fix: collapse context-block validation error cascade

[zhawtof]

Problem

Removing all items from a context block produced a wall of ~25 raw AJV errors in the editor popover (and the issues sheet) — must be equal to constant, must have required property 'hero_image', must match a schema in anyOf, etc. Only one of them was real: the block needs ≥1 element.

Root cause

Two compounding issues:

1. Stale validator. @tightknitai/slack-block-kit-validator was pinned at 0.1.0-alpha.0 — the first alpha, which predates the formatAjvErrors focus-validator collapse. When a block fails its branch in the undiscriminated block-type oneOf, that version reports failures from every branch.
2. Parser coupled to the old format. 0.1.7 collapses the cascade and changes the error-string format (/N/... → blocks[N]..., with caveat messages using a space rather than a colon). error-grouping.ts parsed the old /N/... shape, so a naive bump alone would route every error into the "General" bucket — blanking the per-block popover and the row's error indicator.

Changes

• Bump @tightknitai/slack-block-kit-validator ^0.1.0-alpha.0 → ^0.1.7. Verified API-compatible (identical exports/signatures/result shape); schema diff is 5 additive lines (one optional level field), nothing that newly flags valid blocks.
• Rewrite error-grouping.ts for the blocks[N]... path format — strips the blocks[N] prefix while keeping sub-paths as context, handles space-separated caveat-helper messages, (root) errors, and out-of-range indices.
• Empty-state UX in context-editor.tsx: when the block has no items, show a calm guiding hint ("add an item, or delete the block") instead of relying solely on a red error. Empty is allowed — Send is already gated on errorCount > 0 — rather than fighting the user mid-edit.
• Tests (test/error-grouping.test.ts, 13 cases) including an integration test that runs the real validator on an empty context block, pinning the validator/parser format coupling so future drift fails loudly instead of silently emptying the popover.

Result

The same action now yields a single, correctly-attributed error — elements: fewer than 1 items — plus the empty-state hint. Toolbar shows "1 issue" instead of a wall.

Verification

• pnpm test — 230/230 pass (13 new)
• pnpm typecheck — clean
• pnpm lint — clean
• Reproduced live in the demo app (remove last context item): 1 collapsed error + empty-state hint, no console errors.

🤖 Generated with Claude Code

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
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