Idris2 0.9.0 dependency: SafeCrypto.modernIsSecure / standardIsSecure (case-rewrite eta-expansion)

[hyperpolymath]

Summary

src/Proven/SafeCrypto/Proofs.idr declares two OWED sites that are NOT covered by the Family 3 (covering/totality) refactor track:

• modernIsSecure (line 138) — securityLevel alg = Modern -> isSecure alg = True
• standardIsSecure (line 148) — securityLevel alg = Standard -> isSecure alg = True

Both are classified DISCHARGE-after-totality in docs/proof-debt-triage-tier-a.md, but the actual blocker is NOT totality — it's an elaborator-level issue:

case is not eta-expanded under rewrite in Idris2 0.8.0.

The proof should be a straightforward rewrite + case + Refl per arm, but the elaborator fails to unfold the case scrutinee after the rewrite step. This is a known class of Idris2 0.8.0 limitations that may be fixed in 0.9.0.

Action

This issue tracks the Idris2 0.9.0 release timeline rather than requesting a local refactor:

• Test the discharge attempt against Idris2 0.9.0 once it ships
• If 0.9.0 elaborator fixes the case-rewrite eta-expansion: discharge the 2 proofs locally (~30 min each, ~1h total)
• If 0.9.0 does NOT fix it: file an upstream Idris2 bug and reclassify these as OWED-AXIOM

Workaround (if discharge needed before 0.9.0)

Hand-write the inversion: instead of rewrite prf in case alg of ..., use with blocks or explicit pattern-match on alg first, then rewrite per arm. ~2-3h estimate; acceptable for a one-off but not pattern-worthy.

OWED sites tracked

• src/Proven/SafeCrypto/Proofs.idr:138 — modernIsSecure
• src/Proven/SafeCrypto/Proofs.idr:148 — standardIsSecure

Related

• Not a Family 3 (covering/totality) issue — see Totality refactor: SafePassword.Strength.{detectPatterns, analyzeStrength, ...} (covering → total) #80 and Totality refactor: SafeJson.Access (%default covering → per-function total) #81 for those.
• Phase 2 triage plan: docs/proof-debt-triage.md §8.
• Per-site disposition: docs/proof-debt-triage-tier-a.md § SafeCrypto.

🤖 Filed by Claude during Phase 2 Days 11-14 of the proof-debt triage.