## TL;DR
masscan can be resumed and its partial output is usable, but only if the agent asks for both. Run masscan with `--resume` support via its conf file, write results incrementally, and parse whatever landed before the timeout instead of treating a killed run as zero data.

```text
agent masscan run timed out and the agent failed parsing partial output
```

## Use this when
- masscan is killed by `timeout` or the agent step limit and the agent reports no findings.
- The agent discards the run because the output file looks incomplete.
- A previous masscan run on the same authorized range exists and could be resumed.

## Not for this skill when
- masscan fails immediately with a permissions error (raw sockets need elevated privileges). That is a setup problem.
- masscan completes normally but the agent misreads the output. That is a parsing bug, not a timeout.
- The engagement scope does not permit masscan's speed. Respect the scope.

## Steps
1. Launch masscan with a conf file (`--conf scan.conf`) so the `--resume` state (`paused.conf`) is written automatically; run it under an explicit timeout. Verify: interrupting the scan leaves a `paused.conf` file behind.
2. Choose an incremental output format (`-oJ` for JSON or `-oX` for XML) rather than the default human-readable list. Verify: the output file grows while the scan runs.
3. After a timeout kill, parse the partial output file as-is: read every complete record and ignore the truncated tail. Verify: the parsed host count is greater than zero even though the scan did not finish.
4. Resume with the same command plus `--resume`; masscan picks up where `paused.conf` says it stopped. Verify: the resumed run's first output lines cover unscanned ranges, not repeats.
5. Merge partial parses from each attempt into one findings list, deduplicating by host and port. Verify: the final list has no duplicate host/port pairs.

## Variant phrasings
### masscan timeout left agent with no results
Same resume pattern.
### agent cannot read partial masscan output
Parsing-focused variant.
### resume masscan after agent step timeout
Resume-focused phrasing.

Compatibility: masscan 1.3.x. The `--resume`/`paused.conf` mechanism is built into masscan and needs no extra tooling.

## Why it happens
Agents treat a killed process as a failed process, and masscan's default output gives them nothing until the end. The `--resume` machinery exists precisely for interrupted scans, but agents rarely invoke it because it is not part of the default command they were shown. Partial output plus resume converts a timeout from total loss into a pause.

## Edge cases / pitfalls
- `paused.conf` is written on clean interrupts (SIGINT); a hard SIGKILL may skip it. Prefer interruptible timeouts where the harness allows signal choice.
- masscan's speed can overwhelm small authorized targets. Keep the `--max-rate` within the engagement's agreed limits; resume does not excuse over-aggressive scanning.
- Partial output from a timed-out run is a coverage statement: report which ranges were actually scanned, not just what was found.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_fCROcfoMlyV6dEzhS49FLw