executor: fix sandbox git fetch + inject prior failure history

Fix: use file:// prefix in git fetch during sandbox teardown to force
pack-protocol transfer. The local optimization uses hard links which
fail across devices and with mixed-owner object stores.

Feature: before running a task, query prior failed/timed-out executions
and prepend their error messages to the agent's --append-system-prompt.
This tells the agent what went wrong in previous attempts so it doesn't
repeat the same mistakes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/internal/executor/executor.go b/internal/executor/executor.go
index d1c8e72..df222f8 100644
--- a/internal/executor/executor.go
+++ b/internal/executor/executor.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log/slog"
 	"path/filepath"
+	"strings"
 	"sync"
 	"time"
 
@@ -416,6 +417,10 @@ func (p *Pool) execute(ctx context.Context, t *task.Task) {
 		p.mu.Unlock()
 	}()
 
+	// Inject prior failure history so the agent knows what went wrong before.
+	priorExecs, priorErr := p.store.ListExecutions(t.ID)
+	t = withFailureHistory(t, priorExecs, priorErr)
+
 	// Run the task.
 	err = runner.Run(ctx, t, exec)
 	exec.EndTime = time.Now().UTC()
@@ -478,6 +483,43 @@ var terminalFailureStates = map[task.State]bool{
 	task.StateBudgetExceeded: true,
 }
 
+// withFailureHistory returns a shallow copy of t with prior failed execution
+// error messages prepended to SystemPromptAppend so the agent knows what went
+// wrong in previous attempts.
+func withFailureHistory(t *task.Task, execs []*storage.Execution, err error) *task.Task {
+	if err != nil || len(execs) == 0 {
+		return t
+	}
+
+	var failures []storage.Execution
+	for _, e := range execs {
+		if (e.Status == "FAILED" || e.Status == "TIMED_OUT") && e.ErrorMsg != "" {
+			failures = append(failures, *e)
+		}
+	}
+	if len(failures) == 0 {
+		return t
+	}
+
+	var sb strings.Builder
+	sb.WriteString("## Prior Attempt History\n\n")
+	sb.WriteString("This task has failed before. Do not repeat the same mistakes.\n\n")
+	for i, f := range failures {
+		fmt.Fprintf(&sb, "**Attempt %d** (%s) — %s:\n%s\n\n",
+			i+1, f.StartTime.Format("2006-01-02 15:04 UTC"), f.Status, f.ErrorMsg)
+	}
+	sb.WriteString("---\n\n")
+
+	copy := *t
+	copy.Agent = t.Agent
+	if copy.Agent.SystemPromptAppend != "" {
+		copy.Agent.SystemPromptAppend = sb.String() + copy.Agent.SystemPromptAppend
+	} else {
+		copy.Agent.SystemPromptAppend = sb.String()
+	}
+	return &copy
+}
+
 // waitForDependencies polls storage until all tasks in t.DependsOn reach COMPLETED,
 // or until a dependency enters a terminal failure state or the context is cancelled.
 func (p *Pool) waitForDependencies(ctx context.Context, t *task.Task) error {