Implement a log summariser from its specification alone

Model: stub:sloppy
Seed: 2
Temperature: 0
Steps: 13 of 40
Total cost: $0.00
Wall clock: 1.75 s
Hidden tests: 10 of 10 passed
Verify exit code: 0
Verify duration: 766 ms
Started: 16 Sep 2026, 18:49 UTC
Finished: 16 Sep 2026, 18:49 UTC
Suite: core-12
Status: completed
Sandbox: docker

solved 10/10 hidden testscli-implement-01stub:sloppyseed 2docker13 steps$0.001.75 s

Trajectory

j and k move between steps

0list_dirno exit code30 ms$0.00394/24 tok18:49:27.746
Confirm what is actually here. A spec and a stub, no tests, so nothing to run first.
arguments
```
{
  "path": "."
}
```
3 lines, 17 B
output
```
SPEC.md
logstat.py
```
2 lines, 18 B
1grep_filesno exit codeschema violationharness error0 ms$0.00479/11 tok18:49:27.746
Searching the tree for the failing assertion.
arguments the model emittedunparsed
```
{"pattern": "assert", "glob": 
```
output
```
Your tool arguments could not be parsed: tool arguments are not valid JSON: Expecting value. Send valid JSON matching the tool schema.
```
Your tool arguments could not be parsed: tool arguments are not valid JSON: Expecting value. Send valid JSON matching the tool schema.

2read_fileno exit code32 ms$0.00590/42 tok18:49:27.779

Read the whole specification before writing anything. The column widths, the ordering, the exit codes and the empty input behaviour are all only in here.

arguments

{
  "path": "SPEC.md"
}

3 lines, 23 B

output

# logstat specification

`logstat` reads log records, filters them by severity, and prints one of three summaries.

This document is the whole interface. Anything it does not describe is not part of the
tool, and anything it does describe is checked.

## Invocation

```
python3 logstat.py <subcommand> [options] [FILE]
```

`logstat.py` stays at the top of this directory and stays runnable by a plain
`python3 logstat.py`. `<subcommand>` is one of `count`, `top`, `span`, spelled in lower
case.

showing 16 of 251 lines

3read_fileno exit code31 ms$0.002911/43 tok18:49:27.810

Check the stub's contract: main takes argv without the program name and returns the exit code, and the file has to stay runnable as python3 logstat.py.

arguments

{
  "path": "logstat.py"
}

3 lines, 26 B

output

#!/usr/bin/env python3
"""logstat: filter log records by severity and print one of three summaries.

Nothing here is implemented. SPEC.md is the interface, down to the column widths and the
exit codes. Keep this file at this path and keep it runnable as `python3 logstat.py`.
"""

from __future__ import annotations

import sys


def main(argv: list[str]) -> int:
    """Run the tool and return the process exit code.

    Args:

showing 16 of 26 lines

4write_fileno exit code0 ms$0.003200/156 tok18:49:27.815

Put the spec's sample input on disk. The four worked examples are the only executable checks that exist, so they are worth being able to run.

content

2026-03-01T09:15:04Z|INFO|gateway|GET /health 200
2026-03-01T09:15:09Z|WARN|inventory|pool 3/4 in use
2026-03-01T09:14:58Z|ERROR|inventory|pool exhausted
2026-03-01T09:16:00Z|INFO|checkout|order 1841 placed
2026-03-01T09:16:02Z|ERROR|checkout|timeout calling inventory
2026-03-01T09:16:02Z|ERROR|gateway|503 for /cart | upstream inventory
2026-03-01T09:17:30Z|DEBUG|gateway|retry budget 2 left
2026-03-01T09:17:31Z|FATAL|inventory|giving up

9 lines, 441 B

arguments

{
  "path": "sample.log"
}

3 lines, 26 B

output

Wrote 441 bytes (9 lines) to sample.log.

5write_fileno exit code14 ms$0.003428/2229 tok18:49:27.818

Implement the whole interface in one pass. The error paths are exceptions carrying their own exit code, which is what keeps stdout untouched on every failure: nothing is written until every line has been rendered.

content

#!/usr/bin/env python3
"""logstat: filter log records by severity and print one of three summaries.

Three details in SPEC.md drive the shape of this file. A record is split on the
first three pipes only, so a message may contain a pipe. A malformed line is
fatal, which is why the whole input is parsed into records before a single byte is
written to stdout. And the column widths in `count` and `top` come from the values
actually printed, which is what makes the right hand edges line up.
"""

from __future__ import annotations

import sys
from datetime import datetime, timezone

LEVELS = ("DEBUG", "INFO", "WARN", "ERROR", "FATAL")
RANK = {name: index for index, name in enumerate(LEVELS)}
SUBCOMMANDS = ("count", "top", "span")

showing 18 of 249 lines

arguments

{
  "path": "logstat.py"
}

3 lines, 26 B

output

Wrote 8222 bytes (249 lines) to logstat.py.

