Remove legacy client patch flow / self-heal

[mateicanavra]

TL;DR

Remove legacy client-side patch orchestration and "self-heal" helpers. Move retry logic server-side for single source of truth.

Context

During PER-19 extraction work, we identified that use-patch-application.ts contains retryWithValidationErrors logic (lines 114-265) that duplicates server-side capabilities. The server's assistant-service.ts already validates patches, but the client still carries legacy retry orchestration.

Current state:

• Server validates patches in assistant-service.ts
• Client has retryWithValidationErrors in extracted use-patch-application.ts
• Invalid responses surface as UI text but don't trigger server-side repair
• Dead code and duplicated logic between client and server

Goals

• Single source of truth for patch generation/validation/retry on server
• Client reduced to: display + apply + stale/expired handling
• No loss of current behaviors (retry on invalid, stale detection, apply-time validation)

Plan

1. Server: add auto-repair loop in assistant-service.ts
   • When buildPatchTransactionFromResponse returns invalid, re-prompt with repair prompt
   • Cap retries (1 pass), surface second invalid as-is with reasons
2. Server: standardize error payloads
   • Structured errors (type/message/fix) compatible with existing UI
3. Client: trim legacy orchestration
   • Remove retryWithValidationErrors from use-patch-application.ts
   • Keep UI messaging for invalid/noop/missing-target
   • Retain apply-time stale handling only
4. Contracts & types
   • Update shared types if repair path adds fields (e.g., attempt: "initial" | "repair")
5. Tests
   • Unit tests for server repair flow
   • Integration tests for client handling of invalid payloads

Acceptance Criteria

• Invalid responses trigger exactly one server-side repair attempt
• Client no longer issues generation-time retries
• Stale/expired handling still works
• No unused self-heal helpers in apps/web patch flows
• Tests cover repair success/fail and client handling

References

• docs/projects/slides-v0/issues/remove-legacy-client-patch-flow.md
• apps/web/src/features/slideshow/hooks/use-patch-application.ts
• packages/api/src/slideshow/assistant-service.ts

[linear]

PER-35