Promote newly committed agent version to DEFAULT

[quinnsebso]

Problem

ALTER AGENT ... COMMIT creates a version but does not move the DEFAULT pointer, so the version dbt just deployed was not necessarily the one end users get.

This stayed hidden because Snowflake treats the newest committed version as default implicitly — but only until DEFAULT_VERSION is set explicitly by anything out-of-band (most likely Snowsight's Publish button). From that moment the pointer is pinned and never moves again: every later dbt run commits a version nobody sees, while Snowsight keeps showing an older version as "In use" with history piling up behind it. It never self-corrects.

Changes

• New macro snowflake__set_cortex_agent_default_version — issues ALTER AGENT ... SET DEFAULT_VERSION = 'LAST' after each commit, behind a new set_default_version config (defaults to true). Using 'LAST' keeps it idempotent and makes promotion self-healing: an agent pinned out-of-band is un-stuck by the next dbt run.
• 099106 fix — ADD LIVE VERSION no longer fails with "There is already a live version", the state a prior CREATE OR REPLACE (dbt run --full-refresh) leaves behind. SHOW VERSIONS is now inspected per row, so an existing LIVE working copy is detected and modified in place instead of re-added. This un-wedges a versioned run following a full refresh.
• New test cortex_agent_versioned_test_default_is_newest — asserts the newest committed version is the default.
• README — documents the new option, the promotion step, and the quoting gotcha below.

Reviewer notes

The Snowflake docs are wrong here. The unquoted forms the docs show (SET DEFAULT_VERSION = LAST, = VERSION$3, = "VERSION$3") all fail with a SQL compilation error. Only the single-quoted string form parses. The first deploy attempt failed on exactly this; caught by testing against a live account rather than trusting the page.

Why CI never caught this: the existing ..._has_versions test only checks that versions exist. On a stale pointer it passes — the new test fails. Verified both ways (see below).

Design call worth confirming: set_default_version defaults to true with an opt-out for teams that promote versions themselves (e.g. staged releases via aliases). Happy to make promotion unconditional and drop the flag if preferred.

Verification

All against live Snowflake (TRAINING_SANDBOX.TEST_QS_INTEGRATION_TESTS):

Check	Result
Bug reproduced on unfixed code (pin VERSION$1, deploy)	VERSION$4 committed, pointer stayed on $1
Fix promotes + self-heals (pin VERSION$1, deploy)	VERSION$6 committed and promoted
New test has teeth (stale pointer)	FAIL, while has_versions PASSED
set_default_version=false opt-out	version committed, pointer deliberately untouched
099106 wedge (--full-refresh then plain dbt run)	both succeed
dbt parse + dbt build --select cortex_agent_versioned_test+	clean, PASS=4

Both the CI and local test agents are currently aligned (newest == default, no dangling LIVE version).

🤖 Generated with Claude Code