ACP SDK: Optional array parameters without defaults cause Claude schema validation to fail

[Iman-Sharif]

Bug Description

When using Claude models with OpenCode and the ACP (Agent Client Protocol) SDK, tool registration fails with:

This is distinct from #13618 (missing field on object schemas). This issue affects optional array parameters within schemas.

Root Cause

The ACP SDK's Zod schemas define optional array parameters without default values:

When Claude's strict JSON Schema validator processes this, the field becomes instead of , violating the array type requirement.

Affected Schemas

The following schemas in have optional array parameters without defaults:

Schema	Field
	, OPENCLAW_SERVICE_KIND=gateway
NODE_NO_WARNINGS=1
PWD=/root/.openclaw/workspace
LOGNAME=root
SYSTEMD_EXEC_PID=2287751
OPENCLAW_SHELL=exec
HOME=/root
LANG=en_US.UTF-8
TMPDIR=/tmp
INVOCATION_ID=ccf5ed8fdd0d4116827ddb7fc403ef5a
MANAGERPID=572443
OPENCLAW_GATEWAY_PORT=18789
USER=root
OPENCLAW_SYSTEMD_UNIT=openclaw-gateway.service
SHLVL=0
OPENCLAW_SERVICE_MARKER=openclaw
OPENCLAW_PATH_BOOTSTRAPPED=1
OPENCLAW_WINDOWS_TASK_NAME=OpenClaw Gateway
XDG_RUNTIME_DIR=/run/user/0
OPENCLAW_CLI=1
OPENCLAW_SERVICE_VERSION=2026.4.10
JOURNAL_STREAM=8:1247217910
PATH=/root/.bun/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/root/.local/bin:/root/.npm-global/bin:/root/bin:/root/.volta/bin:/root/.asdf/shims:/root/.nvm/current/bin:/root/.fnm/current/bin:/root/.local/share/pnpm
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/0/bus
_=/usr/bin/env
	,
	,
	,

Fix

Add to all optional array parameters in the Zod schemas:

Difference from #13618

• Claude API rejects tool schemas: missing 'required' field causes 'JSON schema is invalid' error #13618: Missing on object schemas (fixed in PR fix(provider): add required field to object schemas for strict validators #8218)
• This issue: Optional array fields without — a separate problem

Environment

• OpenCode: 1.14.20
• @agentclientprotocol/sdk: 0.19.0
• Model: Claude Opus 4.7 via API Pro
• Error occurs when ACP tools register with Claude

Verification

Tested with Claude Opus 4.7:

• Without fix:
• With fix: Tools register successfully, both GPT and Claude work correctly

Related

• Claude API rejects tool schemas: missing 'required' field causes 'JSON schema is invalid' error #13618: Claude API rejects tool schemas: missing 'required' field
• fix(provider): add required field to object schemas for strict validators #8218: fix(provider): add required field to object schemas for strict validators
• ACP SDK: Missing default values for optional array parameters cause Claude tool schema validation to fail openclaw/openclaw#69849: Same issue reported for OpenClaw's bundled ACP SDK

[Iman-Sharif]

Additional Context: Recommended Fix Location

After deeper analysis, the ideal fix belongs in OpenCode's provider transform layer (similar to PR #8218's approach), not the ACP SDK itself.

Why Transform Layer is Better

The root cause is that Zod's converts arrays to JSON Schema without defaults:

Claude's strict validator rejects this when the value is .

Suggested Fix

In , alongside the existing from PR #8218, add:

This would:

• Fix the issue for ALL ACP SDK versions
• Be provider-gated (could apply only to Claude if needed)
• Follow the same pattern as the merged PR fix(provider): add required field to object schemas for strict validators #8218

Affected Tools

The , , , and other ACP lifecycle tools all exhibit this issue with their , , , OPENCLAW_SERVICE_KIND=gateway
NODE_NO_WARNINGS=1
PWD=/root/.openclaw/workspace
LOGNAME=root
SYSTEMD_EXEC_PID=2287751
OPENCLAW_SHELL=exec
HOME=/root
LANG=en_US.UTF-8
TMPDIR=/tmp
INVOCATION_ID=ccf5ed8fdd0d4116827ddb7fc403ef5a
MANAGERPID=572443
OPENCLAW_GATEWAY_PORT=18789
USER=root
OPENCLAW_SYSTEMD_UNIT=openclaw-gateway.service
SHLVL=0
OPENCLAW_SERVICE_MARKER=openclaw
OPENCLAW_PATH_BOOTSTRAPPED=1
OPENCLAW_WINDOWS_TASK_NAME=OpenClaw Gateway
XDG_RUNTIME_DIR=/run/user/0
OPENCLAW_CLI=1
OPENCLAW_SERVICE_VERSION=2026.4.10
JOURNAL_STREAM=8:1247217910
PATH=/root/.bun/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/root/.local/bin:/root/.npm-global/bin:/root/bin:/root/.volta/bin:/root/.asdf/shims:/root/.nvm/current/bin:/root/.fnm/current/bin:/root/.local/share/pnpm
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/0/bus
_=/usr/bin/env array fields.