Fix like count drift on failed like/unlike mutations

[vagxrth]

Closes #78

Summary

This PR fixes the local like-count drift bug in nostr-like-button when like or unlike operations fail.

Previously, the component used unconditional arithmetic rollback in the catch path. That meant failures could push the displayed count in the wrong direction even when an optimistic mutation had not actually been applied.

This PR replaces that with snapshot-based rollback, clamps displayed counts to non-negative values, and adds a coalesced authoritative resync path after failed mutations.

What changed

Optimistic state helpers

Added a small internal helper module:

• src/nostr-like-button/optimistic-state.ts

It provides:

• LikeUiState
• clampLikeCount()
• applyOptimisticLike()
• applyOptimisticUnlike()
• rollbackOptimisticLikeState()

These helpers keep the mutation/rollback behavior explicit and easy to test.

nostr-like rollback and resync behavior

Updated:

• src/nostr-like-button/nostr-like.ts

Changes include:

• fetched totals are now clamped before being assigned to the displayed count
• like/unlike mutation flows now snapshot the pre-mutation UI state
• optimistic state is applied explicitly via helper functions
• rollback only restores the snapshot when an optimistic update was actually applied
• failure-before-optimistic no longer drifts local count
• failed mutations now queue a best-effort authoritative resync
• resync requests are coalesced so repeated failures during an in-flight resync still result in a final refresh

Why this fixes the bug

The previous implementation assumed that rollback arithmetic should always run in the error path:

• failed like: decrement count
• failed unlike: increment count

That is only valid if the optimistic mutation was already applied.

With this PR:

• if failure happens before optimistic state is applied, the component preserves the current UI state and only clamps the count
• if failure happens after optimistic state is applied, the component restores the exact pre-mutation snapshot

This removes count drift and makes failure handling deterministic.

Tests

Added focused regression tests in:

• src/nostr-like-button/__tests__/optimistic-state.test.ts

Covered cases:

• clamp negative counts to zero
• optimistic like increments count and sets liked state
• optimistic unlike never drops below zero
• failure-before-optimistic preserves current state and avoids drift
• failure-after-optimistic restores the original snapshot

Verification

Ran:

• npm test -- --run
• npm run build-storybook

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ea35cdbf-f012-4014-8f98-514b4b181b2a

📥 Commits

Reviewing files that changed from the base of the PR and between dfc22e5 and 924402c.

📒 Files selected for processing (3)

• src/nostr-like-button/__tests__/optimistic-state.test.ts
• src/nostr-like-button/nostr-like.ts
• src/nostr-like-button/optimistic-state.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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