fix(storage): pin PostgreSQL sessions to UTC timezone

[Kiran01bm]

Pins SchemaBot-managed PostgreSQL sessions to timezone=UTC unless the DSN sets one explicitly.

Why

Storage compares plain timestamp columns against server-side now(), which evaluates through the session TimeZone. On a server whose default TimeZone is not UTC, lease-expiry and staleness predicates would skew — and the UTC default of common container images means tests can't catch it. Pinning the session at connection setup makes the comparisons consistent across pods regardless of server configuration.

What

postgresconn injects timezone=UTC into the connection config after DSN parsing, for both DSN forms and the credential-reload path alike. An explicit timezone in the DSN wins, in either DSN form and under any GUC-name spelling.

Two related gaps are tracked as internal follow-ups, out of scope here:

• MySQL parity: mysqlconn pins no session time_zone, so the same skew class remains live for MySQL lease/staleness predicates — follow-up injects time_zone='+00:00' unless the DSN sets one.
• received_at is written from client-side time.Now() (zone discarded by pgx) and diffed against server now() in the backlog-age metric — follow-up writes it with the dialect's CurrentTimestamp.

Before / after

Before — session timezone follows the server default

  DSN (no timezone) ──▶ pgx session: TimeZone = server default
                                 │
                                 ▼
         now() evaluates in the server's TZ; plain-timestamp
         predicates (lease expiry, staleness) skew whenever
         the server default is not UTC


After — session pinned at connection setup

  DSN (no timezone) ──▶ postgresconn: inject timezone=UTC ──▶ session: TimeZone = UTC
  DSN (timezone=X)  ──▶ postgresconn: leave as-is         ──▶ session: TimeZone = X
                                 │
                                 ▼
         now() evaluates in UTC on every pod; timestamp
         vs now() predicates behave identically across servers

[Copilot]

Pull request overview

Pins SchemaBot-managed PostgreSQL sessions to timezone=UTC (unless explicitly set in the DSN) so storage comparisons between timestamp columns and server-side now() are consistent regardless of the server’s default TimeZone.

Changes:

• Default pgx runtime param timezone=UTC is applied during connection config parsing unless already present in the DSN.
• Unit test added to verify both DSN forms default to UTC and that explicit DSN timezone overrides.
• Integration test added to validate the session reports UTC even when the database default timezone is set to a non-UTC value.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
pkg/postgresconn/postgresconn.go	Sets a default timezone=UTC runtime param during connectionConfig() parsing (DSN timezone still wins).
pkg/postgresconn/postgresconn_test.go	Adds unit coverage for UTC default and explicit timezone override across URL + keyword DSN forms.
pkg/postgresconn/postgresconn_integration_test.go	Adds integration coverage asserting Open() yields a UTC session even when DB default timezone is non-UTC.

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[morgo]

🤖 Approving on Morgan's behalf (automated review).

Clean and PG-only (postgresconn; the MySQL path is structurally untouched). The pin is correctly scoped: it applies only when no timezone GUC is already present under case-insensitive matching — which dodges the real trap here, since pgx preserves DSN key case and a blind write would put both TimeZone=... and timezone=UTC into the startup packet in nondeterministic map order. PGTZ arriving via libpq fallback semantics counts as explicit and is honored. The motivation is load-bearing (storage's lease-expiry/staleness predicates compare plain timestamps against session-timezone-dependent now()), and the tests are exemplary — both DSN forms, both GUC spellings with a no-duplicate assertion, PGTZ honored, and an integration test that first proves a fresh unpinned session observes the non-UTC database default before asserting the pinned session reads UTC.

No nits.