Add partysocket terminal close reconnect predicate

[threepointone]

Summary

• Add shouldReconnectOnClose to ReconnectingWebSocket options so callers can classify a close event as terminal before automatic reconnect scheduling.
• Preserve existing reconnect-by-default behavior when the predicate is omitted or returns true.
• Add reconnect tests for terminal close suppression, default behavior, and explicit reconnect() unsealing after a predicate-stopped close.

Why

Cloudflare Agents needs to distinguish transient WebSocket disconnects from terminal close codes such as policy/auth failures. Today consumers can observe shouldReconnect, but cannot prevent the underlying PartySocket retry loop from continuing on a terminal server close. This PR adds a small upstream hook at the point where the close event is still available and before _connect() is scheduled.

Test plan

• npm run check:test -- src/tests/reconnecting.test.ts from packages/partysocket passed: 49 tests.
• npm run build -w partysocket && npm run check:test -w partysocket passed: package build plus 13 test files / 325 tests.
• npm run check:lint passed.
• npm run check:type passed.

Known check caveat

• Root npm run check currently stops in check:repo on an existing Sherif workspace version mismatch for the partyserver dependency (^0.5.8 in fixtures vs ^0.5.7 in packages). That appears unrelated to this PR.
• Root npm run check:format currently reports pre-existing formatting drift in packages/partyserver/CHANGELOG.md. Formatting it would add unrelated changelog churn, so this PR leaves that file untouched.

Made with Cursor

[changeset-bot]

🦋 Changeset detected

Latest commit: 3b10005

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

This PR includes changesets to release 1 package

Name	Type
partysocket	Minor

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commit: 3b10005