Eliminate raw 'awaiting_agent'/'hibernating'/'failed'/etc string literals
from production status writes. Adds models.WorkspaceStatus typed alias and
models.AllWorkspaceStatuses canonical slice; every UPDATE workspaces SET
status = ... now passes a parameterized $N typed value rather than a
hard-coded SQL literal.
Defense-in-depth follow-up to migration 046 (#2388): the Postgres enum
type was missing 'awaiting_agent' + 'hibernating' for ~5 days because
sqlmock regex matching cannot enforce live enum constraints. The drift
gate is now a proper Go AST + SQL parser (no regex), asserting the
codebase ⊆ migration enum and every const appears in the canonical
slice. With status as a parameterized typed value, future enum mismatches
fail at the SQL layer in tests, not silently in prod.
Test coverage: full suite passes with -race; drift gate green.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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