fix: deliver cancel ack and reap leftover Windows job processes (#996)

## Summary

- When Gitea cancels a job, the reporter cancels its own task context; the final Close() flush then aborted on that same cancelled context and Gitea never received the runner's acknowledgement (missing tail logs and final state).
- On Windows the cancelled context also neutralised terminateRunningProcesses, leaving step grandchildren alive in the workspace, holding file handles, so the runner could no longer clean up and pick up new work.
- Reporter.Close() now flushes on a detached, bounded context via a new rpcCtx() helper and configurable Runner.ReportCloseTimeout (default 10s).
- terminateRunningProcesses now PowerShell-enumerates Win32_Process and taskkill /T /F's every process whose ExecutablePath or CommandLine references the job's workspace directories, on a detached context.
- The daemon heartbeat loop still exits on <-r.ctx.Done(): the runner is intentionally seen as offline by Gitea during cleanup so it isn't handed a new task overlapping the in-progress teardown.

## Test plan

- [x] go test ./internal/pkg/report/... ./act/container/ -run 'TestReporter_ServerCancelStillFlushesFinal|TestBuildWindowsWorkspaceKillScript'
- [x] make fmt && make lint-go - 0 issues
- [x] GOOS=windows go build ./... - clean
- [x] Manual on a Windows runner: trigger a long-running workflow, cancel from Gitea UI; verify (a) the job ends with tail logs + cancelled state in Gitea, (b) workspace cleans up, (c) the runner picks up a new job without restart.

Authored-by: bircni
🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/996
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>

act/container/host_environment.go

@@ -16,9 +16,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
-	"strconv"
 	"strings"
-	"sync"
 	"sync/atomic"
 	"time"
 
@@ -44,9 +42,6 @@ type HostEnvironment struct {
 	CleanUp      func()
 	StdOut       io.Writer
 	AllocatePTY  bool // allocate a pseudo-TTY for each step's process
-
-	mu          sync.Mutex
-	runningPIDs map[int]struct{}
 }
 
 func (e *HostEnvironment) Create(_, _ []string) common.Executor {
@@ -353,24 +348,9 @@ func (e *HostEnvironment) exec(ctx context.Context, command []string, cmdline st
 		go copyPtyOutput(writer, ppty, finishLog)
 		go writeKeepAlive(ppty)
 	}
-	// Split Start/Wait so the PID can be registered before the process can exit;
-	// cmd.Run() would block until exit, by which time the PID may have been reused.
 	if err := cmd.Start(); err != nil {
 		return err
 	}
-	if cmd.Process != nil {
-		e.mu.Lock()
-		if e.runningPIDs == nil {
-			e.runningPIDs = map[int]struct{}{}
-		}
-		e.runningPIDs[cmd.Process.Pid] = struct{}{}
-		e.mu.Unlock()
-		defer func(pid int) {
-			e.mu.Lock()
-			delete(e.runningPIDs, pid)
-			e.mu.Unlock()
-		}(cmd.Process.Pid)
-	}
 	err = cmd.Wait()
 	if err != nil {
 		var exitErr *exec.ExitError
@@ -440,30 +420,80 @@ func removePathWithRetry(ctx context.Context, path string) error {
 	return lastErr
 }
 
