   +21     
- Misses       2131     2134    +3     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.