OpenClaw upstream issue draft: sessions_spawn subagent parameter handling

Title

sessions_spawn tool mishandles runtime="subagent" with streamTo:"parent", and wrongly treats model:"default" as a literal model override

Summary

While using the built-in sessions_spawn tool against an npm-installed OpenClaw 2026.4.22, I hit two user-facing regressions in the tool wrapper for runtime="subagent":

1. streamTo:"parent" is parsed before runtime gating, so a caller/tooling layer that includes that field causes an immediate tool error for subagent runs:
   • streamTo is only supported for runtime=acp; got runtime=subagent
2. model:"default" is forwarded as a literal override instead of being normalized to “no explicit override”, which later resolves to an invalid model ref like:
   • model not allowed: openai/default

Both are fixable in the sessions_spawn tool wrapper without changing subagent runtime behavior.

Affected version

• OpenClaw 2026.4.22 (00bd2cf)
• Install kind: npm package on Windows

Reproduction

Case 1: subagent + streamTo

Call the tool equivalent of:

{
  "runtime": "subagent",
  "task": "Reply with OK",
  "streamTo": "parent",
  "mode": "run",
  "lightContext": true
}

Observed:

streamTo is only supported for runtime=acp; got runtime=subagent

Expected:

• For runtime="subagent", ignore ACP-only streamTo instead of failing the spawn.
• This matters because some caller layers/tool wrappers may always include streamTo:"parent".

Case 2: subagent + model="default"

Call the tool equivalent of:

{
  "runtime": "subagent",
  "task": "Reply with OK",
  "mode": "run",
  "lightContext": true,
  "model": "default"
}

Observed before fix:

model not allowed: openai/default

Expected:

• model:"default" should be normalized to no explicit override so subagent selection falls back to the configured default model.

Root cause

In dist/openclaw-tools-D2PgzZeK.js inside createSessionsSpawnTool(...):

• streamTo is derived unconditionally from params, then rejected for non-ACP runtime.
• model is read directly from params and forwarded unchanged, so the sentinel string default becomes a real override candidate.

Minimal fix

Two targeted wrapper changes were sufficient locally:

1. Only materialize streamTo when runtime === "acp"
2. Normalize model === "default" to undefined

Conceptually:

const modelOverrideRaw = readStringParam(params, "model");
const modelOverride = modelOverrideRaw === "default" ? undefined : modelOverrideRaw;

const streamTo = runtime === "acp" && params.streamTo === "parent"
  ? "parent"
  : undefined;

Verification

After applying those two wrapper changes locally:

• runtime:"subagent" spawn succeeds even when streamTo:"parent" is present
• runtime:"subagent", model:"default" also succeeds and child run completes normally

Notes

I used a local hotfix script against the packaged dist file to confirm the behavior. If useful, I can also turn this into a PR against the source tree once the canonical source file/path is pointed out.