fix(region-filter): honor URL regions across views and clean up page listeners #531

Problem and priority

Medium priority. On fork master 8798f74eeec124f21d0e82a8d64b93b31d7facc0 (24 October 2026), Packets has one-off URL region handling, while other views can open using the saved region instead of the linked one. Packet filter listeners also need lifecycle cleanup so a later region change cannot rewrite another view's URL.

Proposed fork adaptation

• Centralize hash-query region handling in public/region-filter.js, before a view performs its initial region-dependent fetch, including Live's early node fetch.
• Define comma-list trimming, duplicates, unknown codes, empty/no parameter and saved-selection precedence. Preserve today's empty/no-parameter behavior unless explicitly agreed otherwise.
• On SPA navigation, notify active listeners exactly once for a genuine change; no duplicate reload for a no-op selection.
• Remove Packets' duplicate URL handling and unregister RegionFilter/AreaFilter listeners in destroy. Preserve the fork's other URL/filter behavior.
• Coordinate with feat(region-filter): add configurable named region quick-pick groups #416 (named region quick picks and selection notifications), but keep URL/lifecycle correctness separate from optional new controls.

Acceptance criteria

Tests and actual-browser navigation cover fresh load, SPA transitions, saved selections, unavailable codes, multi-region links, request region values, one notification, and no stale Packets listener rewriting the current URL. Show old behavior red and fixed behavior green. No config/schema/workflow change is needed.

Source provenance

Source repository: Kpa-clawbot/CoreScope
Pull request number: 2256
Head commit: 9c2ea45ad155428ab205f8248d248241772b3fda
Merge commit: dbcdca9dc55cdef1af9ed322ee0c6244c759ed8b
Relevant files: public/region-filter.js, public/packets.js

This issue does not authorize deployment or changes to live configuration.