Retry failed queued email notifications

[somethingwithproof]

Summary

• retry failed queued email notifications up to five attempts
• schedule bounded exponential backoff from one to eight minutes
• update grouped deliveries with one owner-scoped CASE statement instead of one query per row
• keep successful and terminal deliveries claimed while releasing only retryable rows
• expose retry state in the queue UI with header/cell ordering kept consistent
• normalize retry errors to valid UTF-8 and the queue schema limit
• prove the worker still owns every row updated by retry bookkeeping
• document retry timing and terminal behavior

Closes #784

Stack

This PR is intentionally based on #813. Notification ownership, leases, orphan recovery, and completion safety live only in #813; this PR adds retry policy and UI behavior on top.

Linux Docker validation

• Pest unit suite: 139 tests, 381 assertions
• patch coverage against fix/notification-claim-recovery: 100% of 80 measurable changed executable lines
• PHP 7.4 syntax lint: pass
• composer.json: tested as supplied and not edited

Overlap audit

No other open plugin_thold PR implements bounded queue retry policy, next-attempt scheduling, grouped retry bookkeeping, or retry UI status. The ownership implementation is not duplicated here because #813 is the explicit base.

[Copilot]

Pull request overview

Implements retry semantics for queued email notifications in the Thold plugin by tracking delivery attempts and deferring reprocessing until a scheduled next_attempt, while exposing this state in the notification queue UI and adding a schema migration plus unit coverage.

Changes:

• Add attempt_count/next_attempt tracking and bounded exponential backoff logic for queued email delivery failures.
• Ensure claim/drain queries skip notifications that are not yet eligible for retry.
• Add schema migration (1.8.3), UI columns, documentation, and focused unit tests.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
thold_notify.php	Claim only retry-eligible rows (next_attempt ready) before draining.
thold_functions.php	Add retry delay + delivery recorder; apply retry gating to queue drains; integrate recorder into send flow.
includes/database.php	Add 1.8.3 migration + table definition updates for attempt_count and next_attempt plus index.
notify_queue.php	Display attempt count and next retry time in the queue UI.
README.md	Document the queue retry behaviour.
INFO	Bump plugin version to 1.8.3.
CHANGELOG.md	Record the issue #784 retry feature.
tests/Unit/NotificationQueueRetryTest.php	Unit coverage for retry delay/recording and retry gating.
tests/Unit/NotificationQueueClaimTest.php	Update claim expectations to include retry gating clause.
tests/bootstrap-unit.php	Minor formatting/alignment update.

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