docs: add error codes IE072-IE089

[PaulieB14]

Summary

Adds documentation for 18 new indexer error codes (IE072–IE089) to docs/errors.md, covering Graph Horizon protocol operations and related failure modes.

Error codes added

Code	Summary
IE072	Failed to execute batch tx (contract: staking)
IE073	Failed to query subgraph features from indexing statuses endpoint
IE074	Failed to deploy subgraph: network not supported
IE075	Failed to connect to network contracts
IE076	Failed to resume subgraph deployment
IE077	Failed to allocate: subgraph not healthily syncing
IE078	No provision found
IE079	Failed to add stake to provision: Invalid stake amount provided
IE080	Failed to add stake to provision: stake not added on chain
IE081	Multiple provisions found
IE082	Graph Horizon protocol not detected
IE083	Failed to thaw stake from provision
IE084	Could not resolve POI block number
IE085	Could not resolve public POI
IE086	Indexer not registered in the Subgraph Service
IE087	Failed to resize allocation
IE088	Failed to present POI
IE089	Failed to collect indexing rewards

Graph Horizon context

These error codes map directly to the Graph Horizon protocol migration:

• IE078–IE083 — Provision lifecycle (the Horizon replacement for legacy allocations). Provisions are the amount of stake assigned to a specific data service via the HorizonStaking contract. See GIP-0066.
• IE086 — SubgraphService registration. Under Horizon, new allocations can only be opened through the SubgraphService contract. See What changes with Graph Horizon.
• IE087 — Allocation resizing. Horizon allows allocations to be resized without closing and reopening.
• IE088 — POI presentation. Under Horizon, POIs are presented periodically to demonstrate ongoing indexing work.
• IE089 — Reward collection. Separate step under the new allocation lifecycle.

References

• GIP-0066: Graph Horizon
• What changes with Graph Horizon — Official Docs
• From Subgraphs to Everything: Horizon Upgrade Live — Graph Blog
• Horizon Implementation Guide — Graph Blog
• Graph Horizon Overview — Graphtronauts / Coinmonks
• Messari Quarterly Reports — The Graph

Each entry follows the existing format with Summary, Description (where applicable), and Solution, including cross-references to related error codes.