question tool: model omits required "header" on later multi-question entries, producing SchemaError

Description

Same root cause as #45524 (insufficient per-entry guidance for repeated questions[] items), but for header instead of question.

When the question tool is called with multiple entries in questions[], the model occasionally omits the required header field on the second or later entries. The schema correctly rejects the call with SchemaError(Missing key at ["questions"][1]["header"]), and a retry usually succeeds, but the failure recurs because later entries are structurally abbreviated and the model-facing tool description never stated that every entry needs its own header.

Impact

• Every occurrence is recorded as an error span in OTel tracing and inflates the opencode.tool.question error rate.
• The question is never surfaced to the user; the interaction is silently lost until a retry succeeds.

Why strict validation should stay: header is meaningful UI data (it labels each question in the prompt), so it cannot be reconstructed deterministically from the question text.

Plugins

No response

OpenCode version

Version 1.18.23

Model: amazon-bedrock/eu.anthropic.claude-sonnet-4-6

Steps to reproduce

Call the question tool with two questions where the second entry omits header:

{
  "questions": [
    {
      "header": "Database",
      "question": "Which database should we use for the new service?",
      "options": [
        { "label": "PostgreSQL", "description": "Relational, ACID-compliant." },
        { "label": "MongoDB", "description": "Document store, flexible schema." }
      ]
    },
    {
      "question": "Which caching strategy should we use?",
      "options": [
        { "label": "Redis", "description": "In-memory, fast." },
        { "label": "None", "description": "Query the database directly." }
      ]
    }
  ]
}

The call fails with SchemaError(Missing key at ["questions"][1]["header"]). A manually constructed call with header present on both entries succeeds; the bug is generative and the schema validator catches it correctly.

Screenshot and/or share link

No response

Operating System

MacOS 26.6.2

Terminal

Warp

Search the TypeScript codebase for the question tool, its questions[] schema, and the model-facing description; begin with the header definition and the guidance for repeated entries. Reproduce the two-entry payload, then verify that each entry is described as requiring its own header and that the call no longer fails with the reported SchemaError.