fix(sessions_spawn): silently strip ACP-only fields for runtime=subagent by skernelx · Pull Request #68397 · openclaw/openclaw

skernelx · 2026-04-18T04:11:36Z

Summary

sessions_spawn currently hard-errors when runtime="subagent" receives streamTo or resumeSessionId, even though the subagent code path never consumes either field. Schema-strict providers (most notably gpt-5.4 via the OpenAI bridge) auto-fill every advertised tool parameter on every call regardless of the runtime value the model also picks, which makes subagent spawns fail 90%+ of the time for those models.

This PR switches the two ACP-only fields from "reject with error" to "silently drop when runtime!=='acp'". ACP semantics are unchanged — when runtime==='acp' the fields flow through unmodified and the existing ACP spawn logic validates them.

Why the silent-drop approach

The subagent branch never reads streamTo / resumeSessionId, so dropping them has no observable effect on the subagent code path.
Schema filtering per-runtime would be the cleaner long-term fix but requires reworking the shared tool-schema pipeline (tracked in Feature: Per-agent tool schema parameter filtering (slim tool definitions for subagents) #59225, sessions_spawn tool schema includes ACP-only fields that break non-native OpenAI providers #66719). Silent-drop unblocks affected users today without that churn.
Hard-erroring loses to a predictable failure mode that many downstream models cannot avoid — the model doesn't know the field is ACP-only because the schema doesn't tell it.

Related issues

Addresses (non-exhaustive):

sessions_spawn auto-injects streamTo:"parent" for runtime="subagent" and causes hard failure #68275 — sessions_spawn auto-injects streamTo:"parent" for runtime="subagent"
[Bug]: sessions_spawn(runtime="subagent") still fails on 2026.4.14 with ACP-only streamTo under GPT-5.4 #67248 — sessions_spawn(runtime="subagent") fails on 2026.4.14 with ACP-only streamTo under GPT-5.4
sessions_spawn rejects subagent runtime when streamTo is auto-filled by strict-mode providers #64714 — sessions_spawn rejects subagent runtime when streamTo is auto-filled by strict-mode providers
sessions_spawn: LLMs pass streamTo for subagent runtime causing 100% spawn failures #63120 — LLMs pass streamTo for subagent runtime causing 100% spawn failures
sessions_spawn(runtime="subagent") fails with "streamTo is only supported for runtime=acp" #61724 — sessions_spawn(runtime="subagent") fails with "streamTo is only supported for runtime=acp"
sessions_spawn schema allows streamTo for runtime=subagent but execute rejects it #60965 — sessions_spawn schema allows streamTo for runtime=subagent but execute rejects it
sessions_spawn(runtime="subagent") can fail because unified schema exposes ACP-only streamTo #59390 — unified schema exposes ACP-only streamTo to subagent spawns
[Bug]: sessions_spawn(runtime="subagent") can receive ACP-only streamTo from the current tool-call bridge #56193 — sessions_spawn(runtime="subagent") can receive ACP-only streamTo from tool-call bridge
Bug: sessions_spawn exposes ACP-only fields and breaks runtime=subagent with schema-following models #56326 — sessions_spawn exposes ACP-only fields and breaks runtime=subagent with schema-following models
[Feature]: Make sessions_spawn more forgiving for ACP-only fields in subagent runtime #53370 — Make sessions_spawn more forgiving for ACP-only fields in subagent runtime
Bug: streamTo in sessions_spawn breaks subagent runtime #43556 — Bug: streamTo in sessions_spawn breaks subagent runtime

Test plan

Updated existing rejects resumeSessionId without runtime=acp and rejects streamTo when runtime is not "acp" cases to assert the new silent-drop contract: the tool forwards to spawnSubagentDirect without the ACP-only keys and returns no error.
Unchanged: runtime=acp path still passes streamTo / resumeSessionId through to spawnAcpDirect (existing tests at lines 177, 226 still cover this).
Suggested: add an integration test that round-trips a runtime="subagent" call with streamTo="parent" through the tool-call bridge to catch future regressions at the schema layer.

greptile-apps · 2026-04-18T04:13:22Z

Greptile Summary

Switches sessions_spawn from hard-erroring to silently dropping streamTo and resumeSessionId when runtime !== "acp". Both fields are now only read/computed on the ACP branch, so schema-strict providers (e.g. gpt-5.4) that auto-fill every advertised parameter can no longer cause subagent spawns to fail. The ACP code path is entirely unchanged.

Confidence Score: 5/5

Safe to merge — no P0/P1 issues; only a minor schema description wording nit remains.

The logic change is minimal and correctly scoped: the subagent call never forwarded these fields before this PR, so the only behavioral delta is that non-ACP callers no longer receive an error result. ACP semantics are fully preserved. Tests are updated to verify both the drop and the continued pass-through for ACP.

No files require special attention.

