SDK AJV crash after successful multi-turn execution with --agent flag

[nick-inkeep]

Description

When using --agent flag to load a custom agent definition, the SDK crashes with an AJV validation error after successfully completing multiple turns and spending API credits. This is different from issues #852/#892 which crash on initialization.

Environment

• Action version: Tested both @v1 (SHA:6867bb3ab0b2c0a10629b6823e457347e74ad6d2) and pinned @01e756b (SDK 0.2.25)
• Agent SDK versions: Both 0.2.31 and 0.2.25 exhibit the issue
• Custom agent: Using --agent pr-review with a custom .claude/agents/pr-review.md definition

Key Observations

• Work completes successfully: 4 turns, $0.27 cost, 17 seconds
• Crash happens post-execution: After the result JSON is emitted
• Comments are partially posted: The review work succeeds before the crash

Error Output

{
  "type": "result",
  "subtype": "success",
  "is_error": true,
  "duration_ms": 16752,
  "num_turns": 4,
  "total_cost_usd": 0.27037100000000003,
  "permission_denials": []
}
SDK execution error: 14 |     depsCount: ${Q},
15 |     deps: ${$}}`};var Pj={keyword:"dependencies"...

error: Claude Code process exited with code 1

Workflow Configuration

- name: Run PR Review
  uses: anthropics/claude-code-action@01e756b34ef7a1447e9508f674143b07d20c2631
  with:
    anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
    claude_args: |
      --agent pr-review
      --allowedTools "Task,Read,Grep,Glob,mcp__github_inline_comment__create_inline_comment,Bash(git diff:*),Bash(git log:*),Bash(gh pr comment:*),Bash(gh api:*)"
    prompt: Review PR #${{ github.event.pull_request.number }}.

Difference from #852/#892

Issue #852/#892	This Issue
Crashes on turn 1, $0 cost	Crashes after 4+ turns, $0.27 spent
SDK initialization failure	Post-execution validation failure
No API calls made	Work completes successfully
Pinning to SDK 0.2.25 fixes it	Pinning does NOT fix it

Hypothesis

The crash appears to happen during output serialization/validation when the agent response contains certain structures. The custom agent may produce output that triggers a bug in AJV's schema validation when the SDK tries to process the result.

Workaround Attempts

• ❌ Pinned to SDK 0.2.25 (@01e756b) - same crash
• ❌ Different allowedTools combinations - same crash

Repository

https://github.com/inkeep/agents (private, can provide access if needed)

Failed runs: https://github.com/inkeep/agents/actions/runs/21688290864