Probe target
  npm package: @meshsdk/core
  version: 1.9.1
  install command:
    npm install --prefix handoffs/mesh-probe --ignore-scripts \
      --no-audit --no-fund @meshsdk/core@1.9.1
  result: exit 0, 214 packages installed

The current release was inspected through its shipped
@meshsdk/transaction TypeScript declarations and implementation.

Inspected API
  MeshTxBuilderCore
    txOut(address: string, amount: Asset[])
    txInRedeemerValue(redeemer: BuilderData["content"], ...)
    changeAddress(address: string)
    setFee(fee: string)
    public meshTxBuilderBody: MeshTxBuilderBody
  MeshTxBuilder
    complete(customizedTx?: Partial<MeshTxBuilderBody>): Promise<string>
    completeUnbalanced(customizedTx?: MeshTxBuilderBody): string
    getActualFee(): bigint
    calculateMinLovelaceForOutput(output: Output): bigint

Implementation evidence
  complete() sanitizes outputs, performs UTxO selection, evaluates redeemers,
  updates fee/change from a TransactionPrototype, serializes the final body, and
  returns CBOR hex. Internal coin-selection callbacks calculate cost, min coin,
  and size, but no public callback receives an assembled candidate transaction.
  txOut and redeemer methods accept fixed values. The final fee/body state and
  CBOR are observable after completion, enabling a caller-owned fresh-builder
  loop.

Conclusion
  P1 is supported. P2 and P4 are expressible with effort through a bounded
  complete -> inspect body/CBOR -> reconstruct loop. P3 has no in-build public
  observation/re-entry hook.