fix(adk): preserve non-UI tool results in MCP app model result callback

[harrisleesh]

Fixes #2716

What

Ports the Python fix from #2579 (compact_mcp_app_response in kagent-adk) to the Go ADK. MakeMCPAppModelResultCallback gated compaction purely on the tool name: once a tool declared _meta.ui.resourceUri at ListTools time (via agentVisibleToolFilter), every non-error result from it was collapsed into mcpAppRenderedNotice — even a call that returned plain text with no _meta.ui and no structuredContent, hiding real content from the model.

How

Same shape as the merged Python fix: check whether this specific result carries a UI resource before compacting, not just whether the tool is UI-capable by definition.

• go/adk/pkg/mcp/mcp_ui.go: export HasUIResource(meta) on top of the existing parseMCPUIMetadata, so the per-result check accepts the same two meta shapes (_meta.ui.resourceUri and the flat _meta["ui/resourceUri"]) used to classify tools — keeping Go and Python MCP App semantics from drifting.
• go/adk/pkg/agent/mcp_apps.go: in compactMCPAppModelResponse, after the existing IsError branch, return the response unchanged when !mcp.HasUIResource(result.Meta). The gate is the result's UI resource only (matching fix(kagent-adk): compact MCP App tool results only when the result carries a UI resource #2579's merged semantics): a data-only result with structuredContent but no UI resource also passes through untouched.

Error handling is unchanged (content preserved, structuredContent dropped), and results that do carry a UI resource are still collapsed into the terminal notice with _meta preserved.

Tests

Ported the #2579 test cases to Go, plus the repro from the issue:

• TestMakeMCPAppModelResultCallbackPassesThroughPlainResultFromAppTool — the issue's repro: app-declared tool returning only text content ("No build found for job demo/1..."), no _meta, no structuredContent; text must reach the model unchanged (failed before the fix with the canned notice).
• TestMakeMCPAppModelResultCallbackPassesThroughDataOnlyResultFromAppTool — structuredContent present but empty _meta; passes through untouched (mirrors test_compact_skips_data_only_result_from_a_ui_capable_tool).
• TestMakeMCPAppModelResultCallbackCompactsFlatUIResourceMetaShape — flat _meta["ui/resourceUri"] still triggers compaction.
• TestHasUIResourceAcceptsNestedAndFlatMetaShapes / TestHasUIResourceRejectsResultsWithoutUIResource in pkg/mcp (mirrors test_result_has_ui_resource_accepts_nested_and_flat_meta_shapes).

Verified locally from go/:

go build ./adk/...
go vet ./adk/...
go test ./adk/...   # all packages ok

Existing callback tests (notice on render payload, isError preservation, non-app tool pass-through) all still pass. Also confirmed the new pass-through tests fail against unpatched mcp_apps.go.

Note: #2793 attempted this earlier and was closed unmerged by its author; this PR uses the same HasUIResource approach but drops that PR's extra structuredContent == nil condition so the gate matches the merged Python semantics exactly.

🤖 Generated with Claude Code