fix(core): treat blank subagent optionals as absent

[K-Mistele]

Problem

In production, Codex sessions on gpt-5.6-sol intermittently emit agent tool calls with every schema property present, using "" for fields they mean to omit:

{"skill": "", "prompt": "...", "agent_id": "", "fork_turns": "", "description": "...", "subagent_type": "rpi:codebase-analyzer"}

parseSubagentCommand rejected these with Error: agent_id must not be blank. — every subagent dispatch in the affected sessions failed (example prod session: 019ff92b-9c3b-70cf-93c5-74aeb76d9389, 6/6 agent calls errored and the model gave up on subagents).

The schema we send is correct (required: ["prompt"], strict: false); the blank-filling is upstream model serving variance — the same host, build, and settings produce omitted-style calls most of the time and blank-filled episodes at others. We can't control that, so blank must mean absent.

Fix

Normalize blank/whitespace optional strings to undefined before validation:

• blank agent_id / subagent_type / skill / description parse as absent
• blank fork_turns falls back to the 'all' default
• blank selectors no longer count toward the mutual-exclusivity check (real ones still do)
• blank prompt is still an error

With this, the failing production calls parse exactly as intended (dispatch-role and fork commands).

Testing

• Updated subagent-tool.test.ts expectations and added a test covering the exact blank-filled production shape
• bun test in agentlayer-core: 506 pass / 0 fail; agents/codelayer: 116 pass / 0 fail
• tsgo --noEmit clean

🤖 Generated with Claude Code

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