Answer

Probe: Go append-to-file recovery check

Verified: go run appends one unix-timestamp line per invocation and the file grows on every call. No toolchain or environment fix is required.

---

Go unix-time append probe (probe.ts)

Root cause analysis

The class go-20261007-pi-agent-recovery-probe is a smoke probe, not a bug report. It checks whether the solver can still compile/run Go after the pi binary was restored.

Findings from the environment:

• go is present and healthy: go version go1.26.0 linux/amd64.
• pi is present and runnable: ~/.local/bin/pi → 0.0.0.
• The probe target probe.ts did not exist beforehand (the earlier lookup exited 1), which is expected — the snippet creates it on first run (O_CREATE).
• Running a standalone .go file works without a go.mod, so no module scaffolding is needed.

The only realistic failure mode for this probe is environmental (missing/restored pi/go), and none is present now. The code below is therefore the complete fix.

Fix

Create ~/probe.go:

package main

import (
    "fmt"
    "os"
    "time"
)

func main() {
    f, err := os.OpenFile("probe.ts", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
    if err != nil {
        fmt.Fprintln(os.Stderr, "error:", err)
        os.Exit(1)
    }
    defer f.Close()

    if _, err := fmt.Fprintf(f, "%d\n", time.Now().Unix()); err != nil {
        fmt.Fprintln(os.Stderr, "error:", err)
        os.Exit(1)
    }
}

Run it from the directory where probe.ts should live:

cd ~
go run probe.go

Key points:

• os.O_APPEND|os.O_CREATE|os.O_WRONLY makes each call append a new line and create probe.ts on the first call.
• time.Now().Unix() writes the current unix time in seconds.
• Errors are propagated to stderr with a non-zero exit, so a failed run is detectable.

Verification

Run the snippet twice and compare the file size / line count between calls.

cd ~
rm -f probe.ts

go run probe.go                 # call 1
lines1=$(wc -l < probe.ts); bytes1=$(wc -c < probe.ts)

sleep 1
go run probe.go                 # call 2
lines2=$(wc -l < probe.ts); bytes2=$(wc -c < probe.ts)

echo "call1: lines=$lines1 bytes=$bytes1"
echo "call2: lines=$lines2 bytes=$bytes2"
test "$lines2" -gt "$lines1" && echo "PASS: file grew" || echo "FAIL: file did not grow"
cat probe.ts

Observed result on this machine:

call1: lines=1 bytes=11
call2: lines=2 bytes=22
PASS: file grew
1791412763
1791412764

A third run grows it to 3 lines / 33 bytes, i.e. exactly one unix timestamp per call. PASS.

# Evidence
- Problem class: go-20261007-pi-agent-recovery-probe
- Model: openrouter/deepseek/deepseek-v4.1-flash
- Solved: 2026-10-07T22:39:28.914Z
- Verification: solution produced by pi in sandbox; see signatures.json

{"description": "Smoke probe: verify solver recovery after pi binary restore. Write a tiny go snippet that appends the current unix time to a file named probe.ts and confirm the file grows between two calls.", "environment": "", "language": "", "model": "openrouter/deepseek/deepseek-v4.1-flash", "problem_class": "go-20261007-pi-agent-recovery-probe", "provider": "openrouter", "solved_at": "2026-10-07T22:39:28.921Z", "version": ""}