fix(opencode): repair malformed JSON in tool call arguments

[ahamza360]

Issue for this PR

Closes #23065

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This PR fixes the recurring JSON parsing errors that occur when LLMs generate malformed/truncated JSON for tool call arguments.

Problem:
LLMs occasionally generate malformed/truncated JSON for tool call arguments, resulting in "JSON parsing failed" errors.

Solution:
Enhanced the experimental_repairToolCall callback in packages/opencode/src/session/llm.ts with improved JSON repair logic that:

• Detects JSON parsing errors in tool call arguments
• Attempts to repair common truncation issues:
  • Unterminated strings ("value → "value")
  • Missing closing brackets/braces ({ "key": "value" → { "key": "value" })
  • Nested structure completion
  • Complex cases like duplicated/overlapping JSON objects
• Falls back to existing 'invalid' tool handler if repair fails

This makes opencode more robust when dealing with imperfect LLM JSON output.

How did you verify your code works?

• Created unit tests covering various malformed JSON cases including complex scenarios
• Built and tested a working binary with the fix
• Verified the solution resolves the JSON parsing errors including the specific case with confluence_confluence_search_content

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on the search results, I found two potentially related PRs:

1. PR fix(opencode): tolerate wrapped workflow tool arguments #20769 - fix(opencode): tolerate wrapped workflow tool arguments

   • Related to handling tool argument parsing issues

2. PR fix(opencode): recover from truncated tool calls instead of failing silently #21688 - fix(opencode): recover from truncated tool calls instead of failing silently

   • Directly addresses truncated tool call recovery, which overlaps with the truncation handling in PR fix(opencode): repair malformed JSON in tool call arguments #23067

These PRs may have addressed related JSON/tool call argument issues. You should verify if they already implement similar repair logic or if this PR provides additional improvements over the previous truncation handling.