[1828703450qqcom-ux]

fix(examples): render function responses in examples as JSON

Summary

• convert_examples_to_text is documented to "Convert function response part
  to json string", but it rendered part.function_response.__dict__ — the
  pydantic model's internal storage.

• That leaks every unset optional field as None into the few-shot example,
  so the model is taught a tool response looks like:

  {'will_continue': None, 'scheduling': None, 'parts': None, 'id': 'call_1',
   'name': 'search', 'response': {'result': 42}}
  

• It is also a Python repr, not JSON: None/True/single quotes, and any
  nested pydantic value inside response renders through its repr, which
  spans several lines and breaks the fenced block that wraps the example.

• Fix: serialize the response fields as JSON with the unset optional fields
  dropped, so the example shows the response shape only.

Reproduction

Public API, on the current tree:

fr = types.FunctionResponse(
    name="search", id="call_1",
    response={"result": 42, "note": "it's fine"},
)
ex = Example(
    input=types.Content(role="user", parts=[types.Part(text="hi")]),
    output=[types.Content(role="model", parts=[types.Part(function_response=fr)])],
)
print(convert_examples_to_text([ex], "gemini-2.5-flash"))

Before, inside the fence:

{'will_continue': None, 'scheduling': None, 'parts': None, 'id': 'call_1',
 'name': 'search', 'response': {'result': 42, 'note': "it's fine"}}

After:

{"id": "call_1", "name": "search", "response": {"result": 42, "note": "it's fine"}}

The nested-value case is worse before — a types.Part in the response dict
renders as Part(\n text='nested_value'\n), so the fenced block contains raw
newlines and the example no longer reads as one tool-output payload. After the
change the same input renders {"nested": {"text": "nested_value"}} on one
line.

Fix

src/google/adk/examples/example_util.py — the function-response branch now
calls a small _function_response_json helper that emits
json.dumps(response.model_dump(exclude_none=True), default=str).
model_dump also recurses into nested pydantic values, so they become JSON
objects instead of multi-line reprs. A non-JSON-serializable value falls back
to its string form rather than failing the whole system-instruction build.

The function-call branch is unchanged: it is documented to render a
python-like call and its existing tests pin that shape.

Validation

Two new regression tests in tests/unittests/examples/test_example_util.py:

case	before	after
function response renders JSON without unset fields	will_continue/scheduling/parts leak, Python repr	clean JSON
nested value in the response dict	Part(\n text=...) breaks the fence	one-line JSON object

Both fail on the unmodified tree (verified by stashing only the source file)
and pass after. The exact before-output is visible in the assertion diff of
test_function_response_nested_values_render_as_json.

The three existing tests that pinned f"{test_function_response.__dict__}"
in their expected string now expect the JSON form; no other expectations
changed. Those tests had echoed the implementation's __dict__ rather than
specifying an output format.

• tests/unittests/examples/: 76 passed.
• tests/unittests/examples/ + tests/unittests/tools/: 3580 passed,
  2 skipped, 4 failed. The 4 failures are
  tests/unittests/tools/test_skill_toolset.py POSIX-environment cases
  (shell metacharacters, FIFO, symlink) and reproduce identically on
  unmodified main; this change does not touch that module.
• mypy 2.4.1 on the changed file: Success: no issues found.
• Pre-commit: ruff, isort, pyink, addlicense, codespell,
  fix end of files, trim trailing whitespace all pass. The three
  native-Windows shebang hooks (check-new-py-prefix, compliance-checks,
  check-docs) cannot start /bin/bash on this host and were run directly
  through Python instead: scripts/check_new_py_files.py (git-detection
  mode), scripts/compliance_checks.py and scripts/check_docs.py all exit
  0. This change adds no new Python files, so the prefix/unit-guide rule is
  not engaged.

Scope

• Exactly 2 files: src/google/adk/examples/example_util.py and
  tests/unittests/examples/test_example_util.py.
• No relation to the open event-alias (fix(events): preserve subclass validation aliases #7922) or delegated-output (fix(workflow): preserve messages and errors alongside delegated output #7950)
  work, or to the route-preservation change already imported into main.