Async opportunistic repair queue for unresolved historical range misses

[unav4ila8le]

Context

We recently disabled blocking live quote repair for range/history requests to restore dashboard and asset-page latency.
That solved UX latency, but it also reduced opportunities to repair historical cache gaps during range reads.

Problem

For range paths (e.g. net worth history), unresolved exact-date misses now rely on fallback behavior without attempting synchronous provider repair.
Result: user-facing performance is good, but historical quote gaps may persist longer unless cron naturally backfills them.

Goal

Add a lightweight async repair mechanism that:

• preserves fast range reads
• gradually repairs unresolved historical quote gaps in the background
• avoids introducing blocking latency on user requests

Proposed Solution

Implement an opportunistic quote repair queue:

1. During range fetches, when a request remains unresolved at exact date (or resolves via fallback), enqueue a repair item.
2. Use a small queue table with dedup and attempt tracking.
3. Extend cron (or add a small cron step) to drain queue in bounded batches and upsert repaired quotes.
4. Mark queue items as resolved/failed with retry/backoff policy.

Suggested Schema (draft)

quote_repair_queue:

• id (uuid pk)
• symbol_id (uuid, indexed)
• target_date (date, indexed)
• status (pending|processing|done|failed)
• attempt_count (int, default 0)
• last_attempt_at (timestamptz null)
• next_attempt_at (timestamptz null)
• last_error (text null)
• created_at, updated_at
• unique: (symbol_id, target_date) to dedupe

Processing Rules (draft)

• Drain in small batches (e.g. 50–200 items per run).
• Respect max attempts and exponential backoff.
• Only treat quote as repaired when exact target-date row is inserted.
• Keep non-fatal failures in queue with next_attempt_at.
• Permanent provider-unsupported symbols can be marked failed after threshold.

Acceptance Criteria

1. Range/read paths remain non-blocking (no live provider fetch in request path).
2. Unresolved historical misses are queued and eventually retried asynchronously.
3. Queue processing is bounded and safe under retries/restarts.
4. Duplicate queue entries are prevented.
5. Observability exists for queue depth, processed count, success/failure count.
6. No regression in existing quote cron behavior.

Out of Scope

• UI changes
• Full worker infrastructure
• Multi-provider quote source redesign

Notes

This is a follow-up to the range-latency fix where liveFetchOnMiss is disabled for range quote fetches in symbolHandler.fetchForPositionsRange.