feat(plugin-misc): add transaction simulation pre-flight skill

[spektre-labs]

What

Adds a new SIMULATE_TRANSACTION agent skill to plugin-misc: a transaction simulation pre-flight action.

Given a base64-encoded serialized transaction, it simulates it against current chain state and returns a clean structured result:

{
  willSucceed: boolean,
  error: string | null,
  unitsConsumed: number | null,
  logs: string[],
  summary: string
}

It supports both legacy Transaction and VersionedTransaction (tries VersionedTransaction.deserialize first, falls back to Transaction.from), and uses { sigVerify: false, replaceRecentBlockhash: true } for versioned transactions so unsigned/about-to-be-built transactions can be checked.

Why

This is the runtime complement to static safety checks: an agent can dry-run a transaction before signing or sending it.

• Avoids paying fees on transactions that would fail on-chain.
• Surfaces compute-unit usage and program logs for debugging/observability.
• Lets an agent reason about outcome before committing.

core/src/utils/send_tx.ts simulates internally as part of sending, but there was no standalone, agent-callable simulation skill — this fills that gap.

API

• Tool: simulateTransactionPreflight(agent, base64Tx, opts?)
• Action: SIMULATE_TRANSACTION (zod schema { transaction: string })

Both are wired into the misc plugin's methods and actions, following the existing ottersec integration pattern (tools/ + actions/ + index registration).

Fail-safe by design

The tool never throws. Any deserialize or RPC failure resolves to willSucceed: false with summary: "⛔ could not simulate — do not assume safe", so a caller can never mistake an unsimulated transaction for a safe one.

Verification done

• pnpm run build:core and pnpm run build:plugin-misc — clean (CJS + ESM + DTS).
• biome check on the new files + index.ts — clean (matches repo style).
• Runtime smoke test of the fail-safe path (garbage / empty base64 → willSucceed: false, never throws) — passes.
• Zero new dependencies (uses @solana/web3.js, already a dependency).