Fix security, resilience, and deduplication issues across AI chat and sync pipeline

[Copilot]

Eight issues flagged in code review: a service-role authorization bypass, a PostgREST empty-in() crash, SQLite/JSONB type mismatch, un-retried network errors, a silent storage-path parse failure, a missing RLS cross-clinic check, @ts-nocheck masking type errors, and duplicated context-selection logic.

Authorization & RLS

• ai-chat-patient: Removed doctorProfile fallback that let any authenticated user hit patient records via service role. Now returns 403 immediately if no doctor row exists for user.id.
• 004_ai_chat.sql: Added EXISTS (SELECT 1 FROM patients p WHERE p.id = patient_id AND p.clinic_id = clinic_id) to the ai_conversations INSERT policy — previously a doctor could reference a patient from a different clinic.

Query correctness

• ai-chat-patient: Replaced nested inline sessions subquery in .in() with an explicit two-step fetch. Empty session arrays no longer reach PostgREST and trigger a 400 parse error; sessions and records errors are surfaced independently.

// Before — crashes when patient has no sessions
.in('session_id', (await supabase.from('sessions')…).data?.map(…) ?? [])

// After — skips records query entirely on empty session list
const { data: sessions, error: sessionsErr } = await supabaseService.from('sessions')…
if (sessionsErr) return jsonResponse({ error: '…' }, 500);
const sessionIds = (sessions ?? []).map(s => s.id);
if (sessionIds.length > 0) { /* records query */ }

Data integrity

• cloudSync.ts: cloudRecord.extracted_data arrives from Postgres as a JSONB object; updateRecordExtraction expects a JSON string for SQLite. Now normalizes with JSON.stringify when the value is not already a string.

Resilience

• geminiService.ts: fetch() was not wrapped in try/catch, so network errors (DNS, TLS) bypassed the retry loop entirely. Now caught and retried with the same exponential backoff. Extracted BASE_RETRY_DELAY_MS = 1500 constant.
• extract-handwriting: toStoragePath returned the original URL verbatim when the storage marker was absent, silently passing an invalid path to storage.download(). Now returns '', which the existing guard converts to a clear 400.

Type safety & deduplication

• ai-chat-patient: Removed // @ts-nocheck; added top-level RecordRow type.
• aiChat.ts: Replaced duplicated tokenization / scoring / truncation loop with selectTopK from the existing lib/contextSelector.ts (which has Jest coverage).

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