Implement a log summariser from its specification alone

1. 0list_dirno exit code31 ms$0.00394/24 tok18:45:25.396

   Confirm what is actually here. A spec and a stub, no tests, so nothing to run first.

   argumentswrap

   {
     "path": "."
   }

   3 lines, 17 B

   outputwrap

   SPEC.md
   logstat.py

   2 lines, 18 B

2. 1read_fileno exit code31 ms$0.00479/42 tok18:45:25.428

   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.

   argumentswrap

   {
     "path": "SPEC.md"
   }

   3 lines, 23 B

   outputwrapexpand 251 lines

   # 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

3. 2read_fileno exit code31 ms$0.002801/43 tok18:45:25.460

   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.

   argumentswrap

   {
     "path": "logstat.py"
   }

   3 lines, 26 B

   outputwrapexpand 26 lines

   #!/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

4. 3write_fileno exit code0 ms$0.003090/156 tok18:45:25.465

   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.

   contentwrap

   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

   argumentswrap

   {
     "path": "sample.log"
   }

   3 lines, 26 B

   outputwrap

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

5. 4write_fileno exit code0 ms$0.003317/2229 tok18:45:25.469

   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.

   contentwrapexpand 249 lines

   #!/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

   argumentswrap

   {
     "path": "logstat.py"
   }

   3 lines, 26 B

   outputwrap

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

6. 5bashexit 0108 ms$0.005778/105 tok18:45:25.580

   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 commandno wrap

   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

   outputwrap

   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

7. 6bashexit 062 ms$0.005998/86 tok18:45:25.641

   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 commandno wrap

   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

   outputwrap

   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

8. 7finishno exit code0 ms$0.006173/26 tok18:45:25.641

   Applied the fix. This should resolve the issue.

   argumentswrap

   {
     "summary": "Applied the fix. This should resolve the issue."
   }

   3 lines, 66 B

   outputwrap

   Run ended by the agent.

8 steps2 commands0 schema violations0 failed commands0 destructive attempts