fix: make PCZT trial decryption generic over MemoSize

[QuantumExplorer]

Summary

• OrchardDomain::for_pczt_action and impl ShieldedOutput<OrchardDomain<ZcashMemo>> for pczt::Action were pinned to ZcashMemo, even though pczt::Bundle/Action/Output and Builder::build_for_pczt are generic over M: MemoSize (feat: make memo size generic via MemoSize trait #1)
• As a result, a pczt::Bundle<DashMemo> had no supported trial-decryption path: a PCZT Signer could not verify the outputs it was being asked to authorize (try_note_decryption(&OrchardDomain::for_pczt_action(action), ...) did not compile for M = DashMemo), and because both the trait and the types live in this crate, orphan rules prevent downstream crates from adding the impl themselves
• Neither impl body was Zcash-specific, so this generalizes both over M: MemoSize

Changes

• OrchardDomain::for_pczt_action moved into the generic impl<M: MemoSize> OrchardDomain<M> block, taking &pczt::Action<M>; now delegates to for_nullifier instead of duplicating its body
• impl<M: MemoSize> ShieldedOutput<OrchardDomain<M>> for pczt::Action<M> replaces the ZcashMemo-only impl; enc_ciphertext returns Option<&M::NoteCiphertextBytes>
• New regression test pczt_trial_decryption_is_memo_size_generic: builds a pczt::Bundle<DashMemo> via Builder::<DashMemo>::build_for_pczt, trial-decrypts the output through for_pczt_action, and checks note value, recipient address, and the 36-byte memo round-trip

No behavior change for ZcashMemo users — the generic impls subsume the old pinned ones.

Test plan

• cargo test --lib pczt — 6 passed (including the full proving PCZT role tests and the new regression test)
• cargo check --all-features
• cargo clippy --all-features clean
• cargo fmt -- --check

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • PCZT trial decryption now works with multiple memo sizes, not just the default one.
  • Decrypted memo recovery is supported across memo-size variants during shielded output handling.

• Tests

  • Added coverage to verify trial decryption succeeds with a non-default memo size.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 82fb7c28-16ce-4710-a137-733309c1d9b7

📥 Commits

Reviewing files that changed from the base of the PR and between f055573 and 0d9f5f9.

📒 Files selected for processing (1)

• src/note_encryption.rs

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📝 Walkthrough

Walkthrough

OrchardDomain::for_pczt_action and the ShieldedOutput implementation for PCZT actions in src/note_encryption.rs are generalized from being specific to ZcashMemo to being generic over any MemoSize. A new test validates trial decryption using DashMemo.

Changes

Generic PCZT action decryption

Layer / File(s)	Summary
Generalize for_pczt_action and ShieldedOutput impl src/note_encryption.rs	for_pczt_action now accepts crate::pczt::Action<M>; the ShieldedOutput<OrchardDomain<M>> impl for crate::pczt::Action<M> is generalized, with enc_ciphertext returning Option<&M::NoteCiphertextBytes>.
DashMemo trial decryption test src/note_encryption.rs	A new test builds a PCZT bundle with DashMemo and verifies decrypted value, address, and memo bytes using the generic for_pczt_action.

Estimated code review effort: 2 (Simple) | ~12 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Test
  participant OrchardDomain
  participant PcztAction as "pczt::Action<M>"

  Test->>OrchardDomain: for_pczt_action(&PcztAction)
  OrchardDomain->>PcztAction: ephemeral_key(), cmstar()
  OrchardDomain->>PcztAction: enc_ciphertext()
  PcztAction-->>OrchardDomain: Option<&M::NoteCiphertextBytes>
  OrchardDomain-->>Test: decrypted note value, address, memo

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: generalizing PCZT trial decryption over MemoSize.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/pczt-memo-generic

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[QuantumExplorer]

Self Reviewed