fix(auth): treat blank session cookies as absent

[BigSimmo]

Summary

• Treat blank/whitespace-only current sb-<ref>-auth-token cookies (including empty chunks) as absent so a still-valid legacy sb-access-token can authenticate during migration.
• Treat blank/whitespace-only legacy sb-access-token cookies as absent so anonymous public APIs are not forced to 401.
• Keep fail-closed behavior for non-empty invalid current or legacy session cookies.
• Extend tests/auth-tri-state.test.ts with blank-presence coverage and a synthetic project-ref fixture for cookie-name resolution.

Verification

• npm exec vitest run tests/auth-tri-state.test.ts — 16 passed
• npm run verify:pr-local — running after PR open
• UI verification not run: no UI behavior changed.
• Live RAG not run: no retrieval or generation behavior changed.

Risk and rollout

• Risk: low. Only blank cookie leftovers change from invalid → absent (or fall through to legacy when blank current + valid legacy). Non-empty invalid modern sessions still do not fall back to legacy.
• Rollback: revert this PR; no schema, data, provider, or deployment mutation.
• Provider or production effects: None. Local/static/mocked checks only.

Clinical Governance Preflight

• Source-backed claims still require linked source verification before clinical use
• No patient-identifiable document workflow was introduced or expanded without explicit governance approval
• Supabase target remains Clinical KB Database
• Service-role keys and private document access remain server-only
• Demo/synthetic content remains clearly separated from real clinical sources
• Source metadata, review status, and outdated/unknown-source behavior remain conservative
• Deployment classification/TGA SaMD impact was checked; clinical decision-support behavior is unchanged

Notes

• Follow-up to Bugbot findings on fix(auth): prefer current session cookies #1079 blank-cookie presence handling.
• RAG impact: no retrieval behaviour change — authentication cookie blank-presence only.

  

[supabase]

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📥 Commits

Reviewing files that changed from the base of the PR and between 6ceaaff and 177e9aa.

📒 Files selected for processing (2)

• src/lib/supabase/auth.ts
• tests/auth-tri-state.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch cursor/fix-blank-auth-cookies-c687

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