fix: go to file in big non-git folders; linear reply handling

- find/git producers piped into head tolerate SIGPIPE, so hitting a cap no
  longer fails the command (and lets ttyd truncate its reply).
- fs-find outside git skips build/cache folders and caps at 10000.
- runCommand checks completion on the stream's tail instead of re-decoding
  the whole reply on every frame.

Refs #37

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/attach.bats

@@ -611,6 +611,12 @@ blob_body() {
     rm -rf "$p/.git"
     run devdesk attach --fs-find alpha
     [ "$(jq -r '.files | sort | join(",")' <<<"$output")" = ".gitignore,debug.log,src/a.js" ]
+    # Hitting the cap must not fail the command (SIGPIPE in the producer).
+    for i in $(seq 1 3000); do : >"$p/src/f$i.txt"; done
     run env DEVDESK_FS_FIND_MAX=1 "$REPO/bin/devdesk" attach --fs-find alpha
+    [ "$status" -eq 0 ]
     [ "$(jq -r '[(.files | length), .truncated] | @tsv' <<<"$output")" = "$(printf '1\ttrue')" ]
+    run env DEVDESK_FS_LIST_MAX=5 "$REPO/bin/devdesk" attach --fs-list alpha src
+    [ "$status" -eq 0 ]
+    [ "$(jq -r '[(.entries | length), .truncated] | @tsv' <<<"$output")" = "$(printf '5\ttrue')" ]
 }