bb CLI: "Error: fetch failed" discards the error cause, making an unreachable backend indistinguishable from a dead one

[sholub-dev]

Version: bb 0.36.0 (macOS)

Problem

Any backend-touching command fails with no diagnostic information:

$ bb thread list --json
Error: fetch failed

fetch failed is a Node constant used for every fetch failure. The real error is on error.cause and is discarded, so "blocked by a sandbox/firewall" is indistinguishable from "bb is not running".

Steps to reproduce

Point the CLI at an address nothing is serving:

$ BB_SERVER_URL=http://127.0.0.1:1 bb thread list --json
Error: fetch failed

The same output appears for any connect-level failure — refused, blocked, wrong port, wrong host — because the message is a constant. bb status still succeeds throughout, since it reads local files and never contacts the backend, which makes it look like a partial outage.

Root cause

The cause carries the diagnosis. Blocked by a sandbox:

cause = connect EPERM 127.0.0.1:38886
        code=EPERM  errno=-1  syscall=connect  port=38886

EPERM means the server is healthy and the caller isn't permitted to reach it; ECONNREFUSED would mean it's down. That distinction is present in the error object and never surfaces.

Where it is dropped

console.error(`Error: ${ii(r)}`), process.exit(1)

function ii(e){ return e instanceof Error ? e.message : String(e) }

ii reads .message only. grep -c "\.cause" over host-daemon/dist/bb returns 0. The exit code is 1 for all failures, so there is nothing to branch on either.

Fix

function ii(e){
  if (!(e instanceof Error)) return String(e);
  let msg = e.message, c = e.cause;
  while (c instanceof Error) { msg += ': ' + c.message; c = c.cause; }
  return msg;
}

Verified against the live failure:

current   -> Error: fetch failed
unwrapped -> Error: fetch failed: connect EPERM 127.0.0.1:38886 - Local (0.0.0.0:0)

Also worth considering: a distinct exit code for connection failures, and mapping ECONNREFUSED to bb is not running at <serverUrl> and EPERM/EACCES to cannot reach bb at <serverUrl> - connection blocked.