+// buildWindowsWorkspaceKillScript builds a PowerShell command that `taskkill
+// /T /F`s every process tree whose ExecutablePath or CommandLine references one
+// of the given absolute workspace dirs, releasing file handles for cleanup.
+//
+// Win32_Process is used because it exposes both ExecutablePath and CommandLine
+// (Get-Process doesn't, wmic is deprecated). Both match the dir+separator
+// prefix, so a sibling dir sharing a name prefix (job1 vs job10) is spared.
+// Ordinal String methods, not -like, so path metacharacters ([ ] ? *) stay
+// literal.
+//
+// Pure function so the quote-escaping can be unit-tested without PowerShell.
+func buildWindowsWorkspaceKillScript(dirs []string) string {
+	quoted := make([]string, len(dirs))
+	for i, d := range dirs {
+		// Single-quoted PowerShell literal; escape ' by doubling it.
+		quoted[i] = "'" + strings.ReplaceAll(d, "'", "''") + "'"
+	}
+
+	return `$paths = @(` + strings.Join(quoted, ",") + `)
+$selfPid = $PID
+Get-CimInstance Win32_Process -ErrorAction SilentlyContinue | Where-Object {
+    if ($_.ProcessId -eq $selfPid) { return $false }
+    foreach ($p in $paths) {
+        $prefix = $p + '\'
+        if ($_.ExecutablePath -and $_.ExecutablePath.StartsWith($prefix, [System.StringComparison]::OrdinalIgnoreCase)) { return $true }
+        if ($_.CommandLine -and $_.CommandLine.IndexOf($prefix, [System.StringComparison]::OrdinalIgnoreCase) -ge 0) { return $true }
+    }
+    return $false
+} | ForEach-Object {
+    & taskkill.exe /PID $_.ProcessId /T /F 2>$null | Out-Null
+}
+`
+}
+
 func (e *HostEnvironment) terminateRunningProcesses(ctx context.Context) {
 	if runtime.GOOS != "windows" {
 		return
 	}
-	e.mu.Lock()
-	pids := make([]int, 0, len(e.runningPIDs))
-	for pid := range e.runningPIDs {
-		pids = append(pids, pid)
-	}
-	e.mu.Unlock()
 
-	if len(pids) == 0 {
+	// Detached: exec.CommandContext won't start on a cancelled ctx, and a
+	// server cancel has already cancelled the parent ctx.
+	killCtx, killCancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer killCancel()
+
+	logger := common.Logger(ctx)
+
+	// Workspace dirs we own. Any process running from or referencing one is a
+	// leftover job process. ToolCache is shared across jobs; Workdir only when
+	// we own it (else it's a caller-provided checkout, e.g. act local mode).
+	owned := []string{e.Path, e.TmpDir}
+	if e.CleanWorkdir {
+		owned = append(owned, e.Workdir)
+	}
+	dirs := make([]string, 0, len(owned))
+	for _, d := range owned {
+		if d == "" {
+			continue
+		}
+		abs, err := filepath.Abs(d)
+		if err != nil {
+			continue
+		}
+		dirs = append(dirs, abs)
+	}
+	if len(dirs) == 0 {
 		return
 	}
 
-	logger := common.Logger(ctx)
-	for _, pid := range pids {
-		// Best-effort: forcibly terminate process tree to release file handles
-		// so that workspace cleanup can succeed on Windows.
-		cmd := exec.CommandContext(ctx, "taskkill", "/PID", strconv.Itoa(pid), "/T", "/F")
-		out, err := cmd.CombinedOutput()
-		if err != nil {
-			logger.Debugf("taskkill failed for pid=%d: %v output=%s", pid, err, strings.TrimSpace(string(out)))
-		}
+	script := buildWindowsWorkspaceKillScript(dirs)
+
+	cmd := exec.CommandContext(killCtx, "powershell.exe", "-NoProfile", "-NonInteractive", "-Command", script)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		logger.Debugf("workspace process-tree kill via PowerShell failed: %v output=%s", err, strings.TrimSpace(string(out)))
 	}
 }
 
@@ -477,14 +507,20 @@ func (e *HostEnvironment) Remove() common.Executor {
 		if e.CleanUp != nil {
 			e.CleanUp()
 		}
+
+		// Detach: a cancelled ctx would skip removePathWithRetry's retries,
+		// which absorb Windows file-handle release lag after the kill above.
+		rmCtx, rmCancel := context.WithTimeout(context.Background(), 30*time.Second)
+		defer rmCancel()
+
 		logger := common.Logger(ctx)
 		var errs []error
-		if err := removePathWithRetry(ctx, e.Path); err != nil {
+		if err := removePathWithRetry(rmCtx, e.Path); err != nil {
 			logger.Warnf("failed to remove host misc state %s: %v", e.Path, err)
 			errs = append(errs, err)
 		}
 		if e.CleanWorkdir {
-			if err := removePathWithRetry(ctx, e.Workdir); err != nil {
+			if err := removePathWithRetry(rmCtx, e.Workdir); err != nil {
 				logger.Warnf("failed to remove host workspace %s: %v", e.Workdir, err)
 				errs = append(errs, err)
 			}