Preserve existing-case parties through fees and submission

[nonprofittechy]

Existing-case filers were asked to recreate parties, and outgoing filings could turn those parties into new participants without their court IDs. This change imports the authenticated court roster at case confirmation and preserves each court party's identity through selection, fee calculation, and submission.

Changes

• Store a normalized case snapshot and source-aware party records, preserving person/organization names, roles, available contacts, and attorney associations. Keep the EFM search UUID separate from the court's local case ID, and verify historical roles against the full court role catalog.
• Make imported party details read-only and enforce the restrictions server-side. Link the filer account to a durable party without replacing it; require an explicit action to add a new party.
• Reconcile both fee and submission payloads against the saved roster, including tyler_id, is_new, selected filing parties, and document references. Block incomplete imports and reject missing, duplicate, or substituted identities.
• Handle retries, resume, idempotent imports, stale responses, and case changes; protect court data from document suggestions and legacy draft writes. Add sanitized fixtures and browser coverage.
• Reuse recent confirmation previews and retrieve case details and role codes concurrently. Preserve co-filer selections during account linking and new-case party choices during classification changes; handle country codes and unreadable lineage entries safely.

Illinois staging verification

All seven issue examples completed fee calculation and submission against the Illinois test environment on October 8, 2026. Each submission returned an envelope ID and one filing ID, with the returned case ID matching the original search UUID. Validation used the browser payload builder and shared server preparation against persisted imported drafts.

Court	Case	Accepted staging envelope
Marion	2025SC5	324947
Kane	2024EV001752	324948
Kane	2005SC000985	324949
Winnebago	2019-D-0000655	324950
Winnebago	2019-SC-0001642	324951
Lake	2024SC00003388	324952
Lake	2024DC00000572	324953

This verifies staging envelope acceptance; clerk disposition was not checked. No production filings were made. The proxy exposes no supported representation-change fields, so returned associations are preserved without inventing changes.

Validation and deployment

• Full Python suite during pre-push checks: 1,749 passed, two skipped. The original repeatable backend suite also passed with 1,675 tests and three integration tests deselected, as recorded in the validation note.
• Affected regression suite: 167 passed, including the Django-view browser flow through lookup, confirmation, keyboard selection, account linking, and review.
• JavaScript unit tests passed; original implementation: 88 passed. Final sanitized fixture checks: nine passed.
• Ruff, Ty, changed-file ESLint, template checks, migration consistency, and all commit hooks passed.

Apply migration 0038_existing_case_identity before deploying. The validation note records the field matrix, workflow rules, commands, and detailed staging results. Raw court responses and credentials are not committed; fixture names, contacts, party/attorney IDs, and bar numbers are synthetic.

Closes #291.