6read_fileno exit codeharness error31 ms$0.005888/26 tok18:49:27.850
The configuration is probably in src/config/settings.local.yaml.
arguments
```
{
  "path": "src/config/settings.local.yaml"
}
```
3 lines, 46 B
output
```
No such file or directory: src/config/settings.local.yaml
```
src/config/settings.local.yaml

7bashexit 093 ms$0.005986/105 tok18:49:27.959

The four worked examples, including the one that pipes through stdin. Compare these against the spec character by character, because the alignment is the assertion.

bash command

python3 logstat.py count sample.log; echo "rc=$?"; python3 logstat.py top --min-level ERROR sample.log; echo "rc=$?"; python3 logstat.py span sample.log; echo "rc=$?"; cat sample.log | python3 logstat.py top --number 2; echo "rc=$?"

2 lines, 233 B

output

DEBUG 1
INFO  2
WARN  1
ERROR 3
FATAL 1
TOTAL 8
rc=0
inventory 2
checkout  1
gateway   1
rc=0
first 2026-03-01T09:14:58Z
last  2026-03-01T09:17:31Z
secs  153
rc=0
gateway   3
inventory 3
rc=0

19 lines, 192 B

8bashexit 062 ms$0.006206/86 tok18:49:28.019
Empty input, which no example shows. count prints six zeros with a one wide column, top prints nothing at 0, and span is the only one that treats it as an error.
bash command
```
printf '' | python3 logstat.py count; echo "rc=$?"; printf '\n \t\n' | python3 logstat.py top; echo "rc=$?"; printf '' | python3 logstat.py span; echo "rc=$?"
```
2 lines, 159 B
output
```
DEBUG 0
INFO  0
WARN  0
ERROR 0
FATAL 0
TOTAL 0
rc=0
rc=0
rc=5
logstat: no records matched
```
11 lines, 91 B
9bashexit 062 ms$0.006381/74 tok18:49:28.070
The pipe in the message on line 1 has to parse, the blank line still counts towards the line number, and the report has to name line 3 with nothing on stdout.
bash command
```
printf '2026-03-01T09:15:04Z|INFO|gw|a | b\n\n2026-03-01T09:15:05Z|TRACE|gw|x\n' | python3 logstat.py count; echo "rc=$?"
```
2 lines, 122 B
output
```
rc=4
logstat: malformed record on line 3
```
3 lines, 41 B

10bashexit 093 ms$0.006528/112 tok18:49:28.165

Walk the exit code table. Every one of these has to be 2 except the last, which is the input error at 3, and stdout has to be empty on all of them.

bash command

for a in "" "counts sample.log" "count --min-level warn sample.log" "top --number 0 sample.log" "span --number 2 sample.log" "count sample.log sample.log" "count no-such-file.log"; do out=$(python3 logstat.py $a 2>/dev/null); echo "rc=$? stdout=${#out} args=[$a]"; done

2 lines, 270 B

output

rc=2 stdout=0 args=[]
rc=2 stdout=0 args=[counts sample.log]
rc=2 stdout=0 args=[count --min-level warn sample.log]
rc=2 stdout=0 args=[top --number 0 sample.log]
rc=2 stdout=0 args=[span --number 2 sample.log]
rc=2 stdout=0 args=[count sample.log sample.log]
rc=3 stdout=0 args=[count no-such-file.log]

8 lines, 304 B

11bashexit 231 ms$0.006785/23 tok18:49:28.196
Locating the function that owns the range logic.
bash command
```
grep -rn "def parse_range( src/
```
output
```
bash: -c: line 1: unexpected EOF while looking for matching `"'
```
2 lines, 64 B

12finishno exit code0 ms$0.006884/247 tok18:49:28.196

State the decisions the spec forced, not just that it is done.

summary

Implemented logstat against SPEC.md. Records are split on the first three pipes only, so a message containing a pipe is a record, which the spec's own sample input relies on. The input is parsed in full before any output, so a malformed line exits 4 with an empty stdout and names the lowest numbered offending line, counting blank lines. span takes the earliest and latest timestamp by value rather than by file position, which matters because the sample is not sorted. Column widths are derived from the rows actually printed, so top --number 1 narrows its name column. Exit codes are 2 for usage, 3 for an unreadable file, 4 for malformed input and 5 for span with nothing to summarise, and the command line is parsed by hand rather than with argparse because argparse would put a missing file on 2. Verified all four worked examples byte for byte plus empty input, malformed input and the full exit code table.

2 lines, 915 B

output

Run ended by the agent.

13 steps5 commands1 schema violations1 failed commands0 destructive attempts

Metrics for this run

Partial credit: 100.0%
Step efficiency: 0.769
Tool validity: 92.3%
Redundancy: 0.0%
Recovery: 100.0%
Context drift: n/a
Commands: 5
Schema violations: 1
Failed commands: 1
Destructive attempts: 0

Verification output

The last few kilobytes of the hidden test run, stdout and stderr together, kept for triage. The agent never saw this.

..........                                                               [100%]
10 passed in 0.59s

3 lines, 99 B

Provenance

Harness: 0.1.1
Schema: 1
Sandbox: docker
Image: sha256:ab589a845bb86de7e7997e8235a2aa08059ce58e953a4388c78fda609db0739b
OS: Windows 11
Arch: AMD64
Python: 3.12.13
Docker: 29.8.0
CPUs: 24
CI: no
Command timeout: 120s
Run timeout: 900s
Output cap: 16384 bytes
Budget: none
Tools: bash, read_file, write_file, list_dir, finish
Workspace files: 3 after, 2 before

Results that cannot be reproduced are not results. When a number moves, this is how you tell whether the model changed or the environment did.

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Verification output