Emit Solana intermediate output for Turnkey policy engine

[prasanna-anchorage]

Summary

• Adds optional bytes intermediate_output = 5 to ParsedTransactionPayload. For Solana, it carries a borsh-serialized, deterministic mirror of solana_parser::SolanaMetadata shaped to the solana.tx.* attributes Turnkey's Solana policy engine evaluates. Empty for other chains.
• Refactors the VisualSignConverter trait to return ConversionResult { payload, intermediate_output: Option<Vec<u8>> }. The existing borsh-based ParsedTransactionPayload signature now covers the new field automatically — wallets can trust it the same way they trust parsed_payload.
• Adds parser_cli --with-intermediate to decode and pretty-print the borsh blob.
• Adds parser_cli --policy <EXPR> to evaluate Google CEL policy expressions against the parsed intermediate output and print PASS/DENY (process exits non-zero on any DENY, so it composes with CI).
• Adds CEL-based unit tests asserting the schema is expressive enough for Turnkey's documented Solana policy patterns.
• Schema lives in visualsign_solana::intermediate (a pub mod) so wallet code can borsh::from_slice directly.

This is a draft PoC — comments welcome on the schema shape and the trait change before we polish.

Why borsh + bytes (vs proto-typed nested messages)?

• One new proto field, no new proto messages.
• Schema in Rust → easier to iterate without proto codegen churn; both ends here are Rust.
• Deterministic by construction (BTreeMap maps + alphabetized program_call_args_json), which keeps the existing borsh::to_vec(&payload) digest stable.
• Trade-off: weaker schema evolution guarantees and no cross-language type info, but acceptable given consumer profile.

Schema (SolanaIntermediateOutput)

Mirrors solana_parser::SolanaMetadata minus signatures (unsigned tx). Per-instruction:

program_key, accounts[{ account_key, signer, writable }],
instruction_data_hex, address_table_lookups[],
parsed_instruction_data?: { instruction_name, discriminator,
                            named_accounts (BTreeMap), program_call_args_json,
                            idl_source ("BuiltIn"|"Custom"), idl_hash }

Plus top-level account_keys, program_keys, transfers, spl_transfers, recent_blockhash, address_table_lookups. Field names match Turnkey's documented solana.tx.* attributes.

CLI invocation (PoC)

Pretty-print the intermediate output:

cargo run --bin parser_cli -- --chain solana --network SOLANA_MAINNET \
  --output text --with-intermediate -t <BASE64_TX>

Trimmed sample (Jupiter swap fixture from the existing unit test):

=== Intermediate Output (Solana, policy schema) ===
SolanaIntermediateOutput {
    account_keys: [ "6DSxAQ2HdBLGYwa3AQf6hXXjNZ762p761ANxBDqrao5P", ... ],
    program_keys: [
        "11111111111111111111111111111111",
        "JUP6LkbZbjS1jKKwapdHNy74zcZ3tLUZoi5QNyVTaV4",
        "TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA",
        "ATokenGPvbdGVxr1b2hvZbsiqW5xWH25efTNsLJA8knL",
    ],
    instructions: [
        SolanaIntermediateInstruction {
            program_key: "JUP6LkbZbjS1jKKwapdHNy74zcZ3tLUZoi5QNyVTaV4",
            instruction_data_hex: "e517cb977ae3ad2a01000000110164...",
            parsed_instruction_data: Some(SolanaParsedInstructionDataIo {
                instruction_name: "route",
                discriminator: "e517cb977ae3ad2a",
                named_accounts: { "destination_mint": "EPjFWdd5...USDC", ... },
                program_call_args_json: "{\"in_amount\":1000000,\"slippage_bps\":50,...}",
                idl_source: "BuiltIn",
                idl_hash: "d189feae...",
            }),
            ...
        },
    ],
    transfers: [ SolTransfer { from: "6DSx...", to: "AEdS...", amount: "1000000" } ],
    ...
}

CEL policy evaluation (--policy)

The --policy <EXPR> flag (repeatable) compiles CEL against the deserialized intermediate output:

$ cargo run --bin parser_cli -- --chain solana --network SOLANA_MAINNET \
  --output text -t <BASE64_TX> \
  --policy "size(solana.tx.transfers) == 1" \
  --policy "solana.tx.transfers.all(t, t.from == '6DSxAQ2HdBLGYwa3AQf6hXXjNZ762p761ANxBDqrao5P')" \
  --policy "size(solana.tx.address_table_lookups) == 0"

=== Policy evaluation ===
[PASS] size(solana.tx.transfers) == 1
[PASS] solana.tx.transfers.all(t, t.from == '6DSxAQ2HdBLGYwa3AQf6hXXjNZ762p761ANxBDqrao5P')
[PASS] size(solana.tx.address_table_lookups) == 0

Process exits with code 2 if any policy denies, so it composes with CI.

The implementation uses cel-interpreter, a Rust port of Google's CEL spec — the same DSL Turnkey says their policy engine is based on. Caveats:

Turnkey docs	Canonical CEL
xs.any(t, p)	xs.exists(t, p)
xs.count	size(xs)

Same semantics, slightly different surface. We could register a thin any alias on the evaluator if byte-identical Turnkey syntax matters; left out here for simplicity.

This is a schema-expressiveness check, not a Turnkey-faithful simulator. Real pass/deny still requires the server-side engine.

Sample policy expressions

Eight patterns adapted from the Turnkey announcement:

# 1. Single-sender restriction
solana.tx.transfers.all(t, t.from == '<sender>')

# 2. Recipient allowlist (native + SPL)
solana.tx.transfers.all(t, t.to == '<a>' || t.to == '<b>') &&
solana.tx.spl_transfers.all(t, t.to == '<a>' || t.to == '<b>')

# 3. Single transaction control
size(solana.tx.transfers) == 1 &&
solana.tx.transfers.all(t, t.to == '<recipient>')

# 4. Block transfers to a denied address
!(solana.tx.transfers.exists(t, t.to == '<bad>') ||
  solana.tx.spl_transfers.exists(t, t.to == '<bad>'))

# 5. Disallow address-table lookups
size(solana.tx.address_table_lookups) == 0

# 6. Restrict program set
solana.tx.program_keys.all(p,
  p == '<jup>' || p == '<token>' || p == '<ata>' || p == '<system>')

# 7. SPL token allowlist (only USDC)
solana.tx.spl_transfers.all(t, t.token_mint == 'EPjFWdd5...')

# 8. IDL-aware: deny risky instructions on a specific program
!solana.tx.instructions.exists(i,
  i.program_key == '<jup>' &&
  i.parsed_instruction_data != null &&
  i.parsed_instruction_data.instruction_name == 'closeUserAccount')

Six of these are exercised in tests/policy_examples.rs against a real fixture (Jupiter swap), demonstrating the schema is expressive enough.

Determinism

The intermediate_output bytes are part of borsh::to_vec(&ParsedTransactionPayload), so the existing signature covers them. To keep the digest stable for identical inputs:

• Vec fields preserve transaction order.
• All maps are BTreeMap (deterministic borsh).
• program_call_args_json is built from a BTreeMap<String, &Value> then serde_json::to_string, producing alphabetized JSON.

A determinism unit test in intermediate.rs round-trips borsh and asserts byte-identical output.

Test plan

• make -C src lint — clippy clean
• make -C src test — all unit + integration + new policy tests pass
• CLI smoke-tested with a Jupiter swap fixture (sample above)
• CEL policy evaluator wired into the CLI (sample above)
• 6 CEL-based policy tests against a real Solana fixture
• Add a Solana integration test in src/integration/tests/parser.rs that decodes parsed_transaction.payload.intermediate_output and asserts shape (follow-up)
• Add an Ethereum integration test asserting intermediate_output.is_none() (follow-up)
• Real-world validation against Turnkey's policy engine (sandbox round-trip or internal tooling)

Follow-ups

• Bump solana_parser from anchorageoss/a0c554d to tkhq/main (e93f042) once solana-parser-fuzz-core rebases onto main; current pin already exposes the API we need.
• Optional: register any / count aliases on the CEL evaluator for byte-identical Turnkey syntax.
• Optional: extend integration tests to cover the new field.

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