Fix error wrapping: use %w for primary child error in tmux action

In runInTmuxChild, the primary failure is the child runFn error; the
echo-through failure is secondary context. Wrap the primary error with
%w (keeping copyErr as %v, since fmt.Errorf allows only one %w) so
errors.Is/As work across the chain.

Audited all other fmt.Errorf %v/%s sites in internal/ and cmd/: they
format strings, ints, status codes, or an []error aggregate (syncer),
none of which is a single primary error to unwrap, so they stay as-is.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/internal/hexaiaction/cmdentry.go b/internal/hexaiaction/cmdentry.go
index ee78307..85e9059 100644
--- a/internal/hexaiaction/cmdentry.go
+++ b/internal/hexaiaction/cmdentry.go
@@ -91,7 +91,10 @@ func runChild(ctx context.Context, infile, outfile string, stdout, stderr io.Wri
 	if err := runFn(ctx, in, out, stderr); err != nil {
 		closeOut()
 		if copyErr := echoThrough(infile, tmp, os.Stdin, stdout); copyErr != nil {
-			return fmt.Errorf("hexai-tmux-action child: %v; echo failed: %v", err, copyErr)
+			// Wrap the primary child error with %w so callers can inspect it
+			// via errors.Is/As; the echo failure is secondary context and
+			// stays as %v (fmt.Errorf supports only a single %w).
+			return fmt.Errorf("hexai-tmux-action child: %w; echo failed: %v", err, copyErr)
 		}
 	} else {
 		closeOut()