feat(snowflake): session context restoration and OAuth2 error detection improvements

[betodealmeida]

SUMMARY

Follow-up to #36856, closing the remaining gaps between the OSS OAuth2 implementation and production usage at Preset.

Changes:

• Session context restoration — overrides execute() to catch Snowflake error 090105 ("This session does not have a current database"), re-issues USE DATABASE / SCHEMA / WAREHOUSE / ROLE statements, and retries the query. This prevents spurious failures after an OAuth reconnect or connection-pool recycle. If the retry also fails, a user-friendly error is raised instead of a raw engine error. Role is skipped during restore when OAuth is active so the token's role takes precedence.

• Expanded OAuth2 error detection — CustomSnowflakeAuthErrorMeta now also matches "User is empty" errors (in addition to "Invalid OAuth access token"), covering the case where Snowflake receives an empty username before the user has completed the OAuth flow.

• Role stripping during impersonation — impersonate_user() removes any hardcoded role= query parameter from the URL when switching to authenticator=oauth, so the OAuth token's role is used rather than being overridden by the connection-level setting.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

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[codecov]

Codecov Report

❌ Patch coverage is 32.65306% with 66 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.69%. Comparing base (defacc3) to head (33f9ccd).
⚠️ Report is 855 commits behind head on master.

Files with missing lines	Patch %	Lines
superset/db_engine_specs/snowflake.py	32.65%	66 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #41440      +/-   ##
==========================================
- Coverage   64.36%   63.69%   -0.68%     
==========================================
  Files        2653     2655       +2     
  Lines      144867   145558     +691     
  Branches    33421    33554     +133     
==========================================
- Hits        93250    92706     -544     
- Misses      49946    51148    +1202     
- Partials     1671     1704      +33     

Flag	Coverage Δ
hive	39.21% <32.65%> (-0.13%)	⬇️
javascript	68.56% <ø> (ø)
mysql	57.90% <32.65%> (-0.16%)	⬇️
postgres	57.96% <32.65%> (-0.17%)	⬇️
presto	40.79% <32.65%> (-0.14%)	⬇️
python	58.17% <32.65%> (-1.40%)	⬇️
sqlite	57.62% <32.65%> (-0.16%)	⬇️
unit	?

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