Comments Outside Diff (1)

src/agents/tools/sessions-spawn-tool.ts, line 92-96 (link)

Schema description no longer reflects actual behavior

The description string still says Requires runtime="acp" but the field is now silently dropped for non-ACP runtimes rather than rejected. A schema-strict model reading this description could still try to honour the constraint, but a human reading the tool schema will see an enforced requirement that no longer exists. A small wording update keeps the schema honest:

Prompt To Fix With AI

This is a comment left during a code review.
Path: src/agents/tools/sessions-spawn-tool.ts
Line: 92-96

Comment:
**Schema description no longer reflects actual behavior**

The `description` string still says `Requires runtime="acp"` but the field is now silently dropped for non-ACP runtimes rather than rejected. A schema-strict model reading this description could still try to honour the constraint, but a human reading the tool schema will see an enforced requirement that no longer exists. A small wording update keeps the schema honest:



How can I resolve this? If you propose a fix, please make it concise.

Prompt To Fix All With AI

This is a comment left during a code review.
Path: src/agents/tools/sessions-spawn-tool.ts
Line: 92-96

Comment:
**Schema description no longer reflects actual behavior**

The `description` string still says `Requires runtime="acp"` but the field is now silently dropped for non-ACP runtimes rather than rejected. A schema-strict model reading this description could still try to honour the constraint, but a human reading the tool schema will see an enforced requirement that no longer exists. A small wording update keeps the schema honest:

```suggestion
  resumeSessionId: Type.Optional(
    Type.String({
      description:
        'Resume an existing agent session by its ID (e.g. a Codex session UUID from ~/.codex/sessions/). Only applies when runtime="acp"; silently ignored for runtime="subagent". The agent replays conversation history via session/load instead of starting fresh.',
    }),
  ),
```

How can I resolve this? If you propose a fix, please make it concise.

_{Reviews (1): Last reviewed commit: "fix(sessions_spawn): silently strip ACP-..." | Re-trigger Greptile}

Schema-following LLMs (notably gpt-5.4) auto-fill every advertised tool parameter, including streamTo and resumeSessionId, regardless of the runtime value they also set. Under runtime="subagent" the executor rejected those fields with a hard error, making subagent spawn effectively unusable for these models (see openclaw#43556, openclaw#56193, openclaw#63120, Since the subagent code path never reads either field, treat them as no-ops when runtime!=="acp" instead of failing. ACP semantics are unchanged: when runtime==="acp" the fields still flow through unmodified and the existing ACP spawn logic validates them. Tests updated to match the new silently-drop behavior.

vincentkoc · 2026-04-26T19:03:28Z

ProjectClownfish could not safely update this branch, so it opened a narrow replacement PR instead.

Replacement PR: #72331
Source PR: #68397
Contributor credit is preserved in the replacement PR body and changelog plan.

vincentkoc · 2026-04-26T20:34:46Z

ProjectClownfish could not safely update this branch, so it opened a narrow replacement PR instead.

Replacement PR: #72331
Source PR: #68397
Contributor credit is preserved in the replacement PR body and changelog plan.

vincentkoc · 2026-04-27T05:38:35Z

ProjectClownfish could not safely update this branch, so it opened a narrow replacement PR instead.

Replacement PR: #72614
Source PR: #68397
Contributor credit is preserved in the replacement PR body and changelog plan.

vincentkoc · 2026-04-27T06:07:46Z

ProjectClownfish could not safely update this branch, so it opened a narrow replacement PR instead.

Replacement PR: #72331
Source PR: #68397
Contributor credit is preserved in the replacement PR body and changelog plan.

openclaw-barnacle Bot added agents Agent runtime and tooling size: XS labels Apr 18, 2026

skernelx force-pushed the fix/sessions-spawn-strip-acp-only-fields branch from b6941a7 to b2e15de Compare April 20, 2026 10:29

openclaw-barnacle Bot added size: S and removed size: XS labels Apr 20, 2026

skernelx force-pushed the fix/sessions-spawn-strip-acp-only-fields branch from b2e15de to e5c2067 Compare April 20, 2026 10:34

skernelx closed this Apr 26, 2026

vincentkoc mentioned this pull request Apr 26, 2026

fix(sessions_spawn): tolerate ACP-only fields for subagent runtime #72331

Merged

clawsweeper Bot mentioned this pull request Apr 27, 2026

[Bug]: sessions_spawn(runtime="subagent") still fails on 2026.4.14 with ACP-only streamTo under GPT-5.4 #67248

Closed

vincentkoc mentioned this pull request Apr 27, 2026

fix(sessions_spawn): tolerate ACP-only fields for subagent runtime #72614

Merged

This was referenced Apr 27, 2026

sessions_spawn rejects subagent runtime when streamTo is auto-filled by strict-mode providers #64714

Closed

Feature: Per-agent tool schema parameter filtering (slim tool definitions for subagents) #59225

Closed

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fix(sessions_spawn): silently strip ACP-only fields for runtime=subagent#68397

fix(sessions_spawn): silently strip ACP-only fields for runtime=subagent#68397
skernelx wants to merge 1 commit into
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skernelx:fix/sessions-spawn-strip-acp-only-fields

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skernelx commented Apr 18, 2026

Summary

Why the silent-drop approach

Related issues

Test plan

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Greptile Summary

Confidence Score: 5/5

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greptile-apps Bot commented Apr 18, 2026 •

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