[kyscott18]

Logs and errors now print in ponder's format, in both pretty and JSON. An error prints its message and its causes. Stacks are printed only for unknown errors (bugs), not for typewriter's own tagged errors.

Output

Pretty:

17:06:51.055 DEBUG Executed mutation mutation=transfer execution_index=12 (3ms)
17:06:51.056 DEBUG Failed RPC request method=eth_getBlockByNumber attempt=2
RpcNetworkError: Failed 'eth_getBlockByNumber' request to http://localhost:8545
  cause: TypeError: fetch failed
  cause: Error: connect ECONNREFUSED 127.0.0.1:8545
17:29:05.145 DEBUG Rejected mutation mutation=A
MutationRevertedError: Mutation reverted with InsufficientBalance("0x0000000000000000000000000000000000000001", 5)
17:07:35.037 ERROR Failed to start typewriter
ConfigError: Typewriter entrypoint file does not exist: /nope/App.sol

JSON (one line per log):

{"level":"error","time":"2026-10-26T17:29:05.358Z","msg":"Stopped typewriter","error":{"name":"TypewriterStoppedError","message":"Typewriter stopped","cause":{"name":"DbError","message":"Failed database query: select 1","sql":"select 1","cause":{"name":"PostgresError","message":"relation \"foo\" does not exist"}}}}

Changes

• Logger (src/logger.ts): a single logger replaces Effect's pretty and structured loggers.
  • Pretty: time LEVEL Msg key=value (duration).
  • JSON: a flat record with level, time, msg, the annotations, and error.
  • Errors are collected from Error message arguments, an error annotation, and the Effect Cause.
  • A _tag marks a known error, which prints as Name: message. Any other error keeps its stack. Causes never print stacks.
• Error messages: tagged errors that had an empty message now have one. This includes the RPC errors (RpcResponseError used to log as a bare RpcResponseError:), DbError, BlockNotFoundError and the revert errors.
• ConfigError: config validation and Solidity parsing throw it instead of Error. A forge build failure includes forge's output.
• Logger provided at the edges: in createTypewriter and in the simulation entrypoint, no longer in typewriter.ts.
  • The simulation's own logs are at Info, and TYPEWRITER_LOG_LEVEL applies only to the runtime. This removes the None level workaround and the category: sim annotation.
• Wording: messages are capitalized and past tense, keys are snake_case, and each simulation log says it's part of the simulation.

Behavior changes to review

• createTypewriter exits the process on a startup failure, instead of rejecting. It logs "Failed to start typewriter" and calls process.exit(1). Bun ignores an overwritten error.stack and always prints a code frame and stack for an uncaught error, so letting the error escape would bring the noise back. A stopped program already crashed the process; it now logs "Stopped typewriter" first. Previously only typed failures crashed it, and a defect stopped the program silently.
• The JSON shape changed: message becomes msg, annotations are flat instead of nested, and levels are lowercase.
• "Rejected mutation" moved from ERROR to DEBUG. It fired on every contract revert, and the caller already receives the error.
• Code that calls createTypewriterEffect directly gets Effect's default logger unless it provides loggerLayer itself.

Testing

• tsc --noEmit, biome check, bun test (27 pass)
• Simulation seed 0x01 passes at the default level and at TYPEWRITER_LOG_LEVEL=debug
• Checked by hand: startup failure output and exit code through a pipe, a failed simulation, and JSON output

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