fix(claude): collapse invalid tool_call Arguments to empty object (not just empty)

[gutopolewacz]

What

convSchemaMessage (components/model/claude/claude.go) only collapsed an empty tool-call Arguments to "{}" before wrapping it in json.RawMessage. A non-empty but invalid Arguments — typically a streamed tool_use truncated mid-payload (the input_json_delta chunks are cut before the JSON object closes) — was passed through raw, so ToolUseBlockParam.MarshalJSON failed on the next request re-assembly:

[NodeRunError] create new streaming message fail: ... *anthropic.ToolUseBlockParam:
json: error calling MarshalJSON for type json.RawMessage: unexpected end of JSON input

This is the same crash as #462 (empty arg, already fixed by the if args == "" guard) and the same family as #304 — but for the invalid/truncated sub-case, which the guard didn't cover. Closes #894.

How

Generalize the existing guard to any non-valid-JSON Arguments via json.Valid:

if args == "" || !json.Valid([]byte(args)) {
    args = "{}"
}

Valid JSON passes through unchanged; empty/invalid both collapse to a valid empty object so marshaling succeeds and the run continues (the model gets a normal tool result and can retry) instead of crashing. encoding/json is already imported.

Tests

Added Test_convSchemaMessage_ToolCallArguments covering: valid args pass through, empty → {}, truncated → {}, malformed → {}, and asserting the assembled MessageParam marshals without error.

Note: I couldn't run the package test binary locally — mockey v1.2.13 fails to build on my toolchain (go1.26 / darwin-arm64: relocation target runtime.duffcopy not defined), which is unrelated to this change (it fails for any test in the package). The non-test package builds and go vet is clean; CI should exercise the new test on a compatible toolchain. The new test does not use mockey.

Why it helps others

We hit this in production in a Go agent harness on Eino's DeepAgent: an agent asked to write a large JSON file in one write_file had its tool_use stream truncate, crashing the whole turn. We worked around it downstream by wrapping the public model interface and sanitizing Arguments on the model boundary — but that's a per-consumer patch for what is a one-line generalization here. Fixing it upstream protects every Eino+Claude streaming user against the same crash, exactly as the empty-arg guard already does.

[CLAassistant]

All committers have signed the CLA.

[gutopolewacz]

Rebased onto latest main and resolved the conflict in claude_test.go (both TestVertexServiceAccountJSON and the new Test_convSchemaMessage_ToolCallArguments now coexist). The fix in claude.go is unchanged. CI was green before the rebase — would appreciate a review when someone has a moment. Thanks!