Fix websocket auth race for newly created test users

[crthpl]

Summary

• fix a race in ensure_user_created where account creation used non-transactional pool reads/writes
• perform existence checks + insert + id lookup in one explicit transaction and commit before auth flow continues
• avoid the transient state where websocket init sends ActingAs before the user portfolio is visible

Root cause

Authentication could create a new account and then immediately continue initialization on a different connection. Without an explicit transaction boundary around creation + lookup, the follow-up portfolio read path sometimes observed the account as missing, causing Account not found logs and occasional client-side KeyError during initialization.

Validation

• raw websocket auth stress test: 500 sequential new-user connections with no missing-portfolio failures
• previously flaky scenarios tests repeated 12 times: all passes
• full scenarios suite (uv run pytest): 26 passed

[vercel]

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Project	Deployment	Actions	Updated (UTC)
platform	Ready	Preview, Comment	Feb 18, 2026 1:59am