feat: Add multihost support for native js driver

[maxbronnikov10]

Summary

• Add host/port array support to Connection.connect() in the pure JS driver, with automatic TCP-level failover to the next host on connection error
• Add targetSessionAttrs config option to Connection and wire it through Client
• Intercept protocol events during startup to collect in_hot_standby and default_transaction_read_only from ParameterStatus messages and validate them against targetSessionAttrs before signalling readyForQuery to the caller
• Fall back to issuing SHOW transaction_read_only; SELECT pg_catalog.pg_is_in_recovery() for older servers that don't advertise those params

Behavior Changes

When host and port are arrays, the driver tries each host in order. TCP-level errors before the first successful connect silently trigger a retry on the next host. With targetSessionAttrs set, hosts that connect successfully but don't match the session requirement are also silently skipped. If the list is exhausted without a match, an error is emitted.

Problem

The pure JS driver previously only accepted a single host and had no targetSessionAttrs support, unlike the native libpq driver. This made it impossible to use driver for high-availability Postgres setups where you want to connect to whichever replica is currently the primary, or explicitly route to a read replica.

The lack of multihost support meant users had to implement their own failover logic outside the driver, or switch to the native bindings just to get this feature.

Related issues

#1470

[Copilot]

Pull request overview

This PR adds multihost connection support to the pg native JavaScript driver's Connection class, enabling TCP-level failover across multiple hosts and PostgreSQL target_session_attrs session attribute filtering (e.g., read-write, read-only, primary, standby, prefer-standby).

Changes:

• Extended Connection.connect() to accept arrays of hosts and ports, with automatic failover to the next host on TCP connection errors
• Implemented targetSessionAttrs support that checks PostgreSQL backend parameters (in_hot_standby, default_transaction_read_only) after connection, with a fallback to SHOW/SELECT queries when parameters aren't available via ParameterStatus messages
• Added comprehensive unit tests covering multihost failover, all targetSessionAttrs modes, and the SHOW query fallback mechanism

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
packages/pg/lib/connection.js	Core multihost and targetSessionAttrs logic in the Connection class, including stream factory support, emit interception for session attribute checking, and the isHostMatchTargetSessionAttrs helper function
packages/pg/lib/client.js	Passes targetSessionAttrs config option through to the Connection constructor
packages/pg/test/unit/connection/multihost-tests.js	Unit tests for multihost connectivity, all targetSessionAttrs modes, fallback SHOW queries, and edge cases
.gitignore	Adds .history directory to gitignore

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[maxbronnikov10]

@brianc @charmander hello! can u please check this PR

[Copilot]

Pull request overview

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

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