[BUG] ERESOLVE in a workspace graph with shared dependents exits 1 with no error message

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

This is not just a request to bump a dependency for a CVE

• This is not solely a request to bump a dependency for a CVE

Current Behavior

When an ERESOLVE conflict involves a package with a dense workspace dependents graph, npm prints only A complete log of this run can be found in and exits 1. Building the full eresolve-report.txt throws RangeError: Invalid string length, and that error is never printed or written to the debug log. Below the crash threshold the report still grows exponentially (400 MB at 28 workspaces).

Expected Behavior

The normal ERESOLVE message is printed, and the full report stays a reasonable size.

Steps To Reproduce

mkdir x && cd x
echo '{"name":"root","workspaces":["w/*"],"dependencies":{"react":"17.0.2"}}' > package.json
# w0 -> react; wN -> w(N-1), w(N-2)
for i in $(seq 0 29); do
  d='"react":"17.0.2"'; [ $i -gt 0 ] && d="\"w$((i-1))\":\"1.0.0\""; [ $i -gt 1 ] && d="$d,\"w$((i-2))\":\"1.0.0\""
  mkdir -p w/w$i && echo "{\"name\":\"w$i\",\"version\":\"1.0.0\",\"dependencies\":{$d}}" > w/w$i/package.json
done
npm i --package-lock-only
npm i react-dom@18.3.1 --package-lock-only; echo "exit=$?"
# expected: "npm error code ERESOLVE ..." then exit=1
# actual: only "npm error A complete log of this run can be found in: ..." then exit=1

Environment

• npm: 12.0.2 and latest (c9876d7ea)
• Node.js: v24.18.0
• OS Name: macOS (Darwin 25.6.0)
• npm config: defaults (install-strategy=linked fails the same way)

Run the provided macOS shell reproduction with the listed npm and Node.js versions, starting with the package.json workspace graph and the two npm install commands. Trace where the ERESOLVE report is built and where failures are logged. Done means the reproduction prints the normal ERESOLVE message, exits 1, and the full report remains a reasonable size.