fix(opencode): skip invalid agent config files instead of crashing startup

[NumerousJLs]

Issue for this PR

Closes #31481
Closes #27133

Type of change

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

What does this PR do?

Skips an invalid agent or mode config file instead of crashing startup or dropping it without an explanation.

Before this change, load() validated each agent file with ConfigParse.schema(), which throws whenever a file does not match the schema. A single malformed file, such as a Cursor-format agent where tools is a YAML array instead of an object, would throw partway through the loop, so none of the agents loaded and startup failed with "4 of 5 requests failed". The loadMode() function right next to it already skipped invalid files, but it did so silently, so a broken mode would just disappear with no explanation (#27133).

This switches both functions to decode with Schema.decodeUnknownExit and skip an invalid file with a warning that names it, instead of throwing or dropping it silently. Valid agents and modes still load normally. I left ConfigParse.schema() itself unchanged, since throwing is the right behavior for a single config file like opencode.json.

How did you verify your code works?

• bun typecheck (clean)
• oxlint (0 warnings, 0 errors)
• git diff --check (clean)
• bun test test/config test/agent (233 pass, 3 skip, 0 fail)
• added test/config/agent.test.ts with a valid + invalid file; it throws on the current code and passes after the fix

Screenshots / recordings

N/A

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 my search, I found two related PRs that address similar issues:

Related PRs:

1. PR fix(config): catch parse errors gracefully during startup #29208 - fix(config): catch parse errors gracefully during startup

   • Addresses the same problem of catching parse errors during config loading

2. PR fix(opencode): report invalid agent/mode configs instead of crashing or dropping them #29784 - fix(opencode): report invalid agent/mode configs instead of crashing or dropping them

   • Very closely related; appears to address the exact same issue of reporting invalid agent/mode configs instead of crashing or silently dropping them

These PRs appear to be attempting to solve the same problem that PR #31992 addresses. You should verify whether these earlier PRs were merged, closed, or abandoned, and confirm that #31992 is not a duplicate effort of #29784 in particular, which has an almost identical title and purpose.