Preserve raw JSON in tool result compaction

[Irakli Gabisonia (gabisonia)]

Fixes #1087

ToolResultStrategy currently formats json.RawMessage results as byte numbers. Preserve the JSON text in the summary by converting raw messages directly to strings, while keeping the existing formatting for other result types.

Added regression coverage in the existing compaction test file for raw JSON objects, arrays, null, empty/nil values, and ordinary string and number results. The raw JSON cases fail before the fix and pass afterward.

Validation: go test -race -shuffle=on ./..., golangci-lint (zero issues), and the local reproduction sample against the fix.

[Copilot]

🟢 Approval recommended

No unresolved review comments remain, and regression coverage is included.

Pull request overview

Preserves raw JSON text in tool-result compaction summaries while retaining existing formatting for other result types.

Changes:

• Formats json.RawMessage results directly as strings.
• Adds regression coverage for JSON and scalar result types.

File summaries

File	Description
agent/compaction/toolresult.go	Preserves raw JSON formatting.
agent/compaction/compaction_test.go	Adds formatter regression coverage.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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[github-actions]

Scope: user-visible behavior
Changed Go contract: DefaultToolCallFormatter (agent/compaction/toolresult.go) — internal call-result stringification for *message.FunctionResultContent.Result now special-cases json.RawMessage, converting it to its raw string form instead of fmt.Sprint, which previously rendered json.RawMessage (a []byte alias) as a numeric byte-slice literal (e.g. [123 34 ...]). No exported signature changed.
Upstream evidence reviewed:

• Python python/packages/core/agent_framework/_compaction.py::_tool_result_text — converts Mapping results via json.dumps(...) and falls through to str(value) for everything else, i.e. it never renders JSON-like payloads as raw byte/character-code sequences.
• .NET dotnet/src/Microsoft.Agents.AI/Compaction/ToolResultCompactionStrategy.cs::DefaultToolCallFormatter (line ~195) — resultsByCallId[frc.CallId] = frc.Result?.ToString() ?? string.Empty;, which for a JsonElement/string result yields the readable JSON text, not a numeric array.
  Result: aligned — this fixes a Go-specific bug where fmt.Sprint on json.RawMessage ([]byte) rendered byte-code arrays instead of JSON text, which was a divergence from both upstream implementations' behavior of preserving readable text/JSON in the tool-result summary. The fix restores parity rather than introducing new divergence. No exported API surface changed (signature of DefaultToolCallFormatter and ToolResultStrategy unchanged), so public-api-change is not applicable. Test coverage (TestDefaultToolCallFormatter_ResultTypes) matches the categories of inputs handled by the upstream formatters (objects, arrays, null, empty, plain string/number).

Generated by Go API Consistency Review Agent · copilot · auto · 27.8 AIC · ⌖ 5.38 AIC · ⊞ 9.6K · ◷

[Quim Muntal (qmuntal)]

Thanks!