fix(session): distinguish malformed known-tool input from unknown tools

[johanhallberg]

Issue for this PR

Fixes #25789

Type of change

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

What does this PR do?

This PR distinguishes two different tool-call repair failure cases:

1. A model calls a tool that does not exist.
2. A model calls a valid/known tool, but the tool input is malformed.

Previously, both cases were routed through the invalid tool in a way that made malformed input for a valid tool look like a generic invalid/unknown tool call.

The change extracts the classification logic into repairToolCallFailure() and keeps the existing lowercase tool-name repair behavior.

The invalid tool now accepts optional type and hint fields so callers can distinguish:

• unknown_tool
• known_tool_invalid_input

This gives users and maintainers clearer feedback when a valid tool was selected but its input could not be parsed.

How did you verify your code works?

Tested locally with:

cd packages/opencode
bun test --timeout 30000 test/session/llm.test.ts
bun test --timeout 30000 test/tool/parameters.test.ts
bun run typecheck

Results:

• test/session/llm.test.ts: 17 pass, 0 fail
• test/tool/parameters.test.ts: 54 pass, 0 fail
• bun run typecheck: pass

I also ran a manual smoke test with a patched source build:

• normal write tool usage still works
• large single-write requests still work
• intentionally unknown tool calls are reported as unknown_tool
• malformed input for a known tool is covered by regression tests

Screenshots / recordings

N/A — this is not a UI change.

Checklist

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

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

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

Based on my search, I found two potentially related PRs:

1. PR fix: Repair truncated JSON tool inputs in LLM session #24289: "fix: Repair truncated JSON tool inputs in LLM session"

   • Related because it also addresses tool input repair and validation in LLM sessions

2. PR fix: prevent invalid tool from leaking into model error messages #23264: "fix: prevent invalid tool from leaking into model error messages"

   • Related because it deals with how invalid tool calls are handled and reported in the session

These PRs share similar concerns around tool-call handling, error classification, and session management, though they may be addressing different aspects of the problem.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[johanhallberg]

Thanks — I checked the related issues.

This PR is intentionally narrow. It does not try to solve all malformed/truncated tool-call recovery behavior. It only distinguishes the repair result for two cases that currently collapse into the same invalid path:

1. unknown tool name → type: "unknown_tool"
2. known tool name with malformed/unparseable input → type: "known_tool_invalid_input"

This should complement, not replace, the broader recovery work discussed in #18108, #15906, and #21900.

The goal is to give downstream handling and users a clearer error classification without changing the existing lowercase tool-name repair behavior.

[github-actions]

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