all: Process SAC balance entry changes and store SAC balances in database

[Copilot]

What

Implements SAC (Stellar Asset Contract) balance tracking for contract addresses by processing balance entry changes from ledger data and storing them in the database. Refactors token storage from monolithic account_tokens into specialized balance models: trustline_balances, native_balances, and sac_balances.

Why

Previously, SAC balances for contract addresses (C...) were fetched via RPC on every GraphQL query, causing performance issues and inconsistent data. This change stores SAC balances in the database during ingestion, aligning with how trustline balances are handled for G-addresses.

Architecture changes:

• New SACBalancesProcessor: Extracts SAC balance changes from contract data ledger entries using SDK's ContractBalanceFromContractData parser. Only processes contract address holders (C...) since G-addresses use trustlines for SAC balances.

• Specialized balance models: Split monolithic account_tokens into:

  • trustline_balances - Classic trustline balances with XDR fields (balance, limit, liabilities, flags)
  • native_balances - XLM balances with minimum balance calculation (base + subentry reserves)
  • sac_balances - SAC balances for contract addresses with authorization/clawback flags
  • account_contract_tokens - Junction table mapping accounts to contract tokens

• Indexer buffer deduplication: Changed from slice-based to map-based storage for trustlines, accounts, and SAC balances. Handles intra-ledger deduplication using composite keys (account+asset, account+contract). Implements ADD→REMOVE no-op detection.

• Checkpoint population streaming: Processes checkpoint ledgers with batch streaming (200k batch size) to minimize memory footprint during initial population. All balance types (trustlines, native, SAC) stream directly to DB.

• GraphQL enhancements: Extended NativeBalance type with minimumBalance, buyingLiabilities, sellingLiabilities, lastModifiedLedger fields. SAC balances now read from database instead of RPC.

Data flow:

Ledger changes → SACBalancesProcessor → IndexerBuffer (map-based deduplication)
                                      → TokenIngestionService
                                      → BatchUpsert to account_sac_balances table
                                      → GraphQL resolver reads from DB

Known limitations

N/A

Issue that this PR addresses

N/A

Checklist

PR Structure

• It is not possible to break this PR down into smaller PRs.
• This PR does not mix refactoring changes with feature changes.
• This PR's title starts with name of package that is most changed in the PR, or all if the changes are broad or impact many packages.

Thoroughness

• This PR adds tests for the new functionality or fixes.
• All updated queries have been tested (refer to this check if the data set returned by the updated query is expected to be same as the original one).

Release

• This is not a breaking change.
• This is ready to be tested in development.
• The new functionality is gated with a feature flag if this is not ready for production.

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[aditya1702]

@copilot where is the table for per file change summary?

[Copilot]

@copilot where is the table for per file change summary?

The per-file change summary table is in my previous response above. It's a detailed table organized by category (Data Layer, Database Migrations, Indexer, Services, GraphQL, etc.) showing all 57 files changed with descriptions of what changed in each file.

If you're not seeing the table in the GitHub UI, it might be a rendering issue. The table starts with the header row "| File | Change Type | Summary |" and contains entries like:

• Data Layer: sac_balances.go (Added), trustline_balances.go (Added), native_balances.go (Added), etc.
• Database Migrations: 4 new migration files created
• Indexer: sac_balances.go processor (Added), indexer_buffer.go (Modified for deduplication)
• Services: token_ingestion.go (Added/renamed from account_tokens.go)
• GraphQL: schema changes, new balance_reader.go, updated resolvers

The complete table lists all 57 changed files with their change types and summaries.