Task 1 Report: Chat deletion and browser transport errors

Implementation

Added the owner-only chat_sessions DELETE policy and authenticated DELETE grant.
Classified both native SyntaxError and WebKit DOMException values named SyntaxError as JSON parse/lost-response errors.
Non-OK responses with malformed JSON now return payload: null; retry logic recognizes the WebKit error form.

frontend/supabase/migrations/20260720000000_chat_delete_and_dynamic_candidate_confirmation.sql
frontend/tests/chat-session-delete-contract.test.ts
frontend/tests/birth-time-client-transport.test.ts
frontend/src/lib/birth-time-client-transport.ts

RED: node --import ./frontend/node_modules/tsx/dist/loader.mjs --test frontend/tests/chat-session-delete-contract.test.ts frontend/tests/birth-time-client-transport.test.ts failed as expected: the migration file was absent and DOMException("SyntaxError") escaped; the native non-JSON case already passed.
GREEN: the same command passed all 3 tests after the minimal implementation.

Focused suite: 3 passed, 0 failed.
Full frontend suite: node --import ./frontend/node_modules/tsx/dist/loader.mjs --test frontend/tests/*.test.ts completed with 461 passed and 1 failed (462 total).
The sole failure is the known baseline in frontend/tests/health-deployment.test.ts: its expected DEPLOY_GIT_SHA expression differs from the existing deployment workflow. It is outside Task 1 scope.
Self-review: inspected the migration against existing owner-scoped RLS patterns, reviewed the four-file diff, and ran git diff --check successfully.

The repository pre-work gate remains blocked by its documented host Python 3.9/fragment-scan baseline; it did not affect this frontend-only task.