Keep worktrees git could not read, never delete them

Any git error on a directory under the worktree root was classified orphan,
and orphan deletes the directory outright, so a transient failure reading the
source root became data loss on a plain `agentws prune --yes`.

- prove a backing repo gone by stat before calling a directory an orphan
- classify an unexplained git failure as keep, naming the error
- refuse to remove a worktree whose git state is unknown, even with --include-keep
- spell out that --include-keep discards uncommitted and in-progress work

cmd/agentws/prune.go

@@ -88,7 +88,7 @@ func newPruneCmd() *cobra.Command {
 	f.BoolVar(&opts.keepBranches, "keep-branches", false, "Never delete a local branch, whatever the classification")
 	f.BoolVar(&opts.noFetch, "no-fetch", false, "Do not fetch; judge against the refs already on disk")
 	f.BoolVar(&opts.jsonOut, "json", false, "Emit JSON instead of a table")
-	f.BoolVar(&opts.includeKeep, "include-keep", false, "Dangerous: also remove worktrees classified keep (needs --yes; never deletes their branch)")
+	f.BoolVar(&opts.includeKeep, "include-keep", false, "Dangerous: also remove worktrees classified keep (needs --yes). Destroys uncommitted changes and paused rebase/merge state, which no branch is carrying; only the branch itself survives")
 	f.BoolVar(&opts.includeUnmanaged, "include-unmanaged", false, "Also remove worktrees that live outside the worktree root")
 	return cmd
 }
@@ -142,11 +142,15 @@ func classifyAll(notes io.Writer, prs prLister, worktrees []managedWt, opts prun
 	byRepo := map[string][]managedWt{}
 	var results []pruneResult
 	for _, w := range worktrees {
-		if w.orphan {
+		switch {
+		case w.inspectErr != nil:
+			// Unknown is not gone: a checkout git refused to answer for keeps.
+			results = append(results, pruneResult{wt: w, verdict: verdictKeep, reason: "inspection failed: " + oneLine(w.inspectErr.Error())})
+		case w.orphan:
 			results = append(results, pruneResult{wt: w, verdict: verdictRemove, reason: "backing repo gone, no git state to read"})
-			continue
+		default:
+			byRepo[w.srcDir] = append(byRepo[w.srcDir], w)
 		}
-		byRepo[w.srcDir] = append(byRepo[w.srcDir], w)
 	}
 
 	srcDirs := make([]string, 0, len(byRepo))
@@ -159,14 +163,14 @@ func classifyAll(notes io.Writer, prs prLister, worktrees []managedWt, opts prun
 		ctx, err := newRepoCtx(notes, prs, srcDir, opts.noFetch)
 		if err != nil {
 			for _, w := range byRepo[srcDir] {
-				results = append(results, pruneResult{wt: w, verdict: verdictKeep, reason: "repo state unknown: " + err.Error()})
+				results = append(results, pruneResult{wt: w, verdict: verdictKeep, reason: "repo state unknown: " + oneLine(err.Error())})
 			}
 			continue
 		}
 		for _, w := range byRepo[srcDir] {
 			res, err := classify(w, ctx)
 			if err != nil {
-				res = pruneResult{wt: w, verdict: verdictKeep, reason: "inspection failed: " + err.Error()}
+				res = pruneResult{wt: w, verdict: verdictKeep, reason: "inspection failed: " + oneLine(err.Error())}
 			}
 			results = append(results, res)
 		}
@@ -210,6 +214,11 @@ func report(out io.Writer, results []pruneResult, opts pruneOpts) error {
 	return tw.Flush()
 }
 
+// oneLine flattens a git error onto a single line so one row stays one row.
+func oneLine(s string) string {
+	return strings.Join(strings.Fields(s), " ")
+}
+
 func dash(s string) string {
 	if s == "" {
 		return "-"